Abstract:
We improve still further the crashworthiness of a tubular-frame chassis by providing a means for absorbing lower-energy impacts without deforming the tubular steel frame, The vehicle comprises a chassis structure including a load-bearing tubular chassis member extending longitudinally within the vehicle, at least one crush structure located laterally outside of the chassis member, the crush structure having an upper and a lower extent that overlap with an upper and lower extent of the chassis member. In this way, the crush structure is able to interact with the chassis member, transferring impact forces to the chassis member and thereby reducing the necessary size (and weight) of the crush structure. The crush structure is preferably removable, to allow replacement after an impact. Alternatively, the crush structure part of a door of the vehicle, positioned as necessary when the door is closed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a vehicle, and to its chassis. 
       BACKGROUND ART 
       [0002]    Our earlier patent applications WO2009/122178, WO 2010/149981 and WO2012/010850 described chassis structures suitable for a compact and lightweight city car. These employ a tubular steel frame to which planar composite sheets are bonded, the combination resulting in a high level of rigidity and crashworthiness. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention seeks to build on and improve further the crashworthiness of the chassis shown in WO2009/122178 et al by providing a means for absorbing lower-energy impacts without deforming the tubular steel frame. Such damage requires significant remedial work in order to return the vehicle to its pre-impact state and repair may therefore be uneconomical. One option is of course to add an outer impact-absorbing structure such as is disclosed in US2013/0088045A1 in which a sill structure is bolted to the chassis members in order to absorb smaller collisions. However, this is an inefficient solution which imposes a significant weight penalty, as a sill that is able to absorb anything other than a trivial collision will be a substantial item, as illustrated in US2013/0088045A1. 
         [0004]    The present invention therefore provides a vehicle, comprising a chassis structure including a load-bearing tubular chassis member extending longitudinally within the vehicle, at least one crush structure located laterally outside of the chassis member, the crush structure having an upper and a lower extent that overlap with an upper and lower extent of the chassis member. In this way, the crush structure is able to interact with the chassis member, transferring impact forces to the chassis member and thereby reducing the necessary size (and weight) of the crush structure. 
         [0005]    The crush structure is preferably held in position relative to the chassis member in a removable manner. This means that after an impact in which there is no damage to the chassis member, the crush structure can be removed and replaced easily. Ideally, the crush structure is held in position relative to the chassis member by at least one detachable fixing, such as a bolt, a rivet, an adhesive, or a spot weld. Alternatively, the crush structure can be held in position relative to the chassis member by a hinged attachment to the chassis structure, such as by providing the crush structure as part of a door of the vehicle. The door, when closed, can locate the crush structure in the correct placement relative to the chassis member. After an impact, the door can be replaced. In such an arrangement, the crush structure can be located in a lower sill of the door. 
         [0006]    The crush structure can comprise a hollow section enclosing an energy-absorbing element, such as a foam. The crush structure can contain one or more internal dividing walls, and the energy-absorbing element (where present) can be located on one side of the internal dividing wall. In that case, the wall can contain an aperture through which the energy-absorbing element can be forced, thereby to assist in absorbing an impact. 
         [0007]    The chassis structure may further comprise cross-members extending between the longitudinal chassis members, and planar sheets bonded to the chassis structure. The planar sheets can be of a composite material. The chassis members and/or the cross-members may be of a circular section tube, or a square section tube, or another cross-section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which; 
           [0009]      FIG. 1  shows a chassis structure according to WO2009/122178; 
           [0010]      FIG. 2  shows a section through a chassis structure according to WO2009/122178 and WO2012/010850; 
           [0011]      FIG. 3  shows the structural concept of the invention; 
           [0012]      FIG. 4  shows a first embodiment of the invention; 
           [0013]      FIG. 5  shows a second embodiment of the invention; 
           [0014]      FIG. 6  shows a third embodiment of the invention; 
           [0015]      FIG. 7  shows a fourth embodiment of the invention; 
           [0016]      FIG. 8  shows a fifth embodiment of the invention; 
           [0017]      FIG. 9  shows a sixth embodiment of the invention; 
           [0018]      FIG. 10  shows a seventh embodiment of the invention; and 
           [0019]      FIG. 11  shows an eighth embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0020]    Referring to  FIG. 1 , this shows a chassis structure as disclosed in WO2009/122178 et seq. The present invention is applicable to this style of chassis, and also to other forms of chassis that include at least one longitudinal section of a circular, square, rectangular or other cross-section. The chassis  10  of  FIG. 1 , by way of example, employs two pairs of longitudinal circular-section tubes which run from the front of the vehicle towards the rear, and are arranged as a left upper tube  12 , a left lower tube  14 , a right upper tube  16  and a right lower tube  18 . The tubes on each side of the vehicle are arranged generally above and below each other, with generally upright sectional elements  20  connecting them. In addition, several cross-members such as that indicated at  22  run between corresponding tubes on either side in order to complete the framework. In this example, the upright sectional elements are circular-section and the cross-members are square section, but either of these could be adapted to use other cross-sections as required. 
