Piezoelectric element and heating element of an electric radiator comprising such a piezoelectric element

Abstract

Title of the invention: Piezoelectric element and heating element of an electric radiator comprising such a piezoelectric element. Piezoelectric element (1) for a heating element of an electric radiator having two opposite faces (20, 21) and electrical properties such that a polarization vector extends in a given direction from one of the two faces opposite the other, characterized in that it comprises an indicator (18) of the direction of the polarization vector. Abstract figure: Figure 3

Description

Title of the invention: Piezoelectric element and heating member of an electric radiator comprising such a piezoelectric element

[0001] The present invention relates to the field of electric radiators, in particular for motor vehicles, and it relates more particularly to the vibration phenomena of such electric radiators.

[0002] Electric radiators are arranged in heating, ventilation and air conditioning (HVAC) installations fitted to motor vehicles, in particular to raise the temperature of the air passing through these installations and intended to be sent into the passenger compartment of the vehicle when a heating command is generated automatically or by one of the vehicle's passengers.

[0003] The electric radiators are for this purpose arranged in a duct of the HVAC installation and comprise a control box and a heating body. The heating body is arranged across said duct and comprises piezoelectric elements whose electrical supply causes the generation of calories to be released to the air circulating in the duct.

[0004] The heating body may more particularly comprise a plurality of heating members extending longitudinally from the control box, one next to the other in parallel and all being electrically connected to the control box and to the electronic components housed therein. Each heating member comprises, within a sheath, electrodes, the ends of which provide the electrical connection with the control box, and between which are arranged several piezoelectric elements aligned longitudinally one after the other. These piezoelectric elements may in particular be ceramics with a PTC effect, for Positive Temperature Coefficient.

[0005] The current resulting from an electrical supply to the electric heater passes through each heating member from one electrode to the other, passing through the piezoelectric elements, the direction of flow of the current being defined by the electrical connection of the electrodes to the electrical circuit formed in the control box. A positive electrode and a negative electrode are defined and the current passes through each piezoelectric element from the face in contact with the positive electrode to the face in contact with the negative electrode.

[0006] This circulation of current within the piezoelectric element causes a production of calories within each heating member. This implements the electrocaloric effect of the piezoelectric elements. The air coming from outside the The vehicle circulates in the HVAC system housing and is brought through the radiator. The calories generated by each electrically powered heating element are first transmitted by conduction to the entire heating body. The air passing through the radiator through the fins recovers the calories by convection.

[0007] As mentioned, electric radiators are inserted into HVAC installation boxes which are fixed to the structure of the vehicle and whose operation generates vibration phenomena and sound radiation which automobile manufacturers seek to reduce in order to lessen the discomfort of vehicle passengers.

[0008] In the context of this research, the inventors identified the role of the electromechanical effect, which accompanies the electrocaloric effect associated with each piezoelectric element, in the importance of the vibration phenomenon experienced by the HVAC installation boxes. More particularly, the inventors were able to observe, on simplified samples with a limited number of piezoelectric elements per heating member, that the vibration phenomena generated could vary greatly from one heating member to another and they deduced from this that the structure of the heating member had a role to consider in optimizing the vibration and acoustic performances of a vehicle equipped with electric radiators.

[0009] In this context, the present invention aims to propose both a particular piezoelectric element, a heating member and an electric radiator for a motor vehicle, as well as their manufacturing method, which make it possible to propose improved acoustic characteristics, in particular through better control of the vibration modes.

[0010] The invention provides a piezoelectric element for an electric radiator heating member comprising two opposite faces and electrical properties such that a polarization vector extends in a given direction from one of the two opposite faces to the other, characterized in that it comprises an indicator making it possible to determine the direction of the polarization vector of the piezoelectric element.

[0011] As mentioned above, this piezoelectric element is in particular intended to be applied in an electric radiator of a motor vehicle.

[0012] The inventors were able to observe that the vibratory response of the heating member depended at least in part on the random orientation of the polarization vector of each piezoelectric element.

[0013] The polarization vector of a piezoelectric element is oriented parallel to the electric field, which is applied between the two electrodes of the heating element and which is directed from the positively charged electrode to the negatively charged electrode. The polarization vector is a data representative of the electromechanical deformation of the piezoelectric element. Depending on the orientation given to the electric field which passes through the same piezoelectric element, the latter can stretch or contrary to retract. The inventors started from this observation to determine that for an electric field of given direction, a piezoelectric element can stretch if it is placed in a first direction relative to the electric field, that is to say if its polarization vector is in a first direction relative to the electric field, in particular in a direction opposite to the electric field, and this piezoelectric element can retract if it is placed in a second direction relative to this electric field, that is to say if its polarization vector is in a second direction relative to the electric field, in particular if it is in the same direction as the electric field.

