EP0685107B1 - Ameliorations concernant des commutateurs electriques - Google Patents

Ameliorations concernant des commutateurs electriques Download PDF

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Publication number
EP0685107B1
EP0685107B1 EP94906339A EP94906339A EP0685107B1 EP 0685107 B1 EP0685107 B1 EP 0685107B1 EP 94906339 A EP94906339 A EP 94906339A EP 94906339 A EP94906339 A EP 94906339A EP 0685107 B1 EP0685107 B1 EP 0685107B1
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EP
European Patent Office
Prior art keywords
switch
conductors
bimetallic
bimetal
moulded plastics
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP94906339A
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German (de)
English (en)
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EP0685107A1 (fr
Inventor
David Andrew Smith
Vincent Andrew Florentine
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Otter Controls Ltd
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Otter Controls Ltd
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Filing date
Publication date
Application filed by Otter Controls Ltd filed Critical Otter Controls Ltd
Publication of EP0685107A1 publication Critical patent/EP0685107A1/fr
Application granted granted Critical
Publication of EP0685107B1 publication Critical patent/EP0685107B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H61/00—Electrothermal relays
    • H01H61/01—Details
    • H01H61/013—Heating arrangements for operating relays
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00—Contacts
    • H01H1/50—Means for increasing contact pressure, preventing vibration of contacts, holding contacts together after engagement, or biasing contacts to the open position
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00—Contacts
    • H01H1/50—Means for increasing contact pressure, preventing vibration of contacts, holding contacts together after engagement, or biasing contacts to the open position
    • H01H1/504—Means for increasing contact pressure, preventing vibration of contacts, holding contacts together after engagement, or biasing contacts to the open position by thermal means
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H81/00—Protective switches in which contacts are normally closed but are repeatedly opened and reclosed as long as a condition causing excess current persists, e.g. for current limiting
    • H01H81/02—Protective switches in which contacts are normally closed but are repeatedly opened and reclosed as long as a condition causing excess current persists, e.g. for current limiting electrothermally operated

