HEATING CARTRIDGE AND THERMOSTATIC ELEMENT COMPRISING
SUCH A CARTRIDGE
This invention relates to a heating cartridge for a thermostatic element. It
further relates to a thermostatic element comprising such a cartridge.
In many applications in the field of fluids, in particular for the cooling of
heat engines of vehicles, thermostatic valves are used to distribute an incoming
5 fluid into various circulation channels, according to the temperature of this fluid.
These valves are referred to as thermostatic in that the displacement of their
internal shutter or shutters is controlled by a thermostatic element, i.e. an element
that comprises a cup containing a heat-expandable material and a piston which
can be displaced by sliding in relation to the cup under the action of the heat-
10 expandable material when the latter expands or contracts.
In order to distribute the fluid according to other parameters, in particular
conditions outside of the valve such as ambient temperature or the load of the
vehicle propelled by the engine provided with the valve, it is known to incorporate
into the valve a electric cartridge in order to heat the heat-expandable material,
15 which makes it possible to control the valve fiom the outside of the latter,
independently or in addition to the temperature of the incoming fluid, in particular
by means of a suitably-programmed calculator onboard the vehicle. The heating
cartridge comprises to this effect a heating resistor, arranged inside the
aforementioned piston or an analogous metal tube: by immobilising, for example,
the piston to the external case of the valve, the electrical power of the resistor
causes a rise in the temperature of the heat-expandable material, which results,
through dilatation of the latter, the sliding of the cup around the piston, a shutter
being carried by this cup to act on the circulation of the fluid through the valve.
5 In practice, the aforementioned heating resistor is substantially comprised
of a resistant filament in the shape of a spire, which is embedded in a heatconductive
powder, such as a magnesium oxide powder, compacted into the
bottom of the tube, and which is connected to two conducting wires rising in the
piston or the tube of the thermostatic element, of which the free ends are to be
10 electrically connected to an external current source. An example of such a heating
cartridge with thermostatic element is provided by DE-A-3709285.
This -heating cartridge design is complex, and therefore expensive, in
particular due to the fact that it requires delicate assembly operations, as well as
operations for electrically connecting the wires of the resistor, such as operations
15 of welding or crimping. In addition, the filamentary structure of the heating
resistor is such that the resistivity of the latter is substantially constant according
to the temperature: the electrical power of the heating resistor must be regulated
and controlled with precision, in particular in order to prevent it fiom overheating
which would risk damaging the thermostatic element irreversibly.
20 US-A-4 697 069 proposes a heating cartridge, not for a thermostatic
element, but for a washing machine. This heating carbridge is based on the same
technology as that of DE-A-3709285, i.e. the presence of an electrical heating
resistor which is constituted of a spire embedded in a magnesium oxide powder.
According to certain forms of embodiments considered in US-A-4 697 069, the
25 aforementioned spire can be supplied electrically either by an inner rod, of which
one end is arranged coaxially inside a first end of the spire, or by an outer rod, of
which one end is arranged coaxially around the first end of the spire, while the
second end of the spire is connected to the source of current supplying either the
rod or the tube in order to close the circulation circuit of the current.
3 0 In the same technical field of washing machines as US-A-4 697 069,
documents DE-U-89 10 145, EP-A-1 1 1 1 962 and GB-A-658 71 1 also propose
heating cartridges of which the resistor is a spire of which the opposite ends are
connected to a source of current. The same spire structure is present for the
heating resistor of the cartridge considered in DE-A-28 56 444, which is
specifically designed for the field of plastic injection moulds.
5 The objective of this invention is to propose a heating cartridge for a
thermostatic element, of which the heating resistor is more economical to
manufacture and simpler to assemble to the rest of the cartridge.
To this effect, the objective of the invention is a heating cartridge for a
thermostatic element, such as defined in claims 1.
