Abstract:
An element with a cup containing a thermally expanding material, a piston capable of translational movement along its axis, a rigid guide for guiding the piston, a seal for sealing in the thermally expanding material having an annular overall shape, centered on the axis and through which the piston passes axially, and which includes first and second opposite axial parts against which the guide and cup press respectively in an antagonistic manner to compress the seal around the piston, and an anti-extrusion washer mounted coaxially around the piston and axially interposed between the guide and first part of the seal. The first part of the seal around the piston can be supercompressed to make the degree of compression equal to a value strictly higher than that associated with an operational thermostatic element formed by the cup, piston, guide, seal and anti-extrusion washer assembled with one another without the supercompression.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a thermostatic element, i.e., an element which, by using a thermally expanding material, converts heat energy into mechanical energy. 
     BACKGROUND OF THE INVENTION 
     Such elements are commonly used in the field of fluid regulation, since they make it possible to divide a fluid supply path into one or more distribution paths, depending on the heat of the fluid to be regulated and/or other heat sources. These elements are for example arranged within cooling circuits in which a cooling fluid circulates, in particular cooling circuits for motor vehicle heat engines or similar. Of course, other application examples can be considered, such as motor oil and gearbox circuits, as well as domestic supply water circuits. 
     Typically, a thermostatic element includes a metal cup with a generally tubular shape and containing a thermally expanding material such as a wax. The element also includes a piston coaxial to the cup and translatable relative to said cup under the effect of the expansion of the thermally expanding material contained in the cup, when that material is heated. In expanding, thermally expanding material partially drives the piston, such that the latter is deployed outside the cup whereas, during cooling of the thermally expanding material, the piston can be retracted inside the cup, generally under the action of a return spring associated with the thermostatic element. To guide the translational movements of the piston, the thermostatic element includes a bored metal guide, inside which the piston slides, that guide thus constituting a guide part that is firmly secured to the cup. Furthermore, to prevent the thermally expanding material from escaping outside the cup during movements of the piston and, at the same time, a liquid outside the thermostatic element, typically in which that thermostatic element is bathed, from being able to infiltrate along the piston up to the end of the piston submerged in the cup, it is known to seal the thermally expanding material relative to the outside using a flexible part whereof a tubular part is arranged coaxially around the piston. Traditionally, two main families of thermostatic elements are distinguished based on the extent of the covering of the piston by the flexible part. More precisely, when the flexible part forms a blind thimble, i.e., a sack delimiting a non-emerging cavity, the piston is received therein without establishing direct contact with the thermally expanding material: during an expansion of that material, it applies pressure forces on the sack, which then becomes pinched such that the piston is ejected therefrom, producing the translational movement. Conversely, when the flexible part is axially passed all the way through by the piston and is thus similar to a globally annular seal, centered on the axis of translation of the piston, the piston plunges directly into the thermally expanding material and is subject, without any intermediary, to the pressure applied by the material when it is heated, as illustrated by EP-A-0,940,577. 
     The invention specifically relates to thermostatic elements that incorporate such an annular seal and in which opposite axial parts of that annular seal are subject to pressing bearing, which is substantially antagonistic, by the guide and the cup, respectively, so as to compress the seal around the piston and thereby seal the cylindrical interface between the seal, which remains stationary relative to the guide and the cup compressing it, and the sliding piston. 
     During use, this sealing gasket is subject to high pressures coming from the thermally expanding material, which tend to extrude the flexible material making up the seal outside the thermostatic element, by forcing the flexible material to pass between the piston and the central bore of the guide. It is therefore known to interpose, axially between the seal and the guide, an anti-extrusion washer that is mounted coaxially around the piston. 
     Over the course of the usage cycles of the thermostatic element, it is observed that the flexible material making up the sealing gasket tends to wear and have permanent deformations, which gradually decreases the contact pressure between the seal and the piston, until the pressure becomes insufficient to guarantee sufficient sealing with respect to the outside of the thermostatic element. Independently of the aforementioned wear phenomenon, a critical situation may also occur when the thermostatic element is subject to a rapid and/or significant decrease in temperature, while bathing in a liquid under high pressure: under these severe usage conditions, the aforementioned liquid quite often succeeds in infiltrating along the piston, due to the accumulation of an abrupt retraction of the piston and the cup and the high pressure of the liquid. To avoid these drawbacks, it is known to attach a flexible packing, forming a sealing bellows, that is fastened to the piston and the guide, while covering the outlet thereof to the outside. That being the case, the placement of such a packing remains complex operation that is therefore expensive to implement. Furthermore, other solutions to prevent an outside liquid from being able to infiltrate the thermostatic element along the piston have been proposed in the past, but like the solution consisting of the aforementioned packing, they systematically cause an excess product cost and a non-negligible excess process cost. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is to propose an improved thermostatic element, the sealing of which with respect to the outside is reinforced simply, reliably and cost-effectively. 
