AU642034B2 - Ionization smoke detector - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 6420 3 COMPLETE SPECIFICATION FOR A STANDARD PATENT 000 0 erg.

ego's e ~so0 Name of Applicant: Address of Applicant: Actual Inventors: Address for Service: HOCHIKI KABUSHIKI KAISHA 10-43, Kamiosaki 2-chome, Shinagawa-ku Tokyo, Japan Yoshinori Kaminaka Hiroshi Yashima Griffith Hack Co.

601 St. Kilda Road Melbourne VIC 3004 S. i is 0r Standard Complete Specification for the invention entitled: IONIZATION SMOKE DETECTOR Details of Associated Provisional Applications: Details of Parent Application for Divisional Applications: 26896/88 Hochiki Kabushiki Kaisha filed December 15, 1988.

The following is a full description of this invention, including the best method of performing it known to me:- TONTZATTON SMOKE DETECTOR BACKGROUND OF THE TNVENTTON Field of the Invention This invention relates to an ionization moke detector having a characteristic moisture-proof structure for preventing penetration of moisture etc. into a circuitry accommodating portion and having a characteristic structure for mounting electrodes on an insulating board within a detector cover.

e Prior Art As conventional ionization smoke detectors, there may be mentioned, for example, a smoke detector as illustrated in Fig.16.

In Fig.16, 50 is a detector body, 51 is a body cover and 52 is an outer cover. The outer cover 52 has smoke S* inlets 53.

An insulating board 54 is disposed in the detector body comprising the body cover 51 and the outer cover 52. An inner electrode 56 with a radiation source 55, an intermediate electrode 58 with a transmitting aperture 57 and an outer electrode 59 into which external smoke may enter are supported and fixed on a Foreside of the insulating board 511. These electrodes constitutes an electrode arrangement for ioni.ation smoke detection. A printed circuit board with detector circui.try packaged thereon is placed on a backside of the insulating board 511.

A space for accommodating the printed circuit board is sealed, at its lower portion, with the insulating board 54 through a rubber packing 61 and, at its upper portion, 2 with an upper li.d 63 through a rubber packing 62, to prevent penetration of moisture or corrosive gases.

However, the number of parts to be employed is large and the manufacturing process is complicated in the conventi.onal i.onization smoke detector as described above, because the rubber packings 61, 62 are used for moisture preventing structure of the circuitry accommodating portion. In addition, the rubber packings 61, 62 increase a height of the detector, which makes it difficult to reduce the size of the detector.

Tn the conventional ionization smoke detector, an intermediate electrode 58 is mounted by screws on the insulating board 511 through a spacer64 for forming an inner ionization chamber between the intermediate electrode 58 and the inner electrode 56.

Tn such an arrangement, a space is needed to fix the intermediate electrode 58 to the insulating board 54 by screws. This increases the space for mounting the intermediate electrode 58 and makes the assembling operation complicated because it needs screw fasteni.ng operation.

Furthermore, the conventional ionization smoke detector has such a disadvantage that an electrode lead of the intermediate electrode 58 extends through the insulating board 54 to be connected to a lead of PET on the backside of the insulating board 54. This allows moisture or corrosive g.,ses to enter the circuitry accommodating space through the opening of the board through which the lead extends. This will possibly corrode the circuit parts.

3 SUMMARY OF THE INVENTION The present invention was developed with a view to providing an ionization smoke detector which is less susceptible to the problems involved in the conventional techniques.

It is an object of the present invention to provide an intermediate electrode mounting structure for an ionization smoke detector which is capable of easily mounting the intermediate electrode and capable of protecting circuit parts, allowing an electrode lead to extend through the insulating board to a circuit accommodating portion.

According to the present invention there is provided an ionization smoke detector, comprising a cover, an insulating board provided within the cover and having a foreside and a backside, a circuit board disposed on the backside of the insulating board, said insulating board ooooo S"having an inner electrode with a radiation source, an :intermediate electrode formed with an opening for transmitting radiation from said radiation source, and an coo• 0 20 outer electrode formed with smoke inlets located within a 0 o 0: side wall thereof, said inner, outer and intermediate electrodes being disposed substantially on the foreside of said insulating board; **oo* o *said intermediate electrode having a 25 plurality of support legs and at least one electrode lead formed integrally with one of said legs; said electrode lead being inserted into a **slit from the foreside of the insulating board and connected V'06'to a lead of an FET incorporated and insulatedly sealed on 30 the backside of the insulating board; and, each said support leg having serrated edges and being inserted and fixed in holes provided within the foreside of the insulating board, wherein said holes do not extend through the insulating board.