[0014] Having an identification of the direction of the polarization vector makes it possible to assemble the piezoelectric elements within the heating member according to a particular orientation. Thus, it is possible on the one hand to homogenize the vibration behavior of mass-produced heating members and electric radiators and preferably to choose a predetermined configuration of orientations which is judged not to generate vibrations or at the very least to generate fewer vibrations.

[0015] It should be noted that throughout the text, the indicator for determining the direction of the polarization vector of the piezoelectric element may also be called the indicator of the direction of the polarization vector, or simply the indicator. As will be detailed below, this indicator may take different forms, and may be either an explicit marking that mentions the direction of the polarization vector or a marking, for example the mark of the manufacturer of this piezoelectric element, provided that it is ensured that this mark is always positioned in the same direction relative to the identified polarization vector.

[0016] According to one embodiment, the piezoelectric element is a pyroelectric element. In other words, the piezoelectric element has pyroelectric properties.

[0017] According to one embodiment, the piezoelectric element is a ferroelectric element.

[0018] According to an optional feature of the invention, the indicator is produced by marking one of the faces of the piezoelectric element. The marking may include ink inscriptions or engraved or molded inscriptions. For example, the indicator may consist of a marking of the face towards which the polarization vector is directed. In this way, if it is desired to have a piezoelectric element positioned in a first direction in the heating member, in particular to have an electromechanical effect generating an enlargement of the piezoelectric element, it is appropriate to position the face marked with the indicator against the positive electrode from which the electric field is intended to be applied when the heating member is powered. Conversely, if it is desired to have a piezoelectric element positioned in a second direction in the heating member, in particular to have an electromechanical effect mechanical generating a shrinkage of the piezoelectric element, it is advisable to position the face marked with the indicator against the negative electrode towards which the electric field is intended to be applied when the heating element is powered.

[0019] According to an optional characteristic of the invention, the piezoelectric element has a parallelepiped shape with two main faces which form the opposite faces, said indicator being positioned on one of the main faces. Advantageously, the two main faces of the parallelepiped are the two opposite faces with the largest surface area. Advantageously, the parallelepiped is a rectangular parallelepiped.

[0020] According to an optional characteristic of the invention, the piezoelectric element is obtained by a sintering process.

[0021] According to an optional characteristic of the invention, the constituent material of the piezoelectric element is Barium Titanate (BaTiO3).

[0022] According to an optional characteristic of the invention, the material constituting the piezoelectric element is polarized during the sintering operation.

[0023] According to an optional characteristic of the invention, the piezoelectric element is obtained by a sintering process during which the direction of the polarization vector is determined. In this way, the orientation of the polarization vector is controlled.

[0024] According to an optional characteristic of the invention, the indicator making it possible to determine the direction of the polarization vector of the piezoelectric element is marked during the sintering operation. The sintering mold may comprise an imprint forming the indicator of the piezoelectric element.

[0025] The invention also relates to a method for manufacturing a piezoelectric element as mentioned above, the method comprising a step of providing a material constituting the piezoelectric element and a step of sintering this material in a mold, the mold comprising an imprint capable of forming the indicator making it possible to determine the direction of the polarization vector of the piezoelectric element.

[0026] The invention also relates to a heating member of an electric radiator of a motor vehicle, the heating member comprising several piezoelectric elements, each piezoelectric element being able to be arranged between two electrodes in two orientations which differ from each other in that in a first position, a defined face of the piezoelectric element is positioned against a first electrode so that the piezoelectric element has a polarization vector in a first direction while in a second position, said defined face of the piezoelectric element is positioned against a second electrode so that the piezoelectric element has a polarization vector in a second direction opposite to the first direction, the heating member being characterized in that it has a predetermined configuration of all the polarization vectors of the elements piezoelectric, each piezoelectric element being arranged between two electrodes in a position defined according to this predetermined configuration of the set of polarization vectors of the piezoelectric elements.

[0027] In the description which follows, mention will be made of piezoelectric elements arranged between two electrodes, but it should be noted that this applies equally to a heating member which comprises only two electrodes, of equal length and which extend opposite one another and enclose all of the piezoelectric elements, as well as to a heating member comprising, for example, two positive electrodes arranged one after the other and respectively opposite the same negative electrode, the piezoelectric elements being, for example, half enclose between a first positive electrode and the negative electrode and half enclose between a second positive electrode and the negative electrode.

[0028] According to an optional characteristic of the invention, the electrodes are made of aluminum and the piezoelectric elements are glued to the electrodes.

[0029] According to an optional characteristic of the invention, the piezoelectric elements comply with what was previously mentioned, namely that they each comprise an indicator of the direction of their polarization vector.

