FR3064071A1 - ACCELEROMETER SENSOR WITH AT LEAST ONE INSULATED WASHER WITH FINS - Google Patents

Abstract

The present invention relates to an accelerometer sensor (1) having a base (2) through which a drum (2a) substantially median to the sensor, the base (2) containing a piezoelectric ring (14) surrounded by two insulating washers (16a, 16b) each having a central recess (8) through which the barrel (2a) passes, a coating (7) of plastic material being overmolded around an outer wall of the base (2) and washers. At least one insulating washer (16a, 16b) has on its periphery at least two fins (3) tapered, the apex angle of the fins (3) being between 10 and 30 °, the fins (3) being embedded in the coating (7), the coating (7) and said at least one insulating washer (16a, 16b) being of chemically compatible materials and having melting temperatures differing by at most +/- 15 ° C so that the fins ( 3) are melted in the coating (7) during its overmolding.

Description

Holder (s): CONTINENTAL AUTOMOTIVE FRANCE Simplified joint-stock company, CONTINENTAL AUTOMOTIVE GMBH.

Extension request (s)

Agent (s): CONTINENTAL AUTOMOTIVE FRANCE Simplified joint-stock company.

154 / ACCELEROMETER SENSOR WITH AT LEAST ONE INSULATING WASHER WITH FINS.

FR 3 064 071 - A1 (5 £) The present invention relates to an accelerometer sensor (1) having a base (2) crossed by a barrel (2a) substantially median to the sensor, the base (2) containing a piezoelectric ring ( 14) surrounded by two insulating washers (16a, 16b) each having a central recess (8) through which the barrel (2a) passes, a coating (7) made of a plastic material being overmolded around an external wall of the base (2) and washers. At least one insulating washer (16a, 16b) has on its periphery at least two tapered fins (3), the angle at the top of the fins (3) being between 10 and 30 °, the fins (3) being embedded in the coating (7), the coating (7) and said at least one insulating washer (16a, 16b) being made of chemically compatible materials and having melting temperatures differing by more than +/- 15 ° C so that the fins ( 3) are melted in the coating (7) during its overmolding.

The present invention relates to an accelerometer sensor with at least one insulating washer with fins, this sensor advantageously being a knock sensor.

Such a sensor comprises a base crossed by a barrel substantially median to the sensor, the base containing electrical and auxiliary elements stacked around the barrel including a piezoelectric ring surrounded by two contact rings then, at the two ends of the stack of an insulating washer. The two insulating washers each have a central recess through which the barrel passes, a plastic coating being overmolded around an external wall of the base and stacked electrical and auxiliary elements and therefore insulating washers.

For such accelerometer sensors, car manufacturers require numerous tests, including leak tests of the interior of the sensor. These tests are carried out by injecting pressurized air into the sensor. During these tests, a leak was found between the base and its coating, in particular in the upper part of the sensor between the barrel of the base and the coating but also in the lower part at the level of a sole. formed by the base for the support of the stacked electrical and auxiliary elements.

This leak is mainly due to the difference in materials, in particular to the coefficients of expansion of these different materials. To resolve this leak, it was planned to extend a leakage path between the coating and the base to slow the infiltration of moisture. For this, grooves have been made in the base which are filled during the overmolding of the material of the coating forming lugs penetrating these grooves.

The state of the art is therefore essentially concerned with a lack of tightness between base and coating but has not considered a possible lack of tightness at the level of the insulating washers forming part of the stack of electrical elements. and auxiliary at both ends of this stack.

According to the state of the art, such an insulating washer is made of FR4 or of epoxy resin reinforced with woven and reinforced glass fibers. This washer is not obtained by injection but by cutting. Its material is incompatible with reacting with overmolding to form local supercoolings ensuring sealing. The coating material is frequently polyamide 66 loaded with 30% glass fiber. These two materials react only very little together during overmolding.

Conversely, a material of the insulating washer very close to the overmolding material can react too much during overmolding and at least partially destroy the insulating washer by fusion with the overmolding or weaken the insulation characteristics of the washer.

The problem underlying the present invention is to guarantee an interface between the coating and at least one insulating washer forming part of a stack of electrical and auxiliary elements present in an accelerometer sensor in order to guarantee sealing of the zone of the sensor base containing these elements.