With this arrangement, the intermediate electrode can be mounted easily simply by inserting the support legs formed on the periphery of the intermediate electrode into holes 4 opening on the foreside of the insulating board. Thus, screw fastening may be omitted to minimise the space for setting the intermediate electrode. This will enable thi entire thickness of the smoke detector to be reduced and the assembling steps to be simplified.

In addition, the support legs each have serrated edges. so that they can fix and support the intermediate electrode positively in place When they are fitted in the engaging holes of the insulating board.

The electrode lead may be formed integrally with the support leg in the form of an extension of the support leg.

The insulating board preferably has openings for passing contact metal members of the outer electrode for the circuit board therethrough, said openings being formed, leaving •"15 a thin, film-like portion before the contact metal members have 00*e been passed therethrough. In this case, possible penetration e of moisture etc. through the openings for passing the contact metal members therethrough can be prevented.

The insulating board may have openings for inserting an LED on the circuit board for alarm indication therethrough.

The openings are formed, leaving a thin, film-like portion gem before the LED has been inserted therethrough. In this case, possible penetration of moisture etc. through the opening for 0 passing the contact metal members of LED therethrough can be 25 prevented.

The inner electrode may be fitted in an opening in S: the insulating board and the inner electrode may be caulked at 4 its shoulder portion to be fixed in place after it has been *:see: fitted in the opening of the insulating board.

In order to facilitate a better understanding of the invention a preferred embodiment will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of one form of an ionization smoke detector according to the present invention; Fig. 2 is an exploded perspective view of the detector shown in Fig. 1; Fig. 3 is a plan view of a backside of an insulating board; Fig. 4 is a centrally taken sectional view of the insulating board; Fig. 5 is a plan view of a foreside of the insulating board; Fig. 6 is a sectional view of the insulating board taken along line VI VI; go00 S S **e 4

S*

&oooop t

S

Fig.7 is a sectional view of the ionization smoke detector with the insulating board fi.xed therein; Fig.8 is a fragmentary sectional view showing the insulating board before it is fixed; Fig.9 is a similar fragmentary sectional view showing the insulating board after it has been fixed; is an enlarged sectional view of an FET accommodating structure: Fig.11 is a plan view of an intermediate electrode and Figs.11 and are side views taken according to arrows A and B, respectively; Fig.12 is a sectional view of the ionization smoke detector with the intermediate electrode mounted thereon; Figs.13 and are sectional views each showing an inner electrode before and after it has been fitted in an opening, respectively; Figs.14 and are sectional views each showing an LED before and after it has been fitted through an opening, 0 respectively; Figs.15 and are sectional views each showing a V ,to. contact metal or an electrode lead before and after it has *o been inserted into a slit or a hole, respectively; and Fig.1! is a sectional view of a conventional ionization g smoke detector.

s FREFERRED EMBODIMENT OF THE PRESENT INVENTION Fig.1 is a vertical sectional view of one form of an ionizaiton smoke detector embodying the present invention.

In Fig.1, 1 designates a detector body which is detachably fitted to a detector base 2 fixed on a ceiling. The detector body 1 comprises a body cover 3 adjacent to the detector base 2 and an outer cover 5 fitted to a lower side of the body cover 3 and having smoke inlets 4 on a side wall thereof.

In the detector body 1, an insulating board 6 is incorporated to partition the inside of the detector body 1 into a circuitry encasing secti.on and an electrode section for ionization smoke detection.

An inner electrode 7 i.s fitted centrally in the insulating board 6. An intermediate electrode 8 having an opening for allowing radiation from a radiation source to be transmitted therethrough is mounted, surrounding the inner electrode 7. An outer electrode 9 having smoke inlets on a side wall thereof is further provided, surrounding the intermeo3 diate electrode 8. An inner ionization chamber A is defined between the inner electrode 7 and the intermediate electrode 8 and an outer ionization chamber B which is formed to allow external smoke to enter thereinto is defined between the intermediate electrode 8 and the outer electrode 9.

