US3581263A

US3581263A - Thermally responsive switch

Info

Publication number: US3581263A
Application number: US743157A
Authority: US
Inventors: Antonio Moro
Original assignee: Borletti SpA
Current assignee: Fratelli Borletti SpA; Borletti SpA
Priority date: 1967-07-08
Filing date: 1968-07-08
Publication date: 1971-05-25
Anticipated expiration: 1988-05-25
Also published as: DE1765713A1; ES139319U; GB1230123A; FR1579109A; ES139319Y

Abstract

A thermally responsive switch comprising a housing including a metal body with a recess therein. A cap of insulating material is secured to the metal body closing the recess. A disc-shaped bimetallic strip is loosely housed in the recess. The fixed contact is carried by a stiff metal bridge which bridges across the recess. The position of the fixed contact is adjustable. Adjustment being made by a tool inserted through an aperture in the cap.

Description

United States Patent [72] Inventor Antonio Moro Milan, Italy [21] Appl. No. 743,157

[22] Filed July 8, 1968 [45] Patented May 25, 1971 [73] Assignee Soc. per Azioni Fratelli Borletti Milan, Italy [54] THERMALLY RESPONSIVE SWITCH 12 Claims, 12 Drawing Figs.

[52] US. Cl 337/380, 337/368, 337/374 [51] Int. Cl ..I-I0lh 37/04, HOlh 37/28, HOlh 37/54 [50] Field of Search 337/343, 347, 360, 362, 365,368, 372, 374, 380, 381, 94, 110, 349, 354, 373, 375

[56] References Cited UNITED STATES PATENTS 3,255,331 6/1966 Ulanet 337/374IX) 3,248,503 4/1966 Huber 337/373(X) 3,329,788 7/1967 Moro 337/365 3,223,806 12/1965 Moro 337/381(X) 2,863,024 12/1958 Romine... 337/372 2,333,291 11/1943 Brannon 337/372 FOREIGN PATENTS 1,342,493 9/1963 France 337/365 Primary ExaminerBernard A. Gilheany Assistant Examiner-Dewitt M. Morgan AttorneyYoung and Thompson ABSTRACT: A thermally responsive switch comprising a housing including a metal body with a recess therein. A cap of insulating material is secured to the metal body closing the recess. A disc-shaped bimetallic strip is loosely housed in the recess, The fixed contact is carried by a stiff metal bridge which bridges across the recess. The position of the fixed contact is adjustable. Adjustment being made by a tool inserted through an aperture in the cap.

PATENTEU m2 5 I971 A ttorney- PATENTED M2519?! SHEET @UF 2 fig-l Inventor fl/vro/v/o Maze %7 77M Attorneys THERMALLY RESPONSIVE SWITCH BACKGROUND OF THE INVENTION 1. Field of the Invention The thermally responsive switch according to the invention is particularly designed to be mounted on the radiators of engines of motor vehicles for the purpose of opening and closing the electric circuit of an electromagnetic coupling which produces the connection and disconnection of the cooling fan for the radiator water, in accordance with the temperature of said water.

More precisely, the switch according to the invention is of the type comprising a bimetallic strip which, when the tem perature increases, snaps out of position, at the temperature value predetermined during construction, in accordance with the conformation and precalibration imparted to it before being inserted in the body of the switch, while, when the temperature decreases, the bimetallic strip snaps out of position at a temperature value predetermined by means of a calibration effected from outside the body of the switch when this is fully assembled.

One of the requirements for this type of switch is that it should have standardized dimensions, at least as regards the means by which it is fitted to the radiator, so as to be interchangeable with other types already in use in motor vehicles for controlling the connection and disconnection of the radiator cooling fan.

Fitting of these thermally responsive switches is effected by screwing them into a flange in the wall of the lower tank of the radiator, which generally has a threaded hole with a standard diameter of 20 mm; any thermally responsive switch intended for this type must therefore have a threaded shank of the above-mentioned diameter.

Reference is made here and hereinafter to the standard diameter of 20 mm, which, however, should be regarded purely as an example and not compulsory for the purposes of the application of the principles and considerations on which the present invention is based.