[0030] The invention also relates to an electric radiator for a motor vehicle comprising several heating members as mentioned above, each heating member extending in a main elongation direction parallel to the other heating members, the heating members being arranged next to each other in a transverse direction perpendicular to the main elongation direction.

[0031] According to an optional characteristic of the invention, the piezoelectric elements of each heating member are arranged within this heating member according to the predetermined configuration of all the piezoelectric elements, the heating members being identical to each other. In other words, all the heating members of the electric radiator have the same predetermined configuration of all the polarization vectors of the piezoelectric elements.

[0032] According to an optional characteristic of the invention, the piezoelectric elements of a heating member are arranged one after the other, starting from a reference piezoelectric element, in a sequence which respects the predetermined configuration of all the piezoelectric elements, the reference piezoelectric element being offset from one heating member to an adjacent heating member in a direction parallel to the main elongation direction of the heating members. If the piezoelectric elements of a heating member are arranged according to the predetermined configuration by having as reference piezoelectric element the piezoelectric element closest to the electronic control unit associated with this member heating element, the reference piezoelectric element of the adjacent heating member is the second closest to the electronic control unit and the sequence respecting the predetermined configuration begins with this offset. Of course, it is understood that to fill this adjacent heating member, when piezoelectric elements remain to be positioned to carry out the sequence but there is no more space at the end opposite the electronic control unit, the sequence is continued by positioning the next piezoelectric element in the position closest to the electronic control unit, and then continues towards the reference piezoelectric element.

[0033] According to an optional characteristic of the invention, the electric radiator comprises a first type of heating members having a first predetermined configuration of the set of polarization vectors of the piezoelectric elements and a second type of heating members having a second predetermined configuration of the set of polarization vectors of the piezoelectric elements in which the direction of the polarization vectors of each piezoelectric element is reversed with respect to the first configuration.

[0034] According to an optional characteristic of the invention, the first and second types of heating members are arranged successively in the transverse direction and regularly alternating one after the other.

[0035] According to an optional feature of the invention, the electric radiator comprises a first group of piezoelectric elements oriented with a polarization vector in a first direction and a second group of piezoelectric elements oriented with a polarization vector in a second direction opposite to the first direction, the piezoelectric elements of the first and second groups being arranged in a staggered pattern. This results in a checkerboard arrangement, which is more advantageous than a random configuration.

[0036] The invention finally relates to a method for manufacturing a heating member as previously mentioned, the method comprising a step of identifying the direction of the polarization vector of each piezoelectric element intended to be received between electrodes of the heating member and a step of predetermining a configuration to be given to the polarization vectors of the piezoelectric elements of the heating member, the method further comprising a subsequent step of assembling the piezoelectric elements and the electrodes according to the predetermined configuration of all the polarization vectors of the piezoelectric elements of this heating member.

[0037] According to an optional characteristic of the invention, the predetermination step comprises a step of controlling acoustic radiation emitted by the operation of the heating member in a basic configuration, with piezoelectric elements arranged with their respective polarization vector in a random direction, the control step consisting in particular of seeking which vibratory mode is the cause of the acoustic radiation considered to be the most penalizing, the predetermination step also comprising a step of analyzing tables of values ​​in which the impacts of different determined configurations of the polarization vectors of the piezoelectric elements for each vibratory mode are listed.

[0038] Other characteristics, details and advantages of the invention will emerge more clearly on reading the description which follows on the one hand, and examples of embodiment given for informational and non-limiting purposes with reference to the appended drawings on the other hand, in which:

[0039] [Fig.l] illustrates an electric radiator for a motor vehicle, comprising a plurality of heating members;

[0040] [Fig.2] illustrates a heating member suitable for equipping the electric radiator of [Fig.l], the tube serving as a sheath for this heating member being removed here to make visible two of the piezoelectric elements equipping this heating member and interposed between electrodes;

[0041] [Fig.3] illustrates a piezoelectric element of [Fig.2];

[0042] [Fig.4] schematically illustrates an electromechanical phenomenon of stretching of the piezoelectric element under the effect of an electric field and a first position of the piezoelectric element between the electrodes;

[0043] [Fig.5] schematically illustrates an electromechanical phenomenon of shrinkage of the piezoelectric element under the effect of an electric field and a second position of the piezoelectric element between the electrodes;

[0044] [Fig.6] schematically illustrates an electric radiator in which all the organs heaters have the same predetermined configuration;

[0045] [Fig.7] schematically illustrates an electric radiator in which the organs heaters have different configurations, alternatively to what has been illustrated in [Fig.6];

[0046] [Fig.8] illustrates a flowchart representing steps in a method of manufacturing a heating member intended to be implemented in an electric radiator as illustrated for example in Figures 6 and 7;

[0047] [Fig.9] illustrates tables of values ​​allowing the realization of one of the stages of the process illustrated in [Fig.8].

