GB2352330A - Apositive temperature coefficient device provided with an elastic heat conducting member - Google Patents

Abstract

A PTC device 2 expands upon temperature increase and in order to maintain good thermal contact between the PTC device and a ceramic/metallic heat sink 5 a dielectric, thermally conductive, elastic heat transfer body 4 is provided. The elastic body may have heat conducting material particles suspended therein or may have an adhesive outer surface. The elastic body may fully enclose the PTC device or may be provided in rings around the device. Plural PTC devices 2 may be enclosed in individual bags made of the elastic heat transfer medium 4 and these bags may be made to be inter-adhering.

Description

2352330 HEAT RADlATION SYSTEM FOR ELECTRIC CfRCUITRY

BACKGROUND OF THE INVENTION

Field of the invention

The present invention relates to a heat radiation system for electric circuitry.

More specifically, the invention relates to a heat radiation system for electric circuitry including a "solid body releasing heat in balance, as it has a higher temperature than a surrounding body" (hereafter called "solid heat source body" or simply "heat source"), a "solid body receiving heat in balance, as it has a lower temperature than the heat source' (hereafter called "solid heat sink body' or simply "heat sink"), and a -body of medium or media conducting beat in balance in between, as it has a gradient or gradients of temperature continuously descending from the heat source to The heat sink" (hereafter called "heat conducting circuit" or simply "heat circ uiC).

In particular, the inyention is associated with elecuic circuitry having a "positive temperature coefficient thermistoe' (bereafter called -YTC device"), and a beat radiatian plate The-PTC device.

Description e i&An

Md PTC--.d&vice is insmIled in an electric circuit connected to an electric load The circuir 66n.,ducts an electric current, which generates Joules heat at -a positive temperature coefficient resistor elemene' (hereafter called "PTC element") of Ehe PTC device, whereby the PTC element is beated and has a EeMPCTature in accordance with an occasional heat balancc. If the temperature exceeds a specified level, the FTC element trips to have a suddenly increased resistance so that the current is interrupted.

To restore the FTC element, its temperature needs to be lowered by dissipating heat through a heat radiation mechanism, in which the PTC element and electrodes in contact therewith release heat and one or more forced or n4tural heat- radiation members and large heat-capacity structural members near the PTC element receives heat.

A known FTC element comprises a body of thermally sensitive polymer and a sytorri of electrically conductive particles suspended therein, and the body of polymer is adapted for a significant thermal expansion to have a decreased density of condoccivc particles to provide an increased resistance. A PTC device with such a PTC element 1S somdurnes employed for electric or elccuonic control in ari automobiie, Conventional techniques for radiating heat from a PTC dmce have been the provision of a metallic enclosure or wall with or without fins, see Japancst Patent Application Laid-Open Publication No- 4-78104, published March 12, 1992, jdpancsc:

Patew Application Laid-Open Publication No. 61-234502, published October 18, 1986, 1 Japanese Utility Model Application Laid-Open Publication No. 62-163902, published October 17, 1987, and Japanese Patent Publication No. 2-41161, published September 14,1990.

SUMMARY OF THE INVENT10N

In view of the inventor, there has been provided a conventional heat radiation system for electric circuitry, the system comprising a combination of an electric-current conducting body and one or more significantly heat-conduciive members in contact thercwith as a "solid heat source body", a surTounding structure or member in a vicinity of the solid heat -source as a "solid heat sink body", and an intervening body of air between the solid heat source and the solid heat sink as a "gaseous heat circuit".

In the case of an electric circuit including a PTC device, the conventional heat radiation system comprises a combination of a PTC clement aild a pair of electrodes in contact therewith as a "solid heat source body with a tendency to thermally expand and contract", a heaE radiation member in a vicinity thereof as a "solid heat sink bod', and an intervening body of air therebetween as, a "gaseous heaE circuit" If the surrounding structure or member in a vicinity is metallic, ffic system comprises a combination of an electric-current conducting body and one or more significantly heat-conductive members such as electrodes in contact therewith as an "electrically conductive solid heat source body", Ebe surrounding structure or member in the vicinity as an "electrically conductive solid heat sink body", and an intervening body of air therebetween as an "electrically non-conductive or insulating (i.e. dielectric) gaseous heat circuit".

In any case, the gaseous heat circuit has a relati vely small tendency to conduct heat, and is extremely susceptive to occasional factors so that it has an uncertain varying nature, unable to support a weight, and flees.

