Battery arrangement having compressed foam plate

A structure of an electric or hybrid vehicle includes a floor, a battery container secured beneath the floor, and a compressed foam plate arranged between the battery container and the floor.

The invention relates to a structure of a motor vehicle. The invention also relates to a vehicle comprising such a structure, and to a method for assembling such a structure.

Vehicles, and in particular motor vehicles, experience vibrations. In order to improve the comfort of these vehicles, it is necessary to reduce these vibrations which in particular give rise to noise.

Document US2008/136110A1 is known which describes a system for sound insulation between the floor of the vehicle and the energy reservoir, whether this is a fuel tank or a battery tray. The space between the fuel tank and the floor is insulated by means of an acoustic seal so as to prevent the noise being transmitted into the sealed empty space.

However, this solution provides partial insulation with respect to noise but does not provide insulation with respect to vibrations.

The aim of the invention is to provide a vehicle structure which remedies the above drawbacks. In particular, the invention serves to provide a vehicle structure which is simple and easy to implement and with which the floor of a vehicle can be insulated with respect to noise and vibrations.

The invention relates to a structure for an electric or hybrid vehicle comprising a floor, a battery tray secured beneath the floor, and a compressed foam plate arranged between the battery tray and the floor.

In one embodiment, the surface of the foam plate comprises microscopic perforations configured for evacuating air contained in the foam when the plate is compressed and/or configured to avoid ingress of water into the foam.

In one embodiment, the foam plate further comprises a hole that opens on one of its faces or that passes through it from one face to the other, this hole being configured for evacuating air contained in the foam when the plate is compressed.

In one embodiment, the foam plate further comprises a portion positioned toward the rear of the vehicle, of which the surface comprises holes configured for evacuating air contained in the foam when the plate is compressed.

In one embodiment, the foam plate is compressed between the floor and the battery tray with a degree of compression of between 20° and 40° inclusive, in particular between 30% and 40% inclusive.

In one embodiment, the thickness of the foam plate when compressed is between 10 mm and 20 mm inclusive, preferably between 13 mm and 14 mm inclusive, in particular equal or essentially equal to 13 mm, with a degree of compression of 30% of the plate.

In one embodiment, the foam plate comprises a polyurethane foam.

In one embodiment, the foam is a foam having cells of dimensions smaller than 2 mm.

The invention also relates to a vehicle, in particular a hybrid vehicle or electric motor vehicle, comprising a structure according to the invention.

Finally, the invention relates to a method for assembling a vehicle structure comprising a step of perforating a foam plate, a step of arranging the foam plate between a vehicle floor and a vehicle battery tray, a step of compressing said foam plate to a degree of compression of between 20% and 40%, and a step of securing the battery tray to the floor in such a way that the foam plate remains compressed to a degree of compression of between 20% and 40%.

An example of a vehicle structure according to one embodiment of the invention is described hereinbelow with reference toFIG.1.

The structure1comprises a vehicle floor3, and a battery tray4. The battery tray4is secured to the floor3. In particular, the battery tray is secured beneath the floor3. The expression “beneath” is to be understood here as meaning that the battery tray4is beneath the floor3when the vehicle comprising the structure is in a position of operation. The battery tray4is therefore preferably intended to be arranged outside the passenger compartment of the vehicle.

The vehicle structure1also comprises a foam plate2. The foam plate2is arranged between the battery tray4and the floor3of the vehicle structure1.

The floor3advantageously constitutes a horizontal platform of the passenger compartment of the vehicle.

The floor3is not restricted to the first layer inside the passenger compartment of the vehicle, but may comprise multiple layers or an assembly of which at least one layer is arranged at the internal surface of the vehicle.

The battery tray4may comprise at least one portion that is parallelepipedal or essentially parallelepipedal in shape.

As shown inFIG.2, the battery tray4comprises a battery43. The battery43is preferably electrically connected to an electric drive motor of the vehicle. In one embodiment, the battery tray4comprises a cooling system42. The cooling system42is preferably arranged beneath the battery43.