[0048] The features, variants and different embodiments of the invention may be combined with each other, in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be imagined comprising only a selection of features described below in isolation from the other features described, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0049] As a reminder, the invention aims to protect a piezoelectric element 1 intended to be arranged in a heating member of an electric radiator, the piezoelectric element being particular in its structure and / or in its arrangement relative to other piezoelectric elements of the same heating member to reduce the piezoelectric vibrations that its operation can generate and the acoustic disturbances that result therefrom.

[0050] An electric radiator as mentioned may in particular be integrated into a heating, ventilation and air conditioning installation (known as an HVAC installation) of a motor vehicle, in particular to heat air circulating in a housing of this installation and intended to be sent into the passenger compartment of the vehicle when a heating command is generated automatically or by one of the passengers of the vehicle. For this purpose, a heating body of the electric radiator is arranged in a circulation duct of a flow of air to be heated.

[0051] [Fig. 1] illustrates an exemplary embodiment of an electric radiator 2 capable of being equipped with piezoelectric elements in accordance with the invention and which comprises, in addition to the heating body 4, an electronic control device 6.

[0052] The electronic control device 6 comprises a control box inside which electronic components are housed, not visible here. These electronic components are in particular fixed on a printed circuit board and they provide power supply and control of heating members 8 present in the heating body 4 and respectively electrically connected to the electronic control device 6.

[0053] The heating body 4 is more particularly formed of a plurality of heating members 8 arranged in parallel with each other, here with radiant elements 10 interposed between the heating members to increase the exchange surface with the air and improve the exchange of calories between the heating members and the air passing through the radiator. Each heating member 8 extends in a main elongation direction parallel to the other heating members, the heating members being arranged next to each other in a transverse direction perpendicular to the main elongation direction.

[0054] Each heating member 8 comprises a tube 12 which houses electrodes associated with piezoelectric elements and which also houses an insulator between the electrodes and the wall of the tube. The radiant elements 10 are welded to the outer face of the tube.

[0055] [Fig.2] illustrates more particularly a heating member 8 capable of equipping such an electric radiator 2, with here the tube and the insulation which have been removed to make visible internal components of the heating member 8.

[0056] The heating member 8 comprises two electrodes 14 arranged parallel to each other, along the longitudinal direction, and piezoelectric elements 1 interposed between the two electrodes 14 and held in position by gluing and / or by a support, so that they are in contact with each of the electrodes 14.

[0057] The electrodes 14 are made of aluminum and have the shape of a flat strip against which the piezoelectric elements 1 can rest. The electrodes 14 have at least one longitudinal end a connection tab 16 for connection to the housing of the electronic control device 6.

[0058] The piezoelectric elements 1 are glued to the electrodes 14 and they can also be held in position via a support which ensures a regular interval in the positioning of the piezoelectric elements 1.

[0059] These piezoelectric elements 1 can be obtained by a sintering process.

[0060] Each piezoelectric element 1 is here made of Barium titanate (BaTiO3), without this material being limiting of the invention since it offers electrocaloric properties.

[0061] Each piezoelectric element 1 also has electromechanical properties specific to it, namely a capacity to deform in proportions which depend on the value of the electric field generated between the electrodes 14 during operation of the electric radiator.

[0062] As mentioned, the polarization vector of a piezoelectric element 1 is directed from the negative electrode of the element to the positive electrode of this element, when the latter is subjected to a given electric field E. In this way, the polarization vector / 5^ is a vector characteristic of the mechanical deformation of the piezoelectric element 1.

[0063] According to the invention, the piezoelectric elements 1 are arranged within the heating member 8 which is specific to them, and more generally within the electric radiator, so that the combined mechanical deformations of each piezoelectric element 1, under the effect of a given electric field E, generate as few parasitic vibrations as possible. In particular, the piezoelectric elements 1, which are all constrained between two electrodes 14, are oriented so that under the effect of a given electric field E, they stretch or retract according to the direction of elongation of the electrodes, and so that the combination of the movements of each piezoelectric element leads to minimizing the amplitude of the vibrations of the heating element.

[0064] The direction of the polarization vector is specific to each piezoelectric element 1 and depends on the configuration that the crystalline structure takes within the piezoelectric element 1 during the sintering operation which makes it possible to obtain these piezoelectric elements.

[0065] This sintering operation may be particular in that the material constituting the piezoelectric element 1 is polarized to ensure the configuration that the atoms will take and generate a permanent dipole moment, and therefore to ensure the orientation of this dipole moment and the polarization vector that characterizes it.

[0066] Figure 3 illustrates more particularly a piezoelectric element 1 according to the invention, which is particular in that it comprises a marking making it possible to identify the direction of the polarization vector JÇ.