However, it has an extreme flexibility to occupy any form of space, accepts any intrusion or physical action, and never resists in a free space.

The present invention has been achieved with such points in view.

It therefore is an objccc of the present invention to providc a heat radiation system for electric circuitry includino a heat circuit in which mcrits and dcmerils of a gaseous heat circuit arc intentionally taken iind improved, rcspectively.

To achieve the object, an aspect of the invention provides a hcat radiation system for electric circuitry comprising a solid heat source body, a solid heat sink body, and a solid heat circuit interconnecting the solid heat source body and the solid heat sink body with each other, wherein the solid hcat circuit comprises an elastic body having a 2 larger tendency to conduct heat than the air.

In the heat radiation system for electric circuitry according to Elie aspect of the invention, the solid heat circuit can have an increased heat conductivity, hold the solid heat source body and the solid heat sink body within a desirable range of relative distance when either body is pushed toward the other, effectively eliminate influences of occasional factors, absorb displacements of and attenuate shocks to or vibrations of the solid heat. source body and/or the solid hear sink body That may be a PTC element having a tendency to thermally expand and contract, provide a flexibility in design of outside dimensions and spacing, and have an improved handling nature The elastic body may preferably have a heat conductivity doner additionally suspended therein to have an increased hear conductivity, Permitting d purposc-orlented control of heat conductivity.

The elasEic body may preferably have an adbesive outer surfact: tu permit an improved close conTaCE with a sufficient retaining force.

The elastic body may preferably hold one of Ebe solid heat source body and the solid heat sink body to eliminate a StrUCEural support therefor.

The elastic body may preferably have an adhesivity doner coated thereon and/or raixed therein so That the adhesive outer surface defines an application surface, permitting a decreased dust deposit.

The adhesive outer surface may preferably be coated With an exfoliaiive body To permit a POSE-application.

In the case of a metallic surrounding structure or mcruber, the elastic body may preferably comprise a dielectric body and the solid heat source body and/or the solid hear sink body may preferably comprise a direcE-current circuit such as a thermistor circuit, to avoid causing an undue induced current.

The solid heat Source body may preferably comprise a PTC element.

The solid heat sink body may preferably comprise it metallic membt:r The solid heat sink body may preferably comprise a ceramic member.

BPJEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the samc- is rcad in comuncilon with the accompanying drawings, in which:

Fig. I A is a schematic perspective view of a "combination of a PTC dcvlcc and an elastic body coated thereon" (hereafter called "PTC artic1c") as an essenti3l portion of -i hcat radiation system according to an embodiment of the invvniloli, which -syslcrn ill 3 constituted as a "combination of the PTC article and a heat radiation piece attached thereto" (hereafter called "PTC radiation systern"), Fig. 113 is a schematic side view of the PTC radiation system; Fig. 2A is a perspective View Of the PTC device in the FTC article of Fig. 1A, and Fig. 213, a cross sectional view of the PTC article of Fig. IA) Fig. 3 is a perspective view of a PTC radiation system according to another embodiment of the invention; Fig. 4 is a schematic side view of an essential portion of a FTC radiaiion system according to another embodiment of the invention; and Fig. 5 is a schematic side view of a "combination of a heat radiation piece and an elastic body attached thereto" (hereafter called "radiation article") as an essential portion of a PTC radiation system according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS is There will be detailed below the preferred embodiments of the present invention with reference to the accompanying drawings. Like members are designated by like reference characters.

Fig- 1A shows a PTC article 1 of a PTC radiation system (1+5) according to a first embodiment of the invention, Fig. 113, the PTC radiation sysiern, Fig. 2A, a PTC device 2 in the PTC article 1, and Fig. 213, a vertical cross section of the PTC article 1.

As shown in Figs. 2A and 2B, the FTC device 2 comprises a PTC element 20, and a pair of left and right electrodes 21 and 22 attached to the PTC element 20.

The PTC element 20 comprises "a substantially rectangular parallelepiped body 20a of a thermally expansive and thermally compressive, heaE-conduclive and adhesive compound of one or more polymers and one or more additives such as for adhesion, and a system of electrically conductive resistor tissues or particles 20b suspended in The body 20a" (hereafter called -conductive polymer compound") that is adapted for -11 1. positive temperature coefficient characteristic" (hereafter called PTC characteristic") and generates heat upon conduction of direct current.