The battery tray4also comprises a compartment or an envelope that is intended to contain the battery and the cooling system. An upper side41of the compartment is in contact with the foam plate2or is oriented toward the foam plate2.

The width and the length of the foam plate2are significantly greater than the thickness of said foam plate2. Thus, the foam plate2preferably comprises two main faces separated by a smaller dimension, called the thickness.

The expression “significantly greater” is to be understood as meaning that the width and the length are at least 10 times greater than the thickness, preferably at least 50 times.

The foam plate2is a solid foam plate2. The foam plate2comprises an open-cell or closed-cell material. The open-cell material comprises a fine-geometry solid matrix that is saturated with a fluid. The open-cell material preferably comprises a continuous solid network in which air bubbles are trapped.

Preferably, the foam plate2comprises a polymer foam.

The polymer foam advantageously makes it possible to obtain a foam plate2.

Preferably, the foam plate2comprises a polymer matrix, most preferably a polyurethane matrix.

The foam plate2may comprise fire-retardant compounds. Thus, the foam plate2may also serve as a firewall between the battery tray4and the floor3of the structure1of the vehicle.

The open-cell or closed-cell material may be defined by its density and by the structure of the matrix, in particular by its porosity and by the shape of its cells.

The loss factor (or internal damping modulus) of the open-cell material may be between 0.1 and 0.3 at a frequency of 10 Hz and at a temperature of 23° C. The loss factor is a measure of the ratio of the energy dissipated by damping to the elastic energy that is conserved and then restored during a deformation cycle.

The loss factor is equal to the tangent of the ratio between the loss modulus over the storage modulus (E′).

The storage modulus in compression (E′) of the open-cell material may be between 1000 and 50 000 Pa at a frequency of 10 Hz and at a temperature of 23° C.

The density of the open-cell material may be between 20 and 100 g/L.

Preferably, the foam plate2comprises a micro-cellular material, that is to say that the size of the cells of the network is between 1 μm and 1 mm.

In one embodiment, the foam is a closed-cell foam and the cells have dimensions smaller than 2 mm.

The foam plate2arranged between the floor3and the battery tray4is compressed or preloaded. Indeed, compressing the foam plate2advantageously permits better absorption of the vibrations of the floor3and of noise. The compression increases the rigidity of the plate.

In one embodiment, the foam plate2is compressed by forces orthogonal to the two main faces or is compressed so as to reduce the thickness of the foam plate2.

The battery tray4may be mechanically secured to the floor3so as to leave a space (between the battery tray and the floor3) that is smaller than the thickness of the foam plate2at rest, that is to say in the absence of any load acting on the plate. Thus, the foam plate2is deformed during installation by the compression provided by the floor3and the upper side41of the battery tray4.

The vehicle structure may comprise securing means so as to be able to secure the battery tray4to the floor3. These securing means preferably permit securing without passing through the foam plate2.

In one embodiment, the degree of compression of the foam plate2is between 20% and 60%. Preferably, the degree of compression of the foam plate2is approximately 30%. The expression “degree of compression” is to be understood as the ratio of the difference between the thickness of the foam plate2at rest and the thickness of the foam plate2when compressed, divided by the thickness of the foam plate2at rest.

The foam plate2may have a thickness of between 10 mm and 20 mm when it is compressed between the floor3and the battery tray4. Preferably, the foam plate2has a thickness of approximately 20 mm at rest. Once the structure is installed, said foam plate2is compressed by approximately 30%. Thus, the thickness of the foam plate2once compressed and installed between the floor3and the battery tray4is approximately 13 mm.

The foam plate2also comprises means for evacuating the air contained in the solid matrix. These air evacuation means make it possible to evacuate the air from the foam plate2when it is compressed. This evacuation of air makes it possible to reduce the risk of the plate2bursting on compression due to the increased air pressure.

In a first embodiment, shown inFIG.3A, at least one surface of the foam plate2comprises micro-perforations. The surface comprising the micro-perforations is preferably an upper surface of the foam plate2. Thus, the evacuation of the air is not hampered by the surface of the floor3or of the battery tray4.

