AU463558B2 - Heat-sensitive device - Google Patents

Description

566/72 This present invention relates to a heat-sensitive

or responsive device.

According to the present invention there is

provided a heat sensitive device comprising a heat-

sensitive element consisting of heating means, thermal

delay means and heat responsive means thermally connected

in series with one another in the mentioned order,

said heating means being for heating said thermal delay.

means, said thermal delay means being for absorbing

substantially all heat output from the heating means,

and said heat responsive means operating when heated

through said thermal delay means by said heating means

or when cooled from a heated condition; switching

means coupling a voltage source to a load circuit; and

means coupling said heat responsive means to said

switching means for on-off control of said switching

means in accordance with the operation of said heat

responsive means.

463.558

50.566/72 The present invention will be more fully understood

from the following description embodying the invention

taken in conjunction with the accompanying drawings,

in which:-

Figs. la, Ib and Ic are perspective view of

typical prior-art bimetal strip arrangements;

Fig. 2 is a graph showing temperature versus

time characteristics of the bimetal strip arrangement

of Fig. 1;

Fig. 3 is a circuit diagram showing a principal-

prior-art circuit arrangement used for controlling a

load with a bimetal strip;

Fig. 4 shows a side view of a bread toaster in-

cluding therein the heat-sensitive device embodying the

present invention;

Fig. 5 is an enlarged side view of the toaster

and the heat-sensitive device shown in Fig. 4;

Fig. 6 and 7 show in perspective and to enlarged

scales, various parts of the heat-sensitive device shown

in Fig. 4;

Fig. 7A, shows a front view of the heat-sensitive

as seen from the direction of arrow A in Fig. 7;

Fig. 8 is an electrical circuit diagram showing

the circuit connection of the heat-sensitive device

shown in Fig. 7;

Figs. 9a to 9d, 10 and 11 illustrate the operation

of the described embodiment of the present invention.

The bimetal strip arrangements usually employed

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50.566/72 in bimetal timers are classed into three types, namely

heater type, self-heating type and radiation type, as

shown in Fig. 1. In the heater type bimetal strip arrangement

(as typically shown in Fig. la), the bimetal strip 2 is and it is indirectly heated by electric heating wire 1, 3 of insulated from the wire by an insulating material mica. low thermal conductivity such as natuiral This arrangement can provide a comparatively temperature of the long delay time before the saturation a in Fig. 2), bimetal.strip is reached (as shown by curve of a wide so that it is applicable to the timing control rigidity variety of apparatus. However, the flexurai prone to soft of mica or like insulating material is it is extremely points depending upon the thickness, and a constant and difficult to produce insulators having Therefore, uniform thickness on.a mass production basis.

the thermal/u 4en of the bimetal strip is .likely mechanical to be impeded by, or fluctuate due to.the state of close resistance of the insulator. Also, the 3 such as contact between heating wire 1 and insulator consisting of mica and between bimetal and heater unit

heater wire and insulator is subject to flutuations, strip and heater so that heat transferred between bimetal are unit is liable to fluctuate. These fluctuations strip arrange- major drawbacks in this type of bimetal

ments. The self-heating type bimetal strip arrange- is simpler in ment (as typically shown in Fig. lb) fluc- construction and is free from the afore-mentioned

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566/72 tuations in the heater type bimetal strip arrangement.

In this arrangement, however, there is no delay in the

temperature rise of bimetal strip 5, and saturation is

reached in an exceedingly short time (as shown by curve

b in Fig. To slow down the temperature rise in

bimetal strip 5 a metal piece 4 serving as heat radiator is usually welded to the bimetal strip, but with this

measure no pronounced effect can be expected (as is seen

from curve b' in Fig. Therefore, the application of

this bimetal strip arrangement is limited due to very

narrow range of controllable time interval.

Like the self-heating type bimetal strip arrange-

ment the radiation type bimetal strip arrangement (as

typically shown in Fig. Ic) does not require any insulator

between the bimetal strip and the heater as in the heater

type arrangement, so that fluctuations of characteristics

are less likely to result from mass production. However,

since the time taken until the reaching of the saturation-

temperature depends solely upon the heat capacity of

bimetal strip 7, the range of controllable time interval

is again narrow (as seen from curve c in Fig. 2).

Besides, in mass production there is a drawback in that

the radiant energy (heat) received by the bimetal strip

is affected by the distance between heating wire 6 and

bimetal strip 7 and temperature of the heating wire

which mainly depends upon voltage supplied.