Definitions

  • This invention concerns improvements relating to electric switches and more particularly concerns thermally responsive electrical switches employing bimetallic elements as thermal actuators.
  • bimetallic switch actuators Many kinds of electrical switches employing bimetallic actuators are known and likewise many different forms of bimetallic switch actuators are known. Early bimetallic switches simply employed a plain bimetal blade which moved relatively slowly in response to temperature changes and gave rise to arcing problems in the switch, and the development of the snap-acting bimetallic actuator, constructed as a dished bimetallic element capable of moving between oppositely curved configurations with a snap-action, provided a major advance in the art.
  • GB 2124429 abovementioned discloses the utilization of a pear-shaped snap-acting bimetallic actuator in a current-sensitive switch where the heating of the bimetal by electric current flow therethrough is designed to trip the switch in a current overload situation.
  • a bimetallic switch having terminal parts formed of a relatively high resistance material, such as nickel chromium alloy or stainless steel for example rather than the more commonly used brass, so that heat is generated in normal operation of the switch and affects the switch characteristics; the response of the switch to a high overload current is not significantly affected by the heat generated in the terminal parts since the bimetal response to the high current will be more rapid than the time taken for the heat generated in the terminal parts to transfer to the bimetal, but the responsiveness of the switch to a current barely at an overload level will be enhanced.
  • a relatively high resistance material such as nickel chromium alloy or stainless steel for example rather than the more commonly used brass
  • the heater With a heater element connected in parallel with the switch contacts, the heater passes a current dependent on the relative resistances of the heater and of the bimetal so long as the switch contacts are closed, and the heater current in this situation may or may not be negligible, but once the bimetal operates the heater passes the full load current and generates heat which is transferred to the bimetal so as to delay its reset period or prevent it from resetting altogether.
  • switch heaters As well as utilizing switch parts formed of relatively high resistance materials, as in GB 2 133 931 abovementioned, it is also known to form switch heaters as thin film resistors, from conductive inks and as ceramic PTC materials (that is to say ceramic materials having a positive temperature coefficient of resistance).
  • PTC material heaters have the advantage that, when connected in parallel with switch contacts, the self heating caused by through current in the PTC material when the switch contacts open not only provides heat to the bimetallic element of the switch but also increases the resistance of the PTC material thereby effectively reducing the current supplied to the switch load. Examples of bimetallic switches incorporating PTC material heaters are described in GB 2 252 674.
  • PTC material resistances have also been used by themselves as overload protection devices for electric motors and GB 1 604 111, for example, discloses the use of a PTC material resistance connected in series with the motor windings and operative to reduce the current through the motor to a safe level in the event that a motor overload causes the resistance of the PTC device to increase significantly.
  • Such devices are also useful as thermal relays in starting circuits for electric motors and GB 2 015 823, for example, discloses the provision of a PTC resistor in series with start windings of an electric motor, the PTC resistor permitting a high initial current to flow for starting the motor and thereafter increasing its resistance so as to correspondingly reduce the current in the start winding.
  • Plastics materials having PTC characteristics are also known and in WO 91/07804, for example, such a PTC thermistor is connected in series with the armature windings of a small DC motor and serves a motor protection function.
  • bimetallic switches bimetallic switches incorporating heating elements and including PTC material heating elements, and PTC material protective devices.
  • motor protection applications particularly for the protection of small DC motors such as for example automotive window lift motors which are becoming ever smaller in size and more powerful
  • simple bimetallic switches gives rise to problems in that the cycling of the switch as it intermittently heats and cools can cause jarring of gears in sensitive gear trains, sets lifetime limits on the switch, and must be carefully controlled to ensure that a stalled motor is held at a protected and limited temperature.
  • the object of the present invention is to provide a thermally responsive bimetallic switch capable of overcoming or at least substantially reducing the abovementioned problems, the switch additionally preferably being of inexpensive and uncomplicated construction.
  • a bimetallic switch enclosed within a moulded plastics switch body formed of a polymeric PTC material.
  • a thermally-responsive switch comprising a moulded plastics body portion capturing therein first and second terminal conductors, and a snap-acting bimetallic actuator secured to one of said conductors and carrying a contact which constitutes the moving contact of the switch, such contact being arranged for co-operation in switching operations with the other of the two conductors, and the moulded plastics body portion being formed of a polymeric PTC material.
  • Any suitable polymeric PTC material can be utilized in the practice of the invention, but it is preferred to utilize a polyolefin material, e.g. polypropylene, incorporating one or more conductive fillers and preferably also incorporating a non-conductive filler such as a fibre to provide stability and reproduceability.
  • a polyolefin material e.g. polypropylene
  • Carbon black is the preferred conductive filler and we prefer to utilize a relatively low proportion (0 to 5%) of a high conductivity carbon black and a relatively high proportion (0 to 30%) of a carbon black such as to make a substantial contribution to the PTC effect.
  • the non-conductive filler may for example be from 0 to 40% glass fibre. The percentages quoted are by weight.
  • the bimetallic actuator of the switch is advantageously of such low thickness as to be responsive to through current as low as 2 amps or less, for example a bimetallic element of the order of 0.076mm (0.003 inch) thickness, and the switch body part preferably provides physical support for the bimetallic element during switching operations.
  • the bimetallic actuator is of a kind having a generally U-shaped cut-out defining a tongue between spaced apart leg portions which are bridged adjacent the free end of the tongue.
  • the terminal conductors are formed as simple wires and the tongue of the bimetal is secured to one of the terminal conductors, for example by welding, and the bridging portion carries the contact which co-operates with the other conductor.
  • No discrete contact is provided on the other conductor which however comprises a silver or silver alloy coating, for example a silver antimony coating as described in WO 92/14282.
  • the moulded plastics PTC material body portion of the switch defines an enclosure for the bimetallic actuator and, as will hereinafter be described, also incorporates portions which provide structural support for the bimetal.
  • the resultant switch is of simple and easily manufactured construction which enables small size to be achieved for enhanced sensitivity to very low overload currents. Furthermore, by variation of the characteristics of the PTC material the switch can readily be customised to suit particular applications.
  • a series-connected heating element could, if desired, be provided for injecting heat into the bimetallic actuator when the switch is in closed condition, and in a particularly convenient arrangement such a series heating element may be constituted by a portion of one or the other or both of the two terminal conductors of the switch which is formed as a resistance heating element. Such an arrangement could be arranged to obtain a more rapid switch response to a current overload situation than would be obtained if the series heating element were not provided.
