Patent Publication Number: US-2010108216-A1

Title: Vehicle Rim for Mounting a Tire

Description:
FIELD OF THE INVENTION 
     The present invention relates to a vehicle rim intended for mounting a tire, having what are called inverted seats. It also relates to a tire/wheel assembly fitted with such a rim. 
     TECHNOLOGICAL BACKGROUND 
     Rims having what are called inverted seats are known, for example, from documents U.S. Pat. No. 5,787,950, U.S. Pat. No. 6,415,839, WO 01/08905 and WO 2006/010681; the latter document is considered to be the closest prior art corresponding to the preamble of claim  1 . 
     Tire/wheel assemblies comprising: 
     a wheel provided with an inverted-seat rim; 
     a suitable tire, mounted on the rim; and 
     a bearing support for the tread of the tire 
     have been marketed under the name “PAX system”, but there are also tire/wheel assemblies having inverted-seat rims and which do not comprise a bearing support. 
     One difficulty linked to using tire-wheel assemblies provided with inverted-seat rims lies in the fact that the geometry and architecture of the bead of a tire intended to be mounted on an inverted-seat rim impart great stiffness to the bead and consequently cause degradation of the “strike through” performance of the tire. This is understood to mean the transmission of stresses to the body of the vehicle when the tire passes over an obstacle such as a pothole or a kerb. 
     DESCRIPTION OF THE INVENTION 
     The invention is aimed at providing a tire/wheel assembly provided with inverted-seat rims and having improved “strike-through” behavior. 
     This aim is achieved using a vehicle rim, of revolution, intended for mounting a tire, this rim comprising 
     a first and a second rim seat; 
     a first and a second safety hump, located axially to the inside of the seats; 
     each of the rim seats being intended to receive a bead of the tire, each of the rim seats having a generatrix the axially inner end of which is on a circle of diameter D I  greater than the diameter D E  of the circle on which the axially outer end is located, at least one of the seats opening on to a groove arranged axially between the seat and the safety hump axially closest to the seat. It should be pointed out that we call a first point “axially internal” to a second point if the first point is closer to the plane perpendicular to the axis of rotation of the tire/wheel assembly (or of the rim) which intersects the rim at mid-width. Conversely, a point is said to be “axially external” to another if it is farther from the plane perpendicular to the axis of rotation of the tire/wheel assembly (or of the rim) which intersects the rim at mid-width. 
     The definition of what is to be understood precisely by “seat” is given in the description of  FIG. 7 . 
     The safety humps may have a geometry such as described, for example, in document WO 2006/010681. 
     The addition of the said groove allows displacement of the bead of the tire mounted on the rim when the tire is subjected to major deformation, for example when the tire passes over a kerb or a pothole. This displacement enables part of the energy to which the tire is subjected to be absorbed and the force transmitted to the wheel centre and, consequently, to the body of the vehicle on which the tire/wheel assembly is mounted to be reduced. 
     According to a preferred embodiment, the depth d of the groove (for definition, see  FIG. 16 ) is less than the difference in the diameters D I  and D E  of the seat which opens on to the groove. This depth is sufficient to permit the displacement mentioned above, while not making the rim fragile. 
     The groove preferably has a circular or ovoid profile, because such a profile is adapted to the form of the part of the deformed bead which lodges in the groove in the event of a severe impact. 
     According to another preferred embodiment, the bottom of the groove is flat, which makes manufacture particularly simple. The plane of the bottom of the groove may be perpendicular to the radial direction or alternatively inclined relative to the axial direction, the angle of inclination being between −35° and +55°. 
     According to one advantageous embodiment, each of the rim seats opens on to a groove arranged axially to the inside of the seat. This makes it possible to obtain the displacement effect mentioned above for each bead of the tire, which is advantageous, insofar as a violent impact may occur on each of the sidewalls of the tire. This embodiment is particularly suited to rims in which the mean diameter of the first rim seat is equal to the mean diameter of the second rim seat (see  FIG. 5 ). 
