Abstract:
Shock absorbing rectangular boxes ( 16, 17 ) are mounted between each one of two structural side beams ( 14, 15 ) of a vehicle and a bumper beam ( 11 ). The boxes are deep drawn from a steel sheet, and their sidewalls have deformation guides ( 35 ) so that the boxes are deformable in a controlled manner during a crash of the vehicle.

Description:
TECHNICAL FIELD 
   This invention relates to a shock absorbing deep drawn rectangular open box between a bumper beam and a vehicle body, having a bottom, side walls and a flange. 
   BACKGROUND OF THE INVENTION AND PRIOR ART 
   Nowadays, bumper beams for passenger cars are usually adapted to absorb impact energy by being deformed plastically. In small cars, the beam can be arranged to absorb enough energy. In bigger cars, energy absorbing elements need to be arranged between the side beams of the car and the bumper beam. DE-19537186-A shows such elements in the form of deep drawn rectangular boxes. U.S. Pat. No. 3,998,485-A shows circular, stepped tubes as extensions of the side beams of a car. 
   OBJECT OF THE INVENTION 
   It is an object of the invention to provide a comparatively short shock absorbing element between a bumper beam and a vehicle body, which element will have a high energy absorption and a high and comparatively even resistance force while being deformed during a crash. 
   SUMMARY OF THE INVENTION 
   This object is fulfilled in principle in that the sides of an element in the form of an open deep drawn rectangular box with a side flange at its opening has different inclination of the part of its side walls adjacent the bottom and the part of its side walls adjacent the flange so that a deformation guide is formed between the two parts of each side wall of the box. To this end, the invention has been given the characteristics stated in the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described with reference to the accompanying drawings which show a shock absorbing box as an example of the invention. 
       FIG. 1  is a transparent perspective view of the shock absorbing mounting box. 
       FIG. 2  is a view of the box shown in  FIG. 1  seen as indicated by the arrows  2 - 2  in  FIG. 3 . 
       FIG. 3  is a section through the mounting element shown in  FIGS. 1 and 2  and it is taken along the line  3 - 3  in  FIG. 2 . 
       FIG. 4  is a top plan view of a bumper beam mounted to the side beams of a vehicle by means of mounting boxes of the kind shown in the  FIGS. 1 and 2 . 
       FIGS. 5 and 6  are two sections, at right angle to each other, through a somewhat modified design of the mounting box shown in  FIGS. 3 and 4 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 4  is shown a bow-formed bumper beam of formed sheet steel. It has two flat mounting areas  12 , 13  adjacent the structural side beams  14 , 15  of the vehicle. Between the side beams  14 , 15  and the areas  12 , 13 , there are two mounting elements  16 , 17  by the intermediate of which the bumper beam is mounted to the side beams. Such a mounting element is shown in the  FIGS. 1-3 . It comprises a box deep drawn from one piece of sheet steel and it has a bottom  22 , four side walls  23  and a flange  24 . The bottom  22  has a central hole  25  and the mounting areas  12 , 13  of the bumper beam have corresponding holes so that the boxes can be mounted to the bumper beam by means of screw and nut fasteners. The flange  24  of the boxes has four holes  28 - 31  and the ends of the side beams have flanges or plates  32 , 33  with corresponding holes so that the boxes  16 , 17  can be fastened to the side beams  14 , 15  by screw and nut fasteners. Suitably, the boxes can be deep drawn from high carbon cold forming steel so that they do not need to be hardened after the forming Such a hardening process could not be carried out without a fixture and would therefore be an expensive operation. 
   The boxes  16 , 17  are rectangular with rounded corners and they taper off slightly towards their bottoms. All four side walls  23  comprise a part  37  adjacent the bottom and a part  36  adjacent the flange and the two parts  36 , 37  have different inclination relative to the centerline of the box so that they form an obtuse angle in the line  35  in which they meet and the walls are thus concave. This line  35  between the two wall parts  36 , 37  form a guide for bending when the box is subjected to a load as will be described. The side wall part  36  adjacent the flange should preferably be shorter than the side wall part  37  adjacent the bottom and it could advantageously be less than ⅓ of the entire wall. The side wall parts  36 , 37  are preferably flat or substantially flat as shown. 
   At a car crash, the bumper beam  11  should be deformed first and then its mounting elements, that is, the boxes  16 , 17 . Then, if the load is heavy, the load should be taken up by the side-beams  14 , 15 . The lines  35  form guides for bending and the side walls  23  bend in these lines so that the parts  36  rotate inwards and upwards in  FIG. 3  until they stop against the end plates of the side beams  14 , 15 . The parts  37  of the side walls will then have a slight S-form and they are inclined inwards. The corners of the upper part  36  have folded in more than one fold. Then, the initial bend in line  35  will roll inwards toward the centre of the box and the corners will continue to fold in several folds. This pattern of movement is efficient as to the energy absorption because a great part of the material will be plastically deformed and thereby take up energy. The resistance force will have no spikes and will be comparatively constant during the entire deformation and it will not have a spike at the end of the elastic deformation before the plastic deformation starts. A curve of the resistance force related to the deformation will thus be comparatively flat which is desirable but difficult to achieve when the distance available for deformation is small. 
   In a box without the guides for bending  35 , the resistance force before the plastic deformation would be much higher, but the total energy take-up much lower. 
     FIGS. 5 and 6  show a modified box. Two opposite side walls  23  are concave as can be seen in  FIG. 5  but the other two side walls  26  are convex as can be seen in  FIG. 6 . This modified design provides for a still better total energy take-up, probably because a more efficient folding of the corners.