FR3060489B1 - HEATING DEVICE FOR PROTECTING A MOTOR VEHICLE RADAR - Google Patents

Abstract

- The invention relates to a device (10) for protecting a radar (20) of a motor vehicle, comprising at least one current generator (30) and a cover (40), the cover (40) comprising at least one area transmission (50) capable of being traversed by waves (60) of said radar (20), characterized in that the transmission zone (50) comprises a coating (70) constituting an electrical resistance, and in that the generator of current (30) is adapted to generate a current in said coating (70).

Description

The present invention relates to the field of motor vehicles equipped with radar, and more particularly, the field of devices for deicing such a radar.

The device according to the invention applies in particular to the radars arranged at the front of the vehicles, for example of the ACC type.

For security reasons in particular, it is known to equip motor vehicles radar, for example ACC type, according to the English expression "Adaptive Cruise Control". Such a radar serves in particular to regulate the speed of vehicles according to the traffic and / or obstacles on the road. The radar detects the speed and distance of the object preceding the carrier vehicle, so as to maintain in particular a safety distance between the vehicles

ACC radars are mounted on the front of vehicles, usually between the bars of the cooling grid.

To hide these radars for aesthetic reasons, and / or to protect them from external aggression (rain, ice, frost, mud, insects, leaves ...), it is known to use a protective part with a plastic cover positioned in front of the sensor.

Such a plastic cover lets the radar waves pass with as little attenuation as possible so as not to disturb the operation of the radar itself.

A common problem is the formation of ice or frost on the ACC radar or on the shield. This ice or frost disrupts the transmission and reception of radar waves and makes the system unreliable or even unusable.

By default, it is possible and preferable to disconnect the ACC function when the outside temperature is below 3 ° C, provided that the driver is informed of this deactivation. However this approach degrades the safety of the occupants of the vehicle although they are warned.

A better solution consists in equipping the protection part with a heating system, making it possible to perform a de-icing function. The heating of the protective part can be achieved using electrically conductive tracks deposited on the surface of the part to be heated.

As a result, the cover can be warmed to melt ice or frost or snow. After defrosting, the ACC function can be used. This solution therefore makes it possible not to disable the ACC function.

However, the use of conductive track surface makes the defrosting system of the protective part fragile. Indeed, external elements can damage the tracks, and thus cut the electrical circuit, and therefore, the heating mechanism.

There is also a solution consisting of drowning (integrating) the conductor son traversed by a current within the protective part.

However, wherever they are located, the major disadvantage of these de-icing systems is that they require the use of electrically conductive materials in order to achieve the heating tracks. This causes disturbances and a weakening of the radar signal due to the presence of metallic conductive elements in front of the radar. The object of the invention is to overcome these disadvantages by providing a robust protective device capable of being traversed by heat without affecting the transmission of radar waves.

Thus, the subject of the invention relates to a device for protecting a motor vehicle radar, comprising at least one current generator and a cache, the cache comprising at least one transmission zone capable of being traversed by waves of said radar. The transmission zone comprises a coating constituting an electrical resistance, and the current generator is able to generate a current in said coating.

The device according to the invention thus has the advantage of allowing the use of the ACC function at temperatures below 3 ° C., while offering increased robustness to the external elements compared with known devices and maximum transmission of radar waves. .

The device may further comprise one or more of the following features, taken alone or in combination: the coating has a resistivity able to release, by Joule effect, sufficient heat to raise the temperature of the transmission zone beyond zero degrees Celsius when traversed by the current of the current generator. the coating has a strength of less than 20kΩ at 300K, and preferably less than 5kΩ, and still more preferably less than 3kΩ. the coating is an automotive body paint enriched with electric conductive fillers. the conductive filler is chosen alone or in combination in the following charge group: graphite, metals, such as copper, silver, iron, indium, graphite alloy and metal. the paint comprises more than 10% by weight of filler, preferably between 20% and 60% by weight. the coating has a thickness of between 10 and 30 microns. the device comprises at least one electrode capable of transmitting to said coating, a current generated by the current generator. the cover is made of glass or plastic resin, such as a resin based on polypropylene. the current generator is positioned outside the transmission zone. at least one of the electrical conductive elements is a metal insert overmoulded during the formatting of the cache. the overmolded metal insert is an eyelet, a wafer or a braid. at least one of the electrical conductive elements is an insert and fixed to the cache after shaping. the insert is a conductive adhesive tape forming a conductive adhesive film. the insert is a superconductive coating layer. The invention also relates to a set of a radar, such as ACC type radar, and a device according to the invention.