The left and right electrodes 21 and 22 comprise: left and right heatconducilivc metallic electrode plates 21a and 22a bound by adhesive forces acting on whole areas of their inner surfaces to left and right sides of the FTC element 20 (more specifically, ol V, (he conductive polymer compound 20a), respectively-, and conductor-.; (in the form ol' straight itrininals 21b and 22b in Fig. 2A or as wirc leads 3 and 3 In Fig. 1A) joined, e.g.

by integration or soldering, at Lipper cnds thereof to SL3ggCTcd lower front and rear ends (Flg 2A) or arbitrary locations on outer surfacus (Fig. 1A) of the left and right clectrodc 4 places 21a and 22a, respectively.

The PTC element 20 and the electrode plates 21a and 22a constitute an electrically conductive, LhermaHy expansive and Contractive solid heat source body in the PTC radiation system of Fig. 1B.

As shown in Fig 1A, the PTC anicle I comprises the PTC device 2 and an adhesive elastic body 4 (or layer or film) put or coated over an entire outer surface of the heat source body (20t2ia+22a).

As shown in Fig- 2B, the elastic body 4 comprises: an object-conforming body of an elastic, wholly or at least partially electrically non-conductive (i.e. dielectric), physically adhesive, heat-conductive and wholly or layer-wise homogeneous compound of a silicon gel and a basic quantity or basic quantities of one or more additives (e.g.

silica or alumina) such as for heat conduction and adhesion; and a wholly or layer-wise homogeneous system of a controlled additional quantity of well heat- conductive minute synthetic or crystalline, dielectric particles 41 (or pieces or tissues) suspended in the compound body 40. The suspended Particles 41 (or pieces or tissues) are identical to [he addifive(s), but may be different. The compound body 40 has a higher heat conductivity than the air, as a whole or layer-wise, as necessary- ne suspended system 41 is higher in beat conductivity than the compound body 40, as a whole or component-wise, as necessary. ThcTefore, the elastic body 4 has a by far stronger tendency to conduct heat than the air. The additives in the silicon gel compound of the elastic body 4, such as for adhesion and heat conduction, may be controlled -in quantity, area and/or layer-wise to provide a flexibility in design. The suspended system 41 may be omitted for general applications where the elastic body 4 is expected to have a significantly stronger tendency to conduct beat than the airThe elastic body 4 may bt 2S applied on the heat source body (20+21a+22a) by a dipping, molding, spraying of other applicable techniques for the coating, e.g- by simply putting.

An outside 4a of an entirety of the elastic body 4 has a substantially rectangular parallelepiped form. An inside 4b of the entirety of tbe elastic body 4 envelopes over and adheres to an entire outer surface of the heat source body, In a respective direction (e.g. X, Y or Z orthogonal direction in an associated coordinate system), the elastic body 4 has greater chicknesse,; than a specified thickness i (preferably aUmm) beiween inside 4b and ouisidr- 4a, as the thickness i is determined for a required conforming, elastic deformation at each application side of the body 4 to allow a maximal linear expansion and contraction through a trip of the heat source body (more specifically, of the PTC element 20) without undue counter force in tht rvspective direction, in con,;idera[lon of a configuration and dimensions of the electrodes 21 and 22 that may have an over-span or under-span relative to the PTC element 20. Such a thickness (t) is to enable applications to a limited spacing (e.g. Fig. 3 or 4), and may be voluntarily determined for general use.

The elastic body 4 may have an envelope form opening at one end or both ends S for insertion of the heat source body and at some locations for joining [he conductors, and may additionally have (a) cover(s) to close the opcning.

The elastic body 4 may comprise a plurality of divided or separable parts of a ring or sheer form. One or more sheets of elastic body (4) may be parched Simply on an application side of the hear source body- Any such elastic body, as already attached or provided alone or as a formatted patch sheer to be scissored, may be - sold in the form of an elastic body article (4 with or without 60 [Fig- 5]) that may be- protected at the remaining side or both sides with a conforming exfoliable sheer (60 [Fig5]) of processed paper and/or resin or metal enCIOSUre put thereon and easy to peel or remove.

The elastic body 4 may comprise a less adhesive or simply frictional inner sarface layer for bolding or accommodating the heat sink body, an elasuc inter-surface layer with a nominal thickness (t), and a significantly adhesive outer surface layer or film for a void-free adherence to The heat sink body.

In a prefabricated form of the PTC article I or in a processed form, the elastic body 4 may be adhesive or may have an adhesive layer or film simply at or over a specified or probable application side to the heat sink body, or may have a Dun-adlicsive edge or surface rcgion, each for an exposed application to an atmosphere needing a cleaner.