     On the other hand, if the mean diameter of the first rim seat is different from the diameter of the second rim seat, it is preferable for at least the rim seat having the greater mean diameter to open on to a groove arranged axially to the inside of the seat. This is because it is on the side of the seat having the larger diameter that the problem of transmission of violent impacts is most acute. It is nevertheless possible, and even preferable, for each of the two seats to open on to a groove arranged axially to the inside of the seat. 
     The invention also relates to tire/wheel assemblies comprising a vehicle rim according to the invention. According to a preferred embodiment, the tire of the tire/wheel assembly comprises a bead wire and the depth (d) of the groove is at least equal to one third of the diameter D of the bead wire (see  FIG. 16 ). According to another preferred embodiment, the width L of the groove (see  FIG. 16 ) is at least equal to half the diameter D of the bead wire of the tire ( 30 ). These two conditions guarantee that the groove is sufficiently deep and wide to accommodate part of the bead in the event of a violent impact. 
     Preferably, the play S between the bead of the tire and the safety hump (see  FIG. 16 ) is greater than or equal to half the diameter D of the bead wire of the tire, in order to facilitate the movement of the bead as described further above. 
     The invention relates equally well to tire/wheel assemblies provided with an annular bearing support capable of supporting a tread of the tire in the event of a loss of inflation pressure from the tire and to tire/wheel assemblies which do not comprise such a bearing support. 
     It should be pointed out that the term “tire” here refers to any type of elastic tires, whether under internal pressure when in use or not. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood thanks to the description of the drawings, in which 
         FIG. 1  depicts a partial perspective view of a tire/wheel assembly according to the prior art; 
         FIG. 2  depicts diagrammatically, in meridian section, a tire/wheel assembly according to the prior art; 
         FIGS. 3 to 5  depict diagrammatically, in partial meridian section, an inverted-seat rim with or without a bearing support; 
         FIG. 6  depicts the force transmitted to the suspension in the event of a violent impact as a function of the diameter of the rim, at a constant diameter of the tire/wheel assembly, for conventional rims and an inverted-seat rim; 
         FIGS. 7(   a ) and ( b ) illustrate the exact extent of the seat for complex rim geometries; 
         FIGS. 8(   a ) and ( b ) depict the contact pressures between the bead of the tire and an inverted-seat rim as a function of the position on the seat; 
         FIGS. 9(   a ) and ( b ) depict two rim seats according to the invention; 
         FIGS. 10(   a ) and ( b ) depict diagrammatically the positioning of a tire bead on a rim according to the invention, in normal operation (a) and upon an impact with a kerb (b); 
         FIGS. 11 to 13  depict rims according to the invention; 
         FIGS. 14 and 15  depict rim seats according to the invention; 
         FIG. 16  illustrates parameters for characterizing a tire/wheel assembly according to the invention; 
         FIG. 17  depicts the force exerted at the centre of the wheel as a function of the loading of the tire (on a Zwick machine) on flat ground; 
         FIG. 18  depicts the force exerted at the centre of the wheel as a function of the loading of the tire (on a Zwick machine) on a corner. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts diagrammatically in perspective view a partial section of a tire/wheel assembly  10  of “PAX system” type comprising a wheel  20  with its inverted-seat rim  22 , a tire  30  provided with sidewalls  31  and a crown  32 , and a bearing support  40 . When the tire deflates, for example following a puncture, the weight of the vehicle causes the sidewalls  31  to flex such that, in the proximity of the contact zone between the tire  30  and the roadway, the crown  32  comes into contact with the bearing ring  40 . The “PAX system” is shown as the most common use of an inverted-seat rim, hut, as has been stated further above, rims of the inverted-seat type are in no way limited to such a use. There are in fact tire/wheel assemblies without bearing support, and the invention also relates to these assemblies. 
       FIG. 2  depicts diagrammatically, in meridian section, a tire/wheel assembly of “AX system” type comprising a wheel (formed of a rim  22  and a disc  21 ), a tire  30  and a bearing support  41 . The axis of rotation  1  of the tire/wheel assembly is also indicated. 
