GB2131616A - Thermostatic switch - Google Patents

Abstract

A thermostatic switch comprises a bimetallic strip 200 with a free end 220 which deflects according to temperature and comes to bear against a fixed contact 410 when the temperature reaches a predetermined value. The fixed contact 410 is mounted on a terminal 400 screwed into a cover 300 of the switch and the movable end 220 of the bimetallic strip is bent at an angled of the order of 45 DEG . By screw-adjustment of the terminal 400 in the cover 300 the position of the fixed contact 410 in relation to the movable end of the bimetallic strip may be regulated so to set the temperature at which contact is closed. <IMAGE>

Description

SPECIFICATION Thermostatic switch The present invention relates to a thermostatic switch which can be used, in particular,forthe control of the temperature ofthe engine of a motor vehicle.

Switches of thins type which permit, for example, the closing of an electric contact underthe action of a rise in temperature, generally comprise a bimetallic strip, one end of which is fixed and rigidly connected to a body of the switch and the other end of which is freely movable in such a manner as to have an increasing lateral deflection under the effect ofthe temperature.

When the temperature reaches a predetermined value,thismovableendcomesto bear against a fixed contactthus effecting, for example, the closing of an electric circuit between this fixed contact and the strip itself, which is generally electrically connected to the earth of the vehicle by means of its fixed end; indeed, in this case,the latter is rigidly connected, in an electrically conducting manner, to the bodyofthe switch, itself screwed into the crank-case.

The temperature at which contact is established depends on various parameters, particularly the thermal characteristics of the bimetallic strip and the distance separating the movable end ofthisfrom the fixed contact. In practice, a wide dispersal ofthe values ofthistemperature is observed in switches leaving the factory and it is therefore necessary to effect regulation ofthe switch before it is mounted on the engine.

Hitherto, this regulation has been obtained by mounting the fixed contact on an angle member consisting of a material which is easily deformed. The body of the switch comprises an aperture opposite this fixed contact enabling a stress to be applied to the end ofthe angle memberto cause an irreversible deformation ofthis having the effect of reducing the distance separating the fixed contact (situated at the end ofthe angle member) and the movable end of the bimetallic strip.

This operation is carried out by bringing the bimetallic strip to the selected triggering temperature: one ofthe arms of the angle member is then pressed down, or successive percussions are applied until the fixed contact, displaced in this manner, comes to touch the movable end ofthe bimetallic strip. Once this result has been obtained, the hole which permitted the introduction of the tool is closed.

It is clearthatthis method of regulation only brings a mediocre regulating precision and requires a certain dexterity to deform the angle member by an amount just sufficient for it to come into contact with the movable end ofthe bimetallic strip, any possibility of reversal forthe regulation being impossible or difficult.

Furthermore,thefact of providing a regulating aperture and means for closing it complicates the structure of the switch and increases its cost.

Finally, this method of regulation is final and does not permit a subsequent alteration to the regulation, for example after a long period of ageing oftheswitch.

In accordance with the present invention, there is provided a thermostatic switch, comprising a bimetallic strip having one end fixed to a body of the switch and a movable end which deflects laterally according to the temperature, a fixed contact against which the movable endof the bimetallic strip comes to bear when the temperature reaches a predetermined value, in such a manner as to close an electric circuit between the bimetallic strip and the fixed contact, and temperature regulating means effective to alter the position of the contact in relation to the body of the switch, by a displacement of said contact, in a continuous manner, in a direction inclined to the bimetallic strip at its movable end.

Preferably, the direction of displacement ofthe contact issubstantially parallel to a longitudinal axis of the bimetallic strip, the latter being bent adjacent its movable end to provide a portion extending in an inclined direction relative to the direction of displace ment qfthe contact. The angle ofthis inclination is preferably between 30 and 60 .

An embodiment ofthe present invention will now be described, by way of example only, with reference to the accompanying drawings, the single Figure of which is a longitudinal section through a switch with differentvariantsshown in the right-hand and lefthand sections.

The switch comprises a body 100 which is hollow so as to accommodate a bimetallic strip 200. Its lower portion is extended in such a manner as to form a plungerfor penetrating into the crank-case to which it is screwed by means of a thread 101,tightening being effected for example by means of faces 102 of a polygonal section,forexample having four or six faces.

In the variant illustrated in the right-hand halfsection, the body 100 is a monobloc part, preferably of brass.

In the variant offthe left-hand half-section,thebody is composite and is formed of a hollow capsule 110 (preferably of brass becauseofthethermal properties offthis material) fixed to a connector 120, for example of steel, provided with the threading 101 and tightening faces 102. The capsule 110 is for example force-fitted into the connector 120 with the interposition of a seal 130. This variant is advantageous since, bearing in mind the dimensions ofthe whole, the extra cost resulting from the structure in two parts is compensated for by the economy in material effected in the amount of brass.

The bimetallic strip 200 has a fixed end 210 which is rigidly connected to the lower portion of the switch, and a movable end 220 capable of lateral deflection under the effect of an increase in temperature (in the direction ofthe arrow A).