2. Description of the Prior Art In switches of this type heretofore employed, it is endeavored to arrange the bimetallic strip in a position as close as possible to the liquid of which the temperature is controlled, or substantially on the bottom of the housing, in a cylindrical seat formed in the threaded shank; this means, however, that the bimetallic strip must be made with a diameter distinctly smaller than that of the threaded shank, and therefore relatively small, and in this case the precalibration, within the restricted tolerance limits required, becomes very difficult indeed, unreliable and costly. The final result, therefore, is that instead of these switches there are very often preferred the types having two separate devices for setting the switch from outside for the double calibration in the phase of increasing temperature and decreasing temperature, respectively, in spite of the greater cost.

SUMMARY OF THE INVENTION It has now been found that keeping the strip in the close vicinity of the liquid to be subjected to control is practically speaking unnecessary, particularly when used as above mentioned for controlling the connection and disconnection of the fan; in the thermally responsive switch according to the invention, it is consequently proposed to carry the bimetallic strip in a seat above the threaded shank. In this way, it becomes possible to increase the diameter of the seat for the bimetallic strip suitably and, therefore, that of the strip itself, and it is consequently possible to effect permanent precalibration of the bimetallic strip with ease before assembly, while keeping the threaded shank within the required standard dimensions.

According to a preferred, but not Iimitative, embodiment of the present invention, the strip is produced with a diameter equal to that of the threaded shank, so as to provide optimum conditions for the transfer of the heat from the shank to the strip itself.

In addition to this characteristic, the switch according to the invention presents advantageous, but not secondary, improvements which permit simple, reliable and cheap construction thereof and which make it possible to insert it in an electric circuit subjected to higher control currents.

Above the bimetallic strip there is disposed a flexible insulating tongue which separates it from a flexible conductive tongue insulated from the housing and carrying a first contact in the center; a second contact, the fixed position of which can be set from outside the body of the switch, is disposed so as to cooperate with the first contact at the instant when the electric circuit is closed.

The upper part, or cap, of the body of the switch is produced by injection moulding insulating plastics material and in it 'there are incorporated in the moulding process conductive plates connected to said first and second contacts, respectively; each plate has one end projecting outside the cap and acts as a pin for effecting connection to a conductor of the electric circuit.

The inner end of a first plate bears directly on a peripheral zone of said conductive tongue carrying the first contact, while the inner end of a second plate bears on a peripheral zone of an insulated metal support carrying the second contact. The latter is mounted in the support so that it can be set through the medium of screw means adapted to be actuated from outside by means of a suitable screwdriver passed through a hole in the cap; this hole is then closed so that it is watertight once the operation of setting, or calibrating, said contact has been carried out.

This setting, in the final calibration stage, is effected so as to position said second contact with respect to the first contact in such manner as to obtain the reverse snap action of the bimetallic strip when the falling temperature reaches the predetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS The object of the invention, the construction thereof and its operation will appear more clearly, however, from the following description of a number of preferred constructional forms illustrated in the accompanying drawings, in which:

FIGS. I and 2 are vertical sectional views of the switch in planes disposed at with respect to one another;

' FIG. 2b shows in section a detail of the insulating tongue and of the movable contact;

FIG. 3 shows the device in plan view;

FIG. 4 illustrates in detail in plan view the flexible tongue carrying the movable contact;

FIG. 5 is an axial section of the bimetallic strip;

FIG. 6 shows in detail the bridge-shaped support carrying the fixed contact;

FIG. 7 and 8 show in vertical section two modified constructional forms of the switch according to the invention;

FIG. 9 shows in detail in perspective view of the plate carrying the fixed contact in the constructional form of FIG. 8;

FIGS. I0a and 10b are two axial sections of two modified constructional forms of the threaded shank of the switch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A metal housing body 1 has a hollow cylindrical zone 2 with a recess 3 in which is freely housed the bimetallic strip 4 in the form of a bent disc and having, in the case in question, its diameter 5 approximately equal to the diameter of the threaded shank 6.

Obviously, the dimensions of the housing I and the diameter of the bimetallic strip 4 may be different, within certain limits, but is preferable to keep the diameter of the bimetallic strip substantially equal to that of the threaded shank so that the transmission of heat from the latter may be as uniform as possible over the entire extent of the strip.