       FIG. 3  depicts diagrammatically, in partial meridian section, a rim  22  and a bearing support  42  for a tire/wheel assembly of “PAX system” type. For the sake of clarity, the tire  30  is not shown. The rim  22  comprises two rim seats  51  and  52  of different mean diameters. Each of the rim seats  51  and  52  is intended to receive a bead of the tire. The generatrix of the rim seat  51  has an axially inner end  512  which is located on a circle of diameter D I   1 , D I   1  being greater than the diameter D E   1  of the circle on which the axially outer end  511  is located; thus the rim seat  51  is an “inverted seat”. Likewise, the generatrix of the rim seat  52  has an axially inner end  522  which is located on a circle of diameter D I   2 , D I   2  being greater than the diameter D E   2  of the circle on which the axially outer end  521  is located. The seats  51  and  52  are delimited axially to the outside by rim hooks  591 ,  592  and axially to the inside by safety humps  571  (here in the form of what is sometimes called a “ledge”, suitable for mounting the bearing support  42 ) and  572 . 
     The rim  22  also comprises a mounting groove  54  intended to permit mounting of the tire and a weight reduction groove  55  intended to reduce the weight of the rim. 
       FIG. 4  represents diagrammatically, in partial meridian section, another inverted-seat rim  23 . Unlike the rim  22 , the mean diameter of the seat  51  close to the wheel disc  21  ( FIG. 2 ) is greater than the mean diameter of the seat  52 . Axially to the inside of each of the seats there is a safety hump  571 ,  572 . 
       FIG. 5  represents diagrammatically, in partial meridian section, a third inverted-seat rim  24 . This rim is distinguished from the rims of  FIGS. 3 to 4  in that the mean diameter of the two seats  51  and  52  is identical. 
       FIG. 6  illustrates one difficulty observed when using inverted-seat rims compared with traditional rims (that is to say ones having non-inverted seats). The graph shows the force transmitted to the suspension in the event of a violent impact, as a function of the diameter of the rim, at a constant tire-wheel assembly diameter. The values corresponding to three different rim diameters (17, 18 and 19 inches) exhibit, for traditional rims (solid circles), an increase in the force transmitted as a function of the diameter: the greater the diameter of the rim (at constant tire-wheel assembly diameter (also known by the name “overall” diameter)!), the lesser the height of the sidewall of the tire and the less the tire is capable of absorbing the impacts to which it is subjected. The value obtained with an inverted-seat rim (empty circle) shows that the force transmitted by a tire/wheel assembly fitted with such rims is greater than the force which would be transmitted by a tire/wheel assembly fitted with a traditional rim of the same diameter. The difference can be assessed by considering the difference in diameter P between a traditional rim and a rim with inverted seats which transmit the same force to the wheel centre when they are stressed in the same manner. Typically, P lies between 0.5 and 1.2 inches. 
       FIG. 7  illustrates the precise extent of the seat for geometries where the transition between the seat and the elements surrounding it is not totally unequivocal. The person skilled in the art will understand “seat” to be that part of the rim which is intended to come into contact with the bead of the tire, permanently. Not considered as forming part of the seat is the rim hook, which comes into contact with the bead of the tire when the latter is stopped but which can lose contact with the bead when the tire is under great stress. 
       FIG. 7(   a ) shows a seat  51  of a traditional inverted-seat rim  22 . The transition between the seat  51  and the rim hook  591  and the transition between the seat  51  and the safety hump  571  is rounded, which makes it difficult to ascertain the precise extent of the seat, all the more so if the latter is not flat, as is the case with the seat  51  of  FIG. 7(   b ). The procedure for determining the axially outer end  511  of the seat is as follows: the mean tangent  101  to the central part of the seat and its intersection with the tangent  102  to the wall of the part of the rim hook  591  on to which the seat opens are determined. The end  511  of the seat then corresponds to the intersection of the radial direction  111 , which passes through the point of intersection between the tangents  101  and  111 , with the surface of the rim. Analogously, the end  512  of the seat  51  is determined, by replacing the tangent  102  to the wall of that part of the rim hook  591  on to which the seat opens, with the tangent  103  to the wall of the safety hump  571  on to which the seat opens. The end  512  of the seat then corresponds to the intersection of the radial direction  112 , which passes through the point of intersection between the tangents  101  and  103 , with the surface of the rim. 
