Chassis of a motor vehicle optimized for absorbing a frontal impact

A chassis of a motor vehicle optimized for absorbing a frontal impact. The chassis includes a firewall separating a passenger compartment of the vehicle from a front portion of the chassis configured to hold an engine, and a mechanism for absorbing a frontal impact including two side rails mounted on at least the front portion of the chassis and arranged on either side of the chassis, each side rail including a front portion and a rear portion assembled to overlap at least partially. The side rails are arranged such that an overlap area is below the plane of the firewall, and the rear portion of the side rail includes a material which is less compressible than the front portion of the side rail.

BACKGROUND

The invention concerns the front part of a motor vehicle chassis, and more particularly the absorption of a frontal impact by the front side rail.

The energy that a motor vehicle receives in the event of a frontal impact is generally transmitted toward the rear of the vehicle with the aid of side rails distributed over the length of the chassis, and notably with the aid of front side rails.

To transmit the energy to the rear part of the chassis, the front side rails are coupled to the rest of the chassis, for example to central side rails mounted under the floor of the vehicle and to side members disposed at the periphery of the chassis.

The energy arising from the frontal impact is absorbed at different levels of the chassis. The chassis is configured to protect the passenger compartment as much as possible, that is to say so that it suffers virtually no deformation, in order to protect the persons inside. To this end the energy is absorbed by various elements of the chassis, notably by the front side rails. The front side rails are the primary means for absorbing energy. They absorb the energy generated by the frontal impact, generally by compression or even rotation of the side rail.

U.S. Pat. No. 6,908,146 describes front side rails of a motor vehicle chassis comprising a front portion and a rear portion welded together so as to overlap partially so as to increase the overall stiffness, the front side rails extending partly under a firewall separating the passenger compartment from the engine. The documents US 2010/0 117 403, U.S. Pat. No. 6,938,948 and U.S. Pat. No. 7,097,235 describe known chassis comprising a pair of side rails. The technical statistics described do not give the side rail section, routing and arrangement characteristics enabling good compressibility and good adaptation to absorbing energy in a compact environment.

SUMMARY

The invention proposes to alleviate these drawbacks with the aid of a chassis comprising front side rails configured to optimize the absorption and the transmission to the rear of the vehicle of a frontal impact, and to prevent intrusion of the engine compartment into the passenger compartment.

In accordance with one aspect of the invention, there is proposed in accordance with one embodiment a motor vehicle chassis comprising a firewall separating the passenger compartment of the vehicle from a front portion of the chassis intended to receive the engine, and means for absorbing a frontal impact including two side rails mounted at least on the front portion of the chassis and disposed on each side of the chassis, each side rail comprising a front part and a rear part assembled so as to overlap at least partially.

In accordance with one general feature, the side rails are disposed so that the overlap area is under the plane of the firewall, and the rear part of the side rail comprises a less compressible material than the front part of the side rail.

By positioning the area in which the front and rear parts of the side rails overlap under the plane of the firewall and by making the rear part of the side rails from a material more resistant to compression forces than the front part, the absorption area of the front side rail comprises the front part of the side rail and the rear part transmits the remaining energy to the rear of the chassis, whilst keeping the passenger compartment safe.

The front part of each side rail preferably comprises a front bend separating a planar front portion and a downwardly inclined rear portion, the front portion having a section smaller than the section of the rear portion.

The increasing section of the front part of the side rails in a direction from the front toward the rear makes it possible to increase the quantity of energy caused by a frontal impact that is absorbed and to optimize the compression of the planar portion.

The rear part of a side rail preferably comprises a rear bend separating a planar rear portion and a front portion inclined upwardly at an absorption angle relative to the rear portion of the rear part of the side rail, the absorption angle being strictly less than 30° (the smaller the better).

By maintaining a low absorption angle, the overhang and consequently the force on the side rail are reduced.

The front bend may advantageously comprise a rotation start point for absorbing energy by inward rotation of the side rail. The rotation start point is implemented in the front bend of the front part of the side rail at the level of the cup boss.

The overlap area preferably extends over an area of 50 mm between the front part and the rear part of the side rail.

The chassis may advantageously comprise a crossmember of the firewall disposed vertically in line with the overlap area, orthogonally to the front side rails. This crossmember enables force to be transferred to the transmission tunnel and makes it possible to maintain rotation of the rear part of the side rail about the vertical axis “z”.

The chassis may also comprise a reinforcement in the front bend area of the front part of the side rail. This reinforcement makes it possible to prevent premature destruction of the side rail in the area of the bend (the area in which the stresses are concentrated).

DETAILED DESCRIPTION

InFIG. 1there is diagrammatically represented a plan view of a motor vehicle chassis1in accordance with one embodiment of the invention.

The chassis1comprises a front portion1aincluding a front bumper2, side rails3and a front crossmember4, a central portion1bincluding central side rails5, side members6and a central floor7, and a rear portion1cnotably including a trunk floor8and a rear bumper9coupled to rear side rails10.