[0067] In this example, the piezoelectric element 1 has the general shape of a parallelepiped, with two main faces 20 in opposition. These main faces 20 are respectively intended to be in contact, and more particularly glued, to one of the electrodes 14 of the heating member 8.

[0068] It results from this arrangement that the electric field E which will be applied and pass through the piezoelectric element 1 within the heating member 8 extends in a direction parallel to that going from one main face 20 to the other. The polarization vector associated with the piezoelectric element 1 is thus oriented parallel to this direction, from one main face 20 to the other.

[0069] The marking of the piezoelectric element is particular in that it forms an indicator 18 of the direction of the polarization vector pÇ, that is to say an indicator of which is the first main face 21 and which is the opposite main face, in a context where the polarization vector / p extends from the first main face 21 to the opposite main face. For this purpose, the indicator 18 may consist, as illustrated, of a mark made on this first main face 21, namely the main face from which the polarization vector extends in the direction of the opposite main face. Thus, during the assembly of the heating member 8 and the positioning of the piezoelectric elements 1, the main face 20 comprising the indicator is positioned against the electrode 14 intended to be the positive electrode when an electric field E is applied, if it is desired that the polarization vector ~p^ be in the same direction as the electric field E-

[0070] Conversely, if we want the polarization vector to have a direction opposite to the direction of the electric field ~E, we position the main face comprising the indicator against the electrode intended to be the negative electrode.

[0071] Without departing from the context of the invention, it is possible to provide that the two opposite main faces are marked since this makes it possible to clearly identify in which way the polarization vector is oriented when an electric field I passes through it.

[0072] Another alternative is illustrated in Figure 2. It can in fact be envisaged, in particular when the piezoelectric element is of parallelepiped shape, that the indicator 18 is positioned on a lateral face 22 of the piezoelectric element, for example by taking the form of an arrow directed from the first main face 21 to the opposite main face. This latter alternative has the advantage of being able to identify the direction of the polarization vector even after the main faces 20 of the piezoelectric elements have been brought against, and glued, to the electrodes 14.

[0073] The direction of the polarization vector can be imposed during the sintering operation, so that the indicator 18 is positioned accordingly on one of the faces of the piezoelectric element 1 during the sintering operation. Alternatively, if the direction of the polarization vector / Ç is kept random during the sintering operation, that is to say it is not imposed by an intentional polarization action, it is appropriate after the sintering operation to carry out a test on the piezoelectric element 1 obtained by subjecting it to an electric field £ and measuring its mechanical deformation, for example under conditions of maintenance of the piezoelectric element which are substantially identical to the maintenance carried out within the heating member 8 by the two electrodes 14. The indicator 18 of the direction of the polarization vector is applied to one of the faces according to the results of this test.

[0074] Figures 4 and 5 illustrate the electromechanical effect applied to the piezoelectric element 1 when it is crossed by an electric field E applied between two electrodes 14 which enclose said piezoelectric element, and the difference between these effects depending on whether the same piezoelectric element 1 is arranged in one direction or the other.

[0075] Figure 4 illustrates a configuration in which the piezoelectric element 1 is positioned according to a first position PI, with the polarization vector / Ç which is arranged in the opposite direction to the direction of the electric field E- In this first position PI and in the embodiment example which has been given of an indicator 18 which makes it possible to identify the first main face 21 from which the polarization vector departs in the direction of the opposite main face, an operator was able to ensure the correct positioning of the piezoelectric element 1 in this first position PI, by pressing the first main face 21 of the piezoelectric element 1 against the negative electrode 14 of the heating member.

[0076] When the electric field E is applied, the opposite direction of the polarization vectors P? and of the electric field E generates an enlargement of the piezoelectric element 1, the original shape of this element being represented in dotted lines in Figure 4. Figure 4 shows an arrow Dxl which illustrates the axial stretching of the piezoelectric element, in a direction perpendicular to the direction of the electric field E and parallel to the elongation planes of the electrodes 14 between which said piezoelectric element is sandwiched.

[0077] Figure 5 illustrates conversely a configuration in which the piezoelectric element 1 is positioned according to a first position P2, with the polarization vector / Ç which is arranged in the same direction as the direction of the electric field. In this second position P2 and in the embodiment example which has been given of an indicator 18 which makes it possible to identify the first main face 21 from which the polarization vector departs in the direction of the opposite main face, an operator was able to ensure the correct positioning of the piezoelectric element 1 in this second position P2, by pressing the first main face 21 of the piezoelectric element against the positive electrode 14 of the heating member.