10 One of the ideas at the basis of the invention is to replace the existing
structures with a resistant filament in the shape of a spire with a resistant tubular
body, arranged both coaxially inside the tube of the cartridge and coaxially around
a central rod of this cartridge, being in electrical contact with both this tube and
this rod. By providing that the tube and the rod are made of electrically
15 conducting materials, typically of metal, it is possible to connect the tube and the
rod respectively to the poles of an external electrical power, and as such to
circulate a current through the aforementioned resistant tubular body: in service,
this body is heated by the Joule effect and the heat energy is then diffused through
the tube, to the heat-expandable material of a thermostatic element. The cost of
20 the heating cartridge according to the invention is low as its primary components,
which are the tube, the rod and the tubular heating resistor, are simple to
manufacture. In addition, the assembly of these components is economical, in that
the corresponding assembly operations, all centred on the common central axis of
these components, can be automated.
25 Advantageous characteristics of the heating cartridge in accordance with
the invention, taken separately or according to all technically possible
combinations, are specified in dependent claims 2 to 12.
The invention further has for object a thermostatic element, such as
defined in claim 13.
The invention shall be better understood when reading the following
description, provided solely by way of example and in reference to the drawings
wherein:
- figure 1 is a longitudinal cross-section of a valve comprising a
5 thermostatic element in accordance with the invention;
- figure 2 is a longitudinal cross-section of the thermostatic element,
shown alone, of figure 1 ;
- figure 3 is a longitudinal cross-section of a heating cartridge, shown
alone, belonging to the thermostatic element of figures 1 and 2;
10 - figure 4 is a view analogous to figure 3, partially showing an alternative
embodiment of the heating cartridge, in accordance with the invention;
- figure 5 is a view analogous to figure 3, showing another alternative
embodiment of a heating cartridge in accordance with the invention; and
- figure 6 is a view analogous to figure 3, showing another embodiment of
15 a heating cartridge in accordance with the invention.
Figure 1 shows a thermostatic valve 1 comprising a case 10, made for
example of plastic material, wherein is intended to circulate, in a manner
regulated by the other components of the valve, a fluid, in particular a coolant
when this valve 1 belongs to a cooling circuit for a heat engine.
20 The case 10 comprises a main tubular body 1 1 which extends lengthwise
in a centred manner around an axis X-X belonging to the section plane of figure 1.
The case 10 further comprises a tubing 12 which opens transversally into one of
the longitudinal ends of the body 11, with this body and this tubing being
connected by an elbow-shaped region 13 of the case 10. In service, the
25 aforementioned fluid flows through the body 11 and the tubing 12, by circulating
in particular in an internal cavity 14 of the case 10, which is delimited in the
elbow-shaped region 13. This flow of fluid is regulated, here on the end of the
body 11 opposite the tubing 12, by a closing flap 20 centred on the axis X-X and
which can be displaced in translation according to this axis: when this flap is
30 pressed in a sealed manner against a seat 15 delimited by the aforementioned end
of the body 11, as shown in figure 1, the flow of the fluid is interrupted, while,
when the flap 20 is separated fiom the seat 15, the fluid can fieely circulate
around the flap and as such enter into or exit fiom the body 11.
In order to control the displacement of the flap 20, the valve 1 comprises a
thermostatic element 30 comprising, as can be seen easily in figure 2 and in a
5 manner that is well known in the field, on the one hand, a cup 3 1, whch contains
a heat-expandable material 32 and around which the flap 20 is made fixedly
integral, for example by press-fitting, and on the other hand, a tube 33 forming a
piston, which is in part plunged into the cup 31 and which can be displaced in
translation according to its central longitudinal axis under the action of the
10 dilatation of the heat-expandable material contained in this cup. The thermostatic
element 30 is arranged across fiom the case 10 in such a way that, on the one hand,
its tube forming a piston 33 is centred on the axis X-X and, on the other hand, this
tube is fixedly connected to the case 10, here on the elbow-shaped region 13 of
this case, as specified in more detail in what follows. As such, in service, the tube
15 33 is fixed in relation to case 10, while the cup 31 and the flap 20 that it cames
can be displaced according to the axis X-X in relation to the case, under the effect
of the heat-expandable material when the latter expands, or, when this material
contracts, under the opposite effect of a return spring 21 positioned between the
flap 20 and a rigid armature 22 integral with the case 10 through arrangements not
20 shown in detail and known per se.
