FR3011497A1 - METHOD FOR FINISHING AN OVERMOLD SENSOR FOR A VEHICLE - Google Patents

Abstract

The present invention relates to a method of finishing a sensor (1a, 1b, 1c) comprising a metal base (10) and a peripheral envelope (20) made of a thermoplastic material molded around said base (10), said method comprising: • a step of heating compression means (30) at a temperature above the melting point of the thermoplastic material so as to melt a portion of the thermoplastic material of the peripheral envelope (20) • a compression step, performed by the compression means (30), the peripheral envelope (20) so as to create a mechanical tension of the thermoplastic material on the metal base (10),

Description

The present invention relates to the field of vehicle overmolding sensor and more particularly relates to a method of finishing a molded sensor to improve the sealing. In a motor vehicle having cylinders, it is known to adjust the ignition of the fuel / oxidant mixture in each cylinder so as to obtain an optimum combustion efficiency of the mixture. When ignition is performed too early, vibrations occur and can damage the engine. When ignition is performed too late, the efficiency of the cylinder decreases significantly. The optimum efficiency is obtained for an ignition performed in a predefined time interval in which the vibrations are extremely low at the beginning of the interval and virtually zero at the end of the interval. In order to proceed with the ignition of the mixture in each cylinder during this time interval, it is known to use one or more knock sensors which detect the vibrations of each cylinder in the predefined time interval from one ignition to one. other. More precisely, the one or more sensors detect, from one ignition to the next, a vibration level corresponding alternatively at the beginning of the predefined time interval and at the end of the predefined time interval so as to ensure that the ignition takes place during said predefined time interval. Such a sensor conventionally comprises a vibration detection body and a protective body protective envelope made of a thermoplastic material deposited by overmoulding at least partly around said body. The body comprises in known manner a metal base and a plurality of components such as, for example, a piezoelectric element, electrical contact elements, insulating elements, a seismic mass, etc.

