Abstract:
A hood  7  is provided for an engine compartment of a motor vehicle including an outer skin  16  and reinforcing ribs  12  connected with the outer skin and imparting rigidity thereto. The ribs  12  have a channel portion  16  mainly formed in an equilateral hexagonal pattern.

Description:
BACKGROUND OF INVENTION  
       Field of the Invention  
         [0001]    The field of the present invention is engine compartment hoods for automotive vehicles. As used herein, the term engine compartment hood refers to the front hood of an automotive vehicle whether or not the hood encloses a compartment wherein an engine is located.  
           [0002]    Many car/pedestrian crashes involve the pedestrian being struck by the forward portion of the vehicle. In a pedestrian vehicle crash situation it is desirable that the pedestrian&#39;s contact with the hood of the vehicle be as “forgiving” as possible so as to minimize possible injury to the pedestrian. Counter to the mandate to minimize the force of impact, it is desirable to keep the deflation of the hood caused by impact to a minimum to protect the pedestrian&#39;s body from hitting a hard portion of the engine within the engine compartment.  
           [0003]    Most vehicle hoods include a generally planar or curvilinear outer skin which is joined to a series of reinforcing ribs provided by a stamped metallic sheet of material. The reinforcing ribs are joined to the outer hood along the peripheral edges of the ribs and along certain portions of the ribs between the ribs peripheral edges.  
           [0004]    Head impact criteria (sometimes referred to as head performance criterion) is measured by a spherical-like object which is impacted with the hood. The spherical like object has an accelerometer mounted therein. Head performance criterion (HPC) is calculated from the resultant of accelerometer time histories as the maximum (depending on t1 and t2) of the equation:  
       HPC   =         [       1       t   2     -     t   1                ∫     t   1       t   2            a           t           ]     2.5          (       t   2     -     t   1       )                             
 
           [0005]    where ‘a’ is the resultant acceleration as a multiple of ‘g’ and t1 and t2 are the two time instants (expressed in seconds) during the impact, defining the beginning and the end of the recording for which the value of HPC is a maximum. Values of HPC for which the time interval (t1 t2) is greater than 15 ms are ignored for the purposes of calculating the maximum value. As a rule lower HPC values are better.  
           [0006]    As mentioned previously, it is desirable that the hood be as forgiving as possible in crash situations. It is also desirable that while the hood is forgiving in crash situations, that the maximum deflection of the hood be minimized. It is further desirable that the hood has torsional rigidity.  
           [0007]    It is also desirable that the above-noted features which are all affected by the structure of the reinforcing ribs be as predictable and uniform as possible so that overall hood height can be held to a minimum to maximize the aerodynamic properties of the vehicle.  
         SUMMARY OF INVENTION  
         [0008]    To make manifest the above and other noted desires, a revelation of the present invention is brought forth. In a preferred embodiment the present invention provides an engine compartment hood with an outer skin. Connected with the outer skin and imparting rigidity thereto are a series of ribs having channel portions formed in a tessellated, generally equally-sized, equilateral hexagonal pattern. The hexagonal pattern aids in providing greater uniformity in the head impact criteria (HIC) of the hood along with uniformity in deformation caused by a predetermined impact. Due to the increased uniformity in head impact criteria and deformation, the height of the hood can be held at a minimum.  
           [0009]    It will be apparent to those skilled in the art of other advantages of the present invention as the invention is further revealed in the drawings and detailed description. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0010]    [0010]FIG. 1 is a perspective view of a preferred embodiment vehicle hood according to the present invention.  
         [0011]    [0011]FIG. 2 is a schematic view taken along lines  2 - 2 - of FIG. 1, illustrating a draft angle of the channel portion of the ribs shown in FIG. 1.  
         [0012]    [0012]FIG. 3 is a schematic view illustrating a draft angle of the channel portion of the ribs of an alternate preferred embodiment hood according to the present invention.  
         [0013]    [0013]FIG. 4 is an exploded view of another alternate preferred embodiment vehicle hood according to the present invention.  
         [0014]    [0014]FIG. 5 is a bottom plan view of the reinforcing ribs utilized in the vehicle hood shown in FIG. 4.  
         [0015]    [0015]FIG. 6 is an inverted enlarged sectional view taken along lines  6 - 6  of FIG. 5.  
         [0016]    [0016]FIG. 7 is an enlargement of a portion of the reinforcing ribs utilized in the vehicle hood shown in FIG. 5.  
         [0017]    [0017]FIG. 8 is a side elevational view taken along line  8 - 8  of FIG. 5 illustrating differences in the heights of the ribs utilized in the hood of FIG. 1 in relationship to lateral distance to the centerline of the hood.  
         [0018]    [0018]FIG. 9 is an enlargement of a portion of the hood shown in FIG. 5 illustrating slots formed in the reinforcing ribs shown in FIG. 5. 
     