In practice, various embodiments can be considered with regards to the
case 10, the flap 20, the spring 21 and the armature 22, without being restrictions
of the invention. As such, for example, rather than the seat 15 supporting the flap
20 being delimited directly par the case 10, this seat can be delimited by a
25 dedicated portion of the armature 22.
The thermostatic element 30 is provided with an electrical heating resistor
34 which, as shown in more detail in figure 3, is arranged inside the tube 33, by
being located in the longitudinal end portion 331 of this tube, which plunges into
the cup 3 1, so that the heating resistor 34 can heat the heat-expandable material 32
30 contained in the cup. For this purpose, the tube 33 is made, at least in regards to
its end portion 331, of a heat conducting material, typically of metal.
As can be seen easily in figure 3, the heating resistor 34 has substantially
the form of a tubular body 341, which is centred on the axis X-X and of which the
transversal section has- an addtional exterior profile, and is even adjusted on the
interior profile of the transversal section of the end portion 331 of the tube 33. In
other words, the tubular body 341 of the resistor 34 is arranged coaxially inside
the end portion 331 of the tube 33, by forming exteriorly a contact interface with
the inner surface of this end portion 3 3 1.
In addition, a rod 35 extends lengthwise inside the tubular body 341, by
being centred on the axis X-X and by extending over the entire axial dimension of
the tubular body 341, as well as by extending beyond this tubular body, in such a
way as to run inside the tube 33, over substantially the entire axial dimension of
this tube. As such, the rod 35 includes a longitudinal end portion 351, which is
arranged coaxially inside the body 341 of the resistor 34 and of which the
transversal section has an additional exterior profile, and is even adjusted on the
interior profile of the transversal section of this tubular body. In other words, the
tubular body 341 of the resistor 34 is radially positioned between the end portions
331 and 351 of the tube 33 and of the rod 35, by forming interfaces, of cylindrical
contact with each of these end portions.
The rod 35 further includes a longitudinal end portion 352, opposed axially
to its end portion 351, which extends coaxially inside of the tube 33, more
precisely on a longitudinal end portion 332 of this tube, opposed axially to its end
portion 33 Between the end portions 332 and 3 52 of the tube 33 and of the rod 35
is radially positioned a tubular bushing 36, which is centred on the axis X-X and
of which the transversal section has exterior and interior profiles which are
respectively complementary, and even adjusted on the exterior and interior
profiles of these end portions 332 and 352.
Contrary to the bushing 36 which is made fiom an electrically insulating
material, for example made exclusively fiom a thermoplastic polymer, the heating
resistor 34 is constituted of a mixture between a thermo-setting polymer, such as
an epoxy glue, at least one conducting powder, such as carbon black, and,
possibly, other additives. In this way, the resistor 34 allows the circulation of an
electric current through it, while still having an electrical resistivity which, by the
Joule effect, induced its heating in service.
In the embodiment considered in the figures 1 to 3, the thermo-setting
nature of the polymer belonging to the material constituting the resistor 34 is also
used to facilitate the manufacturing of the heating cartridge C1 shown in figure 3,
which includes the tube 33, the resistor 34, the rod 35 and the bushing 36. Indeed,
before polymerisation of this thermo-setting polymer, the mixture constituting the
material of the resistor 34 is viscous, while, after polymerisation, this mixture
solidifies and adheres both to the tube 33 and to the rod 35, providing links that
are mechanical, electrical and thermal.
In order to apply an electric voltage between the inner and outer surfaces
of the tubular body 341 of the heating resistor 34, the tube 33 and the rod 35 are
used, by applying on this tube and on this rod a difference in electrical potential,
provided the tube and the rod are connected respectively to the positive and
negative poles of an external current source not shown in the figures. In practice,
it is understood that the tube 33 and the rod 35 must be made of electrically
conducting materials, typically of metal.
