Abstract:
A spoked wheel includes a rim with a plurality of holes for a respective plurality of nipples and an equal plurality of spokes secured to the rim by these nipples. The nipples are arranged to be fitted so as to be substantially gastight in the respective holes in the rim for the purpose of fitting tubeless tires to the rim.

Description:
This application is a U.S. National Phase Application of PCT International Application PCT/IT2004/000708 and incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   The invention relates to a spoked wheel of the type including a rim with a plurality of holes for a respective plurality of nipples, and an equal plurality of spokes secured to the rim by means of the nipples. 
   Wheels of the above-mentioned type are widely used on both pedal cycles and motorcycles. In the latter case in particular, a need has been felt to use pneumatic tires of the tubeless type, without an inner tube. 
   These tires have the advantage of deflating relatively slowly in case of a puncture and are therefore suited to the high speeds which may occur in the case of motorcycles. 
   On the other hand, the use of tubeless tires is not compatible with spoked wheels unless these incorporate special characteristics. 
   A first type of spoked wheel designed for cycle use with tubeless tires provides for the rim to have a double channel. The first channel is formed between the rim and the tire and provides an airtight seal designed to form the inflation chamber of the tire. The second channel, provided with holes, is used for fitting the spoke anchorage devices. Examples of this technical solution are described in U.S. Pat. No. 6,474,746 and US 2003/0025383 A1. 
   However, this type of wheel is not well suited to motorcycle use since it increases appreciably the mass of the rim in rotation. Moreover, it has been found that in wet conditions water tends to accumulate in the second channel (which is not airtight) with disadvantages such as an increase of the mass in rotation, corrosion phenomena and worse still appreciable wheel imbalance. 
   Another type of wheel for the fitting of tubeless tires is described in Japanese patent 2003146001, European patent 1209006 and U.S. Pat. No. 4,824,177. In this case, however, external sealing means are used to eliminate the problem of airtightness between the nipple and the rim. 
   This type of solution provides relatively unreliable sealing which is likely to be damaged if impacts occur. 
   Moreover, it has been found that a serious sealing problem is caused by relative movement between the rim and the nipple due to the inevitable elastic deformation of the rim during use. This is because there may be axial displacement of the nipple and of the spoke secured to it due to the effect of deformation of the rim by even a few millimetres and, when seals are inserted between the nipple and the rim, it is clear that this may cause pressure losses in the inflation chamber of the tire and may even cause sudden deflation of the tire. 
   SUMMARY OF THE INVENTION 
   The main problem addressed by the invention is to make available a spoked wheel structurally and functionally designed to be suitable for the fitting of tubeless tires with the high degree of reliability necessary for use on high-speed motorcycles. 
   A further purpose of the invention is to make available a spoked wheel structure capable of overcoming all the troublesome technical disadvantages noted with reference to the known technology. 
   These problems are solved and these purposes are achieved by the invention of a spoked wheel including a rim with a plurality of holes for a respective plurality of nipples, and an equal plurality of spokes secured to the rim by means of the nipples. The nipples are arranged to be fitted so as to be substantially gastight by screwing into the respective holes in the rim for the purpose of fitting tubular tires to the rim. And the nipples and holes receiving them on the rim have a taper gas thread in the sections where they fit together. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The characteristics and advantages of the invention will become clear from the following detailed description of some preferred embodiments illustrated purely by way of non-limiting example with reference to the appended drawings in which: 
       FIG. 1  is a view in section of a portion of spoked wheel produced according to the invention; 
       FIG. 2  is a view in section of a portion of spoked wheel in a variant of the embodiment shown in  FIG. 1 . 
       FIGS. 3 to 25  are views in section of portions of spoked wheels according to further variants of the embodiment shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the drawings, the number  1  indicates as a whole a wheel including a rim  2 , a hub  3  and a plurality of spokes  4  secured at the respective and opposite ends respectively to the rim  2  and the hub  3  by means of nipples  5  and  6  respectively. The rim  2  is of the single-channel type, that is with the nipples  5  facing directly into the inflation chamber of the tire. 
   The spokes  4  in the first example ( FIG. 1 ) comprise a stem  8  preferably produced from light alloy, for example aluminium alloy, having at its respective opposite longitudinal ends threaded blind holes  7   a, b . Screwed into the blind hole  7   a  facing towards the hub  3  is a threaded end  9  of a stud  10  the opposite threaded end  11  of which is fitted into the threaded hole  12  in the nipple  6  providing the attachment to the hub  3 . 
   Into the blind hole  7   b  at the end facing towards the rim is fitted the threaded stem of the nipple  5  providing the attachment to the rim  2 . 