An FET accommodating portion 13 encased by a partition wall 14 is provided at an appropriate position of the ".St backside of the insulating board 6. An FET 12 is incorpo- S rated in the PET accommodating portion 13. A lead 15 of the interme-....te electrode 8 is passed through the insulating board 6 and connected to a lead of the FET 12 incorporated in the FET accommodating portion 13. A hot melt synthetic resin is filled to pot the FET 12 together with the FET S accommodating portion 13 accommodating the FET 12 and the intermediate electrode lead 15 connected thereto. Thus, the FET accommodating portion 13 together with the FET 12 and the lead 15 are all potted. The lead of the FET 12 is also potted in the synthetic resin.

A capacitor accommodating portion 24 is also formed on the backside of the insulating board 6 in the embodiment as illustrated.

The insulating board 6 further has a circuitry accommodating portion on the backside thereof. A printed circuit board 10 is fitted closely to the backside of the insulating board 6. A capacitor 26 accommodated in the capacitor accommodating portion 211 and the FET 12 potted in the FET accommodating portion 13 are connected to the printed circuit board A cylindrical shield case 11 which opens downwardly is mounted at an upper portion of the circuitry accommodating portion provided on the backside of the insulating board 6 to which the printed circuit board 10 is fitted. The S• reverse side, to wit, the foreside of the insulating board 6 is shield by the outer electrode 9.

Fig.2 is an exploded perspective view of the detector body 1 shown ih Fig.l.

*eq *In Fig.2, the body cover 3 has an inner opening 3a which opens downwardly (as viewed in Fig.2). Two contact pins 16 are provided at the inner opening 3a for electrically connection to the printed circuit board 10. An engaging member 17 is fixed to the lower side of each of the contact pins 16 for engaging with the detector base 2.

The -shield case 11 is assembled in the inner opening 3a of the body cover 3 and the printed circuit board 10 packaging the detector circuitry is in turn assembled therein.

Further to the printed circuit board 10, the insulating board 6 is assembled and the inner electrode 7 comprising an electrode member 7a, a radiation source 7b and an electrode cover 7c is fitted centrally to the insulating board 6.

Around the inner electrode 7, the annular intermediate electrode 8 is mounted and around the intermediate electrode 8, the outer electrode 9 having smoke inlets 9a formed on the side wall thereof is mounted.

The outer electrode 9 is fixed to the insulating board 6 by inserting contact metal members 8 through slits 33 of the insulating board 6. A tip end of each eP th contact metal member 18 extends through the printed circuit board 9

T

to contact a contact portion 19 of the shield case 11. The contact metal member 18 is soldered at a grounding portion of' th.- printed circuit board 10 through which the contact metal member 18 extends. Thus, the contact metal member 18 functions to fix the outer electrode 9 to the insulating board 6 and to provide electrical connection for shielding the accommodating portion of the printed circuit board 10 in combination with the shield case 11.

Further to the outer electrode 9, a bottom board 20 and 0 the outer cover 5 having smoke inlets 4 formed on the side wall thereof are assembled. Inside of the outer cover 5, a fly-screening net 21 is provided.

Figs.3 to 6 illustrates the insulating board 6 shown in Fig.l: Fig.3 is a plan view of the backside of the insulating board 6, Fig.4 is a vertical sectional view of the same taken along a line passing through a center, Fig.5 is a plan view of the foreside of the insulating board 6; and Fig.6 is a vertical sectional view taken along a line VI VI.

As illustrated in Fig.4, an annular engaging flange portion 26 is integrally formed on the outer periphery of the insulating board 6. This engaging flange portion 26 has a free end which extends towards the backside of the insulating board 6 and extends outwardly. On the other hand, the body cover 3 to which the insulating board 6 is fitted has an engaging groove 27 at a position corresponding to the engaging flange portion 26 as best shown in Figs.l, 8 and 9.

The engaging groove 27 is so formed that an outer, inner wall of the groove has an inclined face 27a. The largest diameter of the groove 27 is slightly smaller than the outer diameter of the engaging flange portion 26.