In such a sensor, it is known to perform overmoulding directly in contact with the metal base. However, such a method has the disadvantage of not giving a good seal to the sensor which is often subjected to humidity conditions in the engine. Indeed, in this case, the mechanical tensions caused by overmolding prevent the thermoplastic material from adhering to the metal base, which creates a space at their junction causing a sensor leakage. In addition, the thermoplastic material of the peripheral envelope has a porosity which also degrades the seal of the junction. In order to partially solve these drawbacks, patent application DE3643956A1 discloses a sensor whose metal base comprises a plurality of grooves for receiving the thermoplastic material so as to improve its grip on the metal base and to improve sealing the junction between the base and the envelope. The tightness of this junction is however not satisfactory because, on the one hand, there is always a space large enough to cause a leakage gap 5 between the overmolded peripheral envelope and the metal base and, on the other hand, On the other hand, the porosity of the thermoplastic material always degrades the seal of the junction. The object of the invention is to remedy these drawbacks by proposing a finishing process making it possible to improve the tightness of an overmolded sensor. To this end, the subject of the invention is a process for finishing a sensor 10 comprising a metal base and a peripheral envelope made of a thermoplastic material overmolded around said base, said method comprising: a step of heating means of compression at a temperature above the melting point of the thermoplastic material so as to melt a portion of the thermoplastic material of the peripheral envelope 15 a compression step, performed by the compression means, of the peripheral envelope so as to create a tension mechanical thermoplastic material on the metal base. By the term "compression" is meant both a mechanical compression and any other type of compression, such as for example a compression performed by a gas, a liquid, a laser, etc. The heating step of the compression means at a temperature above the melting point of the thermoplastic material melts a portion of the thermoplastic material of the peripheral envelope, before compression. Such heating makes it possible to deform the thermoplastic material in a localized manner, in order to compress it easily and without deforming the entire peripheral envelope. The contact between the heated compression means and the thermoplastic material allows heat transfer, compression means to the compression zone (s) of the peripheral envelope, which deforms the thermoplastic material and makes compression easy. In a first embodiment of the invention, the method further comprises, between the heating step and the compression step, a step of interrupting the heating followed by a step of contacting the compression means. with the compression zone. In a second embodiment of the invention, the method further comprises, prior to the heating step, a step of contacting the compression means with the compression zone and subsequently after the heating step. , a heating interruption step, preferably performed before the compression step. In order to obtain a necessary and sufficient heating, it is advantageous to heat the compression means beyond the melting point of the thermoplastic material for a predetermined time and then to interrupt this heating before putting the compression means in contact with the thermoplastic material. Indeed, when the heating is not interrupted, there is no creation of a mechanical tension between the thermoplastic material and the metal base since the thermoplastic material can melt as the compression means the compress. The compression means may be heated by any heating means, preferably induction, ultrasound or microwave. Preferably, the thermoplastic material is a thermoplastic resin, such as for example polyamide PA66, which has both good physical and chemical properties while being efficient and inexpensive. Preferably, the base comprising at least one receiving groove of the thermoplastic material, the compression step makes it possible to fill the space in the groove between the peripheral envelope and the base. The invention also relates to an overmoulded sensor obtained by the method as presented above, said sensor comprising a metal base and a peripheral envelope made of a thermoplastic material overmolded around said base and whose metal base comprises at least one groove. receiving the thermoplastic material from the peripheral envelope. The invention also relates to a vehicle comprising a sensor obtained by the finishing process as presented above. Such compression allows both to support the thermoplastic material on the metal base to achieve a junction free of space and reduce the porosity of the compressed portion of the thermoplastic material to improve the seal of the junction. By vehicle is meant both a motorized road vehicle with two, three or four wheels, such as for example a motor vehicle, a vehicle of the aircraft type, such as for example a helicopter, or a vehicle of the same type. snowmobile type. Other features and advantages of the invention will become apparent from the following description made with reference to the appended figures given by way of non-limiting examples and in which identical references are given to similar objects. Figure 1 is a partial sectional view of a first molded sensor prior to the application of the finishing process according to the invention. Figure 2 is a partial sectional view of the sensor of Figure 1 after the application of the finishing process according to the invention. Figure 3 is a partial sectional view of a second molded sensor prior to the application of the finishing process according to the invention. Figure 4 is a partial sectional view of the sensor of Figure 3 after the application of the finishing process according to the invention. Figure 5 is a partial sectional view of a third molded sensor prior to the application of the finishing process according to the invention. Figure 6 is a partial sectional view of the sensor of Figure 5 after the application of the finishing process according to the invention. The invention is described below with reference to an overmoulded sensor for detecting vibrations of a cylinder of a vehicle engine, but it is obvious that it can be applied to any type of molded sensor. Such a sensor usually comprises a vibration detection body and a protective body protective envelope made of a thermoplastic material deposited by overmolding at least partially around said body. The body comprises in known manner a metal base and a plurality of components such as, for example, a piezoelectric element, electrical contact elements, insulating elements, a seismic mass, etc. The sensors 1a, 1b and 1c illustrated in FIGS. 1 to 6 each comprise a metal base 10 and a peripheral envelope 20 made of a thermoplastic material deposited on the metal base 10 by overmoulding in a manner known to those skilled in the art. As explained in the preamble, such an overmolding arranges an ESP space between the metal base 10 and the peripheral envelope 20 which can cause a sensor leakage. The metal base 10 comprises an upper portion PRS of cylindrical shape and a lower portion PRI also of cylindrical shape but of a greater diameter, the two cylindrical portions being coaxial along an axis X.