[0078] When the electric field £ is applied, the identical direction of the polarization vectors and of the electric field £ generates a shrinkage of the piezoelectric element, the original shape of this element being represented in dotted lines in Figure 5. Figure 5 shows an arrow Dx2 which illustrates the axial shrinkage of the piezoelectric element, in a direction perpendicular to the direction of the electric field E and parallel to the planes of elongation of the electrodes 14 between which said piezoelectric element is sandwiched.

[0079] The advantage of such marking of the piezoelectric elements for identification of the direction of the polarization vector / Ç and a determined positioning of this piezoelectric element 1 within a given electric field ~E is particularly advantageous in an electric radiator 2 of a motor vehicle, comprising one or more heating members 8 equipped with piezoelectric elements.

[0080] Figures 6 and 7 illustrate several arrangements of heating members 8 within an electric radiator 2, the arrangements of the heating members being identical from one heating member to another or on the contrary distinct, with reference to the positioning of the piezoelectric elements within a heating member.

[0081] Figure 6 illustrates in particular an electric radiator 2 with here three heating members 8 between which radiant elements 10 extend, each heating member 8 comprising piezoelectric elements 1 positioned according to a predetermined configuration of the set of piezoelectric elements, this particular configuration being able to be implemented in a certain manner thanks to the polarization vector direction indicators 18 which are marked on each piezoelectric element 1.

[0082] Here, the predetermined configuration of the set of piezoelectric elements 1 is the same for each heating member, and it is as follows, considering the position of each piezoelectric element from the end of the heating member 8 closest to the electronic control device 6 to the opposite end:

[0083] PI-P2-P2-P1-P2-P2.

[0084] In other words, for each heating member 8, the piezoelectric element 1 closest to the electronic control device 6 is in a first position PI, with the polarization vector p2 in the opposite direction to the direction of the electric field p and therefore tends to stretch under the effect of the electric field-^, while the two piezoelectric elements 1 which follow moving away from the electronic control device 6 are in a second position P2, with the polarization vector in the same direction as the direction of the electric field E and therefore tend to retract under the effect of the electric field. The same sequence of three piezoelectric elements with these positions is then reproduced.

[0085] Thus, the piezoelectric elements 1 of each heating member 8 are arranged within this heating member 8 according to the predetermined configuration of all the piezoelectric elements, and the heating members 8 are identical to each other.

[0086] Such a predetermined configuration of the set of piezoelectric elements 1 is chosen for its vibration attenuation efficiency for a given vibration mode, according to a determination method which will be described below.

[0087] [Fig.7] illustrates the same electric radiator 2 with three heating members 8 which this time have different configurations of piezoelectric elements 1 from one heating member to another. More particularly, the predetermined configuration of all the piezoelectric elements 1 is respected for each heating member, but it is axially offset, according to the direction of elongation of the heating members, from one heating member to another. Thus, the predetermined configuration of all the piezoelectric elements 1 of each heating member 8 remains a function of the configuration P1-P2-P2-P1-P2-P2, and the axial offset from one heating member to another generates a general staggered arrangement on the entire electric radiator 2.

[0088] In other words, for a first heating member 8, a reference piezoelectric element that initiates the sequence of positioning the piezoelectric elements according to the configuration is the piezoelectric element 1 closest to the electronic control device, which is in a first position P1, with the polarization vector p2 in the opposite direction to the direction of the electric field E and therefore tends to stretch under the effect of the electric field E, while the two piezoelectric elements 1 that follow moving away from the electronic control device 6 are in a second position P2, with the polarization vector pÇ in the same direction as the direction of the electric field E and therefore tend to retract under the effect of the electric field E. The same sequence of three piezoelectric elements with these positions is then reproduced along this first heating member.

[0089] For a second heating member adjacent to the first heating member, this sequence is axially offset, with the reference piezoelectric element, from which the sequence respecting the predetermined configuration is triggered, which becomes the second piezoelectric element closest to the electronic control device. In this way, the piezoelectric element 1 closest to the electronic control device 6 is in a second position P2 to resume the position in which the piezoelectric element furthest from the electronic control device was in the first heating member, while the piezoelectric element 1 which follows moving away from the electronic control device 6 is in a first position PI which corresponds to the first position in which the piezoelectric element closest to the electronic control device of the first heating member is located, and so on.

[0090] Thus, the piezoelectric elements 1 of each heating member 8 are arranged within this heating member according to the predetermined configuration of the set of piezoelectric elements 1, with an offset of said configuration from one heating member to an adjacent heating member in a direction parallel to the main elongation direction of the heating members.

[0091] Again, such a predetermined configuration of the set of piezoelectric elements and an axial offset for a staggered arrangement of the piezoelectric elements are chosen for the vibration attenuation efficiency for a given vibration mode, according to a determination method which will be described below.