         [0021]    A front basket  24  is provided, attached to frontal sections of the longitudinal sections  12 ,  14 ,  16 ,  18  in order to provide a mounting location for steering, and braking systems. A hoop  26  is provided in order to allow for roll-over protection. 
         [0022]    The framework structure of this example is provided with composite panels  28  that are bonded to the framework. These provide bracing to the framework, distributing loads across the chassis. The result is a light and rigid chassis that requires very much less material than a conventional pressed-steel chassis. The present invention is particularly beneficial when applied to a chassis of this type, but can also be applied to other chassis structures. 
         [0023]      FIG. 2  shows a vertical section through a variant of the above-described chassis, as described in our earlier applications WO2009/122178 and WO2012/010850. The right-hand longitudinal tubes  16 ,  18  can be seen, together with their circular section. Composite panels are attached to the tubes, including a lower panel  28   a  that extends horizontally from the lower right tube  18 , and upper panel  28   b  that extends horizontally from the upper right tube  16 , and a side panel  28   c  that extends vertically between the upper right tube  16  and the lower right tube  18 . The lower and upper panels include a directional fibre reinforcement  30   a,    30   b  (respectively) to assist in load distribution via the panels. The lower panel  28   a  carries a battery  32  for powering an electric motor in the vehicle, and is attached to the lower tube  18  via a detachable fixing  34  so that the battery  32  can be removed easily for recharging or replacement. 
         [0024]      FIG. 3  shows a view of the underside of a vehicle according to the present invention. The lower longitudinal tubes  14 ,  18  can be seen, together with the lower panel  28   a,  its reinforcement  30   a  (shown schematically) and the fixings  34 . Rear wheels  35  are attached to the chassis via independent rear suspension (see WO2010/100412) and are driven by a rear-mounted engine  36 . Front wheels  38  are each attached to the chassis via a front suspension  40 . 
         [0025]    In order to protect the longitudinal tubes  12 ,  14 ,  16 ,  18  (especially) against a side impact, the present invention proposes the provision of crush structures  42  covering at least part of the region between the front wheels  38  and the rear wheels  34 , located laterally outside the longitudinal tubes  12 ,  14 ,  16 ,  18 . Whilst the chassis is sufficiently strong to withstand such impacts and comply with the applicable crash standards, this can involve damage to the longitudinal tubes which will be a major task to repair. Thus, if this could be avoided, at least for some levels of impact, the vehicle would be more easily repairable. However, the crush structures  42  must not negate the design aims of the chassis as a whole, i.e. that of light weight with rigidity, and must therefore not be so massive as to impose an excessive weight penalty on the vehicle. This results in a crush structure that is able to absorb only very minor impacts, with a significant impact still resulting in deformation of the longitudinal tubes. 
         [0026]    According to the present invention, the crush structure is designed to work in conjunction with the remainder of the chassis, so that some of the impact is absorbed by the crush structure and some is dissipated into the chassis. This will expand the range of impacts in which the chassis tubes are not deformed and make the small additional weight of the crush structures worthwhile.  FIG. 4  shows the concept by which this is achieved. The chassis  10  carries a side crush structure  44  which is mounted to the upper longitudinal bar  12  and comprises a trapezoidal-section hollow body  46  filled with a crushable foam material  48  such as a closed rigid cell structural foam. The section  46  is mounted level with the longitudinal bar  12  and is supplemented with a bracing panel  50  that extends from an outer edge of the trapezoidal section  46  to a connection point with the lower longitudinal bar  14 . Thus, in a side impact with a solid object  52 , the crush structure  46 ,  48  deforms to absorb some impact energy, but the fact that at least some of the structure is level with the longitudinal bar  12  means that some of the force of the impact is transmitted through the crush structure to the bar  12  and thence into the chassis  10  as a whole. The bracing  50  serves to hold the crush structure  46 ,  48  in the generally correct location during the impact, and also provides some aesthetic benefit at other times. The dimensions of the crush structure  46 ,  48  and its wall thicknesses (etc) are tailored to provide deformation properties so that it deforms slightly before the longitudinal bars  12 ,  14 , thereby limiting the forces that are transmitted to the chassis  10  as necessary. 
