EP0302770B1 - Thermal contacts with a snap disc - Google Patents

Description

The invention relates to thermal switches, or temperature-sensitive contact devices, which include a wax thermostat whose piston, guided longitudinally in translation relative to the body of the thermal switch, acts by pushing, by means of a spring. helical working in compression, on a cup now and centering one of the ends of this spring and engaged in the central hole of a blistering disc which at rest has its convexity towards the piston, said hole being centered on the geometric axis of the piston and spring and the aforesaid body being provided with abutment means for limiting the rebound stroke of the spring during the cooling of the wax.

In the present context, a "blistering disc" is a disc or washer made of elastic material (in particular spring steel or other metal or metal alloy) which is slightly curved at rest and which, when subjected on its central convex part to a thrust of increasing intensity, suddenly passes from a convex shape to a slightly concave shape (if we consider the face of this disc which is subjected to said thrust) for a first determined value of this intensity, then which suddenly resumes its convex shape by elastic effect, when said thrust decreases progressively, for a second value of said intensity less than the first. The blistering disc used in accordance with the invention therefore changes shape under the effect of variations in the thrust which it undergoes and not directly under the effect of temperature variations, unlike bimetallic blistering washers of which an example is given. by FR-A-1,179,564.

A thermal switch in accordance with the first paragraph of this description is described in US-A-3,735,314. In this known thermal switch, there is interposed, between the piston or pusher of the wax thermostat and the above-mentioned helical spring, a spring-carrying cap which surrounds the free end of the piston and which is biased towards this free end by a second helical spring. bearing longitudinally on the body of the thermal switch and guided laterally by the cylindrical inner surface of this body. It is on the cap that the above abutment means act. In addition, the cup engaged in the central hole of the blistering disc carries, on the side opposite to the piston of the thermostat, an insulating finger which acts by pushing on one of the branches of a switch blade with sudden break.

This known thermostat has the advantage of being able to withstand temperatures significantly higher than that which corresponds to its triggering during the rise in temperature because any movement of the piston beyond this triggering temperature simply results in an increase in the compression of the first helical spring. However, it has various drawbacks. In particular, the large number of its constituent parts makes it difficult to assemble and adjust and increases its cost price. In addition, the friction of the second helical spring on the cylindrical surface of the body which guides it introduce uncertainty about the triggering temperature when the temperature rises and the interval between the triggering temperatures respectively when the temperature rises and falls.

The invention aims to remedy the drawbacks of known thermal contacts. It aims in particular to reduce the number of their constituent parts and, consequently, to simplify their assembly and their adjustment and to reduce their cost price. It also aims to reduce friction and / or vibration as much as possible during operation. Finally, it aims to make the construction of the thermostat more compact and lower.

To this end, the thermal switch according to the invention is essentially characterized in that the helical spring, which is a single spring, is held and centered at the other of its ends by the movable piston. Preferably, the cup, made or coated with electrically conductive material, cooperates directly with a contact pad and is interposed with it in the electrical circuit of the thermal switch.

A thermal switch is thus obtained which comprises only a small number of parts, which is therefore easy to assemble and adjust and whose cost price is considerably lowered. In addition, its single coil spring is only maintained and centered by its two ends and is therefore not exposed to friction during operation. Finally, the presence of a single spring makes the construction more compact and less tall.

It should be noted that FR-A-2,454,173 describes a thermal switch which also only includes a small number of parts. However, when this known thermal switch is provided with a helical spring, its thermostat is not of the usual piston type, because its membrane acts on a ball, this ball being housed with very little play in a cylindrical passage of the body where the thrust coil spring. This spring is only held on one side, more or less well, by the spherical surface of the ball and it is free on the other side, so that the friction of the spring on the wall of the cylindrical passage is uncontrollable. In addition, the thermostat membrane may leak in the gap between the ball and this wall, thereby compromising the operation of the thermal switch. In addition, in the absence of stop means for the ball, the blistering disc is no longer held by the spring, as soon as the temperature drops beyond a determined threshold, and the whole blistering disc, the ball and the spring then risk becoming the seat of significant vibrations, in particular when the thermal switch is mounted directly on the engine of a motor vehicle.

According to a preferred characteristic of the thermal switch according to the invention, an anti-extrusion washer is interposed between the piston and a membrane which limits the housing of the wax.

The invention will now be described in more detail using the accompanying drawings.

Figures 1 and 2 of these drawings show in longitudinal section a thermal switch according to a first embodiment, respectively at rest and after tripping.

Figures 3 to 6 show, similarly to Figure 1, thermocontacts respectively conform to four other embodiments of the invention.

