US3870983A

US3870983A - Heat-sensitive device

Info

Publication number: US3870983A
Application number: US318643A
Authority: US
Inventors: Nobuo Kato; Toshio Nakamura; Seishi Terakado
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1972-12-26
Filing date: 1972-12-26
Publication date: 1975-03-11
Anticipated expiration: 1992-03-11

Abstract

A heat-sensitive device, which comprises a heat-sensitive element consisting of an electric heating wire, a metal block and a bimetal strip thermally coupled in series with one another and means to take out an output of said heat-sensitive element made available as a result of heating and cooling thereof, and which can be chiefly used for the time control of a load. It enables a wide range of time control, can adapt itself to apparatus of a wide variety of ratings, and makes it possible to eliminate fluctuations of characteristics resulting from mass production.

Description

United States Patent 191 Kato et al.

Mar. 11,1975

[ HEAT-SENSITIVE DEVICE [75] inventors: Nobuo Kato, lkeda; Toshio Nakamura; Seishi Terakado, both of Osaka, all of Japan [73] Assignee: Matsushita Electric Industrial Co.,

Ltd., Osaka, Japan 22 Filed: Dec. 26, 1972 21 Appl. No.: 318,643

[52] US. Cl 337/107, 337/103, 337/377 [51] Int. Cl. ..H01h 61/02 [58] Field of Search 337/102, 103, 107, 377,

[56] References Cited UNITED STATES PATENTS 3,023,288 2/l962 Bodenschatz et a] 337/107 X Y ullllmlh Primary Examiner-J. D. Miller Assistant E.\aminerFred E, Bell Attorney, Agent, or FirmStevens, Davis, Miller & Mosher [57] ABSTRACT A heat-sensitive device, which comprises a heatsensitive element consisting of an electric heating wire, a metal block and a bimetal strip thermally coupled inseries with one another and means to take out an output of said heat-sensitive element made available as a result of heating and cooling thereof, and which can be chiefly used for the time control of a load. it enables a wide range of time control, can adapt itself to apparatus of a wide variety of ratings, and makes it possible to eliminate fluctuations of characteristics resulting from mass production.

10 Claims, 17 Drawing Figures PATENTEDHARIHQF5 1.870 983 sum 1 9f 5 FIG. 1 \b PRIOR ART FIG. Ic

PATENTED 11975 v3.870383 SHEET 5 0F 5 1 HEAT-SENSITIVE DEVICE This invention relates to heat-sensitive devices comprising a heat-sensitive element consisting of an electric heating wire, a metal block and a bimetal strip thermally coupled in series with one another and means to take out an output of said heat-sensitive element.

An object of the invention is to enable extending the range of the controllable time interval and obtain compatibility with apparatus of a wide variety of ratings, for instance a toasting control section of a bread toaster.

Another object of the invention is to eliminate fluctuations of characteristics due to errors otherwise introduced in the processing of component parts of the heat sensitive element and coupling and assembling of these parts, to thereby permit manufacturing control units of steady and reliable performance on a mass production basis.

A further object of the invention is to make the characteristics of heat sensitive devices free from fluctuations attributable to the mechanical timer construction to thereby provide control units of steady and reliable performance.

A still further object of the invention is to construct a heat-sensitive element from a metal block, a bimetal strip and a heating wire for heating the metal block, so that the elementmay be applied to apparatus of a wide variety of ratings while at the same time eliminating fluctuations of the characteristics of such elements.

Still another object of the invention is to provide inexpensive heat-sensitive devices which are simple in structure.

For the present invention to be fully understood, the prior-art to which the invention pertains and a preferred embodiment thereof will now be described by having reference to the accompanying drawings, in which:

FIGS. la, lb and 1c are perspective views of typical prior-art bimetal strip arrangements;

FIG. 2 is a graph showing temperature versus time characteristics of the bimetal strip arrangements of FIG. 1;

FIG. 3 is a circuit diagram showing a principal circuit arrangement used for controlling a load with a bimetal strip;

FIG. 4 is an elevational sectional view showing a bread toaster incorporating a heat-sensitive device embodying the invention;

FIG. 5 is a side sectional view, to an enlarged scale, showing the heat-sensitive device shown in FIG. 4;

FIGS. 6 and 7 show, in perspective and to enlarged scales, various parts of the heat-sensitive device shown in FIG. 4 and FIG. 7a shows a front view of the heat sensitive element of FIG. 7;

FIG. 8 is'a circuit diagram showing the circuit connection of the heat-sensitive device shown in FIG. 1, and

FIGS. 9a to 9d, 10 and 11 show operational principles underlying the invention.

The bimetal strip arrangements usually employed in bimetal timersv are classed into three types, namely heater type, self-heating type and radiation type, as shown in FIGS. 1a, lb and 1c respectively.

In the heater type bimetal strip arrangement (as typically shown in FIG. la), the bimetal strip 2 is indirectly heated by electric heating wire 1, and it is insulated from the wire by an insulating material 3 oflow thermal conductivity such as natural mica.

