Abstract:
A chassis of a motor vehicle including a mechanism for absorbing a frontal impact including two side rails mounted on a front portion of the chassis and arranged on either side of the chassis, a front crossmember mounted under a floor of a passenger compartment of the vehicle in contact with a transmission tunnel arranged on a central axis and extending from the front crossmember towards a rear portion of the chassis. Each side rail includes one end mounted to engage with the front crossmember.

Description:
BACKGROUND 
     The invention relates to the front part of the chassis of a motor vehicle, in particular an electric-propulsion vehicle, and more particularly to the fastening of a front longitudinal member. 
     In conventional solutions for transferring force from the front of the vehicle toward the rear during a frontal impact, the majority of the forces are transferred from a front longitudinal member toward a central longitudinal member which is situated in the continuation thereof along the longitudinal axis of the chassis. A lesser part of the forces is transferred laterally by a lateral skirt or by a tunnel at the centre of the chassis. 
     U.S. Pat. No. 6,926,352 describes a motor vehicle chassis of this type comprising two longitudinal members at the front of the vehicle distributed on each side, a central floor tunnel, and two central longitudinal members for transferring the forces experienced during a frontal impact to the rear of the vehicle. 
     U.S. Pat. No. 7,810,878 describes a motor vehicle chassis comprising a bumper mounted on front longitudinal members transmitting the forces experienced during a frontal impact to the rear part of a motor vehicle via central longitudinal members passing below the central floor of the motor vehicle and skirts mounted at the periphery of the chassis. 
     In the case of an electric vehicle, the central floor is generally raised so as to allow the battery to be housed therebelow. The central longitudinal member passing below the floor then reduces the available storage space for the batteries, mainly along a transverse axis, that is to say in a direction orthogonal to the front-rear direction of the vehicle. This reduction in the available storage space is highly prejudicial for the storage capacity of the batteries and therefore for the autonomy of the motor vehicle, in particular in a compact vehicle. 
     BRIEF SUMMARY 
     The invention proposes to provide a chassis comprising force transfer means making it possible to free up an available space zone for the storage of the batteries below the central floor of the motor vehicle over its whole width while ensuring that forces due to a frontal impact are transferred from the front to the rear of the vehicle. 
     According to one aspect of the invention, there is proposed in one embodiment a motor vehicle chassis provided with means for absorbing a frontal impact comprising two longitudinal members mounted on a front portion of the chassis and arranged on each side of the chassis, a front crossmember mounted below the floor of the passenger compartment of the vehicle in contact with a transmission tunnel arranged on a central axis and extending from the front crossmember toward a rear portion of the chassis. 
     According to a general characteristic, each longitudinal member comprises an end mounted so as to butt against the front crossmember, the chassis thus comprising a space below the floor free from central longitudinal members. 
     The front crossmember mounted on the longitudinal members of the front portion of the chassis allows a connection to be made between the longitudinal members and the transmission tunnel of the motor vehicle. This connection makes it possible to transfer at least some of the forces due to the frontal impact toward the transmission tunnel and to free up the space below the floor for the storage of batteries. 
     The front crossmember also makes it possible to provide a mount for fastening the battery. 
     Furthermore, the front crossmember allows good protection of the battery in the case of a side impact owing to the position of the crossmember with respect to the battery. 
     Advantageously, the means for absorbing the frontal impact may additionally comprise two brackets each mounted between a longitudinal member and the front crossmember, each bracket being dimensioned so as to have an end at the height of the transmission tunnel and having a shape with a flank inclined at an angle between the front longitudinal member to which it is coupled and the front crossmember. 
     The brackets make it possible, on the one hand, to contribute to the rigidity of the chassis, on the other hand, to optimize the transmission of the forces due to the frontal impact toward the transmission tunnel, and, finally, to limit rotation about a vertical axis of the longitudinal member. 
     Preferably, the chassis comprises two skirts mounted on each side of the chassis, and the means for absorbing the frontal impact additionally comprise two lateral crossmembers each mounted between a longitudinal member and a skirt, at the height of the front crossmember. 
     The fastening of the lateral crossmember between a longitudinal member and a skirt makes it possible to contribute to the rigidity of the chassis, on the one hand, and to transmit some of the forces due to a frontal impact to a skirt so that these forces are transmitted and dissipated toward the rear of the chassis. 
     It is thus possible to form a motor vehicle chassis free from central longitudinal members and capable of transmitting the forces experienced to the tunnel and to the skirts. That additionally makes it possible to increase the space available below the central floor and therefore to use all the space below the floor for the storage of the batteries and thus to increase the capacities of the electric-traction motor vehicle, including the autonomy. 
     Preferably, each lateral crossmember has a shape inclined toward the rear on the skirt side so as to form an obtuse angle between the longitudinal member and the inclination of the lateral crossmember. 
     The inclined shape of the flank of the lateral crossmember makes it possible to promote the transfer of forces toward the rear. 
