Abstract:
A hollow body of plastics material for placing around a motor vehicle steering column, the body including two half-bodies ( 2, 4 ) assembled to each other by tabs ( 22 ) and snap-fastener elements ( 24 ), each tab ( 22 ) including a portion in relief ( 28 ) provided with a first catch bearing surface. The snap-fastener elements ( 24 ) include a housing for each tab, the housing presenting at least one constriction, the portions in relief ( 28 ) being retained in the housings by the constrictions, the bearing surfaces of the tabs coming into contact with the complementary bearing surfaces of the constrictions on planes inclined at an angle (α) selected to enable the portions in relief ( 28 ) to go past the constrictions by elastic deformation when the two half-bodies ( 2, 4 ) are pulled apart from each other with a predetermined force.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates in general to pieces of trim molded out of plastics material for use in motor vehicles. 
     More precisely, the invention relates to a hollow body of plastics material for placing around a motor vehicle steering column, the body comprising two half-bodies and assembly means for assembling the half-bodies to each other in a longitudinal direction, the assembly means comprising a plurality of longitudinal tabs each secured to one of the half-bodies, and snap-fastener means for fastening each tab to the other half-body, each half-body comprising a concave shell with its concave side facing towards the other half-body, said shell presenting an inside face, each tab comprising a longitudinal arm presenting one end secured to the corresponding half-body and a portion in relief projecting along a portion of the arm that is remote from the half-body, said portion in relief including a first catch bearing surface. 
     Document EP-1 391 351 describes such a hollow body comprising two half-bodies assembled together by tabs secured to one of the half-bodies, and having portions in relief that engage in windows formed in the shell of the other half-body. 
     Such hollow bodies need to be manufactured with manufacturing tolerances that are very small so as to guarantee that the portions in relief of the tabs snap properly into the windows. The slightest deformation of the shell in which the windows are formed can lead to the tabs engaging poorly, and thus to the two half-bodies being poorly fastened to each other. Furthermore, the existence of windows formed in the hollow body gives it an appearance that is not very agreeable. 
     In this context, the invention seeks to propose a hollow body in which the assembly means are less sensitive to manufacturing tolerances, and that presents a better appearance, while also enabling the two half-bodies to be separated easily. 
     SUMMARY OF THE INVENTION 
     To this end, the invention provides a hollow body of the above-specified type, characterized in that the snap-fastener means comprise, for each tab, a housing formed on the inside face of the corresponding half-body, the housing presenting an opening and being defined by at least two facing parallel longitudinal walls at a predetermined spacing, comprising a first wall forming a rear bearing surface for the tab and a second wall including at least one constriction locally narrowing the spacing between the two walls, the constriction having a second bearing surface, the tabs being suitable for being inserted longitudinally into the housings via their respective openings, the portions in relief being suitable for going past the constrictions in the longitudinal insertion direction of the tabs by elastic deformation of the tabs and/or of said second walls, the portions in relief being held in the opposite direction by the constrictions by virtue of the respective bearing surfaces of the tabs coming into contact with the complementary bearing surfaces of the constrictions on planes that are inclined at a predetermined angle relative to the longitudinal direction, said angle being selected to make the portions in relief suitable for going past the constrictions by elastic deformation in the opposite direction when the two half-bodies are moved apart from each other by means of a predetermined longitudinal force. 
     The hollow body may also present one or more of the following characteristics considered individually or in any technically feasible combination:
         the walls are ribs formed on the inside face of the half-body;   the walls lie in planes substantially perpendicular to the inside face of the half-body on which they are formed;   each portion in relief is formed on a face of the corresponding tab that is substantially perpendicular to the inside face of the half-body carrying said tab;   the angles of inclination of the contact planes lie in the range 50° to 70°;   at least one housing presents a closure web on a side remote from the inside face of the half-body, the closure web interconnecting the two walls;   the tabs and the housings are integrally molded with the half-bodies;   the tabs are hollow;   the arms of the tabs comprise two spaced-apart facing plane portions together with partitions interconnecting the two walls; and   said portions are perpendicular to the zone of the inside face of the half-body that carries the tab.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention appear from the following description made by way of non-limiting indication and with reference to the accompanying figures, in which: 
         FIG. 1  is an exploded perspective view of the hollow body of the invention; 
         FIG. 2  is an enlarged view of a detail of  FIG. 1 , showing a tab-receiving housing; 
         FIG. 3  is a side view of the  FIG. 1  housing, a tab being engaged in the housing; and 
         FIG. 4  is a view similar to  FIG. 2 , for a variant embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The hollow body  1  shown in  FIG. 1  is a body molded out of plastics material, for placing around a steering column of a motor vehicle (not shown). 
     The body  1  comprises top and bottom half-bodies  2  and  4 , and assembly means  6  for assembling the half-bodies one to the other in a longitudinal direction represented by arrow F in  FIG. 1 . Each of the top and bottom half-bodies  2  and  4  forms a concave shell with its concave side facing towards the other half-body and presenting a free edge  8 , with the top and bottom half-bodies  2  and  4  coming into contact with each other along their respective free edges  8 . 