To this end, the present invention relates to an accelerometer sensor having a base crossed by a barrel substantially median to the sensor, the base containing electrical and auxiliary elements stacked around the barrel including a piezoelectric ring surrounded by two insulating washers each having a central recess through which the barrel passes, a plastic coating being overmolded around an external wall of the base and electrical and auxiliary elements stacked, remarkable in that at least one insulating washer has on its periphery at least two fins tapered, the angle at the top of the fins being between 10 ° and 30 °, said at least two fins being embedded in the coating, the coating and said at least one insulating washer being made of chemically compatible materials and having temperatures of melting differing at most +/- 15 ° C so that said at least two fins are melted in the coating during overmolding.

As previously mentioned, in the prior art, the insulating washer was made of FR4, an epoxy resin composite reinforced with glass fibers. This washer was made by cutting. Numerous attempts to replace it with an insulating washer in another material more favorable to its overmolding had resulted in failure, since the sealing was not improved and the properties which the insulating washer must have were not no longer guaranteed by the washers in these other tested materials.

There followed a strong prejudice against the replacement of this FR4 insulating washer with a washer of another material. The state of the art had therefore evolved in another direction by using for example the presence of slots formed by a succession of grooves receiving lugs between the base and the overmolded coating to guarantee this seal.

In a completely different approach, the present invention has tackled the prejudice of the state of the art and proposes reinforced insulation between an insulating washer and a coating by using similar properties of these two elements in order to allow reflow between material. coating material and washer material.

The reflow phenomenon is obtained when, during overmolding, the fins melt and mix locally with the overmolding material, forming an interface of the two materials melted together thus ensuring a seal between overmolding and washer. The electrical area to be protected is then encapsulated and capillary phenomena are avoided.

It should be borne in mind that such reflow is not automatic with materials having similar chemical properties and temperatures. It is indeed necessary that the material of the washer can reach its melting point which is not obvious. The use of thin and elongated fins, on the other hand, allows these fins to reach their melting point more quickly upon contact with the coating material. The material of these fins mixes with the coating material, the two materials being compatible, giving zones made up of a mixture of these two materials, which makes it possible to guarantee sealing between coating and sealing washer. .

For the washer, the fusion only reaches the fins and not the rest of the washer, which guarantees the conservation of the sealing properties of the washer. This can be adjusted by the thickness of the fins sufficiently thin to be melted and the temperature of the overmolding, the melting not or hardly reaching the rest of the washer. This is why, it may be advantageous, without being limiting, to have fins in a material different from the rest of the washer.

These zones made up of a mixture of these two materials are recognizable in the final accelerometer sensor according to the present invention, zones which were not present in a sensor according to the state of the art, the material of the washer then used does not not suitable for melting with the coating material during overmolding. An accelerometer sensor according to the present invention is therefore indisputably recognizable from a prior art sensor during disassembly.

Advantageously, the fins extend all around said at least one insulating washer. This ensures a seal all around the washer between the washer and the coating by fusion of the fins.

In a first embodiment, the fins are carried by a base of said at least one washer at its periphery, the base extending in a plane containing the central recess of said at least one washer.

Advantageously, the fins extend parallel to a median axis of the central recess of said at least one washer.

In a second embodiment, the fins extend perpendicularly to a median axis of the central recess of said at least one washer, the fins being carried by a wall extending at the periphery of said at least one washer in the direction axial with respect to the median axis of the central recess of said at least one washer projecting towards the coating.

In this case, the fins are driven deeper into the overmolded material of the coating than in the first embodiment and the seal between the washer and the coating is reinforced. This second embodiment however requires the presence of an auxiliary wall for the washer, which was not the case in the first embodiment.

For these two embodiments, said at least one washer carries a wall placed before said at least two fins by referring to an opening for coating material injection located on the outer periphery of the coating of the accelerometer sensor.

This wall is used to prevent, during overmolding, a flow of overmolded material is directed directly towards the fins, which could damage them. The proper positioning of the wall on the washer can be seen on a final sensor, therefore after overmolding, since there remains on the outer periphery of the coating an opening which served for the introduction of overmolded material into the coating, the course of overmolded material with respect to the fins which can be deducted a posteriori from the location of this opening.

Advantageously, said at least two fins have a length of between 0.7 to 1.5 mm. The fins must be thin enough to melt quickly during overmolding. Their length increases the amount of mixture between the material of the fins and the material of the coating.

Advantageously, the fins are at least three in number, the third fin being the furthest from the central recess of said at least one washer and being longer than the other two fins. The third or more fins can serve as protection for the other two fins by being of larger dimensions than the other fins. This third fin may have a length one greater than the other two fins. The presence of a third fin also makes it possible to penetrate more deeply into the coating material, which increases the seal obtained between the washer and the coating.