In order to make the snap action of the bimetallic strip 4 reliable and clean, the strip is preferably shaped with a diametral section such as appears in FIG. 5, that is with a central portion 4' formed with a slight curvature opposite to the main curvature, or even like a very open truncated cone, and with a diameter about one third of the total diameter.

Inside the hollow zone 2 and above the bimetallic strip 4 there is disposed a flat ring 7 with a radial tongue 8 projecting as far as the central zone and made of insulating material, for example of the commonly known Mylar type, which has a high resistance to fracture and to high and low temperatures and is an optimum insulating material.

On the ring 7 there bears the ring 9, which is made of material which is a good conductor and from which a flexible radial tongue 10 projects toward the center. Towards the end of the tongue, in the center of the ring 9 (see FIG. 4), there is provided a hole 11 in which is inserted a stud 12 made of metal suitable for electric contacts and having a head which is preferably spherical; the stud 12 is fixed with the interposition of the washer 13 by flanging its tip over in the form of a spherical head 14.

During assembly, a slight clearance is left between said spherical head 14 and the center of the bimetallic strip to avoid any possible pressure of said head 14 on the bimetallic strip having an influence on the instant when the snap action or movement occurs.

On top of the ring 9 there bears another ring 15 of insulating material, on which the bridge-shaped metal support or bridge 16 bears in turn.

The three

rings

7, 9, 15 and the bridge 16 are held oriented angularly and radially by two pins 17 formed in one piece with the cap 18, said pins being engaged in holes or notches 19, 19'

' prearranged in said parts. The pins 17 are positioned in such manner that on assembly the

rings

7, 9, 15 cannot be fitted upside-down or turned with respect to the prescribed position.

The four

parts

7, 9, 15 and 16 aforesaid are held in position in the seat 2 under pressure from the cap 18 of insulating material, which is held in the seat in turn by means of the flanged over portion 20 of the housing 1 with the interposition of the metal ring 2| and the rubber ring 22, which ensures watertightness of the interior of the housing 1.

The cap 18 is preferably made by injection moulding suitable plastics material (for example Dcln'n) and the

plates

23 and 24 areincorporated in said plastics material in the same moulding stage; that part of the plates which extends outside the cap 18 has the function of a pin for connection to the conductors of the electric circuit.

The contraction of the plastics material (Delrin or the equivalent) by thermal effect produces a strong pressure on the two plates, which are suitably slotted (see HO. 9), thus ensuring watertightness along the surface of the plates themselves.

The internal portion of the plate 24 presses by means of its end 25 on a peripheral zone of the bridge 16, thereby producing electrical continuity; the internal portion of the plate 23, on the other hand, presses by means of its end 26 on a peripheral zone 27 of the surface of the metal ring 9, thereby establishing electrical continuity with the latter and therefore with the contact 12.

As has been said, when the contact 12 is in the inoperative position it is insulated from all the other metal parts of the device except, obviously, the plate 23.

The bridge 16 is formed centrally in the shape of a bridge (see FIG. 6) in which a threaded hole 28 is provided in a position coinciding with the axis of the switch; said threaded hole is widened into a longitudinal slot 29, which enables the hole 28 to be pinched and restricted, due to the flexibility of the two parts separated by the slot, in order to make it possible to produce a certain pressure on the thread of the screw 30 and thus avoid the latter unscrewing as a result of vibration. The screw 30 carries the electrical contact 31 at its lower end; said electrical contact is therefore electrically connected to the plate 24 through the metal bridge 16, while it is insulated from all the other metal parts of the switch.

The fixed contact 31 is coaxial with the movable contact 12 and is spaced therefrom in the inoperative position, as can be seen from the drawing.

Provided in the cap 18 is a hole 32 through which it is possible to obtain access with a suitable tool, such as a screwdriver, a spanner or the like, for the purpose of screwing in and unscrewing the screw 30 during the stage of calibration of the device for adjusting the reverse snap action of the bimetallic strip 4, that is the snap action at the value predetermined for the temperature as it falls, in substantially known manner. In fact, by screwing the screw 30 in, the contact 31 is brought nearer to the contact 12 and, when the bimetallic strip 4 performs its snap action on an increase in the temperature, it is arrested sooner: consequently, the reverse snap action will take place at a higher temperature. The converse is the case if the distance between the two

contacts

12 and 31 is increased.