         [0027]    Of course, there will be a degree of side impact which is high enough to result in deformation of the chassis bars  12 ,  14 ,  16 ,  18 . Such an impact would progressively deform the crush structure  44  until it had reached a limiting deformation at which higher forces would be transmitted to the chassis  10 . Those higher forces will in some circumstances be sufficient to deform the chassis bars. However, the effect of the crush structure is to raise the threshold point at which chassis deformation takes place by an amount generally corresponding with the energy required to completely crush the crush structure  44 . Further, by designing the crush structure  44  so that at least part of it is level with a chassis bar  12 , the two can interact during an impact so that the crush structure is not called upon to absorb all or substantially all the impact energy. This allows the crush structure to be sufficiently small and light to be incorporated into a practical lightweight chassis for a small city car. 
         [0028]    There are a number of possible designs for the crush structure.  FIGS. 5 to 11  show further examples, in which like reference numerals are used to denote like parts. Thus,  FIG. 5  shows a design in which a rectangular composite moulding  54  is located level with the upper bar  12 . A trapezoidal support  56  is located beneath the moulding  54  and is filled with an energy-absorbing foam  58 . Mechanical fastenings such as bolts, rivets, adhesive and/or spot welds are used to attach the structure to the upper and lower bars  12 ,  14 ; these can be easily reversed after an impact in order to remove the original crush structure and replace it. A further foam filling  60  is used inside the chassis to fill space around the batteries  32  to prevent them from moving during an impact; as in our previous applications the batteries are enclosed within a sandwich structure bounded laterally by the chassis bars  12 ,  14 ,  16 ,  18  and vertically by the upper composite panel  28   b  which is bonded to the chassis bars, and the lower chassis panel  28   a  which is fixed mechanically to the remainder of the chassis in order to allow removal of the batteries for replacement or renewal. 
         [0029]      FIG. 6  shows an arrangement with a central composite crush member  62  which is held level with the upper chassis bar  12  (as in  FIG. 5 ) but supplemented by two triangular-section structures  64 ,  66 . The lower triangular structure  66  is attached mechanically to the upper and lower chassis bars  12 ,  14  via mechanical fixings (as before). The upper triangular structure  64  extends from the upper chassis bar  12  to enclose the crush member  62 , and connects to the outermost corner of the lower triangular structure  66  to form a smooth outer surface. The interior spaces of the two triangular structures  64 ,  66  are filled with an energy-absorbent foam  68 , which also assists in supporting the crush structure  62 . 
         [0030]      FIG. 7  shows an embodiment comprising two composite mouldings  70 ,  72 . An upper moulding  70  is located level with the upper chassis bar  12  and contains a high-density energy absorbent foam  74  within its otherwise hollow interior. A lower moulding  72  is located immediately beneath the upper moulding, sharing a dividing wall between the interior spaces of the two mouldings. Relative to the chassis, the lower moulding sits to one side of and vertically between the chassis bars  12 ,  14 . The lower moulding is fixed mechanically to the lower chassis bar  14  and the upper moulding is fixed mechanically to the upper chassis bar  12 . 
         [0031]    The otherwise-hollow interior of the lower moulding is filled with a low-density energy absorbent foam  76 . In this context, “low density foam” denotes a foam having a lower density than the “high density foam”, and vice versa. An exhaust aperture  78  is formed in the shared dividing wall between the two mouldings, so that under impact the high density foam, compressed between the impacting object and the upper chassis bar  12 , will be forced out of the upper moulding  70  and into the lower moulding  72 . That movement will be resisted but not prevented by the lower density foam. In this way, the crush resistance exhibited by the upper moulding  70  can be tailored very closely by variation of the size and shape of the aperture, and by the number and spacing of the apertures if more than one is provided. Ideally, several such apertures will be provided along the length of the section, but is may also be advantageous to provide more than one aperture or row of apertures, spaced laterally. Further tailoring of the crush resistance can be obtained by selection of the actual densities of the two foams. Thus, increasing the density of the high-density foam will increase the crush resistance for a fixed aperture size, but this can be counteracted by reducing the density of the low-density foam as it will then present less resistance to exhaust of the high-density foam via the aperture. 