     The procedure is analogous for the rims according to the invention which comprise a groove  71 . In this case in point, the tangent  104  to the wall of the groove on to which the seat opens is determined and its intersection with the mean tangent  101  is determined. The end  512  of the seat corresponds to the intersection of the radial direction  113 , which passes through the point of intersection between the tangents  101  and  104 , with the surface of the rim. 
       FIG. 8  shows the contact pressures between the bead  33  of the tire  30  and an inverted-seat rim  25  as a function of the axial position on the seat.  FIG. 8(   b ) shows the bead  33  of the tire and the seat  51  of the rim  25 . The bead wire  34  and the anchoring of the carcass ply  35  around the bead wire are also shown.  FIG. 8(   b ) shows the contact pressures calculated between the bead  33  and the rim  25  over the width of the seat  51 , at two inflation pressures (high pressure: unbroken line, low pressure: broken line). The maximum pressure is observed in the zone of contact with the hook  56  of the rim  25 . When moving axially away from the hook, towards the bead wire  34 , the pressure drops, reaching a new peak in the zone compressed by the bead wire  34 . Beyond the line  60 , the contact pressure rapidly drops to zero. 
     The invention departs from the observation that the contact pressure is not applied over the entire width of the seat, but that the part axially inwards of the line  60  does not contribute to establishing airtight contact between the bead  33  and the rim  25 . This surprising observation (given the positioning of the carcass ply) is exploited in a rim according to the invention by the provision of a groove, as shown in  FIG. 9 . 
       FIGS. 9(   a ) and ( b ) depict rim ends according to the invention.  FIG. 9(   a ) shows one end of a rim  26  which corresponds to the end of the rim  22  (see  FIG. 3)  which comprises the seat  52 . Relative to the latter, the seat is shortened and opens axially to the inside on to a groove  71 . This groove is delimited by a safety hump  57  which is narrower than the corresponding safety hump of the rim  22 . The geometry of the rim  22  is suggested by broken lines, in order to facilitate comparison. 
       FIG. 9(   b ) corresponds to the application of the same measures to the end of the rim  23  (see  FIG. 4)  which comprises the seat  51 . Again, the rim according to the invention is distinguished by the addition of a groove  72 ; the seat proper is shortened and the safety hump on to which the seat opens is made narrower. Again, the geometry of the rim  23  is suggested in broken lines, in order to permit easy comparison. 
     Providing such a groove  71  or  72  makes it possible to solve the technical problem posed, for reasons which are illustrated in  FIG. 10 .  FIG. 10(   a ) shows the “normal” configuration, that is to say when the tire/wheel assembly is stopped or travelling on flat ground: the bead  33  of the tire  30  is lodged on the seat  51  of the rim  28  according to the invention, provided with a groove  73 . The bead wire  34  and the end of the carcass ply  35  are also shown. 
       FIG. 10(   b ) depicts a situation in which the tire/wheel assembly is subjected to a violent impact, for example when the tire passes over a large-sized obstacle, such as a kerb. In such a situation, the groove  73  enables the bead wire to be displaced, at least partially filling the groove. Thus it is possible to absorb part of the deformation of the tire  30  and to prevent the impact from being integrally transmitted to the vehicle. When the stress ends, the movement is reversed and the configuration of  FIG. 10(   a ) is regained. 
     When the two seats of the rim are not at the same radial height, as is often the case for inverted-seat rims, it is advisable to provide the groove at least on the seat which has the larger mean diameter. It is nevertheless possible, and even preferable, to provide such grooves for both seats. 
       FIGS. 11 to 13  correspond to  FIGS. 3 to 5 , the rims having been modified according to the invention. The rim  222  is provided with a groove  74  on to which opens the seat  522 , which has a larger mean diameter than the seat  51 . The latter could also have been provided with a groove, as is suggested in broken lines. The rim  232  of  FIG. 12  corresponds to that of  FIG. 4 , but here the seat  512  of greater radial diameter opens on to a groove  75 . Again, it would have been possible also to provide the second seat  52  with such a groove.  FIG. 13  depicts the case of an inverted-seat rim  242 , the mean diameters of which are identical. In this case, it is preferable to provide grooves  76  and  77  at the end of both seats  51  and  52 . 