For the purposes of fixing the tube 33 to the case 10 of the valve 1, the end
portion 332 of the tube is exteriorly provided with a collar 37 rigidly integral with
the outer surface of the tube. To do this, several possibilities of fastening can be
considered: in figure 3, the collar 37 is crimped around the end portion 332 of the
tube 33. As an alternative, in figure 4, a collar 37', functionally similar to the
collar 37, is fixed to the end portion 332 of the tube 33 by a self-locking cone 38'
which is added radially between the collar 37' and the tube 33, by becoming
wedged against an additional tapered surface delimited by the collar 37'.
Before describing the operation of the valve 1 in more detail, in particular
its heating cartridge C1, the manufacturing of this valve is presented hereinafter.
The heating cartridge C1 can firstly be assembled independently of the
other components of the valve 1. To do this, as mentioned hereinabove, the
viscous mixture of thermo-setting polymer, of conductive powder or powders and
of any other additives is set in place between the end portions 331 and 351 of the
tube 33 and of the rod 35. This operation takes advantage of the fact that the fiee
end 33A of the end portion 331 of the tube 33 is axially open, as can be seen easily
in figure 3: in these conditions, the aforementioned viscous mixture coats the
entire end portion 351 of the rod 35, in particular by covering its corresponding
5 fiee end 35A, while still closing in a sealed manner the end 33A of the tube 33.
Then, after having set in place the insulation bushing 36 between the end portions
332 and 352 of the tube 33 and of the rod 35, the assembling obtained is placed in
an oven until polymerisation of the mixture. The collar 37 is then added and made
integral around the tube 33.
10 The heating cartridge C1 obtained as such can then be assembled to the
other components of the valve 1.
In particular, the end portion 331 of the tube 33 is assembled to the cup 3 1,
by being plunged in a sealed manner into the heat-expandable material 32
contained in this cup: the portion of the heating resistor 34, closing the open end
15 33A of the tube 33, seals the inside of this tube with regards to the heatexpandable
material 32. Moreover, in a manner known per se, an annular seal,
arranged at the open end of the cup 21, seals the outside of the tube 33 with
regards to the heat-expandable material.
In addition, the end portion 332 of the tube 33 is introduced axially into the
20 body 11 of the case 10, by being engaged therein via the end of this body opposite
the elbow-shaped region 13. As shown in figure 1, the end portion 332 of the tube
33 is axially passed through a wall 16 of the case 10, which closes the cavity 14
according to the direction of the axis X-X, until empty space 17 delimited in the
thickness of the elbow-shaped region 13 of the case 10 is reached. This operation
25 of assembling the tube 33 to the case 10 leads to axially pressing the collar 37
against the wall 16, with axial positioning of a seal 18 surrounding the tube 33.
This tube 33 is fixedly connected to the case 10, by the maintaining in axial
support its collar 37 against the wall 16 under the action of the spring 21 afier
assembly of the latter to the case thanks to the armature 22.
30 The seal 18 can, in an alternative not shown, be replaced with other
functionally similar means of sealing, such as a glue or a sealing paste.
Inside the aforementioned empty space 17, the end portions 332 and 352 of
the tube 33 and of the rod 35 are respectively connected electrically to two
extended terminal lugs 41 and 42 whch extend lengthwise to the exterior of the
case 10 in order to be connected to an external current source, not shown in the
figures. In the example embodiment considered in figure 1, the terminal lugs 41
and 42 include respective longitudinal ends 41A and 42A which are respectively
connected to the free end 33B of the end portion 332 of the tube 33 and to the free
end 35B of the end portion 352 of the rod 35: in other words, the aforementioned
fiee ends 33B and 35B of the tube 33 and of the rod 35 constitute two connection
terminals for the heating cartridge C1, having respectively tubular and cylindrical
shapes, both centred on the axis X-X, these cylindrical and tubular connection
terminals being provided to be connected to the aforementioned external current
source, respectively by the intermediary of the terminal lugs 41 and 42. For the
purposes of mechanical strength and sealing, the respective current portions 41C
and 42C of the terminal lugs 41 and 42 are coated, typically by overmoulding, by
an insulating material which as such forms a support base 43 which is added in a
sealed manner to the space 17. This base 43 delimits a housing 44 for connecting
the aforementioned external current source, wherein extend the respective ends
41B and 42B of the tenninal lugs 41 and 42, opposite their end 41A and 42A.