         [0032]      FIG. 8  shows an alternative arrangement of sections which collectively form the crush structure. This embodiment is made up of three formed profiles bonded together to make the necessary sectional shape. An inner face  80  sits against the upper and lower chassis tubes  12 ,  14  and is, at either end, partly conformal to the chassis tubes. An outer face  82  joins to the inner face at its upper and lower extremities and extends laterally outward between those two points to define (with the inner face  80 ) a generally trapezoidal shape. An internal rib  84  extends within the trapezoid from the inner face  80  to the outer face  82  and divided the interior of the trapezoid, thus strengthening the structure. The two interior regions thus defined are both filled with impact-absorbing foams  86 ,  88 . The sections can be of a composite material, a plastics material, or a metallic material. The complete structure is then mechanically attached to the chassis tubes  12 ,  14 . 
         [0033]      FIG. 9  shows a similar arrangement to  FIG. 8 , with an inner face  90 , an outer face  92 , an internal rib  94 , and foam fillings  96 ,  98 . In this arrangement, the spatial arrangement is difference such that the outer face  92  is trapezoidal in profile, and the internal rib  94  extends from the meeting point of the inner and outer faces  90 ,  92  across the interior space of the structure to the opposing corner of the outer face  92 . Thus, the structure is divided into two triangular-section shapes, adding to the rigidity of the crush structure and assisting in tailoring its crush properties to those required. 
         [0034]      FIG. 10  shows a further arrangement, also employing an inner face  100 , an outer face  102 , an internal rib  104 , and foam fillings  106 ,  108  in the same general arrangement. The inner face  100  is however provided with two prominent channels corresponding to the chassis tubes  12 ,  14 , which fit snugly over a correspondingly-profiled section  101  attached securely to the chassis tubes  12 ,  14 . A spacing is maintained between the section  101  and the chassis tubes, to accommodate threaded fixings on the inner face of the section  101 ; corresponding holes on the inner face  100  and the overlapping outer face  102  allow bolts  103 ,  105  to be inserted through the holes and engage with the threaded fixings to hold the crush structure in place. This can be repeated at intervals along the length of the crush structure. 
         [0035]      FIG. 11  shows a different embodiment. The chassis rails  12 ,  14  are again braced by chassis panels  28   a,    28   b  and other structures as explained in relation to  FIGS. 1 and 2 . An outer profile  110  is secured to the upper chassis rail  12  via bolts  112  which are repeated at intervals, and to the lower chassis rail  14  by adhesive bonding; the outer profile  110  lies adjacent the two chassis rails but diverges laterally outward between them to define a rigid sill to the vehicle. An impact-absorbent foam  116  is provided behind the divergent portion of the profile  110 . An outer skin  118  is provided for cosmetic purposes, substantially conformal to the upper face of the sill shape so that a foot placed on the sill is supported, but shaped aesthetically elsewhere. The lower chassis panel  28   a  is bolted to the lower chassis bar  14  at intervals via bolts  114  and also extends slightly beyond the chassis rail  14  to provide an anchor point for the outer skin  118 . 
         [0036]    This structure then presents a rigid outer surface at the level of the upper chassis rail  12 . This is filled by a door structure  120  comprising an inner skin  122  and an out skin  124  whose profiles are chosen so as to provide the desired aesthetic effect and to define an internal space for various structures such as a lock mechanism, window winders and the like. At the lower extremity of this internal space, there is a crush structure  126  that is held by the closed door structure just above the sill and substantially level with the upper chassis bar  12 . The crush structure is defined by inner and outer faces  128 ,  130 ; the outer face  130  is largely flat albeit with a slight curve to match the shape of the outer door skin  124  whereas the inner face  128  is trapezoidal with flanged edges to allow attachment to the outer face  130 . The internal space thus defined is filled with an impact-absorbing foam. As above, the various sections can be of a composite material, a plastics material, or a metallic material as desired. 
         [0037]    Block  132  represents standard typical Euro-NCAP or federal side impact test piece and thus, in a standard impact of these types will strike the door over the crush structure  126 . Initially, the door skin will be deformed, followed immediately by the crush structure  126  which will be compressed between the standard impacter type block  132  and the upper chassis rail  12 . Impact forces will thus be transmitted to the chassis as described above, without deforming the chassis. After an impact, the damaged door  120  can be replaced with a new door, thus replacing the crush structure  126  as well. 
         [0038]    The various embodiments all illustrate variations on the basic theme of the invention, and the variants in each specific embodiment can, if desired, be applied to the other embodiments. 
         [0039]    It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention.