Abstract:
The invention relates to a vehicle, notably a motor vehicle, chassis frame side rail made up of two section pieces of U-shaped cross section, welded together by longitudinal connecting tabs juxtaposed contiguously and more or less perpendicularly extending the ends of the branches of the U, in which each section piece has, between each of the tabs and the branches of the U that it extends, a joining area that forms two separate longitudinal plastic hinges that deform if the side rail is deformed by longitudinal compression so as to keep the welded joint between the tabs intact.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is the U.S. national stage under 35 U.S.C. §371 of International Application No. PCT/FR2011/052739, which was filed on Nov. 23, 2011 and which claims the priority of application FR 1060454 filed on Dec. 14, 2010 the content of which (text, drawings and claims) is incorporated here by reference in its entirety. 
     FIELD 
     The present invention relates to the structure of a motor vehicle. More specifically, it relates to the vehicle chassis frame, the side rails of which are deformed when the vehicle is exposed to a frontal impact. 
     BACKGROUND 
     When a motor vehicle is exposed to a strong frontal impact, the front end portions of the side rails extending in the longitudinal direction of the vehicle are indeed deformed. In order to dissipate a large portion of the energy of the impact, it is preferable that this deformation occurs in the form of a longitudinal compression, or bunching, of the side rails, in which successive accordion folds form in planes perpendicular to the longitudinal direction of the side rails. 
     However, during the impact, a side rail commonly folds moving away from its longitudinal axis, a fold forming a vertical rotation axis between two portions of the side rail. In this case, the deformation absorbs a much smaller quantity of energy from the impact. The protection of the remainder of the vehicle, and particularly of the compartment in which the passengers are, is then decreased. 
     In order to stabilize the bunching of the side rails in the case of an impact, the shape and the size of these side rails are generally selected to confer a large amount of inertia to them, and to increase their transverse stiffness. However, these side rails with reinforced inertia in general have a greater weight and they take up more space than unreinforced side rails. The reinforcement thus generates an increase in the production cost of the chassis frames, an increase in the weight of the vehicle resulting in an increase in its fuel consumption, and a greater size making it more difficult to install the different components of the vehicle around the chassis frame. 
     Moreover, when the side rails are not sufficiently stiff transversely and risk undergoing deformation due to rotation around a folding line, these side rails are not sufficient to dissipate the energy of a frontal impact, which makes it necessary to consolidate the passenger compartment of the vehicle. The weight of the vehicle, and thus its fuel consumption, are then increased, as is its manufacturing cost. 
     SUMMARY 
     The present invention provides a remedy these disadvantages of the prior art. 
     In particular, the present invention provides a vehicle chassis frame, in particular for a motor vehicle, which allows considerable dissipation of the energy during a frontal impact of the vehicle. 
     Particularly, the invention provides a chassis frame which has a relatively small weight and space requirement in the vehicle, and which is inexpensive to manufacture. 
     These advantages, as well as others that will become more evident below, are achieved using a vehicle chassis frame side rail, in particular for a motor vehicle, consisting of two section pieces with U-shaped cross section, which are attached by welding longitudinal connecting tabs which are juxtaposed contiguously and which extend the branches of the U substantially perpendicularly, in which each section piece has, between each one of the longitudinal connecting tabs and the branches of the U that it extends, a joining area forming two separate longitudinal plastic hinges that undergo deformation when the side rail is deformed by a longitudinal compression, so as to keep the attachment by welding of the longitudinal connecting tabs intact. 
     Advantageously, each joining area consists of a curve having a radius greater than or equal to 12 mm, between the section piece portion forming the branch of the U and the longitudinal connection tab which extends it. 
     Advantageously, in various embodiments, the curve has a radius between 15 mm and 19 mm. 
     According to another possible embodiment, each joining area consists of a bevel between the section piece portion forming the branch of the U and the longitudinal connecting tab that extends it, the angle formed by the section piece portion forming the branch of the U and the bevel constituting one of the plastic hinges, and the angle formed between the bevel and the longitudinal connecting tab constituting the other plastic hinge. 
     Advantageously, in various embodiments, the side rail includes a plate attached to its end intended to be at the front of the vehicle, the two end edges of each tab of the same section piece being deformed in opposite directions with respect to each other at their attachment to the plate, in order to promote a deformation of the side rail by forming accordion folds in opposite directions at the two tabs, in the case of deformation by longitudinal compression. 
     Advantageously, in various embodiments, the attachment by welding of the tabs consists of a succession of welding points. 
     The invention also relates to a vehicle chassis frame, particularly for a motor vehicle, which includes two side rails, each one being as described above and extending longitudinally toward the front. 
     The invention also relates to a motor vehicle including such a chassis frame. 
    
    
     
       DRAWINGS 
       Other characteristics and advantages of the invention will become clearer when reading the following description of various illustrative and non-limiting embodiments. 
         FIG. 1  is a perspective view of a side rail according to various embodiments of the invention. 
         FIG. 2  is a perspective view of the side rail of  FIG. 1  after a frontal impact of the vehicle, in accordance with various embodiments of the invention. 
         FIG. 3  is a cross section of the side rail of  FIG. 1 , in accordance with various embodiment of the invention. 
         FIG. 4  is a diagrammatic cross section of the side rail of  FIG. 1 , before and after a frontal impact of the vehicle, in accordance with various embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     At the time of a frontal impact of a motor vehicle, it is particularly important that the side rails forming the front of the chassis frame, which are stressed by a longitudinal compression, undergo symmetrical mode deformation, so that they are longitudinally crushed in an accordion like pattern, without moving away from their longitudinal axis. Such a deformation indeed makes possible an effective absorption of the energy of the impact. 
     To achieve this symmetrical mode deformation, it is generally necessary that the structure of the side rail is not torn by the deformation. For example, it is necessary for this deformation to occur without resulting in a rupture of the welds between the elements of the side rail. 
       FIG. 1  represents a side rail  1  forming the front of the chassis frame of a vehicle and ending with a plate  2 . As shown in the cross section of  FIG. 3 , the side rail  1  is formed by two U-shaped section pieces,  11  and  12 , respectively, assembled to each other by the welding points  31  formed between the upper longitudinal connecting tabs,  111  and  121 , respectively, of the section pieces  11  and  12 , and the welding points  32  formed between the lower longitudinal connecting tabs,  112  and  122 , respectively, of the section pieces  11  and  12 . The longitudinal connecting tabs  111 ,  121 ,  112  and  122  are juxtaposed contiguously to allow this welding to take place. On each section piece  11  and  12 , these longitudinal connecting tabs  111 ,  121 ,  112  and  122  extend the ends of the branches  130 ,  132 ,  134  and  136  of the U formed by the respective section piece  11  and  12  substantially perpendicularly. 
     As  FIG. 3  shows, the U-shaped portions of each one of the section pieces  11  and  12  forming the side rail  1  are connected to the longitudinal connecting tabs  111 ,  112 ,  121  and  122 , making possible the welding of the two section pieces  11  and  12 , by the joining areas  113 ,  114 ,  123  and  124  consisting of curves having a large radius. 
     This radius of the curves of the joining area  113 ,  114 ,  123  and  124  are greater than or equal to 12 mm and can be on the order of 17 mm (±2 mm), thereby making it possible for the joining areas  113 ,  114 ,  123 , and  124  to behave, during a deformation of the side rail  1 , like an assembly of two plastic longitudinal hinges rather than a single hinge. The term “plastic hinge” denotes a folding line on which a plastic, and hence irreversible, deformation of the material occurs. 
       FIG. 4  represents in a solid line drawing a simplified modeling of this cross section. As one can see in  FIG. 4 , the curves between the portions of the section pieces  11  and  12  that form bases  126  and  128  of the U shapes and the portions forming the branches  130 ,  132 ,  134  and  136  of the U shapes can each be modeled as a single hinge represented diagrammatically by angles  138 ,  140 ,  142  and  144 . These curves indeed have a small radius, on the order of 6 mm. 