In practice, diverse embodiments can be considered with regards to the
electrical connection between the aforementioned external current source and the
terminals which constitute the ends 33B and 35B of the end portions 332 and 352
of the tube 33 and of the rod 35, without being restrictive of the invention.
An example of the operation of the valve 1 is as follows. After having
connected an external current source in the housing 44, the application of an
electric voltage on the terminal lugs 41 and 42 circulates a current through
successively the tube 33, the heating resistor 34 and the rod 35. As explained
hereinabove, due to its resistivity, the resistor 34, substantially its tubular body
341, is heated by the Joule effect: the heat energy created as such is diffused
through the end portion 331 of the tube 33 and reaches the heat-expandable
material 32. This rise in temperature of the heat-expandable material 32 generates
a dilatation of the latter, with for consequence a translational displacement
according to the axis X-X between the tube 33 and the cup 3 1: with the tube 33
being fixed, the cup 3 1 is translated, by increasing the deployed extent of the tube
33 in relation to it.
5 It is understood that it is necessary to control the electrical power delivered
to the heating resistor 34 in order to correctly control the amplitude of the relative
displacement between the cup 31 and the tube 33, as well as in order to limit the
surface temperature of the tube 33 so that the latter does not deteriorate the parts
in contact with it. In practice, this control of the electrical power can be carried
10 out in two possible ways.
A first way consists in regulating the electrical power via a calculator, by
the variation in the voltage of a continuous signal or by the variation of the
opening cyclic ratio (OCR) of a sliced signal, according to a suitable algorithm
taking into account the temperature of the tube 33 or its position in relation to the
15 cup 3 1 or a parameter that depends on one or the other of the aforementioned
characteristics, for example the temperature of the fluid circulating in the cavity
14. This method of regulation is typically applied in the case where the resistivity
of the heating resistor 34 is practically constant according to its temperature.
The second way of controlling the electrical power delivered to the heating
20 cartridge C1 consists in self-regulating in temperature this heating cartridge, in the
case where the resistor 34 is designed & the form of a resistor with a positive
temperature coefficient. To do this, according to the nature andlor the proportion
of the conductive powder or powders of which is loaded the material constituting
the heating resistor 34, this material advantageously has an electrical resistivity
25 that increases with its temperature, in particular in the operating temperature range
of the heating cartridge C1. In this way, for a constant supply voltage, the power
delivered to the resistor 34 decreases with the temperature since the resistivity of
this resistor increases with the temperature. As such, by supplying the heating
cartridge C1 with a constant voltage, its temperature increases until a balance is
30 reached between the electrical power, which decreases with the temperature, and
the power dissipated to the ambient surroundings, i.e. in the fluid circulating in the
cavity 14 in the case of the valve 1, which increases with the temperature.
This possibility of having a stabilised self-regulated temperature, linked to
the nature of the mixture constituting the material of the heating resistor 34,
5 makes it possible to simplify the algorithm for regulating the supply of the heating
cartridge C1, as well as increasing the reliability of the thermostatic element 30.
Figure 5 shows an alternative embodiment of the heating cartridge C1,
referenced as C 100. This heating cartridge Cl 00 comprises a tube 133, a heating
resistor 134, a rod 135 and an insulation bushing 136, all centred on an axis X-X
10 and functionally similar, respectively, to the tube 33, to the heating resistor 34, to
the rod 35 and to the bushing 36 of the heating cartridge Cl.
The tube 133 is distinguished fiom the tube 33 by the fact that the fiee end
133A of its end portion 1331, wherein is arranged their heating resistor 134, is not
axially open as the end 33A, but is closed by a bottom 139 fonned integrally with
15 the rest of the tube 133. In other words, this tube 133 has the shape of a bucket.
This shape of a bucket guarantees a good seal on the bottom 139 of the tube 133,
in particular in that this bottom 139 covers the corresponding end of the tubular
body 1 341 of the heating resistor 134, radially positioned between the end portion
133 1 of the tube 133 and an end portion 135 1 of the rod 135, fimctionally similar
20 to the end portion 351 of the rod 35. On the other hand, in comparison with the
tube 33 obtained at a lesser cost by drawing, the aforementioned bucket shape of
the tube 133 requires more elaborate manufacturing operations, such as stamping
for the example shown in figure 5, or, in terms of an alternative not shown, the
welding to the rest of the tube 133 of an added part intended to form the bottom
25 139.
Moreover, the aforementioned bucket shape is entirely compatible with the
setting in place in viscous state of the mixture with a thermo-setting polymer base
which, after polymerisation, constitutes the heating resistor 134.
The heating cartridge ClOO is further distinguished fiom the heating
30 cartridge C1 by the additional presence, optionally, of a built-in temperature
sensor 150. More precisely, as can be seen easily in figure 5, this sensor 150, for
example of the thermocouple type or of the platinum filament type, is
advantageously embedded in the heating resistor 144, by being set into place in
this way before polymerisation of the mixture with a thermo-setting polymer base
constituting this resistor. The sensor 150 is as such arranged radially between the
5 end portions 1 331 and 135, of the tube 33 of the rod 35, in the thickness of the
tubular body 1341 of the heating resistor 134. The output signal of this sensor 150
is advantageously transmitted to the outside of the heating cartridge Cl 00 by at
least one element for transmitting 151, typically one or several wires, which run
according to the direction of the axis X-X, radially between the rod 35 and the
10 tube 33. In particular, this element for transmitting 151 runs between the end
portions 1332 and 1352 of the tube 133 and of the rod 135, which are functionally
similar, respectively, to the end portions 332 and 352 of the tube 33 and of the rod
35, and between which the insulation bushing 136 is radially positioned. Of
course, the element for transmitting 15 1 passes axially through on either side the
15 wall constituting this bushing 136, until exiting outside of the tube 133, as shown
in figure 5.
The temperature - sensor 150 can advantageously be used to provide
temperature measurements, taken into account by the algorithm, mentioned
hereinabove, in order to regulate the electrical power delivered to the heating
20 cartridge C 1 00.
Figure 6 shows an alternative embodiment of the heating cartridges C1 and
C100, referenced as C200. This heating cartridge C200 comprises a tube 233, a
heating resistor 234, a rod 235, an insulation bushing 236 and a temperature
sensor 250, which are functionally similar, respectively, to the tube 33 or 133, to
25 the heating resistor 34 or 134, to the rod 35 or 135, to the bushing 36 or 136, and
to the temperature sensor 150 of the heating cartridge C 1 or C 100.
The heating resistor 234 is distinguished from the heating resistors 34 and
134 by the nature of the polymer forming the base of the mixture that comprises
them: the heating cartridge 234 is made of a material constituted of a
30 thermoplastic polymer which, in the same way as for the thermo-setting polymer
of the heating resistors 34 and 134, is loaded with at least one conducting powder
and possibly other additives. The thermoplastic polymer base of the material
constituting the heating resistor 234 is such that, after forming this material, the
heating resistor 234 is made available in the form of a rigid or semi-rigid tubular
body 2341, able to be added via mechanical assembly to the rest of the heating
cartridge C200. In particular, this tubular body 2341 is fitted between end portions
2331 and 2352 of the tube 233 and of the rod 235. In practice, this press fitting can
be carried out first around the end portion 2352 of the rod 235, with the end
portion 2331 of the tube 233 then being press fitted around the tubular body 2341
of the heating resistor 234, or inversely. Moreover, each of these two fittings can
be carried out either in a tightening manner, by taking advantage of a capacity of
elastic deformation, radial in particular, of the body 2341 of the heating resistor
234, or with radial positioning of a conductive paste.
The free end 233A of the end portion 2331 of the tube 233 is closed in a
sealed manner by a bottom 239 forming an electrically insulating cap. Diverse
possibilities of carrying out this bottom forming a cap 239 can be considered: an
insulating glue, such as an epoxy glue, can be applied inside the end 233A of the
tube 233, this glue providing, after polymerisation, both a mechanical connection
with the tube as well as an electrical insulation between the tube and the
respective corresponding ends of the rod 235 and of the tubular body 2341 of the
heating resistor 234, covered by the glue. As an alternative, the bottom forming a
cap 239 is a part made of insulating material, added in a sealed manner, for
example by crimping, in the end 233A of the tube 233.