     The steering column can pass through the hollow body  1  along an axis X that is perpendicular to the longitudinal direction. 
     Each half-body  2 ,  4  comprises a portion  10  in the form of a rectangular parallelepiped with a U-shaped rectangular section in a plane perpendicular to the axis X, and extended axially by an enlarged portion  12 . The free edges  8  of the parallelepipedal portion  10  are straight lines, parallel to the axis X and they lie in a first contact plane perpendicular to the longitudinal direction. The portion  10  is open at both of its axial ends. 
     Opposite from the portion  10 , the enlarged portion  12  presents a plane face  14  that is substantially perpendicular to the axis X, and two noses  16  on respective sides of the face  14 , uniting the face  14  with an axial end of the portion  10 . 
     The face  14  is solid and, in a transverse direction Y perpendicular to the axis X and to the longitudinal direction, it presents a width that is substantially equal to the width of the portion  10 . The noses  16  project transversely relative to the portion  10  and to the face  14 . The face  14  has a semicircular central opening  18  formed in the free edge  8 . This opening  18  is centered on the axis X. 
     Each nose  16  has a semicircular side opening  20  formed in the free edge  8 . The side openings  20  are disposed in the sides of the noses  16  that are opposite from the portion  10 . Each of these openings presents a central axis lying in a plane defined by the axis X and the direction Y, and they are symmetrical to each other about the axis X. 
     The free edge  8  of the enlarged portion  11  lies in a second contact plane perpendicular to the longitudinal direction, that is offset upwards in  FIG. 1  from the first contact plane. 
     The two central openings  18  of the top and bottom half-bodies  2  and  4  together form a circular opening centered on the axis X and suitable for receiving the steering column. Similarly, the side openings  20  of the top and bottom half-bodies  2  and  4  together form two circular openings suitable for receiving other components of the steering column of the motor vehicle. 
     The steering column is suitable for passing through the hollow body  1  so as to engage through the circular orifice formed by the openings  18 , passing through the enlarged portion  12  and then through the portion  10  along its central axis, and leaving the hollow body  1  via the open axial end of the portion  10  opposite from the enlarged portion  12 . 
     The free edges  8  of the portion  10  of the bottom half-body  4  are shaped to form grooves parallel to the axis X and they are suitable for receiving the free edges  8  of the portion  10  of the top half-body  2 . 
     The assembly means  6  for assembling the two half-bodies to each other comprise six longitudinal tabs  22  secured to the top half-body  2 , and six housings  24  formed on an inside face of the bottom half-body  4 , co-operating with the tabs  22  to form snap-fastener means. 
     The tabs  22  and the housings  24  are formed in the enlarged portion  12  of the hollow body  1 . 
     The tabs  22  project longitudinally towards the bottom half-body  4  relative to the second contact face between the two half-bodies. Each tab  22  comprises a longitudinal rectilinear arm  26  presenting one end secured to the top half-body  2  and a portion in relief  28  projecting from a portion of the arm that is remote from the half-body  2 . 
     Each arm  26  comprises two plane walls  30  that are parallel to each other and spaced apart, with partitions  32  interconnecting the two walls  30  at regular intervals. The two walls  30  are perpendicular to the zone of the inside face of the half-body  2  to which the tab is secured. 
     As shown in  FIG. 3 , the walls  30  at the free end of the tab  22  form a head  34  of triangular section in a plane perpendicular to the walls  30 . For this purpose, one of the walls  30  forms a first face  36  going away from the other wall  30  that is extended by a second face  38  that converges towards the other wall  30  and that meets it so as to form a pointed end for the tab  22 . The faces  36  and  38  together define the portion in relief  28 . As shown in  FIG. 3 , the head  34  is hollow, such that the portion in relief  28  is capable of deforming. 
     The faces  36  and  38  form respective angles α and β relative to the opposite wall  30 . The angle α is greater than the angle β. Between them, the faces  36  and  38  form an angle of substantially 90°. 
     The angle α typically lies in the range 50° to 70°, and is preferably selected to be substantially equal to 60°. 
     The angle β typically lies in the range 20° to 40°, and is preferably selected to be substantially equal to 30°. 
     Each housing  24  comprises two substantially parallel facing walls  42 ,  43  formed by ribs provided on the inside face of the bottom half-body  4  and extending substantially perpendicularly to the zone of the inside face carrying said walls. Each of these walls extends in a generally longitudinal direction from the free edge  8 . Between them, the walls define at the free edge  8  an opening  40  for inserting the corresponding tab  22  into the housing  24 . The wall  42  comprises, in succession going away from the free edge  8 , a first longitudinal flat  44  extended by a second flat  46  sloping towards the wall  43 , itself extended by a third longitudinal flat  48  that is closer to the wall  43  than is the first flat  44 . 