  • the switch hereinafter described is in many respects identical to the switch described in WO 92/20086 which, therefore, represents the closest prior art, but differs principally therefrom in that the moulded plastics body portion 1 of the switch is formed of a polymeric PTC material.
  • the accompanying drawings are identical to those in WO 92/20086.
  • the views in the drawings show the switch to an enlarged scale and the dimensions indicated are the actual dimensions of the switch in millimetres.
  • the moulded plastics body portion 1 of the switch is thus generally rectangular with dimensions of 10.5mm x 6.0mm x 2.7mm and the terminal conductors 2, 3 project outwardly by a further 7.0mm.
  • a top cover for the switch has a thickness of 0.5mm.
  • the switch thus has such small overall size that it may conveniently be supplied in a bandolier suitable for use by automatic component insertion equipment.
  • any suitable plastics material exhibiting PTC characteristics could be utilized in the practice of the invention for forming the body portion 1, but it is preferred to utilize a polyolefin material, e.g. polypropylene, incorporating one or more conductive fillers and preferably also incorporating a non-conductive filler such as a fibre to provide stability and reproduceability.
  • Carbon black is the preferred conductive filler and we prefer to utilize a relatively low proportion (0 to 5%) of a high conductivity carbon black and a relatively high proportion (0 to 30%) of a carbon black such as to make a substantial contribution to the PTC effect.
  • the non-conductive filler may for example be from 0 to 40% glass fibre. The percentages quoted are by weight.
  • a simple copper wire conductor 2 has a square or rectangular section and is moulded into the body portion 1 at one end thereof with its forward part received in a recess in the upper surface of the upstand 5, and a simple copper wire conductor 3 has a circular section, though it too could have a square or rectangular section, and is moulded into the opposite end of the body portion 1 so as to be exposed at 7 within the chamber 4.
  • a bimetallic actuator 6 is welded to the forward part of conductor 2.
  • conductor 3 constitutes a switching contact of the subject switch and accordingly conductor 3 is preferably formed of silver plated copper wire or more preferably silver-antimony plated copper wire as described in WO 92/14282; conductor 2 may be similarly formed though this is not essential.
  • a preferred form of conductor wire providing excellent electrical characteristics in combination with superior wear characteristics comprises a copper wire, or a wire formed from a copper alloy having a thermal conductivity at least 90% that of copper, and more preferably 95% to 99% that of 99.95% pure copper, provided with a thick plating layer of silver and antimony, and the conductor wire 3 above-described can advantageously have this construction.
  • a thick plating e.g.
  • microns and preferably 40 microns thickness comprising fine silver (99.9% purity) with a small amount of antimony, typically about 1% and particularly between 0.3% and 0.7%, on a conductor formed of copper or a high thermal conductivity copper alloy, the formation of silver powder during switching operations is inhibited and a life of about 70,000 switching cycles may be obtained.
  • Bimetallic actuator 6 is of the Otter Controls type comprising a dished blade of bimetallic material having a generally U-shaped cut-out 8 which defines a tongue 9 between legs 10 which are bridged by a bridging portion 11.
  • the moving contact of the switch is constituted by a silver contact 12 welded to the underside of bridging portion 11 as best shown in Figure 1.
  • the actuator 6 is secured to terminal conductor 2 by virtue of the tongue 9 being welded thereto.
  • the shape of the bimetallic blade is such as to enhance its responsiveness to through currents by increasing the current density in the legs 10 and in the contact-carrying forward region of the blade.
  • the upstand 5 provides support for the forward portion of conductor 2 which in turn provides support for tongue portion 9 of bimetallic actuator 6, whereas the legs 10 and bridging portion 11 of the bimetal 6 are free to move within the chamber 4.
  • the temperature responsive characteristics of the switch can better be predetermined since switching operations are effected substantially exclusively by flexure of the legs 10 about the stable position established for tongue 9 by virtue of its support on conductor 2.
  • the risk of stress cracking at the root of the tongue is reduced and the working stresses in the bimetal are concentrated towards its elongate legs 10.
  • the switch construction as thus described comprises a simple bimetallic switch, constituted by the conductors 2 and 3 and the bimetal 6, with a PTC heater, constituted by the body portion 1 of the switch, connected in parallel with the bimetallic switch.
  • contact 12 will move away from portion 7 of conductor 3, with a snap-action, whenever the temperature of the bimetal 6 rises to a certain predetermined level, either as a result of thermal conduction from the switch environment, or as a result of heating of the bimetal by current flow therethrough, or as a result of heating of the bimetal by current flow through the PTC material or as combination of any two or more of these three effects.
  • the switch will remake.
  • the characteristics of the polymeric PTC material from which the switch body portion 1 is formed do, however, have an effect upon the overall switch characteristics and may be designed to prevent the bimetal from cooling to such a temperature that it resets so as to cause the switch contacts to remake, or to inject such an amount of heat into the bimetal 6 in its open-contacts condition as to modulate the on-off time of the switch cycles to suit a particular application, for example a motor protection application where the cycling of the switch must not result in a stalled motor being subjected to excessive temperatures.
  • the fact that the PTC characteristics of the switch body portion 1 combine with the switching characteristics inherent in the bimetal 6 provides for the ready design of special switches to suit particular applications. Further design variables which can be manipulated in order to adapt a switch according to the present invention to a specific application can be obtained by inclusion of a series-connected heater in the switch as will hereinafter be described.
  • the closure 15 may conveniently be moulded as an integral part of the switch body which is hingedly coupled thereto and is ultrasonically welded shut after assembly of the bimetal 6 into the chamber 4 and spot welding of the tongue 9 to the forward part of conductor 2.
  • the closure 15 may be formed so as to isolate the chamber 4 from the environment of the switch, or may alternatively be provided with one or more openings 16 as indicated.
  • the bimetallic material of the actuator 6 has a thickness of only 0.076mm (0.003 inch) and had to be specially manufactured for us.
  • Figure 3 shows an alternative form of conductor which could be used in the switch of Figures 1 and 2 in place of the conductor 2.
  • conductor 20 is formed of a resistance heating material and has a forward portion 21 which is adapted to be received within the switch body chamber 4 and is formed generally as a spiral terminating in a pad 22 to which the tongue 9 of the bimetal actuator 6 is spot welded.
  • the dimensions shown in Figure 3 are in millimetres, Figure 3 being an enlarged showing of the conductor.
  • the described switch is well suited to automatic manufacture and installation, comprises a minimum of parts and can be relatively inexpensive, and is capable of miniaturisation for enhanced current sensitivity.
  • the switch is, however, but an example of what is achievable by virtue of the invention and modifications and variations are possible without departure from the spirit and scope of the invention as claimed.
  • the bimetal could be pear-shaped as described in GB 2124429 aforementioned for enhanced current sensitivity, or could take a variety of alternative shapes.
  • wire terminals 2 and 3 could be replaced by appropriate sheet metal parts insert moulded into the polymeric PTC material body portion 1 and having terminal pads accessible in the undersurface of the body portion for surface mounting of the switch to a printed circuit board for example either by soldering or, more preferably having regard to the desirability of avoiding exposure of the switch to extremes of temperature, by means of a mechanical spring fastening arrangement.