The micro-perforations extend over a portion of the volume of the foam plate2. Thus, the air trapped in the network of the solid matrix can more easily leave said matrix by passing through these perforations.

The micro-perforations may have a thickness or a diameter of between 0.05 mm and 3 mm. The micro-perforations may extend in the volume of the foam plate2over a length of between 20% and 99% of the length or of the width of the foam plate2.

In one embodiment, at least one micro-perforations passing through the foam plate2from side to side over its length or over its width.

The foam plate2may comprise a micro-perforation density of between 2 and 10 micro-perforations per mm2, preferably between 2 and 6 micro-perforations per mm2.

These characteristics of the micro-perforations advantageously permit better evacuation of the air contained in the foam during compression of the plate, and serves to prevent ingress of water into the foam.

The micro-perforation can be positioned on both faces of the plate2, preferably only one of the two faces is micro-perforated, this face must be positioned on the upper surface of the plate2, that is to say toward the passenger compartment of the vehicle (in contact with the floor of the motor vehicle structure).

In a second embodiment, shown inFIG.3B, the foam plate2comprises at least one hole7which opens on at least one main face, in particular a hole7passing through the thickness of the plate. The open hole7serves to shorten the minimum distance that the air must travel in order to leave the foam plate2.

If the foam plate2comprises a single open hole7, said open hole7is preferably located in a central region of the foam plate2.

In one embodiment, the area of the orifice of the open hole7is less than 5% or less than 1% of the area of the foam plate2that is intended to come into contact against the battery tray4or of the area of the foam plate2that is intended to come into contact against the floor3.

In the embodiment in which the foam plate2comprises multiple open holes7, the sum of the areas of the orifices of the open holes7is less than 20% or less than 10% of the area of the foam plate2that is intended to come into contact against the battery tray4or of the area of the foam plate2that is intended to come into contact against the floor3.

The above-described second embodiment may also be combined with the first embodiment.

In a third embodiment, shown inFIG.3C, which is compatible with the first and/or the second embodiment, the foam plate2comprises a portion located toward the rear of the vehicle, of which the surface comprises holes8for evacuating the air.

Indeed, positioning larger-diameter holes8in the rear region makes it possible to evacuate a larger volume of air. This solution is particularly effective in the case where the micro-perforations do not make it possible to evacuate a sufficiently large volume of air in a relatively short time. The rear region, counter to the direction of travel of the vehicle, is subject to less stringent demands in terms of durability.

Thus, the risk of overpressure of air at the heart of the matrix is limited.

Thus, the assembly comprising the battery tray4and the foam plate2beneath the floor3creates a mass-spring-mass effect. The vibrations in the wall of the battery tray4and the sound waves are damped in the spring (the foam plate2). Finally, the sound and the vibrations are damped.

In one embodiment, the battery tray4comprises at least one securing region6. The at least one securing region6may extend laterally relative to the upper side41.

The upper side41may be arranged so as to leave a space (between the battery tray4and the floor3) for the insertion of the foam plate2as described hereinabove.

The at least one securing region6may comprise securing means such as bores or tapped holes for securing the battery tray4to the floor3.

The invention also relates to a vehicle comprising such a structure1. The vehicle is preferably a motor vehicle, most preferably a motor vehicle comprising an electric motor for driving the vehicle.

The invention also relates to a method for assembling a vehicle structure1. One embodiment of an assembly method is described below. The vehicle structure1is preferably a vehicle structure1as previously described.

The method comprises the following steps:arranging a foam plate2between a vehicle floor3and a battery tray4;compressing said foam plate2to a degree of compression of between 20% and 40%;securing the battery tray4to the floor3in such a way that the battery tray4and the floor3are separated by a distance which is smaller than the thickness of the foam plate2at rest.

Preferably, said distance is between 60% and 80% of the thickness of the foam plate2at rest.

In one embodiment, the compressing and securing steps are carried out at the same time.

In the present application, the expression “approximately”, when followed by a numerical value, is to be understood as a range of 10% either side of said numerical value.