     At the free edge  8 , the wall  43  comprises a first longitudinal flat  50  placed facing the flats  44  and  46  of the wall  42 . The wall  43  also has a convex central wedge  52  forming a constriction that locally narrows the spacing between the walls  42  and  43 . Finally, the wall  43  has a third longitudinal straight flat  54  in the same plane as the first flat  50 . 
     The constriction  52  is defined by two free faces  53  and  53 ′ respectively facing towards the opening  40  and away from the opening  40 , and meeting at a tip at the narrowest point of the constriction  52 . Relative to the longitudinal direction, the faces  53 ′ and  53  form angles α and β that are respectively equal to the angles formed by the faces  36  and  38  of the portion in relief  28 . 
     The flats  48  and  50 / 54  present a predetermined mutual spacing that is greater than the maximum thickness of the tab  22  between the tip of the portion in relief  28  and the wall  30  opposite from the portion in relief. 
     In contrast, the spacing between the flat  48  and the tip of the constriction  52  is less than said maximum thickness of the tab  22  so as to hold the tab  22  in the housing  24  once the tab  22  has snap-fastened. 
     The six tabs  22  are distributed along the free edge  8  of the enlarged portion  12  of the top half-body  2 . A tab  22  is situated between each of the side openings  20  and the central opening  18 . 
     The tabs  22  and the housings  24  are molded integrally with the half-bodies  2  and  4 . 
     While the tabs  22  are being inserted into the housings  24 , the pointed portion of each head  34  begins by penetrating into an opening  40 . This is made easier by the fact that the first flat  44  is spaced apart from the wall  43 . 
     Thereafter, the face  38  of the head  34  comes into contact with the face  53  of the constriction  52  that faces towards the opening  40 . The face  38  slides over the constriction  52  and brings the wall  30  opposite from the portion in relief  28  against the flat  48  of the wall  42 . 
     As the longitudinal movement of the tab  22  continues, the portion in relief  28  is deformed elastically, such that the portion in relief  28  goes past the constriction  52  and the tab  22  snap-fastens in the housing  24 . 
     This is made easier by the fact that the head  34  is hollow. This is also made easier by the pointed profile of the head  34 , with the angle β being selected to facilitate penetration of the tab. 
     This leads to the situation shown in  FIG. 3 , in which the free edges  8  of the top and bottom half-bodies  2  and  4  are in contact with each other, the face  36  of the head  34  then bearing against the face  53 ′ of the constriction  52  that faces away from the opening  40 . The faces  36  and  53 ′ thus form bearing surfaces that retain the tab  22  in the housing  24 . The contact plane between these bearing surfaces forms an angle α with the longitudinal direction. 
     As shown in  FIG. 3 , the wall  42  forms a rear abutment for the tab, against which the wall  30  of the tab  22  opposite from the portion in relief  28  is capable of sliding. 
     The tab  22  can be disengaged from the housing  24  if traction is exerted on the half-bodies  2  and  4  in the direction for separating the half-bodies from each other, while applying a predetermined longitudinal force. 
     To this end, the angle α is selected so as to enable the portion in relief  28  to deform elastically when such a longitudinal force is exerted on the half-bodies  2  and  4 . 
     The above-described body presents numerous advantages. The manufacturing tolerances on the top and bottom half-bodies have practically no impact on the quality of the snap-fastening between the tabs  22  and the housings  24 . Large manufacturing tolerances for the half-bodies give rise essentially to a mere modification in the zones of the surfaces  36  and  53 ′ that bear mutually one against the other. 
     Furthermore, it is possible to make tabs  22  and constrictions  52  that bear one against the other over a long length. This provides a large amount of tolerance on the longitudinal position of the tab  22  relative to the housing  24  when the free edges  8  of the two half-bodies come into contact one against the other. 
     The appearance of the hollow body is most advantageous since none of the means for assembling the two half-bodies together is visible once the half-bodies have been assembled together. 
     In addition, it is easy to separate the two half-bodies from each other since this is done merely by applying longitudinal traction. 
     The position of the tab  22  relative to the constriction  52  is particularly well defined, because this tab bears rearwards against the wall  42 . 
     Finally, because of the flexibility of the head  34  of the tab and of the wall  43 , it is possible to engage the tab  22  in the housing  24  and then to disengage it a large number of times without damaging the tab or the housing. 
     In a variant embodiment shown in  FIG. 4 , each housing  24  has a closure web  56  connecting the flat  44  of the wall  42  to the flat  50  of the wall  43 . 
     The web  56  lies on a side of the housing  24  that is remote from the inside face of the half-body  4 , i.e. that is towards the inside of the hollow body. It serves to stiffen the walls  42  and  43  and to guide the tab  22  in its movement in longitudinal translation. 
     In a variant or in addition, the wall  43  may be made to be elastically deformable to the right in  FIG. 3  in the region of the wedge  52 .