This arrangement can provide a comparatively long delay time before the saturation temperature of the bimetal strip is reached (as shown by curve a in FIG. 2), so that it is applicable to the timing control of a wide variety of apparatus. However, the flexural rigidity of mica or like insulating material is prone to soft points depending upon the thickness, and it is extremely difficult to produce insulators having a constant and uniform thickness on a mass production basis. Therefore, the deflection of the bimetal strip is likely to be impeded by or fluctuate due to the mechanical resistance of the insulator. Also, the state of close contact between heating wire 1 and insulator 3 such as mica and between bimetal and heater unit consisting of heater wire and insulator is subject to fluctuations, so that heat transferred between bimetal strip and heater unit is liable to fluctuate. These fluctuations are major drawbacks in this type of bimetal strip arrangements.

The self-heating type bimetal strip arrangement (as typically shown in FIG. lb) is simpler in construction and is free from the afore-mentioned fluctuations 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. 2). 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. 2). Therefore, the application of this bimetal strip arrangement is limited due to a very narrow range of controllable time interval.

Like the self-heating type bimetal strip arrangement the radiation type bimetal strip arrangement (as typically shown in FIG. 1c) 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 the temperature of the heating wire which mainly depends upon the 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 heater wire.

The afore-mentioned prior-art bimetal strip arrangements all lack a factor to permit the control of the time interval until the reaching of the saturation temperature of the bimetal strip, so that their compatibility with apparatus of different voltage and power ratings is difficult to realize.

The above drawbacks inherent in the prior-art bimetal strip arrangements are overcome with an arrangement of simple construction according to the invention. An embodiment of the invention applied to an electric bread toaster will now be described.

Referring now to FIGS. 4 and 5, there is shown an electric bread toaster having outer and inner cases 11 and 13. The inner case supports upper and lower heater supports 12, between which heater boards 15 each wound with heater wire 14 are clamped. Numeral l6 designates a bread guard serving to prevent a slice of bread inserted into the toaster from getting into contact with the heater 14.

Supported by a support 17 is a bread seat holder guide rod 18, along which a bread seat holder 19 is vertically movable. The bread seat holder 19 is normally upwardly biased by a 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 according to the invention, and which will now be described in detail by also having reference to FIG. 6.

Numeral 24 designates a base having an upright side projection 25, to which an electric magnet 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 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 30 provides a spring force A consisting of component forces a and a, as shown in FIG. 11.

The component force a tends to cause counterclockwise 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 member 28. The other component force a" is adapted to surpass frictional force between bimetal circuit changeover contacts described hereinafter so as to lower the slide 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 a pair of power supply terminals, as shown in FIG. 8. The movable contact 35 can be connected to or disconnected from fixed

contacts

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

The base 24 also has a horizontal projection 41 for engagement with the afore-mentioned

protuberances

32 and 33 of the slide member 28. A hook member 42 is pivoted by a retainer pin 43 to the base 24 and has a hook to anchor the holder 19. Its end opposite the hook is engageable with the lower end of the slide member 28. It is always biased counterclockwise by a spring 44. Numeral 45 designates an insulator secured by a screw 46 to the base 24 and has component elements to be described later.

Referring in particular to FIGS. 6 and 7, numeral 47 designates a bimetal strip, and numeral 48 an enlarging rod to enlarge the deflection of the bimetal strip. The enlarging rod is provided at its free end with a needle contact 49. On opposite sides of the needle contact 49, there are provided

contacts

50 and 51 facing 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 a toast color adjustment knob 52. Numeral 54 designates a metal 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 connected between

terminal plates

57 and 58. The bimetal strip 47, metal ball 54 and heating wire 56 are thermally coupled in series in the mentioned order, as shown in FIG. 10. In the Figure, G represents the metal ball 54 and G 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 heating wire 56 and bimetal strip 47 sufficiently apart from each other, it is possible to obtain thermal flow as shown in FIG. 10 without any thermal effect such as radiation from theheating 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 controllable time interval and promises ready application of the heatsensitive device according to the invention to apparatus of different ratings and specifications.

The operation of the embodiment of the above construction will now be described.

By bringing the holder 19 to the toasting position, it is anchored by the hook member 42 and locked in that position. Concurrently, the slide member 28 is downwardly urged by the spring 30 and is lowered until the protuberance 33 is brought into engagement with the projection 41 provided in the base 24, whereupon it is locked in that position. At this time, the contact 38, which has previously been in the off position (as shown in FIG. 9a), is brought into contact with the fixed contact 39 on the 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 simultaneously 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 heated in the above way is enlarged by the enlarging rod 48, so that the needle contact 49 having initially been in contact with the fixed contact 51 is detached therefrom 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 41 (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 protuberance 34, so that the slide member 28 experiences a rotational force in the direction of the 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 open the electromagnet circuit. Thus, the bimetal heating circuit is disconnected from the power supply, so that the bimetal strip 47 immediately starts to be 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 30.

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 30, 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-toasting position by the force ofthe spring 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 of position to bring an end to the toasting operation.