[0092] In variants not illustrated here, other types of arrangement of the heating members can be provided, for example with an alternation of predetermined configurations of the piezoelectric elements from one heating member to another. A first type of heating members has a first predetermined configuration of the set of polarization vectors of the piezoelectric elements and a second type of heating members has a second predetermined configuration of the set of polarization vectors of the piezoelectric elements, the first and second types of heating members being arranged successively in the transverse direction and regularly alternating one after the other.Advantageously, in this arrangement, it may in particular be provided that the two predetermined configurations differ from one another with the direction of the polarization vector of a piezoelectric element of a heating member which is reversed with respect to the direction of the polarization vector of the piezoelectric element which occupies the same position in the heating member adjacent to the different configuration.

[0093] With reference to the flowchart of FIG. 8, a method 100 for manufacturing a heating member as mentioned will now be described, with a marking identifying the direction of the polarization vector / Ç.

[0094] The method comprises a step 102 of identifying the direction of the polarization vector of each piezoelectric element 1 intended to be received between electrodes 14 of the heating member 8. This identification step 102 can be integrated into the step of manufacturing the piezoelectric element, in particular a sintering step, or it can take place after the manufacturing step. In the first case, the manufacturing step can comprise a polarization operation to give a determined direction to the polarization vector and allow it to be marked immediately according to the determined direction. In the second case, the direction of the polarization vector jÇ cannot be known and it is appropriate to test the piezoelectric element, in particular by holding it and passing an electric field g through it, to determine whether it extends or retracts under the effect of this electric field £.The identification consists of a marking of one or other of the faces of the piezoelectric element, the marking being able to consist of a pictogram or a letter, without this being limiting of the invention.

[0095] The method 100 also comprises a step 104 of predetermining a configuration to be given to the polarization vectors of the piezoelectric elements of the heating member. In an example of the invention, the predetermination step 104 uses tables of values ​​112 as illustrated in [Fig.9], the analysis of which makes it possible to define a configuration particularly suited to the appearance of a particular vibration mode of the electric radiator.

[0096] The method 100 finally comprises an assembly step 106, which takes place after the predetermination step 104 and the identification step 102, during which an operator, or a robot equipped with means for identifying the marker affixed to the piezoelectric elements, places piezoelectric elements 1 on one of the electrodes 14 of a heating member 8 in a defined position, namely the first position PI or the second position P2 as mentioned previously, to respect the predetermined configuration of all the polarization vectors of the piezoelectric elements 1 of this heating member.

[0097] The predetermination step 104 previously mentioned can be split into at least two sub-steps. A first sub-step 108 consists of measuring the acoustic radiation generated by the operation of the electric radiator 2 when the heating member(s) 8 are electrically powered for their electrocaloric effect, this measurement sub-step 108 making it possible to identify which vibration mode is the cause of the acoustic radiation considered to be the most penalizing. A second sub-step 110 consists of analyzing tables of values ​​112, such as those illustrated in FIG. 9, in which the impacts of different determined configurations of the polarization vectors / ½ of the piezoelectric elements for a plurality of vibration modes are listed.

[0098]

[0099]

[0100]

[0101]

[0102] More particularly, these tables of values ​​112 make visible, for a given vibration mode, the impact of a determined configuration of the set of piezoelectric elements, compared to a reference configuration, on such or such electromechanical value, and for example the average of the polarization vectors j ^y on the set of the heating member(s) as it is listed in the first column of each table. In the example which will follow, it is this average of the polarization vectors j / rjy which will be considered but other characteristics could be considered as a quantity of displacement u, w, a force Nx, Tz or even a moment My. For example, if it has been identified in the first sub-step 108 that it is mode 3 which generates the most acoustic radiation, reading the value tables 112 must make it possible to identify which configuration of piezoelectric elements 1, in this mode 3, makes it possible to bring the most stability from an electromechanical point of view for the electric radiator, the value closest to 0, whether positive or negative, being synonymous with mechanical stability for the entire heating member and therefore with less vibration. Here, the most effective configuration for attenuating vibrations in mode 3 is configuration Cl for which the value 0.3 dB is as close as possible to 0 if we consider the average of the polarization vectors ^rfy, configuration C2 giving a value of 1.3 dB, configuration C3 giving a value of -2.7 dB, configuration C4 giving a value of 1.0 dB and configuration C5 giving a value of -2.6 dB.. In this example, it is the configuration of piezoelectric elements C1 which is chosen, this configuration being a configuration P1 / P1 / P2 / P1, with the piezoelectric element closest to the electronic control device which is arranged between the electrodes according to the first position previously mentioned and the following piezoelectric elements which are arranged between the electrodes successively according to the first position, the second position and the first position, the positioning according to such or such position being allowed thanks to the indicator of the direction of the polarization vector which is present on the piezoelectric elements 1. As a further example, if it has been identified in the first sub-step 108 that it is mode 4 which generates the most acoustic radiation, the most effective configuration for attenuating vibrations in mode 4 is configuration C2 for which the value -0.4 dB is as close as possible to 0 if we consider the average of the polarization vectors j^y In this additional example, it is the configuration of piezoelectric elements C2 which is chosen, this configuration being a P1 / P1 / P2 / P2 configuration, with the piezoelectric element closest to the electronic control device which is arranged between the electrodes according to the first position previously mentioned and the following piezoelectric elements which are arranged between the electrodes successively according to the first position, the second position and the second position, the positioning according to such or such position being allowed thanks to the indicator of the direction of the polarization vector which is present on the piezoelectric elements.