One of the interests in using a thermoplastic polymeric base for the
material constituting the heating resistor 234 is linked to the possibility of, before
assembling the tubular body 2341 of this heating resistor to the rest of the heating
cartridge C200, covering this body with an electrically conductive thin layer,
typically with a metal layer, in particular made of silver, i.e., more generally, with
a conductive layer of which the conductivity is greater than or equal to that of the
tube 233 and of the rod 235. In this way, the electrical contact between, on the one
hand, the tube 233 and the rod 235 and, on the other hand, the heating cartridge
234 covered as such is improved, by being particularly reliable.
Inversely, assembling mechanically the heating resistor 234 to the rest of
the heating cartridge C200 required ad hoc assembly operations and requires the
provision of the bottom forming a cap 239.
Note that this form of embodiment of the heating resistor 234 makes it
5 possible, as for the forms of embodiment of the resistors 34 and 134, to
incorporate the temperature sensor 250, which is then arranged in contact with the
tubular body 2341, as well as to obtain, according to the nature and the proportion
of the conductive powder or powders mixed with the thermoplastic polymer, that
the electrical resistivity of the mixture obtained be constant or increasing
10 according to the temperature, at least within a certain temperature range
corresponding to the operating range of the heating cartridge C200.
In terms of an alternative not shown, the tube 233 of the heating cartridge
C200 can have, at its end 233A, the same structure as that of the tube 133 of the
heating cartridge C 100.
15 According to another alternative not shown of the heating cartridge C200,
the material constituting the heating resistor 234 is not a mixture with a polymer
base, but is a conductive ceramic having a certain resistivity. This is in particular
the case with polycrystalline doped ceramic materials, with a barium titanate base.
Such a ceramic can in particular be chosen in order to have characteristics of a
20 resistor with a positive temperature coefficient. In practice, with regards to the
rigidity of such a resistant material with a ceramic base, the heating resistor 234
which is constituted of it is assembled and connected to the rest of the heating
cartridge C200 in a way similar to what has just been described with regards to
figure 6.
2 5 Finally, in addition to the preceding, various arrangements and alternatives
to the heating cartridges C1, ClOO and C200, as well as to the thermostatic valve
1 described until now can moreover be considered. In particular, note that, in the
examples of embodiments considered in the figures, the tube 33,133 or 233 of the
heating cartridge C1, ClOO or C200, wherein is arranged the heating resistor 34,
30 134 or 234, constitutes the piston of the thermostatic element 30: however, for
other thermostatic valve construction geometries, this tube of the heating cartridge
and the piston of the thermostatic element, of which the heat-expandable material
is heated by the heating resistor belonging to the cartridge, can consist of two
separate parts. In this case, generally, the tube of the heating cartridge extends
through the bottom of the cup of the thermostatic element, opposite the piston of
5 this element, the cup then being fixed in relation to the case, while the piston
carries a shutter in order to control the opening and the closing of the latter with
regards to the case.

CLAIMS
1. Heating cartridge (CI; ClOO; C200) for a thermostatic element (30),
comprising:
- a tube (33; 133; 233), which is both thermally and electrically conductive
and of which a &st end portion (331; 133i; 2331) is adapted to be embedded
5 within a heat-expandable material (32) of a thermostatic element (30), and
- a heating resistor (34; 134; 234) which is arranged inside the first end
portion of the tube,
characterised in that the heating cartridge (CI; ClOO; C200) further
comprises a rod (35; 135; 235), which is electrically conductive and which
10 extends at least partially into the tube (33; 133; 233) in a substantially coaxial
manner,
in that the heating resistor (34; 134; 234) comprises a tubular body (34i;
134i, 234i), which is constituted of an electrically resistant material and which is
radially positioned between a first end portion (35i; 135i; 235i,) of the rod (35;
15 135; 235) and the &st end portion (33i; 133i; 233i) of the tube (33; 133; 233), by
forming a cylindrical interface for electrical contact between the rod and the inner
surface of the tubular body as well as a cylindrical interface for electrical contact
between the tube and the outer sxirface of the tubular body,
20
# 18
and in that the tube (33; 133; 233) and the rod (35; 135; 235) include
respectively, opposite their first end portion, second end portions (332, 352; 1332,
1352; 2332, 2352) which are respectively adapted to be connected to the poles of
5 an external current source in such a way as to apply an electrical voltage between
the inner and outer surfaces of the tubular body of the heating resistor.