     To that end, the invention relates to a thermostatic element including: 
     a rigid cup, which contains a thermally expandable material, 
     a rigid piston, which is translatable, along its axis, relative to the cup, under the action of the thermally expandable material during an expansion of that material, 
     a rigid guide for guiding the translation of the piston, said guide being rigidly secured to the cup, 
     a flexible seal for sealing the thermally expandable material with respect to the outside of the thermostatic element, said flexible seal having a globally annular shape that is centered on the axis and that is axially crossed all the way through by the piston, said flexible seal including first and second opposite axial parts, against which the guide and the cup are respectively pressed substantially antagonistically so as to compress the seal around the piston, and 
     an anti-extrusion washer, which is mounted coaxially around the piston and is axially interposed between the guide and the first part of the seal, 
     wherein a raised portion protruding from a surface of the guide is pressed against the first part of the seal so as to over-compress the first part of the seal around the piston, the raised portion being suitable for making the compression rate of the first part of the seal equal to a value strictly greater than its value associated with an operational thermostatic element formed by the cup, the piston, the guide, the seal and the anti-extrusion washer assembled to each other without the raised portion. 
     The invention relates also to another thermostatic element, including: 
     a rigid cup, which contains a thermally expandable material, 
     a rigid piston, which is translatable, along its axis, relative to the cup, under the action of the thermally expandable material during an expansion of that material, 
     a rigid guide for guiding the translation of the piston, said guide being rigidly secured to the cup, 
     a flexible seal for sealing the thermally expandable material with respect to the outside of the thermostatic element, said flexible seal having a globally annular shape that is centered on the axis and that is axially crossed all the way through by the piston, said flexible seal including first and second opposite axial parts, against which the guide and the cup are respectively pressed substantially antagonistically so as to compress the seal around the piston, 
     an anti-extrusion washer, which is mounted coaxially around the piston and is axially interposed between the guide and the first part of the seal, and 
     at least one additional washer in addition to the anti-extrusion washer, which is mounted coaxially around the piston and which is axially interposed either between the guide and the anti-extrusion washer, or between the anti-extrusion washer and the first part of the seal, so as to over-compress the first part of the seal around the piston, said at least one additional washer being suitable for making the compression rate of the first part of the seal equal to a value strictly greater than its value associated with an operational thermostatic element formed by the cup, the piston, the guide, the seal and the anti-extrusion washer assembled to each other without the at least one additional washer. 
     The invention relates also to yet another thermostatic element, including: 
     a rigid cup, which contains a thermally expandable material, 
     a rigid piston, which is translatable, along its axis, relative to the cup, under the action of the thermally expandable material during an expansion of that material, 
     a rigid guide for guiding the translation of the piston, said guide being rigidly secured to the cup, 
     a flexible seal for sealing the thermally expandable material with respect to the outside of the thermostatic element, said flexible seal having a globally annular shape that is centered on the axis and that is axially crossed all the way through by the piston, said flexible seal including first and second opposite axial parts, against which the guide and the cup are respectively pressed substantially antagonistically so as to compress the seal around the piston, and 
     an anti-extrusion washer, which is mounted coaxially around the piston and is axially interposed between the guide and the first part of the seal, 
     wherein a bead, which is provided radially protruding inward from the wall of a through hole, centered on the axis and delimited by the seal to receive the piston, and canceled out by radial crushing when the piston is received in the through hole in the assembled state of the thermostatic element so as to over-compress the first part of the seal around the piston, the bead being suitable for making the compression rate of the first part of the seal equal to a value strictly greater than its value associated with an operational thermostatic element formed by the cup, the piston, the guide, the seal and the anti-extrusion washer assembled to each other without the bead. 