Advantageously, the fins have rectilinear edges while being symmetrical or asymmetrical. The rectilinear edges are more favorable for demolding the fins and the sealing washer carrying them during the manufacture of the washer by injection or molding.

Advantageously, the two insulating washers each carry at least two fins. This ensures the sealing of the upper and lower faces of the stack comprising the piezoelectric ring.

Advantageously, said at least two fins of one of the two insulating washers point in the opposite direction of said at least two fins of the other of the two insulating washers. The fins then sink deeper into the overmold material forming the coating than if the fins of one insulating washer were pointing towards the fins of the other insulating washer. This provides a stronger anchoring and reinforced sealing of the two upper and lower faces of the stack formed by a lower insulating washer, a piezoelectric ring surrounded by contact rings and an upper washer, the stack being taken in reference to a base of the base extending vertically.

The present invention also relates to a process for overmolding a coating around a base and an insulating washer of such an accelerometer sensor, remarkable in that it implements the following steps:

injection of at least one insulating washer with formation on its periphery of at least two fins of a plastic material chemically compatible with a plastic material for overmolding the coating, the two materials having melting temperatures differing from each other at most + / 15 ° C, the dimensions of the fins being predetermined to at least partially melt at a predetermined temperature fixed for overmolding,

- overmolding in a mold of the coating all around the base and said at least one washer provided with said at least two fins at said given overmolding temperature with at least partial melting of said at least two fins and local mixture of plastics fins and coating making a seal between washer and coating,

- removal of the accelerometer sensor thus coated from the mold.

This process is easy to implement and makes it possible to obtain a sensor that does not require a change in shape or a large difference in assembly, the overmolding remaining unchanged. The grooves and lugs in particular at the top of the sensor are no longer necessary to lengthen a leak path. The dimensions of the sensor may even decrease.

Other characteristics, aims and advantages of the present invention will appear on reading the detailed description which follows and with regard to the appended drawings given by way of nonlimiting examples and in which:

FIG. 1 is a schematic representation of a sectional view of an embodiment of an accelerometer sensor according to the present invention, the sensor comprising two insulating washers provided with fins according to a first embodiment,

FIG. 2 is a schematic representation of a view in radial section of an insulating washer according to one embodiment, this insulating washer being able to be integrated into a sensor according to the present invention,

- Figure 3 is a schematic representation of a radial sectional view of an insulating washer according to another embodiment than that shown in Figure 2, this insulating washer being adapted to be integrated into a sensor according to the present invention.

In what follows, for an accelerometer sensor, the base designates the median body of the sensor having a barrel and a central bore for the passage of a fastening element, this without plastic coating and without element for measuring the acceleration , such as piezoelectric electrodes.

The words external or external to the barrel or the base qualify a portion of the barrel or the base furthest from the central bore passing through this barrel or this base. The words upper or lower are to be taken in reference to a barrel of the sensor extending vertically by opening upwards through its portion not carrying a sole.

All the figures are to be taken into consideration together for the numerical references even when reference is made more particularly to a specific figure.

Referring to all the figures and more particularly to Figure 1, the present invention relates to an accelerometer sensor 1, more particularly a knock sensor or a camshaft or crankshaft sensor. The present invention is not, however, limited to the designated sensors. Conventionally, such an accelerometer sensor 1 comprises a base 2 forming the main body of the sensor 1.

The base 2 comprises a barrel 2a having a central bore 4 which can receive a fixing element intended to secure the accelerometer sensor 1 against a support element, for example a casing of an internal combustion engine for a knock sensor. It is known to overmold a coating 7 of a plastic material around an external wall of the base 2, therefore by partial surround of the base 2.

In addition, it is known that the sensor 1 has electrical and auxiliary elements including a piezoelectric ring 14. The electrical and auxiliary elements are housed in a cavity 5 arranged between the coating 7 and the base 2.

In one embodiment of the electrical and auxiliary elements and of the cavity 5 for their housing, the cavity has a support sole 13 formed by a portion of the external wall of the barrel 2a projecting radially from the base 2.

This sole 13 supports a stack consisting of a piezoelectric ring 14 surrounded by contact rings 15a, 15b serving as electrodes then by washers 16a, 16b at the ends of this stack including a lower washer 16b and an upper washer 16a when the barrel 2a is vertical and opens upwards through its portion opposite the sole 13.