Fig. 3 shows the principal/circuit arrangement

for the time control using a bimetal strip. In the Figure,

numeral 8 designates a load, for instance a heater,

numeral 9 a bimetal strip, and numeral 10 a bimetal strip

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heater wire. arrangements The afore-mentioned prior-art bimetal strip of the time in all lack in a factor to permit the control time interval intil the a factor to permit the control of the of the bimetal strip, so reaching of the saturation temperature of different voltage and that their compatibility with apparatus power ratings is difficult to realize prior-art bimetal strip The above drawbacks inherent in the embodiments having a arrangements are reduced with a preferred simple construction according to the invention. invention applied The preferred embodiment of the present

to an electric bread toaster will now be described. there is shown an Referrring now to Figs. 4 and 5, and inner cases 11 and 13. electric bread toaster having outer heater supports 12, The inner case supports upper and lower wound with heater wire Id are between which heater boards 15 each guard serving to prevent clamped. Numeral 16 designates a bread from getting into a slice of bread inserted into the toaster contact with the heater 14. seat holder guide Supported by a support 17 is a bread 19 is vertically movable. rod 18, along which a bread seat holder upwardly biased by a The bread seat holder 18 is normally

spring 20 and carries a bread seat 21 extending from its one side. It is provided on its other side with an operating lever 22.

Designated generally at 23 in Fig. 4 is a timer comprising

a heat-sensitive device embodying the invention, and which will

now be described in detail by also having reference to Fig. 6.

566/72 Numeral 23 designates a base having an upright

side projection 25, to which an elc triz magnct^26 is secured. A slide member 28 is retained to the base 24

by a retaining pin 27 extending therefrom and engaged

in a slot 29 formed in the member 28 for vertical sliding

movement and pivotal movement about the pin 27 within a

predetermined angle. The top of the slide member 28 is

coupled by a spring 30 to the holder 19. The slide

member 28 is thus upwardly urged when the holder 19 is

in an upper set position, while it is downwardly urged

when the holder 19 is in a toasting position. The slide

member 28 is provided adjacent its lower end with an iron

piece 31, which can be attracted to the iermItent magnet

26 when the magnet is energized. The slide member 28

also has protuberances 32 and 33 provided on one side

of the slot 29 and another protuberance 34 provided on

the other side of the slot and located intermediate

between the opposing protuberances 32 and 33. When the holder 19 is lowered to the toasting position, the spring

provides a spring force A consisting of component

forces a' and as shown in Fig. 11.

The component force-a' tends to cause counter-

clockwise rotation of the slide member 28 about the pin

27, and the electromagnetic force of attraction provided

when the electromagnet is energized is adapted to surpass

this component force so.as to cause clockwise revolution

of the iron piece 31 together with the slide mejnber 28.

The other component force a" is adapted to surpass

frictional force between bimetal circuit changeover con-

tacts described hereinafter so as to lower the slide

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member 28.

The slide member 28 carries at its one shoulder a

movable contact 35, which is connected through electromagnetic coil 26 to one of two power supply terminals,

as shown in Fig. 8. The movable contact 35 can be connected or break to or disconnected from fixed contacts 36 and 37 to make 28 the electromagnet energizing circuit. The slide member to also carries another movable contact 38, which is 'connected the other power supply terminal. with The vertical movement of the slide member 28 in cooperation 38 to the holder 19 has the effect of causing the movable contact moveable connected to or disconnected from fixed contacts 39 and circuit contact 49 to make or break the aforementioned bimetal main and main circuit. The movable contact 38 also serves as in the non- circuit on-off contact, and it is in an '!off" position toasting state.

The base 24 also has a horizontal projection 41'for engage- the ment with the afore-mentioned protuberances 32 and 33 of

slide member 28. A hook member 42 is pivoted by a retainer pin Its enc 43 to the base 24 and has a hook to anchor the holder 19. slide mE opposite the hook is engageable with the lower end of the ber 28. It is always biased counterclockwise by a spring 44. the Numeral 45 designates an insulator secured by a screw 46 to base 24 and has component elements to be described later. Referring in particular to Figs. 6 and 7, numeral 47 desi-

gnates a bimetal strip, and numeral 48 a rod for increasing

the deflection of the bimetal strip. The rod is provided at

its free end with a needle contact 49. On opposite sides of faci the needle contact 49, there are provided contacts 50 and 51

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566 /72

the contact 49. When the bimetal strip 47 is cooled down, the needle contact 49 is brought into contact with the contact 51,

and when the bimetal strip is heated it is eventually brought into

contact with the other contact 50. The support plate carrying the contact 51 is provided with a toast color adjustment screw 52

operable by a cam 53 coupled to an toast color adjustment knob 52'.