In these three examples, the metal base 10 comprises a first upper groove GSa, a second upper groove GSb, a third lower groove Gla and a fourth lower groove Glb. The first groove GSa is closer to the upper end ES of the base 10 than the second groove GSb and, likewise, the third groove Gla is closer to the lower end El of the base 10 than the fourth groove. glb. The terms "upper" and "lower" are defined with respect to the arrangement of the sensors 1a, 1b and 1c in FIGS. 1 to 6. FIGS. 1, 3 and 5 all show an embodiment of a sensor 10 overmoulded, respectively 1 a, 1 b, lc, prior to the application of the finishing process according to the invention. The peripheral envelope 20 of the overmolded sensor 1 shown in FIG. 1 has a flat upper face FS1 and a flat lower face F1. The overmoulded sensor 1b illustrated in FIG. 3 has an upper face FS2 comprising a first protrusion PS2 and a lower face F11 comprising a second protrusion P12. The overmolded sensor 1c illustrated in FIG. 5 has an upper face FS3 comprising a first protrusion PS3 and a lower face FI3 comprising a second protrusion P13. A first space ESP1 is arranged between the upper end ES of the base 10 and the first protrusion PS3 so that the first upper groove GSa is free of thermoplastic material. Similarly, a second space ESP2 is arranged between the lower end El of the base 10 and the second protrusion PI3 so that the third lower groove Gla is free of thermoplastic material. As illustrated in FIGS. 1 to 6, compression means 30 are used to implement the method according to the invention and to strongly press at least one localized portion of the thermoplastic material of the peripheral envelope against the metal base. 10 so as to significantly enhance the sealing of the sensor 1a, 1b and 1c. In these three examples, the compression means 30 are adapted to compress an upper portion of the peripheral envelope 20 at a higher compression zone ZCS and a lower portion of the peripheral envelope 20 at a zone lower compression ZCI. In order to melt the thermoplastic material of the peripheral shell 20 to facilitate compression and further press against the metal base 10, the compression means 30 are adapted to be heated beyond the melting point of the thermoplastic material of the invention. the peripheral envelope 20.

In the examples illustrated in FIGS. 1 to 6, the compression means 30 comprise two compression rings (partially illustrated): an upper compression ring AS and a lower compression ring Al. A compression in the upper compression zone ZCS allows 5 to improve the sealing of the sensor 1a, 1b, 1c at the upper grooves GSa and GSb. Similarly, compression in the lower compression zone ZCI makes it possible to improve the sealing of the sensor 1a, 1b, 1c at the level of the lower grooves Gla and Glb Preferably, the compression means 30 are first heated. beyond the melting point of the thermoplastic material, for example above 260 ° C. The heating is preferably performed by an induction coil. Of course, the heating can be achieved by any suitable means, for example by an ultrasonic heating module or by microwave. Once heated beyond the melting point of the thermoplastic material of the peripheral shell 20, the heating is interrupted. The compression rings AS and Al are then brought into contact respectively with the upper compression zone ZCS of the peripheral envelope 20 and the lower compression zone ZCI of the peripheral envelope 20 in order to transfer calories to the thermoplastic material and to Melt a portion at the ZCS upper and lower ZCI compression zones. A force is exerted on each ring AS, Al in order to compress the thermoplastic material while, as a result of the heat transfer, the temperature of each ring AS, Al goes back below the melting point of the thermoplastic material. The compression of the thermoplastic material then moves a portion thereof to the metal base so that the thermoplastic material fills a portion of the ESP space between the metal base 10 and the peripheral shell 20 and strongly bearing against the base 10 so as to improve the sealing of the sensor. In the example of the first sensor 1a shown in FIGS. 1 and 2, the upper ring 30 vertically compresses the upper planar face FS1 of the first sensor 1a at a higher compression zone ZCS located in the vicinity of the base 10. and in particular the first upper groove GSa and the second upper groove GSb. The compression causes a depression of the upper face FS1 of the peripheral envelope 20 thus defining a groove 40a in the upper part of the peripheral envelope 20. Similarly, the lower ring Al vertically compresses the flat lower face F11 of the first sensor 1a at a lower compression zone ZCI located in the vicinity of the base 10 and in particular the third lower groove Gla and the fourth lower groove Glb. The compression causes a depression of the lower face F11 of the peripheral envelope 20 thus defining a groove 40b in the lower part of the peripheral envelope 20.

The thermoplastic material is thus compressed at two compression zones respectively 50a and 50b in the grooves GSa, GSb and Gla and Glb respectively so as to be strongly press against the base 10 and eliminate the space ESP between the base 10 and the envelope 20 at said compressed zones 50a and 50b.

In each of the examples illustrated in FIGS. 1 to 6, it goes without saying that the compression of the peripheral envelope 20 by the upper ring AS at the level of the upper compression zone ZCS and the compression of the peripheral envelope 20 by the lower ring A1 at the lower compression zone ZCI can be performed simultaneously or one after the other.