The electrical and auxiliary members also include a seismic mass 17 completing the stack around the barrel 2a. The two insulating washers 16a, 16b each have a central recess 8, visible in Figures 2 and 3, through which the barrel 2a passes.

To hold this stack, it is possible to glue these elements together in which case the accelerometer sensor 1 is said to be glued or to screw these elements onto the base 2, in which case the accelerometer sensor 1 is said to be screwed. The present invention can be applied to both a bonded sensor and a screwed sensor.

At least one electrical connection pin connected to each of the contact rings 15a, 15b passes through the coating 7 towards the outside of the accelerometer sensor 1 by a protective sleeve 19 overmolded in the coating 7.

Without this being an essential characteristic of the present but entirely optional, to promote the anchoring of the coating 7 on the base 2, the external wall of the base 2 can have at least one groove 21, advantageously annular, filled of plastic material of the coating 7. The coating 7 can thus carry lugs 20 of overmolded plastic material penetrating into the groove or grooves 21.

Advantageously, there may be at least one pair of grooves in the upper part of the accelerometer sensor 1, that is to say the part farthest from the sole 13 and at least one pair of grooves 21 in the lower part of the accelerometer sensor. 1.

The grooves 21 in the upper part of the accelerometer sensor 1 can be carried by the barrel 2a of the base 2 while the grooves 21 in the lower part of the sensor 1 can be carried by the base 2, advantageously below the sole 13 projecting laterally from the base 2. These grooves 21 and lugs 20 were used in the prior art to lengthen a leakage path between base 2 and coating 7 and which may become superfluous by the use of washers insulators 16a, 16b proposed by the present invention.

Referring to all the figures, according to the present invention, at least one insulating washer 16, 16a, 16b, advantageously the two insulating washers 16, 16a, 16b has on its periphery at least two tapered fins 3, the angle at the top has fins 3 being between 10 ° and 30 °, this angle being shown in FIGS. 2 and 3.

The two fins 3 or more are embedded in the coating 7, the coating 7 and said at least one insulating washer 16, 16a, 16b being made of chemically compatible materials and having melting temperatures differing by more than +/- 15 ° C so that said at least two fins 3 are melted in the coating 7 during its overmolding.

A reflow phenomenon occurs with local mixing of the material of the fins 3 with the overmolding material, which contributes to strengthening the resistance of the insulating washer 16, 16a, 16b or the insulating washers 16, 16a, 16b in the overmolding. and also to ensure the seal between coating 7 and the or each insulating washer 16, 16a, 16b. The grooves 21 and the lugs 20 in the upper part of the accelerometer sensor 1 are no longer necessary, which is a simplification of the construction of the base 2. It can be the same for the grooves 21 and the lugs 20 in the lower part of the accelerometer sensor 1.

The fins 3 can extend all around the washer or each insulating washer 16, 16a, 16b. A series of fins 3 can be distributed over a circumference all around the periphery of the or each insulating washer 16, 16a, 16b and be concentric with a second series of fins 3 or more.

In Figures 2 and 3, there is shown an insulating washer 16 which may be a lower washer 16b or an upper washer 16a with reference to the washers shown in Figure 1. This is why the insulating washer of Figures 2 and 3 bears the reference 16, possibly being one of the two insulating washers 16a, 16b.

In a first embodiment, shown in FIG. 3 and used in the sensor 1 illustrated in FIG. 1, the fins 3 can be carried by a base 6 of the washer 16 at its periphery. The base 6 of the insulating washer 16, advantageously substantially circular, can extend in a plane containing the central recess 8 of the washer 16, forming the thickness of the washer. In this embodiment, the fins 3 can extend parallel to a median axis of the central recess 8 of the washer 16, the median axis being shown in dotted lines in FIG. 3.

In a second embodiment, shown in FIG. 2, the fins 3 extend perpendicularly to a median axis of the central recess 8 of the washer 16. The fins 3 are carried by a wall 10 extending at the periphery of the insulating washer 16 in the axial direction relative to the median axis of the central recess 8 of the washer 16 projecting towards the coating 7, the median axis being illustrated in dotted lines in FIG. 2.

In this FIG. 2, it is visible that the washer 16 can carry a protective wall 9, constituting an obstacle against a direct passage of the flow of overmolded material intended to make the coating 7 in the direction of the fins 3, the wall 9 by deflecting this flow. The low wall 9, thicker than a fin 3 for opposing a resistance to the flow of material and of similar length to a fin, can be recognized during the dismantling of the final product, which is the accelerometer sensor 1.