     One of the ideas at the base of the invention is to seek further tightening around the piston, specifically the part of the seal turned toward the guide, while only marginally modifying the overall pre-existing structure of the thermostatic element and thus not causing a significant excess cost regarding the parts making up the thermostatic element and the assembly of those parts. Thus, the thermostatic element according to the invention copies all of the preexisting parts in a thermostatic element of the prior art and additionally incorporates mechanical means that are specific to the invention and that include the above defined bead, additional washer(s) and/or the raised portion: the aforementioned parts can be assembled to each other, without incorporating the aforementioned specific means, so as to form a thermostatic element of the prior art that is operational, i.e., that can be used in a satisfactory manner, but with limited sealing performance levels of its seal with respect to the outside, as explained above. The aforementioned specific means are, in a way, added to the pre-existing and self-sufficient parts, so as to increase the crushing of the first part of the seal, i.e., the part turned toward the guide, within the thermostatic element according to the invention in the assembled state: more specifically, the means specific to the invention are designed to increase the compression rate of the flexible material making up the first part of the seal, which amounts to saying that in the presence of the aforementioned specific means, the material making up the first part of the seal is forced to occupy a smaller volume than that occupied by the material of the first part in the absence of said specific means and/or that, in the presence of the aforementioned specific means, the first part of the seal is forced to occupy the same volume, but includes more material than that first part in the absence of those specific means. The contact pressure between the first part of the seal and the piston is increased as a result, which locally reinforces and/or extends the sealing over time with respect to a liquid outside the thermostatic element, without significantly altering the cooperation between the rest of the seal and the piston. In particular, the reinforced sealing at this first part of the seal is such that the latter performs a real anti-absorption function of liquid under severe usage conditions, in particular in case of abrupt retraction of the piston into the cup, related to a rapid and/or significant decrease in temperature, whereas the thermostatic element is in a high-pressure liquid medium. As explained in more detail below, the invention provides that the implementation of the aforementioned specific means may relate to the guide and/or the anti-extrusion washer and/or the first part of the sealing gasket. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood upon reading the following description, provided solely as an example and done in reference to the drawings, in which: 
         FIG. 1  is a longitudinal cross-section of a thermostatic element of the prior art; 
         FIG. 2  is an exploded view of part of the thermostatic element of  FIG. 1 ; 
         FIGS. 3 and 4  are views similar to  FIGS. 1 and 2 , respectively, illustrating a first embodiment of a thermostatic element according to the invention; 
         FIGS. 5 and 6  are views similar to  FIGS. 1 and 2 , respectively, illustrating a second embodiment of a thermostatic element according to the invention; and 
         FIGS. 7 and 8  are views similar to  FIGS. 1 and 2 , respectively, illustrating a third embodiment of a thermostatic element according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  show a thermostatic element  1  including a rigid cup  10  typically made from a metal alloy that conducts heat well, for example brass. This cup  10  has a globally tubular shape, centered on an axis X-X. In the example embodiment considered in the figures, the cup  10  includes a main barrel  11  with a cylindrical shape, with a circular base centered on the axis X-X. This barrel  11  is closed at one of its axial ends by a bottom wall  12 . In this way, the cup  10  contains a thermally expandable material  20  stored inside the barrel, that thermally expandable material for example being made up of a wax, optionally filled with a powder having good heat conductivity, for example a copper powder. 
     For convenience, the rest of the description is oriented considering that the terms “lower” and “bottom” designate a direction extending along the axis X-X and oriented toward the bottom wall  12 , in other words toward the bottom part of the figures, while the terms “upper” and “top” designate an opposite direction. 
     The thermostatic element  1  includes a piston  30  arranged coaxially to the cup  10 . The lower end part of that piston  30  is housed inside the barrel  11  to undergo the action therein of the thermally expandable material when that material expands after heating. Through the developments described below, the variation of the volume of the heated thermally expandable material causes an upward translational movement of the piston  30  along the axis X-X relative to the cup  10 . 
     The translational movement of the piston  30  is guided by a rigid part forming a guide  40  belonging to the thermostatic element  1 . This guide is in particular made from metal, like the piston  30 . The guide  40  includes a bored upper plate  41 , which extends globally in a plane perpendicular to the axis X-X and whereof the central bore  42  is centered on that axis. In cross-section transverse to the axis X-X, the bore  42  has a profile substantially adjusted on the outer profile of the piston  30 , such that the piston is axially received and guided in the bore  42 . The guide  40  also includes a globally tubular lower collar  43 , which is centered on the axis X-X and extends axially protruding downward from the plate  41 . Outwardly, this collar  43  is adapted to be rigidly secured, in particular by crimping, to a collar  13  of the cup  10 , provided at the upper end of the barrel  11 ,  FIG. 2  illustrating the assembled state of the thermostatic element  1  with the cup and the guide assembled to one another by crimping of the collar  13  on the collar  43 . 