Numeral 54 designated-a metal block in the shape of a ball serving-

to provide a"heat accummulation effect or thermally lagging effect.

It is secured by means of spot welding to a holder 55. Numeral"

56 designates a heating wire to heat the metal ball 54 and conn-

ected between terminal plates 57 and 50. The bimetal strip 47, metal ball 54 and heating Wire 56 are thermally coupled in

series in the mentioned order, as shown in Fiq. 10. In the Figure, G1 represents the metal ball 54 and G2 the bimetal strip 47.

As is shown in this block diagram, the individual elements

are thermally coupled in series, so that it is readily possible

to provide a considerably long delay time until the reaching of a

saturation temperature of the bimetal strip 47. By appropriately setting the temperature of the heating wire 56 or spacing the

heating wire 56 and bimetal strip 47 sufficiently apart from

each other, it is possible to obtain thermal flow as shown in Fig. 10 with minimal thermal effect such as radiation from the

heating wire upon the bimetal strip. Also, where the heat capacity

of the bimetal strip is constant, the thermal delay time may be varied by varying the heat capacity of the metal ball 54,

which means the possibility of extending the range of controll-

able time intervals and promises ready application of the heat-

sensitive device to apparatus of different ratings and specif-

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5f96 /m

ications.

Regarding the merits of the metal block,

it is pointed out that a sphere-shaped body gives a minimum

surface area, providing that its volume is fixed.

Also:-

A thermal time constant of

the metal block determines or gives a delay function of the switching operation of the thermal responsive element.

The termal time constant of the metal block

is determined by the ratio of the thermal capacity and

the heat dissipation coefficient. One formula is indicated in

this connection:

T T 1 3 v- t) wherein T:

temperature rise, T f"ial temperature rise,

c v: thermal capacity, Aq' heat dissipation coefficient, t:

time interval, the factor c v/A is called the thermal time

'constant.

The delay time of the heat responsive device should not have a large degree of depndence upon the ambient

temperature, namely the delay time should be minimally affected

by the ambient temperature. Accordingly it is necessary to operate the metal block at a sufficiently high temperature range as

compared to the range of possible ambient temperatures.

It is, of course preferable to lower the electrical power consumption of the heat responsive device, since the quantity

of heat supplied from the heater wire to the metal block is not unlimited. Under these conditions, it is preferable to select the

heat dissipation coefficient of the metal block as small as possibi

in order to establish a sufficiently high temperature of the

metal block.

in 463.558

50.566 72

In view of the above items to it is

clear that the sphere shape is most preferable as the shape of temperature .and the metal block in order to obtain the sufficient of heat. the sufficient time constant with the limited supply present The operation of the embodiment describeding the

invention will now be explained. position, it is By bringing the holder 19 to the toasting prosition. anchored by the hook member 42 and locked in that Concurrently, the slide member 28 is downwardly urged by

lowered until the protuberance 33 is the spring 30 and is 41 provided in the brought into engagement with the projection At this time, the base 24, whereupon it is locked in that position. position(as contact 38, which has previously been in the "off" the fixed contact shown in Fig. 9a), is brought into contact with

39 on the

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side of the bimetal circuit, thus connecting

the bimetal circuit to the main circuit (as

shown in Fig. 9b). As a result, main current

is caused to pass through the heating wire 56

into the heater 14, so that the toasting of

the inserted bread and heating of the bimetal

heating wire 56 are sumultaneously started.

Since the bimetal strip 47, metal ball 54 and

heating wire 56 are thermally coupled in series

as mentioned earlier, the heat transferred from

heating wire 56 to metal ball 54 is accummulated in

and thermally lagged by the metal ball 54 to

provide a long delay time until the temperature

of the bimetal strip 47 is elevated to the

saturation temperature.

The deflection of the bimetal strip

47 being

463.5 58

50.566 in

heated in the above way isj4rgt; cd- by the e4l&gF rod

48, so that the needle contact 49 having initially been

in contact with the fixed contact 51 is detached there-

from and is eventually brought into contact with the

fixed contact 50, whereupon the electromagnetic coil 26

is activated to attract the movable iron piece 31 while

at the same time causing the clockwise rotation of the

slide member 28 integral with the iron piece 31 about

the pin 27, thus releasing the engagement between the

protuberance 33 of the slide member 28 and the projection

41 of the base 24, causing the slide member 28 downwardly

urged by the spring 30 to be further lowered until the

upper protuberance 32 is brought into engagement with

the projection Jtr(as shown in Fig. 9c).