    
     DETAILED DESCRIPTION  
       [0019]    Referring to FIGS. 1 and 2, a vehicle hood  7  for an engine compartment of an automotive vehicle is provided. The hood includes a 1.0 mm thick aluminum outer skin  10 . In other embodiments not shown, the skin can be fabricated from steel. Connected with the outer skin  10  are a series of reinforcing ribs  12 , which are formed from 1.0 mm thick aluminum. The reinforcing ribs  12  have a cross-sectional shaped channel portion  14 . The channel portion  14  has a valley  16 . The valley  16  is joined by two side walls  18 . The side walls  18  have a draft angle  20  with the valley  16  of approximately 30°. The side walls  18  are joined to plateaus  22 .  
         [0020]    The plateaus  22  can be selectively joined with the skin  10  by welding, sealer or adhesive  24 . In many applications, the peripheral edge of the skin will be bent over to form a seam  26  which captures a peripheral boundary of the ribs  12 . The ribs  12  are shaped to form polygonal tessellated, generally equally-sized hexagonal patterns  28  having cut outs  30  and three-legged intersections  31 . The pattern  28  is generally symmetrical about a longitudinal centerline  33  of the hood.  
         [0021]    Referring to FIG. 3, a preferred embodiment hood  37  according to the present invention is provided. The hood  37  has a skin  10  similar or identical to the skin previously described for the hood  7 . The ribs  40  have a channel portion  42  having a valley  44  with extending walls  46  with plateaus  48 . Between the plateaus  48  and the skin  10  is a layer of installation material  50 . The walls  46  have a draft angle  52  which is approximately 5°.  
         [0022]    The height  54  of the walls  46  is approximately 10 cm versus the height  56  of the walls  18  (FIG. 2) which is approximately 15 mm. The difference in design is due to the fact that the ribs  40  are fabricated from steel and the ribs  12  are fabricated from aluminum.  
         [0023]    Referring to FIGS. 4-9 an alternate preferred embodiment hood  107  is provided. The hood  107  has an outer skin  108 . The hood  107  also has reinforcing ribs  112 . The ribs  112  have a tessellated generally equally sized pattern in a shape having equilateral hexagonal cut outs  114 . The ribs  112  are typically stamped from a single sheet of material. The hexagonal cut outs  114  as shown have a diameter of approximately 194 mm.  
         [0024]    Joined to the ribs  112  are hinge reinforcements  116  and hood striker, wires and reinforcements  118 . Additionally, there is provided a hood safety release reinforcement  119 . The striker is attached to the ribs  112  along location  122 . Accordingly, the striker is positioned rearward of a forward edge  117  of the ribs reinforcements in order to improve adult upper leg impact performance. As best shown in FIG. 6, the ribs  112  have a channel portion  126  having a valley  128  with projecting side walls  130  which are connected with plateaus  132 . At the peripheral edges of the sheet that forms the ribs, the partial equilateral hexagonal rib cutouts  134 ,  136 ,  138  and  140  are typically configured to have at least four sides.  
         [0025]    Alternating plateaus  132  of the ribs  112  will be joined to the skin  108  by the utilization of adhesive strips  141 . Accordingly, each rib  112  will have one plateau joined to the skin by an adhesive strip. Additionally, it has been found preferable from a performance standpoint, to provide the ribs valleys with similarly semi-oval shape punch outs  142 .  
         [0026]    Referring to FIG. 8, the hood  107  has a central portion  150  which is closely adjacent a longitudinal centerline  152 . The hood  107  also has an outer portion  154  which is adjacent a lateral perimeter of the hood. Between the central portion  150  and the outer portion  154  is a blend portion  158 . In the central portion  150  the walls have a height  160  which are approximately 12.5 mm. Along the outer portion  154 , the height of the walls  130  is approximately 10 mm. In the blend portion  158  the height of the walls  130  makes a transition from 12.5 to 10 mm. It has been found that this change of wall height yields a more homogeneous stiffness to the vehicle hood.  
         [0027]    Experience has shown that the peripheral frame should be as narrow as possible. Along the frame, the ribs  112  can be joined to the skin by either having the skin being hemmed about the ribs or by utilization of a structural adhesive.  
         [0028]    The present invention has been shown in several embodiments. However, it will be obvious to those skilled in the art of the various modifications which can be made to the present invention without departing from the spirit or scope of the invention as is defined in the accompanying claims.