The elastic body 4 may comprise an adhesive elastomer such as an adhf-. sive rubber or polymer. Note the body 40 is not an adhesive tape.

As shown in Fig. 1B, a substantially rectangular heat-conductive metallic and/or ceramic, crystalline or synthetic heat radiation place 5 is attached to an outside (4a in Fig. 2B) of the PTC device 1, to be carried by adhesive forces of the elastic body 4. The condUCEOr 3 (or 21b and 22b in Fig. 2A) is soldered to a printed circuit on a substrate or fitted in a connector, or may be a free-sfanding lead to support an entire system. The radiation plait: 5 may be part of a structure or subsirdic and may carry thc PTC device I attached thereto.

Thv. radiation plate 5 consilcute a solid heat sin- body in ihC PTC radiation qstern (1+5). Hcdi is effectively conducttd from the heat sourcc body (20+ 21a+22LI) via the elastic body 4 to the heat -sink body (5) and to outside cliereof, -,c) ihul (he PTC 3 clcmriit 2U has a conirollcd temperaturc rlSe.

According to the first embodiTneric, ds 2 hcat source body of a PTC dcvlcc-. 2 has 6 an adheqlve elastic body 4 coated [hereon, a radiation plate 5 can be attached Thereto with case by t3se of the adhesiviTy of elastic body 4. A resultant provision of The elastic! body 4 in between and in void-free contact with both the hear source body and the radiation plate 5 as a beat sink body permits an enhanced heat conduction from the heat source body To the heat sink body, giving rise to an increased radiation efficiency, allowing for the PTC device 2 Lo be designed with an increased capacity for current conduction. Further, in application to an automobile or the like, the elastic body 4 effectively absorbs or attenuates occasional shocks or vibrations to the PTC device 2, as the radiation plate 5 is cooperative therefor.

Fig. 3 shows a PTC radiation system (1+5) according to asecond embodiment of the invention In this radiation system, a pair of left and right spaced and aligned PTC articles I are supported by lead terminals 3 thereof, which (3) are joined at their lower ends by solder ts to a printed circuit board 7. The left and right PTC articlcs 1 have elastic bodies 4 thereof supporting a pair of front and rear horizontal heat radiation plates 5.

These radiatiori plates 5 are attached by adhesion to front and rear application surfaces of the elastic bodies 4, and are fastened to each other by a machine screw 6 provided through the plates 5 and between the PTC articles 1 so that the plates 5 are spaced from each other at a distance a little smaller than a normal thickness of each article I at a room temperature. The left and right PCIaTticles 1 may be attached to each other at their side faces, and the plates 5 may be fastened by a pair of left and right screws spaced from each other at a larger distance than a doubled width dimension of each article 1.

According to the second embodiment, a tnippirig thermal expansion in a ihickness direction of a heat source body of either PTC article I can be absorbed as front and rear portions of an elastic body 4 between the heat source body and radiation plates, elastically conformingly deform in a laterally escaping manner, and The plates 5 can be brought into void-free full contact with each PTC article 1, permitting the more frihanced heat conduction, achieving an enhanced radiation efficiency Fig- 4 shows a PTC radidLion system (I t5) according to a third embodiment Of' the invention.

In this radiation system, a pair of front and rear PTC articles I adhere io each other at mutually facing sides of their elastic bodies 4 without voids, and an oppositz:

sidc of either or each article I is to likewise stick tu d single or corresponding hcai radiation plate S.

According to the third ciribudlincrit, 3 pair of Joined hua[ circuits pcririll an 7 enhanced in(erfacial beat dissipation capacity and an increased device density. A pair of mutually adhering elastic bodies 4 work as an efficient thermal coupler with an increased heat dissipation capacity.

Fig. 5 shows a heat radiation arTicle (St40+60) for a PTC radiation system according to a fourth embodiment of the invention.

The radiation article comprises a metallic or ceramic heat radiation plate 5, an elastic sheet of adhesive compound 40 adhering to [lie radiation plate 5, and an exfoliable sheet 60 of paper or resin Covering an outer surface of the compound 40 and adapted to be peeled off with ease by fingers.

For application, the sheet 60 of paper is removed, and The outer surface of the compound 40 is brought into void-free contact with a heat sink body of the radiation system.