As has already been mentioned earlier, there are no other adjustments to be carried out, because the snap action, when the temperature increases, takes place at the desired value,

,which is determined solely by the conformation of the bimetallic strip itself, without any other operations. There is thus obtained, in simple and rapid manner, a switch which is perfectly calibrated at the two tripping temperatures of the bimetallic strip, the increasing and decreasing-temperature, respectively.

The calibration having been effected through the medium of the screw 30, the threaded hole 32 is closed and sealed by screwing into it a conical-headed screw 33 which is pressed against the flared or countersunk portion of hole 32.

As a greater safeguard, watertightness may be ensured by covering the head of the screw with suitable sealing material.

The operation of the switch is obvious: when the threaded shank 6 of the housing is placed in contact with the water, or other liquid, the heat of the latter is transmitted to said shank and from this to the bimetallic strip 4; when the predetermined temperature value is reachcd, the strip performs its snap action or trips, causing the contact 12 to press against the contact 31. The electric circuit which leads to the two

plates

23 and 24 is then closed through the end 25, the bridge 16, the contact 31, the contact 12, the disc 9 and the end 26.

When the temperature decreases, the bimetallic strip snaps or trips in the direction opposite to the previous direction at the predetermined value: the contact 12 moves away from the contact 31 and the electric circuit is broken again.

The bimetallic strip is constantly maintained at the temperature of the element with which the device is in contact due to the transfer of heat effected by the metal mass of the threaded shank 6 which, as has been said, is always in direct contact with said element; in effect, the temperature of the latter always varies gradually and not instantaneously, so that, in prac tice, the mass 6 is never subjected to substantial temperature gradients and it can be considered that the bimetallic strip is practically speaking always at the same temperature as said element.

A modified constructional form is shown in FIG. 7. In this variant, the bridge 16 is dispensed with and its function is performed by the plate 24', the internal end 34 of which, bent at right angles at 35, has a threaded hole 28 into which the screw 30 carrying the contact 31 is screwed directly. All the other elements remain the same as those which have already been described in the case of the first constructional form.

A second modified constructional form is shown in FlG.-8. The bridge 16 is also eliminated in this embodiment and is replaced by the plate 24". This plate, in turn, is bent at right angles at 35' and extends in the form of a uniplanar spiral 36, preferably as shown in FIG. 9.

The central terminal end of the spiral 36 is able to undergo small elastic displacements without being permanently deformed. Fixed to said end is the contact 31', on the bottom of which the movable contact 12 presses on the tripping of the bimetallic strip 4. The adjusting or calibrating screw 37 bears on the upper face of the contact 31 this screw is screwed into the threaded hole 32' provided directly in the insulating cap 18 and the position of the contact 31' is set by means of said screw in the calibration stage. The calibration having been carried out, the screw 37 is sealed with a suitable lacquer or cement, so as to ensure watertightness and at the same time lock the screw 37 itself against any possible unscrewing due to vibration. I

What has already been described in the case of the first constructional form applies to all the other elements.

As has been said, in any one of the constructional forms hereinbefore described, the bimetallic strip is constantly kept at the temperature of the element with which the device is in contact, due to the transfer of heat effected by the metal mass of the threaded shank 6, which is always in direct contact with said element; in effect, the temperature of the latter always varies gradually and not instantaneously, so that, in practice, the mass 6 is never subjected to substantial temperature gradients and it can be considered that the bimetallic strip is practically speaking always at the same temperature as said element.

lt-is possible, however, if certain system conditions make this advisable, to modify the threaded shank 6, as shown in FIG. a or FIG. 10!). A cylindrical chamber 38 (see FIG. l0a) is formed in the shank 6, leaving a wall 39 of small thickness below the bimetallic strip, and a number of radial holes 40 are made at the root of the thread to prevent the formation of cushions of air. in an even simpler manner (see FIG. 1011), the chamber 38' may be made in the form ofa truncated cone without any radial holes.

In both these cases, the liquid of which it is desired to control the temperature is separated from the bimetallic strip by a thickness of metal which is reduced to the minimum.