As can be seen in the Figure, this movable end 220 is bent in such a mannerthat its general direction forms an angle oc with the axis of displacement of a terminal 400 (described later) which, in the case in question, coincides with the axis XX ofthe switch.

The body 100 is closed by a cover 300,for example fixed to the body byforce fitting and crimping (reference 140), the cover then comprising a shoulder 150forming a stop.

The cover 300 is provided, in its middle, with an axial bore3l0receivingtheterminal400,this latter preferably being provided with a thread engaging in a corresponding tap formed in the bore 310.

At its lower portion, this terminal 400 carries a contact 410 forming the fixed contact of the switch and preferably consisting of a spherical bead, integral or added. It is against this fixed contact that the face 230 of the movable end of the bimetallic strip will cometo bear in the event of a rise in temperature.

Moreover, at its upper portion, the terminal 400, which is of conducting material, comprises electrical connecting means, for example a flat plug 420 (right-hand half-section) or a threaded end 430 (lefthand half-section) to connect the switch to the electrical circuits ofthevehicle.

This terminal 400 thus fulfils a triple function of: contact element (owing to the spherical bead 410), electrical connecting terminal (by means ofthe electrical connecting means 420,430), and above all of regulating member owing to the possibility off displacement which results from the screwing inside the cover.

Indeed, the screwing enables the position of the spherical bead 410 to be adjusted in an axial direction indicated bythe arrow B,thusforming an anglewith the end ofthe bimetallic strip, in a continuous and reversible manner (as distinct from the prior art described above). This angle is preferably between 30 and 60 and may advantageously amountto about 45 .

The screwing is facilitated if a polygonal section, for example with four or sixfaces, is provided in the emerging non-threaded portion 440 oftheterminal.

Finally, provision may be madeto widen the bore of the cover at its emerging portion in such a manner as to form a receptacle 450 for a composition for sealing the terminal to the cover, which is injected when the final regulation is reached.

Itwill be noted that the mean anchoring plane YY of the thread ofthe terminal 400 is situated substantially atthe leveloftheplanewherethecover300 bears on the body ofthe plunger 100.

The regulation is effected in the following manner: the switch is mounted in such a manner as to obtain a position of minimum engagement ofthe terminal 400 in the cover300; the switch isthen broughttothe desired triggering temperature and the regulation is obtained by screwing the terminal until the latter comes into contact with the end 220 ofthe bimetallic strip, the lateral deflection of which depends on the temperature.

The end 220, bent at an angle oc, for example of 45 , permits a translation of the axial regulating movement into a lateral displacement.

After regulation, the bedding and sealing product is injected into the receptacle 450 for a rigid connection oftheterminal 400 and the cover 300.

Claims (12)

1. Athermostatic switch, comprising a bimetallic strip having one end fixed to a body ofthe switch and a movable end which deflects laterally according to the temperature, a fixed contact against which the movable end of the bimetallic strip comes to bearwhen the temperature reaches a predetermined value, in such a manneras to close an electric circuit between the bimetallic strip and the fixed contact, and temperature regulating means effective to alter the position of the contact in relation to the body ofthe switch, by a displacement of said contact, in a continuous manner, in a direction inclined to the bimetallic strip at its movable end.

2. A switch as claimed in Claim 1, in which the direction of displacement of the contact is substantially parallel to a longitudinal axis ofthe bimetallic strip, the latter being bent adjacent its movable end to provide a portion extending in an inclined direction relative to the direction of displacement ofthe contact.

3. Aswitch as claimed in Claim 1 or 2, in which the angle between the direction of displacement of the contact and the bimetallic strip at its movable end is between 30 and 60 .

4. Aswitch as claimed in any one of Claims 1 to 3, in which the fixed contact has the shape of a spherical bead.

5. Aswitch as claimed in any one of Claims 1 to 4, in which the body ofthe switch comprises a hollow plunger of conducting material supporting the fixed end of the bimetallic strip, a cover of insulating material closing said plunger and traversed by an axial bore, a terminal inserted through this axial bore, carrying the fixed contact at its inner end, and carrying electrical connecting means at its projecting end.

6. A switch as claimed in Claim 5, in which the terminal is a threaded terminal screwed into the tapped axial bore of the cover.

7. A switch as claimed in Claim 6, in which the terminal hasa polygonal section in its non-threaded projecting portion.

8. A switch as claimed in any one of Claims 5to 7, in which the bore is widened, at the outer side ofthe cover, in such a manner as to form a receptacle to receive a composition for sealing theterminal to the cover.

9. A switch as claimed in any one of Claims 5 to 8, in which the cover is fixed to the plunger by force fitting andcrimping,thecovercomprising a shoulder forming a stop againstthe plunger.

10. Aswitch as claimed in Claim 9, in which the mean plane of anchoring theterminal in the cover substantially coincides with the plane of said shoulder of the cover.

11. A switch as claimed in any one of Claims 5to 9 in which the plunger is formed from a hollow capsule of brass fixed to an outer supporting connector of steel.

12. A thermostatic switch substantially as herein described with reference to the left-hand or right-hand half-section ofthe single Figure of the accompanying drawings.