Finally, the invention also relates to a motor vehicle equipped with an assembly according to the invention. The invention will be better understood on reading the appended figures, which are provided by way of examples and are not limiting in nature, in which: FIG. 1 illustrates an embodiment of the device according to the invention; FIG. 2 illustrates the positioning of the device according to the invention with respect to the radar; Figure 3 illustrates an example of positioning of the electrodes.

Referring now to FIG. 1, the protection device 10 of a motor vehicle radar 20 according to the invention comprises at least one current generator 30 and a cache 40.

As illustrated in FIG. 2, the cover 40 is intended to be placed in front of the radar 20. The cover 40 may be made of glass or plastic.

The cover 40 comprises at least one transmission zone 50 adapted to be traversed by the waves 60 of the radar 20. According to one embodiment, the material constituting the transmission zone 50 is a plastic resin, advantageously based on polypropylene.

The current generator 30 is of course positioned outside the transmission zone, that is to say it is not located in the path of the radar waves, so as not to disturb the radar waves.

The transmission zone 50 comprises a coating 70 capable of constituting an electrical resistance, the heat emitted by the Joule effect is sufficient to raise the temperature of the transmission zone beyond zero degrees Celsius (melting temperature of the ice).

Electrical resistance refers to the property of a component to oppose the passage of an electric current. Resistance is responsible for energy dissipation in the form of heat (Joule effect). Thus, the term "resistance" refers to the ability of a conductive material to heat when passing an electric current.

According to the invention, the electric current is generated by the current generator 30, and it is transmitted to the coating 70 of the transmission zone 50 via electrodes 80.

The coating 70

properties

In the description, all resistance values are measured using an ITW Ransburg resistivity meter, using electrodes 25mm apart and positioned in the center of a 200mm by 600mm rectangular plate. These measurements are carried out for coatings having a thickness of between 10 and 30 microns, at a temperature of 300K.

A primer conventionally used in a car body part paint line has a resistance greater than 30kΩ and less than 1ΜΩ.

Due to its high strength, such a coating can not be crossed by a current not exceeding 15V (current generally used industrially for safety reasons). This is why, according to the invention, a coating 70 having a resistance of less than 20 kΩ, preferably less than 5 kΩ, more preferably less than 3 kΩ, is used so that the coating can be traversed by a current even if it is does not exceed 15V. However, its resistance allows Joule heat release sufficient for the desired application.

Formulation

The formulation of the coating 70 according to the invention also has the following properties: its formulation is adapted to the bodywork parts; it must in particular have good adhesion to the material of the part, for example on a treated polypropylene; its formulation is sufficiently transparent to radar waves to allow radar operation; its formulation is compatible with the material of the cache 40.

According to one embodiment, the coating 70 is an automotive body paint enriched with electrical conductive pigments.

The amount of the pigments is defined according to the resistivity of the pigment used, therefore depending on the nature of the pigment, and depending on the amount of heat desired. For example, powdery graphite pigments can be used.

According to an exemplary embodiment, the coating 70 comprises: a paint, for example polyurethane; a solvent, for example water, xylene or butyl acetate glycol a binder, for example isocyanate or polyol; charges of conductive pigments; such charges may be chosen alone or in combination in the following group of charges: graphite in its various forms (tube, nanotubes, powders), metals such as copper, silver, iron, indium, etc. in different forms (tube, powder, wire), graphite alloy and metal; optionally a rheology agent, for example an anti-sag agent; optionally a thickening agent, for example talc; optionally additives and traditional adjuvants, for example an adhesion promoter.

In general, the paint comprises more than 10% by weight of pigments, preferably between 20% and 60% by weight.

The particle size of the pigments is preferably less than 25 micrometers. Such a particle size also makes it possible to obtain better dispersibility and to increase the distribution of the graphite pigments in the resin.

According to another embodiment, a paint is used as described in the patent application FR2967271. The coating 70 then comprises: a paint, for example: vinyl, acrylic, epoxy, polyurethane, glycerophthalic; a solvent, for example water or the aromatic type (xylene, toluene, etc.), aliphatic, alcoholic (isopropyl alcohol, methoxylopropyl alcohol, ethanol) ...; a binder, for example based on modified acrylic resin; charges of graphite pigments; optionally a rheology agent, for example an anti-sag agent.

Thickness

In order to provide the heat necessary to defrost the cover 40, while allowing the radar waves to pass, the coating 70 has a thickness of between 10 and 30 microns.

The current generator 30 and the electrodes 80

The electrodes 80 constitute electrical conductive elements reported on the device 10, so as to connect the current generator 30 to the coating 70. They are preferably positioned outside the transmission zone 50, that is to say that they are not located on the path of the radar waves 60, so as not to disturb the radar waves.