Fig.7 shows an arrangement of the insulating board 6 in relation with the detector body 1 which comprises a body cover 3 and the outer cover 5. In Fig.7, a part of the electrode structure is omitted.

More particularly, the i.nsulating board 6 is assembled by inserting the annular engaging flange portion 26 formed on the outer periphery thereof into the engaging groove 27 formed in the body cover 3. Simultaneously the insulating board 6 is assembled, the shield case 11 is set in the circuitry accommodating portion. The outer cover 5 is fitted thereafter, intervening the outer electrode 9.

Before the insulating board 6 is mounted as illustrated in Pig.8, the annular engaging flange portion 26 has a free end bent to extend outwardly. When the annular engaging .Wp flange portion 26 is pushed into the engaging groove 27 of the body cover 2 as indicated by arrow, the annular engaging flange portion 26 is pressed inwardly by the engaging groove 4. s. 27. Thus, the tip end of the insulating board 6 is pressed against the outer inclined inner face of the engaging groove 27 by a reaction of the compressed annular engaging flange porti6n 26. As a result of this, possible penetration of .moisture or corrosive gas into the circuitry accommodating portion can be positively prevented without using a rubber packing etc.

When the annular engaging flange portion is pushed into the engaging groove, the inner face of the flange 26 is forced to press against the inner wall 27b of the g.oove to prevent penetration of the outside air.

In Fig.4, The insulating board 6 has an opening 28 at o S its central position thereof for mounting the inner electrode 7 thereon. When the inner electrode 7 is mounted in the opening of the insulating board 6, an edge 7a of the inner electrode 7 is caulked after the inner electrode 7 has b'en inserted through the opening 28 as illustrated in Figs.13 and Thus, the inner electrode 7 is fixed in the opening 28 of the insulating board 6. Because the inner electrode 7 is fixed by caulking, a gap between the inner electrode 7 and the opening 28 is fully sealed. As a result of this, possible penetration of moisture etc.

through the gap can be prevented.

A multi-annular groove structure 29 comprising a plurality of annular grooves is formed around the opening 28 for acquiring a creeping distance between the electrodes. A slit 30 is formed in the insulating board 6 for passing the electrode 15 of the intermediate electrode 8 as shown in Fig.11 from a right portion (in Fig.4) of the multi-annular groove structure 29 to the FET accommodating portion 13 encased by the partition wall 14 on the backside of the insulating board 6.

In this connection, it is to be noted that the capacitor accommodating portion 31 is formed on the backside of the insulating board 6 on the left side of the opening 28.

00 Referring now to Fig.3 which shows a plan view of the backside of the insulating board 6, the FET accommodating portion 13 formed in an elliptical shape and encircled by the partition wall 11 on the right side of the opening 28 is disposed centrally in the insulating board 6. The FET accommodating portion 13 has at a bottom portion thereof an FET receiving hole 32 and the slit 30 if formed at an inner 0* position for passing the lead 15 of the intermediate electrode 8.

The configurations of the FET accommodating portion 13 and the capacitor accommodating portion 31 will be more apparently understood from a centrally taken sectional view of the insulating board 6 as illustrated in Fig.4.

In Fig.3 and 5, Two slits 33 are formed at positions deviated from the center of the insulating board 6 for passing the contact metal members 18 for fixing the outer electrode 9 towards the backsi.de of the .insulating board 6.

Each of the slits 33 is so shaped that it has an inner diameter reducing towards the top as illustrated in Fig.6 The slit 33 is shaped to point at the top, leaving a very thin, film-like portion at the backside of the insulating board 6. The contact metal member 18 is inserted into the slit 33, while breaking the thin, filmlike portion of the slit 33 as shown in Fig.15 Since the thin, film-like portion is left for the slit 33 and the contact metal member 18 is inserted breaking the thin film portion, the thin film-like portion closely contact the contact metal member 18 after the contact metal member 18 is inserted therethrough. As a result of this, possible penetration of moisture etc. through the slit 33 can be prevented.