[0103] As is apparent from the present description, the invention achieves the aims it set itself by proposing a heating member and an associated electric radiator which makes it possible to limit the acoustic radiation of the vehicle heating installation in which they are integrated, and by achieving this acoustic performance with simple and inexpensive means consisting of identifying a polarization vector direction of the piezoelectric elements making up the heating member and positioning these piezoelectric elements in accordance with a determined and no longer random configuration.

[0104] The present invention cannot, however, be limited to the means and configurations described and illustrated here and it also extends to any equivalent means and configuration as well as to any technically operative combination of such means.

Claims

Claims

1. Piezoelectric element (1) for an electric radiator heating member comprising two opposite faces (20, 21) and electrical properties such that a polarization vector (7¾) extends in a given direction from one of the two opposite faces to the other, characterized in that it comprises an indicator (18) making it possible to determine the direction of the polarization vector (7¾) of the piezoelectric element (1).

2. Piezoelectric element (1) according to claim 1, wherein the indicator (18) is produced by marking one of the faces of the piezoelectric element (1).

3. Piezoelectric element (1) according to claim 2, characterized in that it has a parallelepiped shape with two main faces (20) which form the opposite faces, said indicator (18) being positioned on one of the main faces (20).

4. Piezoelectric element (1) according to one of claims 2 or 3, wherein the piezoelectric element is obtained by a sintering process during which the direction of the polarization vector (p^) is determined.

5. Heating member (8) for an electric radiator of a motor vehicle, the heating member (8) comprising several piezoelectric elements (1) according to one of claims 1 to 4, each piezoelectric element (1) being able to be arranged between two electrodes (14) in two orientations which differ from each other in that in a first position (PI), a defined face of the piezoelectric element is positioned against a first electrode so that the piezoelectric element has a polarization vector (7¾) in a first direction while in a second position (P2), said defined face of the piezoelectric element is positioned against a second electrode so that the piezoelectric element has a polarization vector (7¾) in a second direction opposite to the first direction,the heating member being characterized in that it has a predetermined configuration of the set of polarization vectors (Pz) of the piezoelectric elements, each piezoelectric element being arranged between two electrodes (14) in a position (PI, P2) defined according to this predetermined configuration of the set of polarization vectors (7¾) of the piezoelectric elements.,

6. Electric radiator (2) for a motor vehicle comprising several heating members (8) according to claim 5, each heating member (8) extending in a main elongation direction parallel to the other heating members (8), the heating members (8) being arranged next to each other in a transverse direction perpendicular to the main elongation direction.

7. Electric radiator (2) according to claim 6 in which all the heating members of the electric radiator have the same predetermined configuration of the set of polarization vectors (Pz) of the piezoelectric elements.

8. Electric radiator (2) according to claim 6 in which the piezoelectric elements of a heating member are arranged one after the other, starting from a reference piezoelectric element, in a sequence which respects the predetermined configuration of the set of piezoelectric elements, the reference piezoelectric element being offset from one heating member to an adjacent heating member in a direction parallel to the main elongation direction of the heating members.

9. An electric radiator according to claim 6, comprising a first type of heating members having a first predetermined configuration of the set of polarization vectors (Pz) of the piezoelectric elements and a second type of heating members having a second predetermined configuration of the set of polarization vectors (Pz) of the piezoelectric elements in which the direction of the polarization vectors (Pz) of each piezoelectric element is reversed with respect to the first configuration.

10. An electric radiator according to claim 9, wherein the first and second types of heating members are arranged successively in the transverse direction and regularly alternately one after the other.

11. A method of manufacturing (100) a heating member (8) according to claim 5, the method comprising a step of identifying the direction of the polarization vector of each piezoelectric element intended to be received between electrodes of the heating member and a step of predetermining a configuration to be given to the polarization vectors of the piezoelectric elements of the heating member, the method further comprising a subsequent step of assembling the elements piezoelectric elements and electrodes according to the predetermined configuration of the set of polarization vectors (7¾ J of the piezoelectric elements of this heating member.

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