     Advantageously, the front crossmember, the longitudinal members and the brackets may be assembled with the aid of spot welds. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages and features of the invention will become apparent on examining the detailed description of a nonlimiting embodiment and the appended drawings, in which: 
         FIG. 1  schematically illustrates a plan view of a chassis of a motor vehicle according to one embodiment; 
         FIG. 2  shows a perspective bottom view of a front portion of the chassis. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically represents a plan view of a motor vehicle chassis  1  according to one embodiment of the invention. 
     The chassis  1  comprises a front portion  1   a  comprising inter alia a front bumper  2 , longitudinal members  3  and a front crossmember  4 , a central portion  1   b  comprising inter alia a transmission tunnel  5 , skirts  6  and a central floor  7 , and a rear portion  1   c  comprising in particular a luggage compartment floor  8  and a rear bumper  9  which are coupled to rear longitudinal members  10 . 
     In the front portion  1   a  of the chassis  1 , the front bumper  2  extends in a transverse direction T, that is to say orthogonal to the front/rear direction of the chassis  1 , and is assembled with two longitudinal members  3  extending in a longitudinal direction L, parallel to the front/rear direction of the chassis. 
     Each longitudinal member  3  comprises a first end  31  to which is fixed the bumper  2  and a second end  32  to which is fixed the front crossmember  4  extending in the transverse direction T parallel to the bumper  2 . The longitudinal members  3  help to stiffen the chassis  1  and provide a mount for engine elements and for body elements of the motor vehicle. They are also designed to help in absorbing energy during a frontal impact in particular. They make it possible for the forces experienced by the front bumper  2  during a frontal impact to be transmitted toward the rear portion  1   c  of the chassis  1  while absorbing some of the energy associated with the forces. 
     In this example, the longitudinal members  3  are produced as a front part  33  and a rear part  34  assembled together. The longitudinal members may also be produced as a single part. 
     The second end  32  of each longitudinal member  3  rests in abutment against the crossmember  4 , as is illustrated in  FIG. 2 , which shows a detailed perspective view of part of the front portion  1   a  of the chassis. The front crossmember  4  is a profile having a U-shaped cross section oriented so as to receive the longitudinal members  3  in the hollow of the profile. 
     The longitudinal members  3  therefore do not extend beyond the front crossmember  4 . They are fastened to the crossmember  4  by spot welds  11 . 
     The front portion  1   a  of the chassis  1  also comprises two brackets  12 , as is illustrated in  FIGS. 1 and 2 . Each bracket  12  is mounted between a longitudinal member  3  and the crossmember  4  so as to stiffen the structure of the chassis  1  and to improve the degree of energy transfer during a frontal impact between the longitudinal members  3  and the transmission tunnel  5  along a longitudinal axis centred on the chassis  1 . 
     Each bracket  12  is assembled with a longitudinal member  3  and the front crossmember  4  with the aid of fastening tabs  13  bearing below the front crossmember  4  and below the longitudinal member  3 . The brackets  12  are also fastened by spot welds  11  to the longitudinal member  3  and to the front crossmember  4 . 
     Each bracket  12  has an oblique reinforcing face  12   r  ( FIG. 1 ) extending between the longitudinal member  3  to which it is coupled and the front crossmember  4 . The brackets  12  are dimensioned in such a way that the end  12   e  of the reinforcing face  12   r  is arranged facing the inlet  50  of the transmission tunnel  5 . In this way, the degree of energy transmitted toward the transmission tunnel  5  during a frontal impact is maximized. 
     The chassis  1  also comprises two lateral crossmembers  14  each extending between a longitudinal member  3  and a skirt  6  extending in the longitudinal direction L at the periphery of the chassis  1  between the front portion  1   a  and the central portion  1   b . Each lateral crossmember  14  is fastened to a longitudinal member  3  at the height of the second end  32  by spot welds  11 . 
     The lateral crossmembers  14  extend between the longitudinal member  3  and the skirt  6  in an oblique direction such that the portion of the lateral crossmember  14  coupled to the skirt  6  is to the rear with respect to the portion of the lateral crossmember coupled to the longitudinal member  3 . The angle thus formed between the longitudinal member  3  and the lateral crossmember is an obtuse angle. 
     There is thus obtained a longitudinal member  3  coupled to a front crossmember  4  having two elements for transmitting force, namely the bracket  12  and the lateral crossmember  14 , along two vanishing lines leading away from the longitudinal member and oriented toward the rear of the chassis  1 . 
     The front portion  1   a  of the chassis  1  thus comprises means for absorbing a frontal impact comprising a front bumper  2 , longitudinal members  3  coupled, on the one hand, to a crossmember  4  with brackets  12 , and coupled, on the other hand, to lateral crossmembers  14  coupled to skirts  6 . 
     The energy due to a frontal impact on the front bumper  2  is thus transmitted to the rear portion  1   c  of the chassis  1 , on the one hand, via the central transmission tunnel  5  passing over the central floor  7  and mounted on the front crossmember  4 , and, on the other hand, via the skirts  6  extending on each side of the chassis  1 . 
     Such means for absorbing a frontal impact thus make it possible to keep the zone below the central floor  7  entirely free for the storage of batteries, and thus to increase the possible autonomy, for example, of an electric-traction motor vehicle given the available volume below the central floor  7 .