In the example of the second sensor 1b illustrated in FIGS. 3 and 4, the upper ring AS vertically compresses the upper face FS2 of the second sensor 1b at an upper compression zone ZCS covering the upper protuberance PS2 and in the vicinity of the base 10 and in particular the first upper groove GSa and the second upper groove GSb. The compression causes a depression of the upper protrusion PS2 so as to flatten the upper face FS2 of the peripheral envelope 20. Similarly, the lower ring Al vertically compresses the lower face FI2 of the second sensor lb at a zone of lower compression ZCI covering the lower protuberance PI2 in the vicinity of the base 10 and in particular the third lower groove Gla and the fourth lower groove Glb. The compression causes a depression of the lower protuberance PI2 so as to flatten the lower face FI2 of the peripheral envelope 20. The thermoplastic material is thus compressed at two compression zones respectively 51a and 51b in the grooves GSa, GSb and respectively Gla and Glb so as to be strongly press against the base 10 and eliminate ESP space between the base 10 and the casing 20 at said compressed areas 51a and 51b. In the example of the third sensor 1 c illustrated in FIGS. 5 and 6, the upper ring AS compresses the upper face FS3 of the third sensor 1c at a higher compression zone ZCS covering the upper protuberance PS3 in the vicinity of the base 10 and in particular the first upper groove GSa and the second upper groove GSb. The compression causes a depression of the upper protrusion PS3 thus defining a groove 42a in the upper part of the peripheral envelope 20. Similarly, the lower ring Al compresses the lower face FI3 of the third sensor 1c at a zone of lower compression ZCI covering the lower protuberance PI3 in the vicinity of the base 10 and in particular the third lower groove Gla and the fourth lower groove Glb. The compression causes a depression of the lower protuberance PI3 thus defining a groove 42b in the lower part of the peripheral envelope 20. The thermoplastic material is thus compressed in the grooves GSa, GSb, Gla and Glb so as to come and press hard In this third example, the compression is not only vertical but includes a vertical component and a horizontal component so as to effectively fill the spaces respectively ESP1 and ESP2. The thermoplastic material is thus compressed at two compression zones 52a and 52b respectively in the grooves GSa, GSb and Gla and Glb so as to be pressed firmly against the base 10 and eliminate spaces ESP1 and ESP2 between the base 10 and the casing 20 at said compressed zones 52a and 52b. The method according to the invention thus makes it possible to effectively seal an overmoulded sensor by locally reinforcing the junction between the sensor base and its overmolded peripheral envelope.

Claims (8)

REVENDICATIONS1. A method of finishing a sensor (1a, 1b, 1c) comprising a metal base (10) and a peripheral envelope (20) made of a thermoplastic material overmolded around said base (10), said method being characterized in that it comprises: - a heating step of compression means (30) at a temperature above the melting point of the thermoplastic material so as to melt a portion of the thermoplastic material of the peripheral envelope (20) a compression step, carried out by the compression means (30), the peripheral envelope (20) so as to create a mechanical tension of the thermoplastic material on the metal base (10), 2. Method according to the preceding claim, the method being characterized in that it comprises, between the heating step and the compression step, a heating interruption step followed by a contacting step of the means. compression (30) with the compression zone (ZCS, ZCI). 3. Method according to claim 1, the method being characterized in that it comprises, prior to the heating step, a step of contacting the compression means (30) with the compression zone (ZCS, ZCI). and subsequently, after the heating step, a step of interrupting the heating, preferably carried out before the compression step. 4. Method according to any one of the preceding claims, characterized in that the heating of the compression means (30) is carried out by induction, ultrasound or microwaves. 5. Method according to any one of the preceding claims, characterized in that the thermoplastic material is a thermoplastic resin. 6. Method according to any one of the preceding claims, wherein, the base (10) comprising at least one groove (GSa, GSb, Gla, Glb) for receiving the thermoplastic material, the compression step makes it possible to fill the space located in the groove (GSa, GSb, Gla, Glb) between the peripheral envelope (20) and the base (10). 7. Overmolded sensor obtained by the method according to any one of the preceding claims, characterized in that said sensor (1a, 1b, 1c) comprises a metal base (10) and a peripheral envelope (20) made of a thermoplastic material overmolded around said base (10) and whose metal base (10) comprises at least one groove (GSa, GSb, Gla, Glb) for receiving the thermoplastic material of the peripheral envelope (20). 8. Vehicle comprising a sensor (1a, lb, 1c) obtained by the method according to one of claims 1 to 6.