These electrically conductive elements 80 are distributed over the surface of the cover 40 in such a way that the current flows in a surface of the coating 70 that is large enough to produce enough heat in the transmission zone 50. Indeed, it is not necessarily necessary. that all the coating heats, the important thing is that the amount of heat released allows a defrosting of the transmission zone 50.

Of course, according to one embodiment, the electrical conductive elements 80 are distributed on the surface of the cover 40 in such a way that the current flows through the entire surface of the coating 70, and therefore over the entire surface of the transmission zone 50, thus allowing optimal defrosting.

It will thus be possible to use two electrodes 80, positioned on opposite edges of the cover 40, or diametrically opposed if the cover is circular.

Electrodes may be added to the edge or edges of the cover 40, in order to increase the circulation surface of the current, and therefore the thermal efficiency.

FIG. 3 illustrates an example of positioning of the electrodes 80 on a device 10, in which the device 10 comprises two diametrically opposite electrodes 80.

According to a variant, an electrode 80 may consist of a conductive adhesive tape which forms an adhesive-coated film on the mask 40, between the generator and the transmission zone 50.

In a variant, an electrode 80 may consist of an insert, preferably a metal insert, molded during the molding of the cover 40. Such an insert may be chosen from the following list: eyelet; plate; braided. Such an insert may be in particular copper or silver.

In another variant, an electrode 80 may consist of a local application of a superconductive coating, which has a resistance of less than 20 kΩ for a thickness of between 10 and 30 microns, with a distance between the electrodes of 25 mm. Compared with a conventional coating which has a resistance greater than 30 kΩ under the same conditions, this superconductive coating thus provides a better conductivity on the surface of the device 10, between the generator and the transmission zone 50.

According to one example, the current generator 30 is positioned close to the transmission zone 50.

The cover 40 is adapted to be fixed on a bumper of a motor vehicle, in front of the radar. The invention also relates to a set of a radar 20, in particular of ACC type, and a device 10 according to the invention, as well as a motor vehicle equipped with such an assembly.

Example of realization

Using a graphite-based coating as described above, and using a current generator 15v, 0.1 amp, a temperature of 30 ° C is obtained on the coating, or 30 ° C using a current generator 15v, 0.2 ampere,

List of references 10: protection device 20: radar 30: current generator 40: cache 50: transmission zone 60: waves 70: coating 80: electrodes

Claims (17)

1. Device (10) for protecting a radar (20) of a motor vehicle, comprising at least one current generator (30) and a cover (40), the cover (40) comprising at least one transmission zone (50). ) adapted to be traversed by waves (60) of said radar (20), characterized in that the transmission zone (50) comprises a coating (70) constituting an electrical resistance, which coating (70) has a thickness of 10 and 30 microns, and in that the current generator (30) is adapted to generate a current in said coating (70). 2. Device (10) according to claim 1, wherein the coating (70) has a resistivity able to release, by Joule effect, sufficient heat to raise the temperature of the transmission zone (50) beyond zero degrees Ceisius when traversed by the current of the current generator (30). 3. Device (10) according to one of the preceding claims, wherein the coating (70) has a resistance less than 20kO to 300K, preferably less than 5kQ, and still preferably less than 3kD. 4. Device (10) according to one of the preceding claims, wherein the coating (70) is an automotive body paint enriched with electric conductive fillers. 5. Device (10) according to the preceding claim, wherein the conductive filler is chosen alone or in combination in the following load group: graphite, metals, such as copper, silver, iron, indium, graphite alloy and metal. 6. Device (10) according to one of claims 4 and 5, wherein the paint comprises more than 10% by weight of filler, preferably between 20% and 60% by weight. 7. Device (10) according to one of the preceding claims, comprising at least one electrode (80) adapted to transmit to said coating (70), a current generated by the current generator (30). 8. Device according to one of the preceding claims, wherein the cover (40) is made of glass or plastic resin, such as a polypropylene-based resin. 9. Device according to one of the preceding claims, wherein the current generator (30) is positioned outside the transmission zone (50). 10. Device according to one of the preceding claims, wherein at least one of the electrically conductive elements (80) is a metal insert overmoulded during the shaping of the cover (40). 11. Device according to the preceding claim, wherein the overmoulded metal insert is a vest, a wafer or a braid. 12. Device according to one of claims 1 to 9, wherein at least one of the electrical conductive elements (80) is an insert and fixed on the cover (40) after shaping. 13. Device according to the preceding claim, wherein the reported element is a conductive adhesive tape forming a conductive adhesive film. 14. Device according to the preceding claim, wherein the insert is a superconductive coating layer. 15. The assembly of a radar (20) and a device (10) according to one of the preceding claims. The assembly of claim 16, wherein the radar (20) is an ACC type radar. 17. Motor vehicle equipped with an assembly according to one of claims 15 and 16.