Patent Application
20200369230
This invention relates to the field of bumpers, more particularly energy absorption systems such as shock-absorbers for a motor vehicle.
Absorbers for a motor vehicle intended to be interposed between a transverse impact beam and side members which connect the assembly to the vehicle body are already known in the prior art. They may be fitted at the front and/or at the rear of the vehicle, extending in the longitudinal direction. Such absorbers absorb energy in the event of an impact in order to limit the deformation of other components and the repair costs.
Currently, car manufacturers are increasingly trying to reduce the energy consumption of motor vehicles, especially by reducing their weight. In this perspective, they try to reduce the size of the bumpers, in particular that of the beam and of the absorbers in the longitudinal direction. At the front of the vehicle, a 50 mm reduction in the distance between the front of the beam and the rear of the absorbers lightens the vehicle by about 5 kg. This distance reduction induces a reduction in the vehicle overhang, which also brings greater freedom of vehicle style, especially with more vertical bumpers and shorter bonnets.
However, the reduction of this distance (between the front of the beam and the rear of the absorbers), and therefore the overhang, is limited by safety standards which require satisfactory strength for the bumper and the surrounding parts. One way of reducing the overhang is to increase the efficient length of the absorber, in other words the distance over which the absorber deforms before reaching its incompressibility, characterised by a large increase in force. In the context of this invention, compressibility is understood to mean the ability of a body to be crushed considerably, in other words to leave an incompressible residue that is as small as possible, for an equivalent quantity of absorbed energy (given in the specifications).
By way of example, a metal absorber can be compressed by about 75% and has an incompressibility of about 25%. The aim is therefore to increase the compressibility of the absorbers so that they can absorb as much energy as much as possible in the event of an impact in a reduced axial space. This axial space is therefore the total of the crushing distance (during which energy is absorbed), and the incompressible residue remaining at the end. In other words, the aim is to reduce the incompressible portion of the absorbers which does not contribute to energy absorption.
An absorber of an impact beam made of composite material is known, in which the absorber consists of two shells each integrated in a connecting element. The way these half-shells are connected together implies a progressive folding type deformation of the absorber favoured by the discontinuous connection of these two half-shells (screws, rivets, etc.) and by initiation which takes place between these connecting points (energy absorption by deformation of successive waves of the half-shells). “Progressive folding” (known by the specialists) is less efficient than delamination in terms of energy absorption since it creates an incompressible residue after an impact (approximately 25%). With a delamination mode, an incompressible residue of about 5% may be achieved. This reduction of the incompressible residue induces an increase in the efficient length of the absorber and therefore a greater energy absorption potential for an identical force calibration.
Initiation which is not carried out at the front of the absorber is not optimum for the energy absorption.
In addition, since these connecting elements are by definition rigid, they induce non-compressible areas around themselves which increase the incompressible residue after an impact. The multiplication of these connections amplifies this phenomenon.
Energy absorbing systems based on axial compression of a composite tube are also known. Conventionally, this tube consists of a resin forming the matrix of the composite and the fibres.
To favour energy efficiency, continuous fibres stacked across the thickness of the tube are used. The stack may consist of one or more reinforcements, oriented unidirectionally (UD fibres) or in different orientations (for example) 0°/+45°/−45°/0°).
The continuous fibres known include in particular UDs, stitched biaxial reinforcements, woven reinforcements, mats which are used in particular in the pultrusion method. Reinforcement using tapes oriented substantially at +/−45° as described in patent U.S. Pat. No. 6,601,886B1 is also known.
The mode recommended for axial deformation of such a composite tube during the compression phase under a force (impact) is delamination. During such delamination, the fibre reinforcements shear across their thickness over the (entire) length of the tube.
In particular, patent U.S. Pat. No. 4,336,868A is known, which describes methods for manufacturing a composite tube and the performance of matrices and fibre reinforcements in terms of energy absorption capacity (specific absorption energy). This document illustrates in particular the tube delamination mode under an axial compression force.
Conventionally, the resin is reduced to dust and the various reinforcement layers are delaminated in the direction of the impact (therefore mainly “axial”), and thus absorb energy.
Initiation modes are also known to generate delamination by compression of a composite tube which consist in creating a weakness locally on the tube to initiate its deformation. Conventionally, a shape discontinuity such as a notch or a chamfer located at one end of the tube is used as initiation area. This discontinuity will be called the initiator.
The invention aims to remedy these disadvantages by providing a shock-absorbing system of reduced size, offering the vehicle good impact resistance. This absorbing system has a minimum incompressible residue while having maximum energy efficiency in order to reduce the vehicle overhang.
Thus, the invention relates to a shock-absorbing system for a motor vehicle, intended to be interposed between a side member and a transverse impact beam, characterised in that it comprises:
The term “delamination” is understood to mean the property of a body to shear across its longitudinal thickness. Delamination of the absorbing element causes irreversible destruction of at least a large portion of the absorbing element such that it no longer consists of a single piece. Thus, the compressibility of the absorbing element is significantly increased. The length required by the shock-absorbing system is therefore reduced, helping to reduce the overhang and lighten the vehicle considerably. Such an absorbing element can achieve a compressibility of more than 90% (corresponding to an incompressible residue of less than 10%) compared with an aluminium absorber having a compressibility of about 75%.