In the above operation, upon releasing of the

lower protuberance 33 the slide member 28 is lowered by

the spring force of the spring 30. At this time, the

projection 41 strikes the inclined edge of the protube-

rance 34, so that the slide member 28 experiences a

rotational force in the direction of arrow shown in Fig.

9b. Thus, the upper protuberance 32 is readily and

reliably brought into engagement with the projection 41.

As the slide member 28 is further lowered in

the above manner, the contact 38 is detached from the

fixed contact 39 and brought into engagement with the

other fixed contact 40, while concurrently throwing the

contact 35 over to the side of the fixed contact 36 to

al-the electromagnet circuit. Thus, the bimetal

heating circuit is disconnected from the power supply,

so that the bimetal strip 47 immediately starts to be

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cooled down. Thus, the needle contact 49 is eventually detached from the contact 50, so that the movable iron piece

31 is returned to its initial position by the force of the

spring

The above sequence of actions takes place almost momentarily. Thereafter, the bimetal strip 47 continues to be cooled, and the needle contact 49 is eventually brought back into contact with the contact 51. At this time, the electromagnet circuit changeover contact 35 remains in contact with the contact 36, so that electromagnetic coil 26 is activated once again to attract the movable iron piece 31. By this second action of the electromagnet, the engagement between protuberance

32 and projection 41 is released, causing the slide member 28 to

be lowered still further by the urging force of the spring

so that the lower end of the movable iron piece 31 provided at

the lower end of the slide member 28 strikes one end of the hook

member 42 and causes counterclockwise rotation of the hook 42

against the spring force of the urging spring 44, thus releasing

the holder 19 from engagement with the hook. As a result, the holder 19 is returned to its upper set position or non-toast-

ing position by the force of the spring 20 and also returns the

slide member 28 to the upper set position thereof, thus bringing the contact 38 for making and breaking the bimetal circuit and main circuit into the "off" position to bring an end to the

toasting operation. As has been described in the foregoing, according to the

preferred embodiment of the present reduce invention it is

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possible to reduce fluctuations of characteristics due to

otherwise possible

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errors introduced in the processing of component parts

of the bimetal strip or element and coupling and

assembling of these parts, so that the heat-sensitive and device provides time control units of steady

reliable performance. Also, the characteristics

of the bimetal timer consisting of the above bimetal

element for activating the electromagnet to switch

the bimetal circuit and for releasing the bread such seat holder has minimal frictional resistance timer as is involved in the operation of- the mechamical

constructions. Thus, it is possible for the bimetal

strip to serve the sole role of temperature detection

for closing the electromagnet circuit. Further,

as is apparent from the preceding embodiment, without

any restriction to the bread toaster, it is possible

to achieve temperature control of electric apparatus

of various voltage and power ratings. It is

further possible to obtain bread toasters having

various specifications by varying merely the heat

capacity of the metal ball and working temperature

of the metal ball heating wire and without changing

the construction of the rest of the timer, which

is extremely convenient for mass production of

such timers.

Furthermore, the main switch also serves the

switch of the bimetal heating circuit, which is

advantageous in the aspect of cost reduction.

463.5 58

Claims (3)

1. 566 72

   THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: a heat-sensitive i. A heat sensitive device comprising thermal delay means and element consisting of heating means, connected in series with one heat responsive means thermally said heating means being for another in the mentioned order, said thermal delay means being heating said thermal delay means, heat output from the heating for absorbing substantially all operating when heated means, andsaid heat responsive means by said heating means or when through said thermal delay means switching means coupling a cooled from a heated condition; and means coupling safd heat voltage source to a load circuit; said means for on-off control of responsive means to said switching the operation of said heat switching means in accordance with responsive means. to claim 1, 2. A heat-sensitive device according electric heating wire, said wherein said heating means is an block having a low heat thermal delay means is a metallic heat responsive means is a bimet- dissipation cooefficient, said through said thermal delay allic strip deflecting when heated cooled from a heated condition means by said heating means or when controlled in accordance with and said switching means is on-off strip. the deflection of said bimetallic to claim 2, wherein 3. A heat-sensitive device ,according steel ball. said metallic block is a spherical to claim 2 or 4. A heat-sensitive device according for increasing or mangifying the claim 3, further comprising means

   deflection of said bimetallic strip. to claim 4, A heat-sensitive device according