     In order to seal the thermally expandable material  20  with respect to the outside of the cup  10 , in particular in order to limit, or even prevent a liquid, typically in which the thermostatic element  1  is bathed during use, from being able to infiltrate downwardly along the piston  30 , the thermostatic element  1  includes a sealing gasket  50  that is made from a flexible material, in particular either natural or synthetic rubber, i.e., elastomer. This seal  50  has an annular overall shape, centered on the axis X-X. Thus, the seal  50  delimits a through hole  51 , which crosses axially all the way through the seal, connecting its upper end surface  50 A, which is turned toward the guide  40 , and its lower end surface  50 A, which is turned toward the thermally expandable material  20  contained in the cup  10 , to each other. 
     In the assembled state of the thermostatic element  1 , the piston  30  is received coaxially in the through hole  51 , while extending axially both on either side of the seal  50 , protruding axially upward from the surface  50 A and protruding axially downward from the surface  50 B, and the inside of the seal  50 , between the surfaces  50 A and  50 B thereof. The seal  50  is mounted gripped around the piston  30 , i.e., mounted compressed around the longitudinal part of the piston, extending between the surfaces  50 A and  50 B. To that end, in the assembled state of the thermostatic element  1 , in particular under the effect of the rigid securing between the cup  10  and the guide  40 , at least part of the upper end face  50 A of the seal  50  is pressed downward by a bearing face  43 A, which is delimited by the guide  40  inside the collar  43  and on which the bore  42  emerges downward, whereas, substantially antagonistically, at least part of the lower end surface  50 B of the seal  50  is pressed upward by a bearing surface  13 A, which is delimited by the cup  10  inside the collar  13  and on which the barrel  11  emerges upward, thus, by downward bearing of the bearing surface  43 A against an upper terminal part  52  of the seal  50  and by antagonistic upward bearing of the bearing surface  13 A against a bottom terminal part  53  of the seal  50 , the seal is compressed, with the result that its through hole  51  tends to contract radially inward, which results in radially gripping the seal  50  all around the piston  30  in light of the presence of a longitudinal part of the latter between the opposite surfaces  50 A and  50 B of the seal. It will be noted that this compression of the seal  50 , making it possible to compress the latter around the piston  30 , relates to both the upper  52  and lower  53  parts, as well as an intermediate part  54  of the seal  50 , which, in the embodiment considered in  FIGS. 1 and 2  as an example, axially connects the upper  52  and lower  53  parts to each other: thus, in this example embodiment, the seal  50  is made up of the parts  52 ,  53  and  54 , with the result that on the one hand, the through hole  51  extends successively, along the axis X-X, through the parts  52 ,  54  and  53  and, on the other hand, the upper  50 A and lower  50 B end surfaces are respectively delimited by the top  52  and bottom  53  parts, while the intermediate part  54  outwardly delimits a peripheral side surface  50 C of the seal  50 , which is cylindrical and centered on the axis X-X, and which, in the assembled state of the thermostatic element  1 , is received in an adjusted manner in the downward opening of the collar  43 . 
     Advantageously, in particular for reasons related to distribution of the bearing stresses pressing the guide  40  on the seal  50 , the bearing surface  43 A is at least partially, or even completely, as in the example embodiment considered in  FIGS. 1 and 2 , made in the form of a sphere portion, allowing the axis X-X as the geometric axis of revolution. For its part, the bearing surface  13 A delimited by the cup  10  advantageously includes, as in the example embodiment considered in the figures, both a planar surface, which fits into a geometric plane substantially perpendicular to the axis X-X, in particular for axial positioning purposes of the seal  50  during the assembly of the thermostatic element  1 , and a flared element, which connects, while becoming gradually narrower toward the bottom, the aforementioned planar surface to the inner wall of the barrel  11 , in particular for centering purposes on the axis X-X of the seal  50  during the assembly of the thermostatic element. 
     In order to prevent the extrusion of the flexible material making up the seal  50  outside the thermostatic element  1  via the bore  42  of the guide  40 , the thermostatic element  1  further includes an anti-extrusion washer  60 , which is mounted coaxially around the piston  30  and which is axially interposed between the guide  40  and the upper part  52  of the seal  50 . In the assembled state of the thermostatic element, this washer  60  is upwardly curved, while hugging the perimeter of the downward opening of the bore  42 . 