Indeed, on the one hand, this low wall 9 has not entirely melted like a fin 3 due to its greater thickness. On the other hand, although the flow of overmolding material is not visible in the final product, this flow can be deduced from an injection opening visible at the external periphery of the coating 7 and remaining present on the final sensor 1 being closed by overmolding material.

The wall 9 is therefore placed before the two fins 3 or more with reference to the presumed passage of the deductible flow from the injection opening of overmolding material located on the outer periphery of the coating 7 of the accelerometer sensor 1 .

In FIG. 3, a low wall 9 is not illustrated as in FIG. 2, but such a low wall 9 may be present in the embodiment shown in FIG. 3.

The fins 3 can have a length of between 0.7 and 1.5 mm. By considering this length and the apex angle a between 10 and 30 °, it can be deduced therefrom the width of a fin 3. These lengths, apex angles and widths can be variable. One of the parameters is the melting temperature of the material of the fins 3 relative to the melting temperature of the overmolding material, these temperatures differing by less than +/- 10 to 15 ° C.

If this melting temperature of the material of the fins 3 is higher than the melting temperature of the overmolding material, it is advantageous to reduce the angle at the top of the fins 3 so that the fins 3 are sufficiently melted. On the contrary, if the melting temperature of the material of the fins 3 is lower than the melting temperature of the molding material, the angle at the top of the fins 3 can be increased.

As shown in Figures 2 and 3, the fins 3 may be three in number or more. In this configuration, as shown in FIG. 2, the third fin which is furthest from the central recess 8 of the washer 16 can be longer than the other two fins 3 while serving as protection. This protection can be effective in attenuating the vibrations of a vibrating bowl or when transporting the isolation washer. This is not mandatory and Figure 3 shows three fins 3 of substantially the same size.

The fins 3 may have rectilinear edges. This is in fact favorable to their release from the mold during the manufacture of the insulating washer 16 carrying them. They can be symmetrical or asymmetrical by presenting a half angle at the top higher on one side of the fin than the other.

As previously mentioned, in an accelerometer sensor 1, as shown in Figure 1 while referring to Figures 2 and 3, it is preferable that the two insulating washers 16, 16a, 16b, that is to say the upper washer and the lower washer each carry at least two fins 3. This improves the sealing and the resistance of the washers in the coating 7.

It is possible that the fins 3 of one washer point towards the fins 3 of the other washer. The opposite is however preferred, the fins 3, at least two in number, of one of the two insulating washers 16, 16a, 16b pointing in the opposite direction of the fins 3, at least two in number, of the other insulating washer 16, 16a, 16b. The fins 3 thus sink into a larger surface of the coating 7 than when the fins 3 point towards each other with anchors in the coating 7 in opposite directions.

Referring to Figures 2 and 3, as nonlimiting examples of an insulating washer 16 used in a sensor according to the present invention, this insulating washer 16 may be circular with an outer periphery of diameter 24.2 mm including the length of the fins 3 when these fins 3 protrude radially from the insulating washer 16, a central recess 8 of diameter 14.2 mm and a base thickness 6 of 0.25 mm. In FIG. 2, the wall 10 carrying the fins 3 can have a length of 3 mm and a thickness of 0.25 mm. In FIG. 3, the fins 3 can be supported by the base 6 over a length of mm.

Referring to all the figures, the invention also relates to a process for overmolding a coating 7 around a base 2 and an insulating washer 16, 16a, 16b of such an accelerometer sensor 1. This process comprises the steps which will now be described.

The first step relates to the injection of at least one insulating washer 16, 16a, 16b with formation on its periphery of at least two fins 3 in a plastic material chemically compatible with a plastic material for overmolding the coating 7. The two materials have melting temperatures differing from each other at most +/- 15 ° C. The dimensions of the fins 3 are predetermined to at least partially melt at a predetermined temperature fixed for overmolding, in order to participate in a reflow phenomenon during this overmolding.

The second step is the overmolding in a mold of the coating 7 all around the base 2 and said at least one washer 16, 16a, 16b provided with said at least two fins 3 as well as the rest of the electrical and auxiliary elements 14 , 15a, 15b stacked, as previously mentioned. This overmolding is done at the given overmolding temperature. During this overmolding, an at least partial melting of said at least two fins 3 and a local mixture of the plastic materials of the fins 3 and of the coating 7 is obtained, these materials being still hot and malleable in order to obtain a connection between washer d insulation 16, 16a, 16b and coating 7 guaranteeing a seal.