Landscapes

  • Thermally Actuated Switches (AREA)

Abstract

Un commutateur réagissant à la chaleur, conçu pour ouvrir un circuit en réaction à des courants de surcharge relativement faibles de l'ordre de 2 ampères et moins, comprend un boîtier de matière plastique moulée contenant deux bornes simples de fil de cuivre, ainsi qu'une cavité interne où une lame bimétallique à action instantanée de très faible épaisseur est soudée par points à l'une des bornes de fil et porte un contact en argent qui coopère, pour les opérations de commutation, avec l'autre borne de fil. La construction interne de cette cavité de boîtier de commutateur est conçue pour offrir un support physique à cette lame bimétallique grâce à la borne de fil respective laquelle est fixée cette lame. Le boîtier de matière plastique moulée est constitué d'un polymère de PTC et intervient en tant que corps de chauffe en parallèle avec le commutateur bimétallique.

Claims (13)

  1. Commutateur bimétallique enfermé dans un corps de commutateur en matière plastique moulée constitué d'un matériau polymérique du type PTC.
  2. Commutateur thermiquement sensible et comportant une partie de corps (1) en matière plastique moulée capturant un premier et un second conducteur formant borne (2, 3) et un actionneur bimétallique (6) à passage par un point mort fixé sur l'un desdits conducteurs et supportant un contact (12) qui constitue le contact mobile du commutateur et est agencé pour coopérer lors d'opérations de commutation avec l'autre des deux conducteurs, la partie de corps en matière plastique moulée étant formée d'un polymère du type PTC.
  3. Commutateur selon la revendication 2, dans lequel le premier et le second conducteur formant borne est constitué d'un simple conducteur en fil conducteur.
  4. Commutateur selon la revendication 2 ou 3, dans lequel au moins ledit autre des deux conducteurs est constitué de cuivre ayant un revêtement d'argent contenant de l'antimoine.
  5. Commutateur selon la revendication 4, dans lequel ledit contact est constitué d'argent.
  6. Commutateur selon l'une quelconque des revendications 2 à 5 dans lequel le premier et le second conducteur sont capturés dans des extrémités opposées espacées du corps en matière plastique moulée.
  7. Commutateur selon l'une quelconque des revendications 2 à 6, dans lequel le conducteur sur lequel le bilame est fixé a une section carrée ou rectangulaire et le bilame est soudé sur une surface plate du conducteur.
  8. Commutateur selon l'une quelconque des revendications 2 à 7, dans lequel l'actionneur bimétallique comporte une lame bimétallique en forme de disque ayant une découpe (8) ayant la forme générale d'un U définissant une languette centrale (9) s'étendant entre deux pattes extérieures (10), et la languette du bilame est fixée sur ledit premier des conducteurs.
  9. Commutateur selon la revendication 8, dans lequel la lame bimétallique a une épaisseur de 0,076 mm.
  10. Commutateur selon l'une quelconque des revendications 2 à 9, et dans lequel un premier et/ou l'autre desdits conducteurs est constitué d'une partie chauffant par résistance adaptée pour pomper de la chaleur à l'intérieur de l'actionneur bimétallique.
  11. Commutateur selon l'une quelconque des revendications précédentes et dans lequel le matériau de polymère du type PTC comporte une ou plusieurs charges conductrices donnant au matériau de polymère des caractéristiques de type PTC, et une charge non-conductrice.
  12. Commutateur selon la revendication 11, dans lequel les charges conductrices sont constituées de noir de carbone.
  13. Commutateur selon la revendication 11 ou 12, dans lequel la charge non-conductrice est constituée d'un matériau en fibres.
EP94906339A 1993-02-18 1994-02-16 Ameliorations concernant des commutateurs electriques Expired - Lifetime EP0685107B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB9303292 1993-02-18
GB9303292A GB2275823B (en) 1993-02-18 1993-02-18 Improvements relating to electric switches
PCT/GB1994/000315 WO1994019815A1 (fr) 1993-02-18 1994-02-16 Ameliorations concernant des commutateurs electriques