2. Heating cartridge according to claim 1, characterised in that the material
constituting the tubular body (34i; 134i; 234i) of the heating resistor (34; 134;
234) is a polymer loaded with at least one electrically conductive powder.
10 3. Heating cartridge according to claim 2, characterised in that the polymer
is a thermo-setting material adapted, before polymerisation, to be set in place in
viscous form between the first end portion (33i; 133i) of the tube (33; 133) and
the first end portion (35i; 135i) of the rod (35; 135), by adhering to these first end
portions.
15 4. Heating cartridge according to claim 2, characterised in that the polymer
is a thermoplastic adapted to, after put into form, render the tubular body (234i) of
the heating resistor (234) able to be added via mechanical assembly to the rest of
the heating cartridge (C200).
5. Heating cartridge according to claim 1, characterised in that the material
20 constituting the tubular body of the heating resistor is a doped ceramic material, in
particular with a barium titanate base.
6. Heating cartridge according to claim 4 or claim 5, characterised in that
the tubular body (234i) of the heating resistor (234) is fitted between the first end
portion (233i) of the tube (233) and the first end portion (235i) of the rod (235), in
25 a tightening manner and/or with radial positioning of electrically conductive paste.
7. Heating cartridge according to any of claims 4 to 6, characterised in that
the tubular body (234i) of the heating resistor (234) is lined, interiorly and/or
exteriorly, with an electrically conductive layer, of which the conductivity is
greater than or equal to that of the tube (233) and of the rod (235), and which,
30 after assembly of this tubular body to the rest of the heating cartridge (C200), is in
19
t
contact with the first end portion (2331) of the tube (233) and/or the first end
portion (235i) of the rod (235).
8. Heating cartridge according to any of the preceding claims,
characterised in that the material constituting the tubular body (34i; 134i; 234i) of
5 the heating resistor (34; 134; 234) has, in service, a resistivity that is substantially
constant according to its temperature.
9. Heating cartridge according to any of claims 1 to 7, characterised in that
the material constituting the tubular body (34i; 134i; 234i) of the heating resistor
(34; 1234; 234) has, in service, a resistivity which increases with its temperature.
10 10. Heating cartridge according to any of the preceding claims,
characterised in that the tube (33) is, at the free end (33A) of tiie first end portion
(33i) of the tube, axially open on the heating resistor (34).
11. Heating cartridge according to any of claims 1 to 9, characterised in
that, at the free end (133A; 233A) of the first end portion (133i; 233i) of the tube,
15 the tube (133; 233) is closed by a bottom (139; 239), which covers an axial end of
the heating resistor (134; 234) and which is either integrally formed with the rest
of the tube, or added in a sealed maimer in this free end of the tube.
12. Heating cartridge according to any of the preceding claims,
characterised in that the heating cartridge (CI00; C200) further comprises a
20 temperature sensor (150; 250), which is incorporated between the tube (133; 233)
and the rod (135; 235) by being arranged in the thickness of or in contact with the
tubular body (134i; 234i) of the heating resistor (134; 234), and of which the
output signal is fransmitted to the outside of the heating cartridge by an element
for fransmitting (151) which runs between the second end portion (1332) of the
25 tube (133) and the second end portion (1352) of the rod (135).
13. Thermostatic element (30), comprising a heating cartridge (CI; CI00;
C200) in accordance with any of the preceding claims, and a cup (31) containing a
heat-expandable material (32) wherein is embedded the tube (33; 133; 233) of the
heating cartridge.