The third step is the removal of the accelerometer sensor 1 thus coated as a final product from the mold. Only an overmolding injection opening then blocked with overmolding material is visible on the external periphery of the coating 7 and therefore of the accelerometer sensor 1.

Claims (12)

1. Accelerometer sensor (1) having a base (2) crossed by a barrel (2a) substantially median to the sensor, the base (2) containing electrical and auxiliary elements stacked around the barrel (2a) including a piezoelectric ring ( 14) surrounded by two insulating washers (16, 16a, 16b) each having a central recess (8) through which the barrel (2a) passes, a coating (7) made of a plastic material being overmolded around an external wall of the 'base (2) and stacked electrical and auxiliary elements, characterized in that at least one insulating washer (16, 16a, 16b) has on its periphery at least two tapered fins (3), the angle at the top (a ) fins (3) being between 10 and 30 °, said at least two fins (3) being embedded in the coating (7), the coating (7) and said at least one insulating washer (16, 16a, 16b ) being of chemically compatible materials and having different melting temperatures at most +/- 15 ° C so that the at least two fins (3) are melted in the coating (7) during its overmolding. 2. accelerometer sensor (1) according to claim 1, characterized in that the fins (3) extend all around said at least one insulating washer (16, 16a, 16b). 3. accelerometer sensor (1) according to claim 1 or 2, characterized in that the fins (3) are carried by a base (6) of said at least one washer (16, 16a, 16b) at its periphery, the base (6) extending in a plane containing the central recess (8) of said at least one washer (16, 16a, 16b). 4. accelerometer sensor (1) according to claim 3, characterized in that the fins (3) extend parallel to a median axis of the central recess (8) of said at least one washer (16, 16a, 16b) . 5. accelerometer sensor (1) according to claim 1 or 2, characterized in that the fins (3) extend perpendicularly to a median axis of the central recess (8) of said at least one washer (16, 16a, 16b), the fins (3) being carried by a wall (10) extending at the periphery of said at least one washer (16, 16a, 16b) in an axial direction relative to the median axis of the central recess (8) of said at least one washer (16, 16a, 16b) projecting towards the coating (7). 6. accelerometer sensor (1) according to any one of the preceding claims, characterized in that said at least one washer (16, 16a, 16b) carries a wall (9) disposed before said at least two fins (3) in referring to a coating material injection opening (7) located on the outer periphery of the coating (7) of the accelerometer sensor (1). 7. accelerometer sensor (1) according to any one of the preceding claims, characterized in that said at least two fins (3) have a length of between 0.7 and 1.5 mm. 8. accelerometer sensor (1) according to the preceding claim, characterized in that the fins (3) are at least three in number, the third fin being the furthest from the central recess (8) of said at least one washer (16, 16a, 16b) and being longer than the other two fins (3). 9. accelerometer sensor (1) according to any one of the preceding claims, characterized in that the fins (3) have rectilinear edges being symmetrical or asymmetrical. 10. Accelerometer sensor (1) according to any one of the preceding claims, characterized in that the two insulating washers (16, 16a, 16b) each carry at least two fins (3). 11. accelerometer sensor (1) according to the preceding claim, characterized in that said at least two fins (3) of one of the two insulating washers (16, 16a, 16b) point in the opposite direction of said at least two fins (3) on the other of the two insulating washers (16, 16a, 16b). 12. Method for overmolding a coating (7) around a base (2) and an insulating washer (16, 16a, 16b) of an accelerometer sensor (1) according to any one of the preceding claims, characterized in that it implements the following steps: - injection of at least one insulating washer (16, 16a, 16b) with formation on its periphery of at least two fins (3) in a plastic material chemically compatible with a plastic material for overmolding the coating (7), the two materials having melting temperatures differing from each other at most + / 15 ° C, the dimensions of the fins (3) being predetermined to melt at least partially at a predetermined temperature fixed for overmolding, - overmolding in a mold of the coating (7) all around the base (2) and said at least one washer (16, 16a, 16b) provided with said at least two fins (3) at said given overmolding temperature with at least partial melting of said at least two fins (3) and local mixing of the plastic materials of the fins (3) and of the coating (7) providing a seal between the washer and the coating (7), - removal of the accelerometer sensor (1) thus coated out of the mold. 1/2