     In practice, this washer  60  has a rigidity greater than that of the seal  50 , but lower than that of the guide  40  and the piston  30 . Thus, in the event the piston  30  and the guide  40  are made from metal and the seal  50  is made from rubber, the anti-extrusion washer  60  is advantageously made from PTFE (polytetrafluoroethylene). 
       FIGS. 3 and 4  show a thermostatic element  101  that includes a cup  110 , a thermally expandable material  120 , a piston  130 , a seal  150  and an anti-extrusion washer  160 , which are respectively identical, both functionally and structurally, to the cup  10 , the thermally expandable material  20 , the piston  30 , the seal  50  and the washer  60  of the thermostatic element  1 . In particular, the cup  110  comprises a barrel  111 , a bottom wall  112  and a collar  113 , which are centered on an axis X-X and which are respectively identical to the barrel  11 , the bottom wall  12 , and the collar  13  of the cup  10 . Likewise, the seal  150  is made from an upper part  152 , a lower part  153  and an intermediate part  154 , which are respectively identical to the upper  52 , lower  53  and intermediate  54  parts of the seal  50 . 
     The thermostatic element  101  also includes a guide  140 , which includes both an upper plate  141 , identical to the plate  41  of the guide  40 , in particular while being inwardly provided with a bore  142  identical to the bore  42 , and a collar  143 , which is identical to the collar  43 , with the sole difference that its bearing surface  143 A, which is functionally similar to the bearing surface  43 A of the guide  40 , bears an additional string  144  that protrudes downward from the surface  143 A. Thus, in the example embodiment considered in  FIGS. 3 and 4 , the bearing surface  143 A, as described above in light of  FIGS. 1 and 2 , assumes a spherical shape of revolution around the axis X-X, while the string  144  runs over that spherical bearing surface  143 A while being centered on the axis X-X and while being integral with that bearing surface. 
     The shape of the string  144  described just above is not limiting on the embodiment of the invention illustrated by  FIGS. 3 and 4 , inasmuch as that string  144  can, as an alternative that is not illustrated, be replaced by any form of raised portion protruding from the surface  143 A: in the assembled state of the thermostatic element  101 , this string  144  or, more generally, the aforementioned protruding raised portion locally crushes the flexible material making up the upper part  152  of the seal  150 , while locally increasing the compression of the material by the guide  140 , compared to the compression of the rest of that material by the bearing surface  143 A. When the upper part  152  of the seal  150  is considered globally, it is understood that its volume compression rate, i.e., the ratio between its volume in a compressed state of the material making up that upper part  152  when the thermostatic element  101  is assembled and the volume of the same material in the free state of the seal  150 , in particular before assembly with the rest of the thermostatic element  101 , has a value strictly greater than the value of the compression rate of the upper part  52  of the seal  50  of the thermostatic element  1  in the assembled state thereof. In other words, in light of the identity between the thermostatic element  1  and the thermostatic element  101  except regarding the additional presence of the string  144  or, more generally, the aforementioned protruding raised part, the upper part  152  of the seal  150  is compressed more, under the action of that seal or that protruding raised portion, than the upper part  52  of the seal  50 , which amounts to saying that that string or, more generally, that protruding raised portion makes it possible to over-compress the top part  152  around the piston  130 . The sealing of that piston with respect to the outside of the thermostatic element  101  is strengthened as a result. 
       FIGS. 5 and 6  show a thermostatic element  201  that includes a cup  210 , a thermally expandable material  220 , a piston  230 , a guide  240 , a seal  250  and an anti-extrusion washer  260 , which are respectively identical, both functionally and structurally, to the cup  10 , the thermally expandable material  20 , the piston  30 , the guide  40 , the seal  50  and the washer  60  of the thermostatic element  1 . In particular, the cup  210  comprises a barrel  211 , a bottom wall  212  and a collar  213 , which are centered on axis X-X and which are respectively identical to the barrel  11 , the wall  12 , and the collar  13  of the cup  10 . Likewise, the guide  240  includes an upper plate  241 , a central bore  242  and a lower collar  243 , which are respectively identical to the plate  41 , the bore  42  and the collar  43  of the guide  40 . Additionally, the seal  250  includes an upper part  252 , a lower part  253  and an intermediate part  254 , which are respectively identical to the upper  52 , lower  53  and intermediate  54  parts of the seal  50 . 