     On the other hand, the curves of the joining areas  113 ,  114 ,  123  and  124  having a large radius between the section piece portions forming the branches  130 ,  132 ,  134  and  136  of the U shapes and the longitudinal connecting tabs  111 ,  112 ,  121  and  122  are each modeled by two hinges, that is to say by two angles  146 ,  148 ,  150  and  152  separated by a metal sheet portion, also referred to as bevel portions  113 ,′  114 ′,  123 ′ and  124 ′. Indeed, the large radius of these curves makes possible the appearance in each one of two separate and parallel folding lines. 
     The presence of the two plastic hinges of each one of the joining areas  113  and  123  makes it possible, during the deformation of the side rail  1 , to prevent the upper longitudinal connecting tabs,  111  and  121 , respectively, from being moved apart from each other exerting traction on the welding points  31  that assemble them. Similarly, the presence of two plastic hinges of each one of the joining areas  114  and  124  makes it possible, during the deformation of the side rail  1 , to prevent the lower longitudinal connecting tabs,  112  and  122 , respectively, from being moved apart from each other exerting traction on the welding points  32  that assemble them. 
     When the vehicle is exposed to a frontal impact, the side rail  1  is crushed as shown in  FIG. 2 . During this crushing, the cross section of the chassis frame changes from the cross section represented diagrammatically using a continuous line to the cross section represented diagrammatically with a dotted line in  FIG. 4 . 
     During the impact, the plastic hinges of the joining areas  113 ,  114 ,  123  and  124  enable a deformation of the side rail  1 , having the effect of maintaining the longitudinal connecting tabs  111 ,  112 ,  121  and  122  one against the other, without exerting traction on the welding points  31  and  32  that connect them. The welding points  31  and  32  are thus kept intact, which prevents an asymmetric deformation of the side rail  1 . 
     In the various embodiments represented, the joining areas  113 ,  114 ,  123  and  124  between the U-shaped portion of the section pieces  11  and  12  and the longitudinal connecting tabs  111 ,  112 ,  121  and  122  are produced by a curve of large radius. According to other possible embodiments of the invention, it would be possible to replace these curves of large radius of the joining areas  113 ,  114 ,  123  and  124  by the bevel-shaped connecting areas  113 ,′  114 ′,  123 ′ and  124 ′ (shown in  FIG. 4 ) having two angles, i.e., angles  146 ,  148 ,  150  and/or  152 , each forming a plastic hinge, or by longitudinal weakened areas of the metal sheet of the section pieces  11  and  12 , each forming a plastic hinge. 
     For the side rail  1  to be deformed in an accordion like pattern in longitudinal compression, it is important that, on a given cross section, the upper and lower longitudinal connecting tabs  111 ,  112 ,  121  and  122  are deformed by moving in different directions, some to the right and some to the left (shown in  FIG. 2 ). Thus, in the representations drawn with dotted lines of the cross section of  FIG. 4 , the upper longitudinal connecting tabs  111  and  121  are moved to the left, identified in  FIG. 4  as  111 ′ and  121 ′, when the lower longitudinal connecting tabs  112  and  122  move to the right, identified in  FIG. 4  as  112 ′ and  122 ′. 
     To start this deformation and thus ensure a correct longitudinal compression of the side rail  1 , the upper and lower longitudinal connecting tabs  111 ,  112 ,  121  and  122 , respectively, are inclined to the right and to the left, respectively, over the last centimeters at the front of the sidepiece. Thus, in  FIG. 1 , it is possible to see that the upper longitudinal connecting tabs  111  and  121  are inclined slightly to the right at the weld  41  of the end of these tabs to the plate  2 . Similarly, the lower longitudinal connecting tabs  112  and  122  are inclined slightly to the left at the weld  42  of the end of these tabs to the plate  2 .