Referring now to Fig.5 which shows the foreside of the insulating board 6, engaging holes 34a, 34b anc 34c are formed at positions outer than the opening 28 for mounting the intermedi.ate electrode 8. The engaging holes 34a, 34b ar" engaged with support legs 24a, 24b of the intermediate electrode 8 having no electrode lead as illustrated in S Fig.11. The slit 30 for passing the electrode 15 provided on a support leg 24c of the intermediate electrode 8 as 0. shown in Fig.11 opens within the engaging hole 34c.

An opening 39 formed on a leftside projection corresponding to the capacitor accommodating portion 24 is used for fitting an LED 40, which is provided on the printed circuit board 10 for indication of alarm, therein. This opening 39 is formed, leaving a thin film-like portion on the foreside O of the insulating board 6 as illustrated in Fig.14 Thus, the diameter of the opening 39 is smaller than an outer diameter of the LED 40. With this formation, when the LED 40 is pushed into the opening 39, a peripheral portion at a forward end of the opening 39, namely the thin filmlike portion of the opening 39 is urged to closely contact the LED 40. Thus, a gap is not formed between the opening 39 and the LED 40, which can prevent possible penetration of moisture etc. through the opening 39.

1 As illustrated in Fig.11, the intermediate electrode 8 .i.s formed in an annular shape in plan. The intermediate electrode 8 has an openi.ng 22 for allowi.ng radiation from the radiation source 7b as shown by a broken line to transmit therethrough and an electrode portion 23 formed integrally with the intermediate electrode 8 to extend towards a center of the opening 22. The electrode portion 23 is provided for compensating decrease of an ionization current in the inner ionization chamber which would otherwise be caused by widening the irradiation range of radiation from the radiation source 7b for the outer ionization chamber.

More particularly, since the electrode portion 23 extends to a portion where central radiation from the radiation source 7b is concentrated, sufficient ionization current in the inner ionization chamber can be acquired by the electrode portion 23 despite of the large opening 22.

The intermediate electrode 8 further has the support legs 24a, 24b, 24c formed on the periphery of the interme- *g djate electrode 8 integrally with the electrode 8.

The electrode lead 15 is integrally formed with one of the support legs 24a to 24c, namely, the support leg 24c as illustrated in the side elevational views of Figs.11 and The electrode lead 15 extends through the insulating board 6 to be connected to the lead of the FET 12 set in the FET accommodating portion 13. The support legs 24a to 24c each have serrate side edges 25 as illustrated in Figs.11 and Fig.12 is a sectional vi.ew showing the intermediate electrode 8 shown in Fig.11 whi.ch is now mounted on the insulating board 6 shown in Fi.g.4. The insulating board 6 is shown in section taken along line X X of In Fig.12, the intermediate electrode 8 is engaged, at its two support legs 24a 24b formed on the periphery of the intermediate electrode 8, wi.th the two holes 34a, 34b opening on the foreside of the insulating board 6 as shown in respectively. Since the support legs 24a, 24b have serrate side edges 25, they can be fixedly held in the holes 34a, 34b, respectively, when they are fitted in the respective holes.

On the other hand, as shown in Fig.12, the electrode lead 15 Formed integrally with the support leg 24c of the intermediate electrode 8 is fitted in the slit 30 formed at a bottom portion of the hole 34c of the insulating board 6.

**ei A tip end of the electrode lead 15 is soldered to a lead 12a of the FET 12 accommodated in the FET accommodating portion 13 formed on the backside of the insulating board.

Since a hot melt synthetic resin is filled over FET 12 with the electrode lead 15 of the intermediate electrode 8 soldered to the lead 12a of the FET 12 to be insulatingly sealed as shown in Fig.lO, the slit 30 of the insulating board 6, through which the electrode lead 15 of the interme- &.fee diate electrode 8 extends, is sealed by the insulating seal 4 of' the FET accommodating portion 13. Thus, possible penetration of moisture or corrosive gases into the circuitry accommodating portion on the backside of the insulating board 6 through the slit can be positively prevented.

Due to the insulating seal by injecting a potting material such as a hot melt synthetic resin into the FET accommodating portion 13 after the lead has been soldered, possible electrostatic breakdown can be prevented when the FET accommodating portion 13 is touched by hand in the assembling process.