Publications (2)

Publication Number Publication Date
EP0685107A1 EP0685107A1 (fr) 1995-12-06
EP0685107B1 true EP0685107B1 (fr) 1997-10-22

Family

ID=10730659

Family Applications (1)

Application Number Title Priority Date Filing Date
EP94906339A Expired - Lifetime EP0685107B1 (fr) 1993-02-18 1994-02-16 Ameliorations concernant des commutateurs electriques

Country Status (8)

Country Link
EP (1) EP0685107B1 (fr)
JP (1) JPH08508603A (fr)
KR (1) KR960701458A (fr)
AU (1) AU6008994A (fr)
CA (1) CA2155961A1 (fr)
DE (1) DE69406429D1 (fr)
GB (1) GB2275823B (fr)
WO (1) WO1994019815A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102011016133A1 (de) * 2011-03-29 2012-10-04 Marcel P. HOFSAESS Temperaturabhängiger Schalter mit Vorwiderstand

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19546005C2 (de) 1995-12-09 1999-07-08 Hofsaes Marcel Schalter mit einem temperaturabhängigen Schaltwerk
DE19546004C2 (de) * 1995-12-09 1998-01-15 Hofsaes Marcel Schalter mit einem bei Übertemperatur schaltenden Schaltwerk
WO2005073996A1 (fr) * 2004-01-30 2005-08-11 Danfoss Compressors Gmbh Protecteur bimetallique
DE102007014237A1 (de) * 2007-03-16 2008-09-18 Hofsaess, Marcel P. Temperaturabhängiger Schalter und dafür vorgesehenes Schaltwerk
EP2287878B1 (fr) * 2008-04-18 2015-09-02 Tyco Electronics Japan G.K. Dispositif de protection de circuit
GB2481240B (en) 2010-06-17 2017-04-12 Otter Controls Ltd Thermally responsive electric switches

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB8614198D0 (en) * 1986-06-11 1986-07-16 Salplex Ltd Information handling & control systems
DE3711666A1 (de) * 1987-04-07 1988-10-27 Hofsass P Temperaturschalter
JPH0834075B2 (ja) * 1988-03-29 1996-03-29 東部電気株式会社 サーマルスイッチ
ES2071697T3 (es) * 1990-04-25 1995-07-01 Ulrika Hofsass Interruptor termico.
GB9109316D0 (en) * 1991-04-30 1991-06-19 Otter Controls Ltd Improvements relating to electric switches

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102011016133A1 (de) * 2011-03-29 2012-10-04 Marcel P. HOFSAESS Temperaturabhängiger Schalter mit Vorwiderstand
DE102011016133B4 (de) * 2011-03-29 2012-10-18 Marcel P. HOFSAESS Temperaturabhängiger Schalter mit Vorwiderstand

Also Published As

Publication number Publication date
EP0685107A1 (fr) 1995-12-06
JPH08508603A (ja) 1996-09-10
WO1994019815A1 (fr) 1994-09-01
KR960701458A (ko) 1996-02-24
AU6008994A (en) 1994-09-14
CA2155961A1 (fr) 1994-09-01
GB9303292D0 (en) 1993-04-07
GB2275823A (en) 1994-09-07
DE69406429D1 (de) 1997-11-27
GB2275823B (en) 1996-11-27

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