In the front portion1aof the chassis1, the front bumper2extends in a transverse direction T, i.e. orthogonally to the front/rear direction of the chassis1, and is assembled with two side rails3extending in a longitudinal direction L, parallel to the front/rear direction of the chassis1.

Each side rail3comprises a first end31to which the bumper2is fixed and a second end32to which is fixed the front crossmember4extending in the transverse direction T parallel to the bumper2. The side rails3contribute to the stiffness of the chassis1and provide a support for engine and bodywork elements of the motor vehicle. They are also designed to contribute to the absorption of energy in the event of a frontal impact in particular. They enable transmission of the forces to which the front bumper2is subjected in the event of a frontal impact to the rear portion1cof the chassis1and absorb some of the energy linked to these forces.

The side rails3are produced with a front part3afixed to the front bumper2and a rear part3bfixed to the front crossmember4. The front part3aand the rear part3bare assembled together so as to overlap partially in an overlap area R.

The front portion1aof the chassis1also comprises two brackets12mounted between a side rail3and the crossmember4so as to stiffen the structure of the chassis1. Each bracket12is assembled to a side rail3and the front crossmember4by means of fixing tongues that come to bear on the underside of the front crossmember4and on the underside of the side rail3. The brackets12are also fixed by spot welds to the side rail3and to the front crossmember4.

The chassis1also comprises two side crossmembers14each extending between a side rail3and a side member6extending in the longitudinal direction L at the periphery of the chassis1between the front portion1aand the central portion1b. Each side crossmember14is fixed to a side rail3at the height of the second end32by spot welds.

The side crossmembers14extend between the side rail3and the side member6in an oblique direction so that the portion of the side crossmember14coupled to the side member6is to the rear of the portion of the side crossmember coupled to the side rail3. The resulting angle between the side rail3and the side crossmember is an obtuse angle.

The front portion1aof the chassis1therefore comprises means for absorbing a frontal impact comprising a front bumper2, side rails3coupled on the one hand to a crossmember4with brackets12and on the other hand to side crossmembers14coupled to side members6.

The energy caused by a frontal impact on the front bumper2is therefore transmitted to the rear portion1cof the chassis1on the one hand via the central side rails5coupled to the front crossmember4and to a rear crossmember15and passing under the central floor7and on the other hand via the side members6extending on each side of the chassis1.

InFIG. 2there is shown a detailed side view of a side rail3of the front part1aof the chassis1fromFIG. 1.

The rear part3bof the side rail3comprises a planar rear portion33fixed to the front crossmember4via the end32and a front portion34inclined upwardly at an absorption angle β relative to the planar rear portion33. The planar rear portion33and the inclined front portion34are separated by a rear bend35.

The front part3aof the side rail3comprises a planar front portion36coupled to the front bumper2, and a downwardly inclined rear portion37. The planar front portion36and the inclined rear portion37are separated by a rear bend38.

The absorption angle β is strictly less than 30° (the smaller the better). The absorption angle β is kept low so as to obtain a smoother trajectory of the side rail3and so as to increase the quantity of energy absorbed by compression. Indeed, with a larger absorption angle, the compression of the side rail3is mainly localized at the front and rear bends35and38, which enables less energy to be absorbed than with a smoother side rail trajectory that enables better distribution of the compression of the side rail, and notably of the front part3a, over the whole of its length.

The planar front portion36of the front part3ahas a section having dimensions “a” smaller than the dimensions “b” of the section of the inclined rear portion37of the front part3a. This section gradient toward the rear of the front part3aof the side rail3makes it possible to increase the quantity of energy absorbed in the event of a frontal impact.

Moreover, the front bend38comprises a rotation start point38afor absorbing some of the energy transmitted by the side rails3by inward rotation of the side rail3, and notably by inward rotation of the front part3a. The rotation start point38afacilitates the compression by rotation of the side rail3. It is disposed in the cup boss mask C.

The overlap area R is situated under the plane P of the firewall T and under a firewall crossmember41on which the firewall T rests. The rear part3bis made from a relatively incompressible material, while the front part3ais made from a compressible material. The overlap area R is therefore disposed at the level of the limit area of intrusion into the passenger compartment. The side rail3is configured to be compressed longitudinally and by rotation over a part in front of the plane P of the firewall T.

The planar front portion36of the front part3aof the side rail3also includes an impact reinforcement (not represented) for increasing the quantity of energy absorbed by the front portion36. The impact reinforcement may be pressed onto the bottom or the web of the side rail, for example, and this reinforcement may also have the engine cradle support function.

The invention therefore makes it possible to produce a chassis comprising front side rails configured to optimize the absorption and the transmission to the rear of the vehicle of a frontal impact and to prevent intrusion of the engine compartment into the passenger compartment.