Since the FET accommodating portion 13 is formed on the insulating board 6 and the potting is attained in the course of the assembling on the insulating board 6, the number of manufacturing steps can be reduced as compared with the conventional process in which the potting is carried out before the assembling step.

Furthermore, according to the present invention, the mounting of the intermediate electrode 8 onto the insulating board 6 can. be attained only by fitting the support legs 24a to 24c of the intermediate electrode 8 into the holes 34a to 34c opened on the foreside of the insulating board 6, respectively. Thus, no screws are needed to mount the intermediate electrode 8 onto the insulating board 6 and the space for mounting the intermediate electrode 8 can be minimized.

The mounting operation itself is easy and simple. In this connection, it is to be noted that the hole 34c into which the support leg 24c is inserted is so formed that the diameter is reduced to point, leaving a thin, film-like portion

*SSS

at the end of the hole, as the slit 33 into which the contact metal member 18 is inserted as shown in Fig.i5 Therefore, when the support leg 24c is inserted into the hole 34c, the electrode lead 15 formed integrally with the support leg 24c is inserted, piercing the thin film-like S portion until it reaches to the backside of the insulating board 6. Thus, possible penetration of moisture through the hole 34c can also be prevented.

Although support leg 24c formed integrally with the electrode lead 15 of the intermediate electrode 8 has serrate edges 25 in the embodiment as illustrated in Fig.ll, the serrate edges 25 may be provided only on the support o legs 24a, 24b which have not an electrode lead and inserted in the holes 34a, 34b opening at the foreside of the insulating board 6, respectively, but not provided on the support leg 24 having the electrode lead. This is because the electrode lead 15 extends from the fore:ide to the backside of the insulating board 6 to be fixed to the lead 12a of FET 12 by soldering and the fixation is possibly loosened by heating at the time of soldering. However, the number of the support legs is preferably increased to assure more positive fixation.

Tn this connection, it i~s to be noted that a cutout formed on the periphery of the intermediate electrode 8 as shown in Fig.11 i.s formed so as-to be complementary with the cylindrical projection for the capacitor accommodating portion 31. In the case where the capeci.tor accommodating portion 31 is provided outside of' the intermediate electrode 8, the cutout 35 may be omitted.

6 *vdip

Claims (4)

1. 2. An ionization smoke detector according to oeo• 25 claim i, in which said electrode lead is formed integrally i. with the support leg in the form of an extension of the support leg.
2. 3. An ionization smoke detector according to claim 2, in which said insulating board has openings for passing contact metal members of the outer electrode for the circuit board therethrough, said openings being formed, leaving a thin, film-like portion before the contact metal members have been passed therethrough. 18 4 I T! 0 ji
3. 4. An ionization smoke detector according to claim 3, in which said insulating board has an opening for inserting a LED on the circuit board for alarm indication therethrough, said opening being formed, leaving a thin, film-like portion before the LED has been inserted therethrough. An ionization smoke detector according to claim 4, in which said inner electrode has a shoulder portion and said insulating board has an opening for fitting the inner electrode, said inner electrode being caulked at said shoulder portion to be fixed in place after it has been fitted in the see*: opening of the insulating board. Stee
4. 6. An ionization smoke detector according to claim 1, S: substantially as herein described with reference to and as ,illustrated in any one or more of Figures 1 to 15 of the accompanying drawings. Dated this 12th day of August 1991. 0 HOCHIKI KABUSHIKI KAISHA By Its Patent Attorneys: 0S So GRIFFITH HACK CO. Fellows Institute of Patent S, Attorneys of Australia. A i r ABSTRACT An ionization smoke detector of the present invention is provided with an intermediate electrode having a plurality of support legs (24a, 24b, 24c) formed integrally on the periphery of the intermediate electrode which may be simply inserted into an opening of the insulating board to fix and support the intermediate electrode without using screws or other fastening members. Each of the support legs (24a, 24b, 24c) have serrated edges (25) and are inserted and fixed in holes (34a, 34b, 34c) provided in the foreside of the insulating board Thus, a space needed to mount the intermediate electrode can be minimized. An electrode lead (15) formed integrally with support leg (24c) is connected to a lead of an FET (12) insulatedly potted at an appropriate place on the backside of che insulating board with a hot melt synthetic resin. *0 0e 0 0. S oo* ooOO