All the constructional forms hereinbefore described may easily be modified to adapt them to the case where the electric circuit controlled is closed through the mass of the device. To achieve this, the

plate

23, 26 is eliminated, and thus also the insulating ring 7; the conductive disc 9 is pressed directly against the body 1 by the cap 18 and the closing of the circuit is effected through this earthed contact. in this case, the bimetallic strip bears directly against the contact 12. Only the contact 31 remains insulated and, as before, the contact 12 bears against this at the moment the circuit is closed.

It is understood, however, that the constructional forms hereinbefore described are not to be regarded as restricting the invention, but that other variants all coming within the scope of said invention may be different therefrom.

Iclaim:

l. A thermally responsive switch having a housing including a metal body with a threaded shank for anchorage to a member whose temperature is to control the switch, themetal body having a recess therein, a cap of insulating material secured to said body and closing the recess, a disc-shaped bimetallic'strip loosely housed in said recess, a movable contact and a fixed contact, terminal means connected to said contacts and extending exteriorly of said housing, said strip changing position at a given temperature to apply the movable contact against the fixed contact to complete an electric circuit, astiff metal bridge that bridges across said recess and carries said fixed contact, calibrating means accessible from outside the switch to move the fixed contact relative to the bridge to adjust the temperature at which the contacts move apart from each other to open said circuit, said body having shoulders in said recess which support the ends of said bridge, and electrical insulation means between said bridge and said body.

2. A switch as claimed in claim 1, said cap having an internal cavity that opens toward said recess, said fixed contact being disposed in said cavity.

3. A switch as in claim 1, the ends of said bridge on opposite sides of said recess being gripped between said cap and said body.

.4. A switch as in claim I, said bridge having a central portion that is concave and that opens in the direction of the bottom of said recess.

5. Switch as in claim 1, wherein the central portion of the bimetallic strip acts on said movable contact through a flexible insulating tongue on said insulation means.

6. Switch as in claim I, wherein said movable contact is fixed to the free end of a flexible arm projecting radially towards the center from a peripheral ring supported by said shoulders.

7. Switch as in claim 6, wherein a metal plate in said insulating cap has its lower end disposed inside the recess bearing under pressure on said peripheral ring carrying the movable contact, so as to establish continuity of electrical connection between the contact and the plate.

8. Switch as in claim 5, wherein said metal plate is formed externally as a pin comprising one of said terminal means.

9. Switch as in claim 5, wherein said insulation means comprises an insulating ring from which there projects radially a tab forming said flexible insulating tongue interposed between the movable contact and the bimetallic strip.

10. Switch as in claim 7, wherein a second metal plate in said insulating cap has its lower end disposed inside the chamber bearing under pressure on a peripheral zone of the surface of said bridge carrying the fixed contact, so as to establish continuity of electrical connection between the latter and said plate.

11. Switch as in claim 10, wherein said second plate is formed externally as a pin comprising one of said terminal means.

12. Switch as in claim l0, wherein the peripheral zone of said bridge carrying the fixed contact is separated from the ring carrying the movable .contact through the medium of a ring of insulating material.

Claims

1. A thermally responsive switch having a housing including a metal body with a threaded shank for anchorage to a member whose temperature is to control the switch, the metal body having a recess therein, a cap of insulating material secured to said body and closing the recess, a disc-shaped bimetallic strip loosely housed in said recess, a movable contact and a fixed contact, terminal means connected to said contacts and extending exteriorly of said housing, said strip changing position at a given temperature to apply the movable contact against the fixed contact to complete an electric circuit, a stiff metal bridge that bridges across said recess and carries said fixed contact, calibrating means accessible from outside the switch to move the fixed contact relative to the bridge to adjust the temperature at which the contacts move apart from each other to open said circuit, said body having shoulders in said recess which support the ends of said bridge, and electrical insulation means between said bridge and said body.

4. A switch as in claim 1, said bridge having a central portion that is concave and that opens in the direction of the bottom of said recess.

6. Switch as in claim 1, wherein said movable contact is fixed to the free end of a flexible arm projecting radially towards the center from a peripheral ring supported by said shoulders.

12. Switch as in claim 10, wherein the peripheral zone of said bridge carrying the fixed contact is separated from the ring carrying the movable contact through the medium of a ring of insulating material.