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   wherein the increasing or mangifying means is an elongate member

   having a moveable electrical contact, the elongate member being

   attached to the bimetallic strip and being for increasing or

   magnifying said deflection of thei bimetallic strip so as to cause

   switching of said moveable electrical contact. 6. A heat-senitive device according to claim wherein the switching of the moveable electrical contact

   is effected in a direction parallel with the direction of

   deflection of the bimetallic strip and by the moveable

   electrical contact near its free end remote from the bimetallic

   strip. 7. A heat-sensitive device! according to claim: 5 or claim 6, wherein the means coupling said heat responsive means

   tosaid switching means includes said moveable electrical contact,

   and an electromagnetic coil actuated through said moveable electrical contact as said heat-sensitive element is heated or coc

   dd. 8. A heat-sensitive device according to claim 7, wherein said electromagnetic coil is coupled to said switching means by

   means comprising a moveable piece attractable to said electromagn-

   etic coil; and a slide member driven by said moveable piece and provided with first and second contacts, said first contact

   controlling energization of said electromagnetic coil and said

   second contact switching the electric heating wiere and said load. 9. A heat-sensitive device according to any one of claims 2 to 8 further comprising first and second terminal plates

   between which the longitudinal axis of said electric heating wiere extends, said metallic block being coupled thermally

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   50.566 /72 heating wire, and said bimetallic strip being coupled

   thermally in series with said metallic block and being

   disposed perpendicularly to the longitudinal axis of

   said heater wire.

   A heat-sensitive device according to claim 2,

   wherein said switching means includes a first switch

   having two switch positions and said load circuit consists

   of said electric heating wire and a load connected in

   series with said first switch; said means coupling the

   heat responsive means to said switching means com-

   prising a second circuit in parallel with said load

   circuit and consisting of an electromagnetic coil, a

   second switch having two switch positions and being

   for switching said electromagnetic coil and a third

   switch having a moveable contact coupled to said bi-

   metallic strip, a fixed heating contact and a fixed

   cooling contact, said electromagnetic coil being

   activated when said bimetallic strip is heated to a

   predetermined temperature at which temperature the

   moveable contact is brought into contact with said fixed

   heating contact, the activation of the electromagnetic

   coil causing said first switch to move from one of its

   said two switch positions to the other of its said two

   switch positions to thereby deenergise said heater wire

   and simultaneously causing said second switch to move

   from one of its said two switch positions to the other

   of its said two switch positions to thereby open-circuit

   said second circuit, said electromagnetic coil being

   subsequently reactivated when said bimetallic strip

   is cooled, due to the deenergization of said heater

   wire, such that said moveable contact 463.558

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   of said third switch is brought into contact with

   said fixed cooling contact, the subsequent reactivation

   of the electromagnetic coil causing said first switch

   to move to an off position intermediate the two switch

   positions of the first switch thereby removing power

   from said load.

   11. A heat-sensitive device according to claim

   wherein said one of the two switchpositionsof the second

   switch is connected to said fixed heating contact and

   said the other of the two switchpositions of the second

   switch is connected to said fixed cooling contact.

   12. A heat-sensitive device according to claims

   or 11, wherein when said first switch is in said

   one of its said two switch positions said voltage source

   supplies power to said heater wire and said load, when

   said first switch is in said the other of its said

   two switch positions, the voltage source supplies power

   only to said load, and when said first switch is in

   said off position the voltage source supplies no

   power to said load or said heater wire.

   13. A heat-sensitive device substantially as

   hereinbefore described with reference to Figures 4

   to 11 of the accompanying drawings.

   14. A heat-sensitive device as claimed in any

   one of claims 1 to 13 in a bread toaster.

   DATED THIS 9th Day of JULY, 1975.

   MATSUSHITA ELECTRIC INDUSTRIAL CO. LTD., By its Patent Attorneys:

   CLEMENT HACK CO.

   Fellows Institute of Patent Attorneys of Australia.

   21 4 635 58

   50.566 /72

   F IG. Ia PRIOR ART

   F IG. l b PRIOR ART

   F IG. I c PRIOR ART

   F IG.
2. 2. PRIOR ART

   F IG.
3. 3 PRIOR ART

   TIME

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   F IG. 4

   F iG.

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