According to the various embodiments shown, the thermoswitch in accordance with the invention comprises a wax thermostat 1, the piston 2 of which, guided longitudinally in translation relative to the body 3 of thermostat 1, acts by pushing, via a helical spring 4 working in compression, on a cup 5 now and centering one of the ends of this spring 4 and engaged in the central hole 6 of a blistering disc 7 which at rest has its convexity towards the piston 2. The hole 6 is centered on the geometric axis XX of the piston 2 and of the spring 4.

In known manner, the thermostat 1 comprises a wax 9 inside a housing limited by a relatively flat membrane 8 on which the piston 2 rests directly or indirectly, preferably by means of an anti-extrusion washer 10 .

The body 3 is provided with abutment means 11 for limiting the rebound stroke of the spring 4 during the cooling of the wax 9.

According to the invention, the spring 4, which is a single spring, is held and centered, at its end opposite to that which is received by the cup 5, by the piston 2 on which, according to the embodiments of Figures 1 to 5, the stop means 11 act directly. To this end, the piston 2 is advantageously provided with a flange 12 which is arranged so as to come to bear, by one of its faces, on a transverse surface 16 fixed by relative to the body 3. Preferably, the opposite face of the collar 12 serves as a support for the spring 4 which is centered by a finger 13 integral with the piston 2 and projecting with respect to this latter face of the collar 12.

According to the embodiments of FIGS. 1 to 3 and 5, the housing of the wax 9 is limited laterally and on the side opposite to the membrane 8 by the body 3 and by a bottom 14 made in one piece with this body 3 and the membrane 8 is pinched, on its periphery, between a shoulder of this body 3 and an attached tubular part 15 which not only serves as a guide for the piston 2 but also offers the transverse surface 16 which cooperates with the flange 12 to constitute the means stop 11.

According to the embodiment of Figure 4, the housing of the wax 9 is limited laterally and on the side opposite to the membrane 8 by a cup 17 attached, for example by crimping, on the body 3. In this case, the membrane 8 is pinched on its periphery between the body 3, devoid of bottom, and the rim 18 of the cup 17. The attached tubular part 15 of the previous embodiments is replaced by a tubular element 15a, made in one piece with the body 3 and offering the aforesaid transverse surface 16.

According to a preferred construction, the cup 5, made or coated with electrically conductive material, cooperates directly with a contact pad 19 and is interposed therewith in the electrical circuit of the thermal switch.

The thermal switch according to the invention lends itself to the production of numerous electrical circuits.

According to the embodiment of FIGS. 1 and 2 and that of FIG. 4, the electrical circuit comprises two terminals 20 and 21 of which the first 20 carries the stud 19 and the second of which 21 is permanently electrically connected to the blistering disc 7 and, through it, to the cup 5.

According to the embodiment of FIG. 3, the electrical circuit comprises a single central terminal 22, one of the ends of which constitutes the stud 19, the return of the current taking place via the cup 5, the blistering disc 7 and body 3.

The embodiment of Figure 5 differs from those of Figures 1, 2 and 4 in that the terminal 21 is not electrically connected to the cup 5 directly by the blistering disc 7 (or not only by this blistering disc 7 ) but by a flexible conductor 23, which has the advantage of allowing the passage of currents of higher intensity.

Whatever the embodiment adopted, the body 3 is preferably closed, on the side opposite to the thermostat 1, by an insulating cap 24 which is crossed by at least one of the terminals 20 to 22.

In known manner, the body 3 is provided with a threaded surface 25 which makes it possible to adapt the thermal contact in the tapped hole of a support (not shown), such as the cooling radiator of an internal combustion engine, so that the bottom 14 of the housing 3 or the attached cup 17 (Figure 4) can be bathed by the liquid whose temperature determines the functioning of the thermal switch.

A thermal switch is thus obtained which operates in the following manner. When the wax 9 is relatively cold, the blistering disc 7 turns its convexity towards the piston 2, as shown in FIGS. 1 and 3 to 5. The spring 4, by bearing on the disc 7, immobilizes the piston 2 while maintaining its flange 12 against the transverse surface 16 of the part or tubular element 15 or 15a. The assembly constituted by the disc 7, the cup 5, the spring 4 and the piston 2 is therefore prevented from vibrating.

As its temperature rises, the wax 9 expands and causes the piston 2 to rise, increasing the compression of the spring 4. On crossing a determined temperature threshold, the thrust exerted by the spring 4 on the blistering disc 7 becomes sufficient to make it pass from its convex form to its concave form illustrated in FIG. 2, for which the previously interrupted circuit closes between terminals 20 and 21 or between terminal 22 and the body 3. Any additional rise in temperature occurs translated only by an increase in the compression of the spring 4. In this closed circuit situation, the assembly formed by the disc 7, the cup 5, the spring 4 and the piston 2 is still prevented from vibrating.

When the temperature of the wax drops, the elements of the thermal switch return to their initial position, for a temperature a little different from that which corresponds to the closing of the contacts.