       FIG. 14  represents diagrammatically an inverted seat  51  of a rim  252  according to the invention. This seat  51  has an inclination alpha (α) which is defined as the angle, in a radial section plane, between the tangent  80  to the central part of the seat and a direction parallel to the axis of rotation  81  of the rim. In this case, the angle alpha (α) is 15°. “Radial” is understood here to mean a direction perpendicular to the axis of rotation of the tire/wheel assembly (which is identical to the axis of rotation of the rim) and which intersects this axis. A radial plane is a plane comprising the axis of rotation. 
     The groove  78  on to which the seat  51  opens corresponds to the space between the rim and the prolongation of the tangent  80  towards the safety hump  57 . In this case, this groove is rounded, but this is only one embodiment among others.  FIG. 15  shows ends of other rims  262  and  272  according to the invention where the groove has a flat bottom, which may be inclined ( FIG. 15(   b )) or not ( FIG. 15(   a )) relative to the axial direction. If the bottom is flat and inclined, its inclination may or may not be identical to the inclination of the seat; preferably, the angle of inclination thereof lies between −35° (the negative sign indicates an inclination opposed to that of the seat) and +55°. An ovoid geometry corresponds to another preferred embodiment. 
       FIG. 16  illustrates parameters for characterizing a tire/wheel assembly according to the invention. The depth “d” of the groove  793  is defined as the maximum distance between the prolongation of the tangent  80  to the seat and the bottom of the groove. 
     The width “L” of the groove  793  corresponds to the distance between the axially inner end of the seat and the point of intersection between the tangent  80  to the seat and the safety hump  57 . 
     Finally, the play “S” between the bead  33  of the tire  30  and the safety hump  57  is defined as the minimum distance between a point of the bead  33  and a point of the safety hump  57  when the tire/wheel assembly is stopped and not loaded. 
       FIGS. 17 and 18  represent results obtained with tire/wheel assemblies according to the invention.  FIG. 17  depicts the force exerted at the centre of the wheel as a function of the loading of the tire (on a Zwick machine) on flat ground. A tire/wheel assembly of the “PAX system” type (broken-line curve) is compared with an assembly according to the invention (unbroken line). When loaded on flat ground, a slight “delay” is noted for the assembly according to the invention, which conveys the fact that the assembly according to the invention has to be deflected by several additional millimeters in order to transmit as much force to the wheel centre. 
     The effect is far more pronounced when the loading is on a corner, as shown in  FIG. 18 : the lag or “delay” here corresponds to about ten millimeters. When equally loaded, the tire/wheel assembly according to the invention thus transmits distinctly less force to the wheel centre than the reference assembly. 
     This improvement was also demonstrated in a test of “pothole” type, known to the person skilled in the art. This test makes it possible to determine the forces at the wheel centre in the event of a severe impact. The results were obtained with a PAX 235-660R480U tire on a BMW series 7 vehicle, for a travelling speed of close to 50 km/h and a pothole of a depth of approximately 70 mm. The results are summarized in Table 1: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Results obtained in a test of “pothole” type 
               
            
           
           
               
               
               
            
               
                 Force transmitted to the 
                 “PAX system” 
                 Assembly according 
               
               
                 chassis [kN] 
                 (reference system) 
                 to the invention 
               
               
                   
               
               
                 Fx 
                 27 
                 22 
               
               
                 Fz 
                 53 
                 42 
               
               
                 Fxz = (Fx 2  + Fy 2 ) 1/2   
                 60 
                 47 
               
               
                   
               
               
                 Fx designates the force transmitted in the direction of displacement of the vehicle, and Fz the force transmitted in the vertical direction. 
               
            
           
         
       
     
     It will be noted that the modification of the rim reduces the forces at the wheel centre by approximately 20% in the event of a severe impact. 
     It should also be noted that the invention has no adverse impact on the ease of mounting or demounting the tire.