The adhesive compound 40 may have a system of particles (41 in Fig. 2B) suspended therein is It will be seen that the foregoing embodiments can be combined in a voluntary The embodiments described have such an aspect that, in a beat radiation system for a PTC device provided with a hear radiation plate as a beat sink body to be attached thereto, a surface of a heat sourcr- body of the PCT device is coated with a heat conductive adhesive elastic agent, and the heat radiation place is attached by an adhesive force of the coated agent.

As the coated elastic agent is adhesive, the radiation plate can be attached to the heat source side with ease. As the heat-conducEive agent is in void- free Contact with both the heat source body and the heat sink body, heat is efficiently conducted between from heat source to heat sink, ptTmitting an enhanced radiation.

Moreover, a pair of hear radiation plates are attached to both sides, each to one side, of a heat source body of z PTC device coated with a heac-conductive adhesive elastic agent, and are fastened to be fixed relative to each other by a screw.

AS the elastic agent absorbs an occasional tripping th(=al expansiaii of the heat source body of the PTC device, the hear source body coatcd W[ch [hc agent can bc fitted in a void-frce manner between the radiddon plates.

Further, a pair of PTC devices hijvinp I _, their heat sink bodics coated wit], adliesive elasiic layers are fixedly attached to each oTher by ihc adhesive layer,.,, pcr-miLting a void-frce contact in between, acbleving an enhanced heat couphlig characteristic.

While prefvrr-fd embodiments of [he presenc invention have been described 8 using specific terms, such description is for illustrative purposes, and it 'Is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.

Claims (15)

Reference is hereby made to co-pending UK Patent Application No. 9828568. 7, the matter for which protection is claimed being: a heat radiation system for electric circuitry comprising: A heat radiation system for electric circuitry comprising: a solid heat source body; a solid heat sink body; and a solid heat circuit interconnecting the solid heat source body and the solid heat sink body with each other, wherein the solid heat circuit comprises an elastic body of a compound having a larger tendency to conduct heat than the air and a thermal conductivity donor additionally suspended in the elastic body to increase the thermal conductivity of the solid heat circuit, and wherein the compound further includes an adliesivity donor. 9 CLAIMS:

1. A heat radiation system for electric circuitry comprising: a solid heat source body; a solid heat sink body; and a solid heat circuit interconnecting the solid heat source body and the solid heat sink body with each other, wherein the solid heat circuit comprises an elastic body of a compound having a larger tendency to conduct heat than the a1r, and wherein the solid heat source body comprises a PTC element.

2. A heat radiation system for electric circuitry according to any preceding Claim, wherein the compound includes an adhesivity donor.

3. A heat radiation system for electric circuitry according to Claim I or 2, wherein the elastic body has a thermal conductivity dorior additionally suspended therein to increase the thermal conductivity of the solid heat circuit.

4. A heat radiation system for electric circulti-y according to Claim 3, wherein the elastic body has a hoinogenOLIS systein of pailicles of the heat conductivity donor suspended thereill.

5. A heat radiation system for electric cli-culti-y accordHig to Claim 4, wherein the homogeiious system has a larger heat cotiductivity than the compound.

6. A heat radiation system for electric circulti-y according to Claim 1, wherein the elastic body conformingly adheres to the solid heat source body and the solid heat sink body.

7. A heat radiation system for electric circuitry according to Claim 6, wherein the elastic body comprises a container for accommodating the solid heat source body.

8. A heat radiation system for electric circultry according to Claim 7, wherein: the solid heat source body comprises a plurality of PTC elements; and the container comprises an inter-adhering combination of a plurality of bags individually enclosing the plurality of PTC elements.

9. A heat radiation system for electric circuitry according to any preceding Claim, wherein the solid heat source body is thermally expansive-

10. A heat radiation system for electric circuitry according to Claim 6, wherein the elastic body supports one of the solid heat source body and the solid heat sink body at a variable distance relative to the other.

11. A heat radiation system for electric circuitry according to Claim 10, wherein: the solid heat sink body comprises a pair of plate members fixed to each other, with the solid heat source body interposed flierebetween; and the elastic body intervenes bet\veen the solid heat source body and the pair of plate members.

12 12. A heat radiation system for electric circulitry according to Claim 1, wherein: the elastic body comprises a dielectric body; and the solid heat sink body comprises a direct-current cil,cult.

13, A heat radiation system for electric circuitry according to Claim 1, wherein the solid heat sink body comprises a metallic member.

14. A heat radiation system for electric circuitiy according to Claim 1, wherein the solid heat sink body comprises a ceramic member.

15. A product as substantially as hereinbefore described, witli reference to Figures 1B, 3 and 4.