     The thermostatic element  201  differs from the thermostatic element  1  through the additional presence of a washer  270 , which is separate from the anti-extrusion washer  260  and which, advantageously, as in the example embodiment considered in  FIGS. 5 and 6 , is individually identical to that anti-extrusion washer  260 . In the assembled state of the thermostatic element  201 , the additional washer  270  is mounted coaxially around the piston and is axially interposed between the anti-extrusion washer  260  and the upper part  252  of the seal  250 . As an alternative that is not shown, the position of the additional washer  270  may be provided on the other axial side of the anti-extrusion washer  260 , which amounts to saying that, in that case, the additional washer is axially interposed between the guide  240  and the anti-extrusion washer  260 . 
     Irrespective of the axial side of the anti-extrusion washer  260  where the additional washer  270  is provided, it will be understood that the presence of the latter reduces the space available for the upper part  252  of the seal  250  during the compressed mounting of that seal within the thermostatic element  201 : in other words, the presence of the additional washer  270  increases the value of the volume compression rate of the material making up the top part  252  of the seal  250 , compared to the value of the compression rate associated with the top part  52  of the seal  50  of the thermostatic element  1  in the assembled state thereof. This results in over-compression of the upper part  252  of the seal  250  around the piston  230 , thereby reinforcing the sealing of the thermostatic element  201  with respect to a liquid outside the thermostatic element. 
     As an alternative that is not shown, two, or even more additional washers  270  are provided. 
       FIGS. 7 and 8  show a thermostatic element  301  that includes a cup  310 , a thermally expandable material  320 , a piston  330 , a guide  340  and an anti-extrusion washer  360 , which are respectively identical, both functionally and structurally, to the cup  10 , the thermally expandable material  20 , the piston  30 , the guide  40  and the washer  60  of the thermostatic element  1 . In particular, the cup  310  comprises a barrel  311 , a bottom wall  312  and a collar  313 , which are centered on an axis X-X and which are respectively identical to the barrel  11 , the bottom wall  12  and the collar  13  of the cup  10 . Likewise, the guide  340  includes an upper plate  341 , a central bore  342  and a lower collar  343 , which are respectively identical to the plate  41 , the bore  42  and the collar  43  of the guide  40 . 
     The thermostatic element  301  also includes an annular sealing gasket  350  that is formed by an upper part  352 , a lower part  353  and an intermediate part  354 , the lower  353  and intermediate  354  parts respectively being identical to the lower  53  and intermediate  54  parts of the seal  50 , while the upper part  352  is identical to the upper part  52  of the seal  50  with the sole difference that that upper part  352  of the seal  350  bears an additional bead  355 . As clearly shown in  FIG. 8 , this bead  355  is arranged in the upward opening of the through hole  351  of the seal  350 , which is functionally similar to the through hole  51  of the seal  50 , i.e., the bead  355  protrudes radially inward from the wall of the through hole  351 , delimited by the upper part  352  of the seal  350 . 
     During the assembly of the thermostatic element  301 , the bead  355  interferes radially with the piston  330  received in the hole  351 , until it is canceled out by the radial crushing under the action of the piston  330 , as shown in  FIG. 7 . It will be understood that this cancellation of the bead  355  results in increasing the quantity of the flexible material making up the seal  350  in the available free space, within the thermostatic element  301 , for the upper part  352  of the seal  350 , whereas the aforementioned free space is unchanged compared to the case of the thermostatic element  1 . In other words, the volume compression rate of the upper part  352  of the seal  350  is, under the effect of the cancellation of the additional bead  355  by the piston  330  in place in the through hole  351 , increased relative to the compression rate of the upper part  52  of the seal  50  in the assembled state of the thermostatic element  1 . This upper part  352  of the seal  350  is thus over-compressed as a result around the piston  330 , then reinforcing the sealing of the thermostatic element  301  with respect to the outside. 
     Various arrangements and alternatives to the thermostatic elements  101 ,  201  and  301  described thus far can also be considered. For example: 
     the three embodiments, respectively associated with the thermostatic elements  101 ,  201  and  301 , can be combined two by two, or combined all three, further accentuating the over-compression of the upper part of the seal of the thermostatic element thus obtained by combination, around the piston of that thermostatic element; and/or 
     optionally, the piston  130 ,  230  or  330  may be inwardly provided with an electric heating resistance, designed to heat the thermally expandable material  120 ,  220  or  320  through the inside, electricity supply conductors of that heating resistance extending from the end of the piston opposite that submerged in the cup  110 ,  210  or  310 .