The presence of the connecting element holds, secures the beam to the side member, in particular after disintegration of at least a portion of the absorbing element after an impact. It does not participate or participates only very slightly (less than 10%) in the energy absorption and its thickness after an impact (called its incompressible residue) is lower than that of the absorbing element so that the absorbing element can compress up to its maximum compressibility without being affected by the connecting element. The presence of a programmed zone of mechanical weakness allows the connecting element to initiate the absorbing element compression mode in the event of an impact, for example by folding at the programmed zone of mechanical weakness, and to follow the absorbing element compression movement.
A “programmed zone of mechanical weakness” is understood to mean a zone where the mechanical strength of the material is weakened so as to initiate and direct the folding of the mechanical part when it is subjected to a force.
The absorber according to the invention may further comprise the following characteristics, taken alone or in combination:
The invention also relates to an assembly of an impact beam, a side member and at least one shock-absorbing system according to the invention, the shock-absorbing system being secured respectively to the beam and to the side member by attachment plates. Advantageously, the shock-absorbing system is inserted in the plates outside the compression area, so as not to generate an incompressible residue between the two plates.
The invention also relates to a method for assembling an assembly according to the invention, comprising the following steps:
The invention also relates to an impact beam, comprising at least one shock-absorbing system according to the invention.
The invention also relates to a motor vehicle front module comprising at least one shock-absorbing system according to the invention.
The invention also relates to a motor vehicle comprising at least one shock-absorbing system according to the invention.
The invention will be better understood on reading the accompanying figures, which are given solely by way of example and not limiting in any way, in which:
We now refer to
According to one embodiment, the impact beam absorber is configured so that the initiator is on the side of the bar, such that the absorber compresses substantially longitudinally from the bar towards the side members (direction X in the vehicle coordinate system). The initiator is therefore preferably located towards the front of the tube, more preferably at its end so that delamination occurs from the front towards the rear.
According to one embodiment, the absorbing element 40 is a hollow body, preferably a tube having a cross-section selected from the following list: circular, rectangular, conical, hexagonal, scalable.
Advantageously, the absorbing element 40 is made in one piece, in other words it is not manufactured by assembling different parts. It may, for example, be manufactured by moulding composite material, in particular by reactive pultrusion or by extrusion.
According to one embodiment, the absorbing element 40 comprises at least one layer of composite material having a plastic matrix and reinforcement elements.
The plastic matrix is, for example, a thermoplastic material, preferably selected alone or in combination from the following materials: polyamide, polypropylene, polyurethane.
The plastic matrix may alternatively be a thermosetting material, preferably selected alone or in combination from the following materials: epoxy, polyester, vinyl ester.
The reinforcement elements may be continuous fibres, preferably based on a material selected alone or in combination from the following materials: carbon, glass, aramid.
The reinforcement elements are preferably unidirectional fibres oriented in a direction not parallel to a longitudinal direction of the vehicle.
Advantageously, the absorbing element 40 comprises internal ribs 45.
According to an example shown on
The absorbing element 40 comprises, at its end intended to be positioned on the side of the beam 30, an initiator which initiates delamination by compression of the absorbing element 40 from the front towards the rear (in the direction of the impact), and which deforms according to a delamination mode. This tube is able to delaminate over substantially its entire length.
According to one embodiment, shown on
The programmed zone of mechanical weakness 66 comprises a pre-fold, a slit or a thickness reduction.
The connecting element 50, between the impact beam 30 and the side member 20, forms a guiding system not continuously connected to the absorbing element 40 (composite tube on the figures). One of its functions is to guide the absorbing element 40 during its compression in the event of an impact, without however contributing to energy absorption. It allows a connection after an impact between the bar of the impact beam 30 and the side member 20 of the vehicle. It has the ability to deform, in particular due to the programmed zone of mechanical weakness 66, and not generate an incompressible residue after total compression.
Advantageously therefore, the connecting element 50 has an incompressibility rate of less than 5% after an impact.
The invention also relates to an assembly of an impact beam 30, a side member 20 and at least one shock-absorbing system 10 according to the invention.
The shock-absorbing system 10 is secured to the impact beam 30 by an attachment plate 70, and to the side member 20 by an attachment plate 80.
The plates 70 and 80 comprise recesses 75 and 85, or housings, to accommodate, for example by insertion, the tube forming the absorbing element 40.
To avoid generating an incompressible residue between the two plates 70 and 80, the tubes (absorbing element 40) are inserted in the plates 70 and 80 outside the compression area (see
The invention also relates to a method for assembling such an assembly comprising the following steps (
The invention also relates to an impact beam 30, comprising at least one shock-absorbing system 10 according to the invention.
The invention also relates to a motor vehicle front module comprising at least one shock-absorbing system 10 according to the invention.
The invention also relates to a motor vehicle comprising at least one shock-absorbing system 10 according to the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1663534 | Dec 2016 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2017/053455 | 12/8/2017 | WO | 00 |