During operation, the spring 4 remains perfectly centered without being subjected to external friction, which gives excellent repeatability of the passage temperature from one position to the other.

The use of the anti-extrusion washer 10 avoids the extrusion of the rubber from the membrane 8 around the piston 2. This extrusion would have the effect of causing thermal adjustment of the thermal switch, after a long operating time, and even complete failure. of the thermal switch by jamming the piston 2.

It is possible to use a piston 8 or a guide 15 made of sintered material, which would ensure lifetime lubrication of the thermal switch. Finally, the blistering disc 7 could be silver (or gold) to improve the electrical conductivity.

As indicated in the foregoing, the thermal switch according to the invention comprises only a limited number of parts, that is to say, in addition to those of the wax thermostat 1, the spring 4, the cup 5 and the disc. blistering 7.

The invention is not limited to the embodiments which have been described above but encompasses the variants which are within the reach of specialists in the field and an example of which is shown in FIG. 6. According to this variant, of which the general construction is similar to that of the embodiment of Figure 5 and whose electrical circuit is similar to that of the embodiment of Figure 3, the single spring 4, at its end remote from the cup 5, is maintained and centered by the piston 2 not directly as previously, but by a spring-carrying cap 26 which covers the tubular part 15b of the guide 15 and which has an outer rim 26a against which the spring 4 bears. The above abutment means are then constituted by the free end of the tubular part 15b which cooperates with the bottom of the cap 26.

The operation of the embodiment of FIG. 6 is similar to that which has been described above, the stop means 11 however not acting directly on the piston 2. In applications where the piston 2 would risk vibrating between the membrane 8 and the bottom of the cap 26 when the wax is very cold, it would suffice to secure (for example by gluing) the piston 2 to the cap 26 to eliminate this drawback. The advantage of the embodiment of FIG. 6 is that it makes it possible to reduce the height of the thermal switch.

Claims (10)

1. Temperature switch comprising a wax thermostat (1) whose piston (2), longitudinally movable relative to the body (3) of the temperature switch, acts by means of thrust, via a helical spring (4) in compression, on a plate (5), holding and centring one end of this spring (4) and inserted in the central hole (6) of a snap disk (7) which when at rest, curves outwards towards the piston (2), the said hole (6) being centred on the geometrical axis (X-X) of the piston (2) and the spring (4) and the said body (3) being fitted with stop motion devices (11) to limit the expansion stroke of the spring (4) when the wax (9) cools, characterised in that the helical spring (4) is a single spring, held and centred at its other end by the movable piston (2).
2. Temperature switch according to claim 1, characterised in that the plate (5), made of or covered with electroconductive material, co-operates directly with a contact bank (19) and is interposed with the latter in the electric circuit of the temperature switch.
3. Temperature switch according to either of claims 1 and 2, characterised in that the wax temperature switch comprises wax (9) inside a housing bounded by a membrane (8).
4. Temperature switch according to any of claims 1 to 3, characterised in that the stop motion devices (11) act directly on the piston (2).
5. Temperature switch according to claim 4, characterised in that the piston (2) is fitted with a collar (12) which is arranged such that one of its sides rests on a transverse surface (16) which is fixed relative to the body (3).
6. Temperature switch according to claim 5, characterised in that the opposite side of the collar (12) acts as a support for the spring (4) which is centred by a pin (13) integral with the piston (2) and projecting relative to this latter side of the collar (12).
7. Temperature switch according to either of claims 3 and 5, characterised in that the housing for the wax (9) is bounded laterally and on the side opposite the membrane (8) by the body (3) and by a base (14) formed in one piece with this body (3) and in that the periphery of the membrane (8) is gripped between a shoulder on this body (3) and a tubular insert (15) which not only serves as a guide for the piston (2) but also provides the transverse surface (16) which cooperates with the collar (12) to form the stop motion devices (11).
8. Temperature switch according to either of claims 3 and 5, characterised in that the housing for the wax (9) is bounded laterally and on the side opposite the membrane (8) by a second plate (17) mounted on the body (3), in that the periphery of the membrane (8) is gripped between the body (3), which has no base, and the rim (18) of the second plate (17) and in that the abovementioned transverse surface (16) is provided by a tubular component (15a) formed in one piece with the body (3) and serving as a guide for the piston (2).
9. Temperature switch according to any of claims 1 to 3, characterised in that the spring (4) is held and centred by the piston (2) by means of a spring-holder cap (26), covering a tubular insert (15) which serves as a guide for the piston (2) and which grips the periphery of the membrane (8) against a shoulder on the body (3), and in that the stop motion devices (11), preferably constituted by the free end of the tubular insert (15), act on the spring-holder cap (26).
10. Temperature switch according to any of claims 3 to 9, characterised in that an anti-extrusion washer (10) is interposed between the piston (2) and the membrane (8).

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