As has been described in the foregoing, according to the invention it is possible to eliminate fluctuations of characteristics due to otherwise possible errors introduced in the processing of component parts of the bimetal element and coupling and assembling of these parts, so that time control units of steady and reliable performance can be obtained. Also, the characteristics of the bimetal timer consisting ofthe above bimetal element for activating the electromagnet to switch the bimetal circuit and for releasing the bread seat holder is free from any effect of frictional resistance involved in the operation of the timer construction. 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 construc tion 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.

What we claim is:

1. A heat sensitive device comprising heat sensitive means comprising an electric heating wire, bimetal means, and metal means having a heat storaging function thermally arranged in series with said wire and bimetal means for controlling the amount of heat to be transmitted from said wire to said bimetal means, said heat being generated by said heating wire; and means for providing an output responsive to heating or cooling of said heat sensitive means.

2. A heat-sensitive device comprising bimetal means; metallic means for accumulating heat positioned adjacent said bimetal means; heating means for heating said metallic means and said bimetal means positioned adjacent said metallic and bimetal means, said bimetal, metallic and heating means being thermally coupled in series for controlling the amount of heat transmitted from said heating means to said bimetal means; and output means coupled to said bimetal means for providing an output corresponding to the heat stored in said bimetal strip.

3. A heat sensitive device comprising a heat-sensitive element consisting of an electric heating wire, a metal block and a bimetal strip thermally connected in series with one another in the mentioned order, said bimetal strip deflecting when heated through said metal block by said electric heating wire; switching means coupling a voltage source to a load circuit; and means coupling said bimetal strip to said switching means for on-off control of said switching means in accordance with the deflection of said bimetal strip.

4. A heat-sensitive device according to claim 3 wherein the means coupling said bimetal strip to said switching means includes an electrical contact affixed to said bimetal strip, and an electromagnet actuated through said contact as said heat-sensitive element is heated and cooled.

5. A heat sensitive device according to claim 4 wherein said electromagnet is coupled to said switching means by means comprising a movable piece attractable to said electromagnet; and a slide member driven by said movable piece and provided with first and second'contacts, said first contact controlling energization of said electromagnet and said second contact switching said electric heating wire and said load.

6. A heat-sensitive device according to claim 3 wherein said switching means includes a first switch and said load circuit consists of said electric heater wire and a load connected in series with said first switch; said device further comprising a second circuit in parallel with said load circuit consisting of an electromagnetic coil, a second switch for switching said electromagnetic coil and a third switch having a movable contact coupled to said bimetal strip, a fixed heating contact and a fixed cooling contact, said electromagnetic coil being activated when said bimetal strip is heated to a predetermined temperature to actuate said first switch to deenergize said heater wire and simultaneously switch said second switch from said heating contact to said cooling contact, said electromagnetic coil being subsequently reactivated when said bimetal strip contact of said third switch is brought into contact with said cooling contact thereby removing power-from said load.

7. A heat-sensitive device comprising a heat-sensitive element consisting of an electric heating wire, a metal block and a bimetal strip thermally connected in series with one another in the mentioned order, said bimetal strip deflecting when heated through said metal block by said electric heating wire; means for enlarging the deflection of said bimetal strip; and means coupling said enlarging means to a load for controlling said load in accordance with the heating and cooling of said heat-sensitive element.

8. A heat-responsive device including a heatresponsive switching element comprising heating means, thermal delay means and a bimetal strip disposed thermally in series in said order for performing a switching operation in accordance with the thermal response of said bimetal strip due to heating or cooling of said switching element.

9. A heat responsive device according to claim 8 wherein said heating means comprises a heater wire and said delay means comprises a metal block, said device further comprising first and second terminal plates having said heating wire extending therebetween, said metal block being coupled to said heater wire, and said bimetal strip being engaged with said metal block and extending at a right angle to said heater wire.

10. A heat-sensitive device according to claim 9,

wherein said metal block is a steel ball.

Claims

5. A heat sensitive device according to claim 4 wherein said electromagnet is coupled to said switching means by means comprising a movable piece attractable to said electromagnet; and a slide member driven by said movable piece and provided with first and second contacts, said first contact controlling energization of said electromagnet and said second contact switching said electric heating wire and said load.

6. A heat-sensitive device according to claim 3 wherein said switching means includes a first switch and said load circuit consists of said electric heater wire and a load connected in series with said first switch; said device further comprising a second circuit in parallel with said load circuit consisting of an electromagnetic coil, a second switch for switching said electromagnetic coil and a third switch having a movable contact coupled to said bimetal strip, a fixed heating contact and a fixed cooling contact, said electromagnetic coil being activated when said bimetal strip is heated to a predetermined temperature to actuate said first switch to deenergize said heater wire and simultaneously switch said second switch from said heating contact to said cooling contact, said electromagnetic coil being subsequently reactivated when said bimetal strip contact of said third switch is brought into contact with said cooling contact thereby removing power from said load.

8. A heat-responsive device including a heat-responsive switching element comprising heating means, thermal delay means and a bimetal strip disposed thermally in series in said order for performing a switching operation in accordance with the thermal response of said bimetal strip due to heating or cooling of said switching element.