   On the nipple  5  there is a cylindrical shank  13  having at one end a broadened head  14  which forms a shoulder  15  relative to the shank. A driving key feature  16  is made in the head and is used to screw the nipple into the hole  7   b . This driving key feature may be produced in various forms, for example a polygon, a hexagonal recess, a slot for a screwdriver or other provision. 
   Once the nipple  5  is screwed into the hole  7   b  it is locked for example by means of thread locking adhesives known in themselves. 
   The nipple  5  has a threaded portion  20  on the shank  13 , having a taper gas thread. 
   Similarly, the hole  21  in the rim  2  into which the nipple  5  is fitted has a taper gas thread so as to engage with the taper gas thread of the nipple forming a fluid-tight seal. 
   Sealing may be further improved using adhesives, sealants and the like. In that case, conventional parallel threads may be used or sealing components fitted between the head of the nipple and the rim. 
   This structure lends itself particularly to the use of light alloy spokes. If it is wished to use spokes with steel stems instead, the solution illustrated in  FIG. 2  is preferred, differing from the preceding example in that the nipple  5  securing the spoke to the rim has a blind threaded hole  27  into which is fitted a threaded end  28  of the stem  29  of the spoke. 
   At the opposite end the spoke has the same threaded end fitted into the hole  12  in the nipple  6 . In this case too, the shank of the nipple  5  is threaded externally with a taper gas thread and the same thread is made in the hole made in the rim  2  to house the nipple. 
   Although the solution using taper gas threads is indicated as preferred, it should be understood that these threads may also be of different pitch and profile, with or without taper. 
   Another example of embodiment of the present invention is described with reference to  FIG. 3 . Similar parts are indicated by the same reference numbers as in the preceding drawings. In this case the nipple  5 , with a shank  13  provided with either a parallel or taper external thread has internally a threaded blind hole  27  into which is screwed a threaded end of a stud  30  the opposite end of which, also threaded, is screwed into a corresponding blind hole  7   b  in the spoke  4 . The spoke and nipple have facing surfaces  31   a  and  31   b , respectively which can be butted together so that by means of the stud  30  the spoke and nipple are attached to each other to form a single unit. Provision is also made, by way of a variant, for the spoke and nipple to be produced in one piece. 
   A variant of this example is illustrated in  FIG. 4 . In this case, a groove  32  is made in the shank  13  of the nipple  5 , and this houses an O-ring  33  (OR) which is fitted in the threaded wall of the hole  21  in the rim  2 , forming a seal. 
   It will be noted that in this case too, since the nipple  5  is locked axially bidirectionally in the hole  21  in the rim due to the effect of the shoulder  15  at one end and of the thread  20  at the other end, there is no relative slippage between the nipple and the hole in the rim so that the airtightness of the seal  33  is not compromised. 
   Another preferred example of embodiment of the invention is described with reference to  FIG. 5 . 
   In this example the O-ring  33  is fitted between the shoulder  15  and an annular seating  34  preferably with a cylindrical wall, made at the mouth of the hole  21 . In this case the groove  32  is made close to the shoulder  15  and fluid-tightness is achieved with the cylindrical wall  35  of the seating  34 . In this case too the nipple  5  is locked axially in the hole  21  in both directions. 
   Two other examples are described with reference to  FIGS. 6 to 9 . These examples differ in that they allow spokes with a light alloy stem to be used rather than spokes with a steel stem; in the latter case, the invention allows entirely conventional spokes to be used. 
   In both cases, a nipple is used similar to that described with reference to the example in  FIG. 5  which, instead of being fitted into the hole  21  in the rim  2  by being screwed in, is fitted into it so as to be able to rotate freely and is locked axially and bidirectionally by means of a nut  36  screwed onto the threaded section of shank  13  projecting from the rim  2  through the hole  21 . Axial bidirectional locking is obtained here between the shoulder  15  and the nut  36 . The O-ring  33  as in the case of the previous example is subjected to a limited axial load and is fitted to form a seal with the cylindrical wall  35  of the seating  34 . 
   Using both these examples, but in particular with the one shown in  FIGS. 8 and 9  which employs an entirely conventional spoke, it is possible to rotate the nipple  5  to obtain correct tensioning of the wheel and then lock the nut  36  to obtain complete and final assembly of the wheel. 
   Assembly of the wheel in all examples except the last one just described proceeds as follows. First of all the nipples  5  are screwed into the respective holes in the rim  2  housing them and are tightened by means of the driving key feature  16 . Then the spokes are fitted by screwing them to the respective nipples. The free end of the spokes is then secured with appropriate adjustment to the hub by means of the nipples  6 . 
   Another variant embodiment of the invention is illustrated in  FIG. 10 . 
   This variant takes account of the problems deriving from the fact that in assembling the wheel, if the holes receiving the nipples in the rim are not perfectly aligned with the corresponding holes in the hub (and there never is perfect alignment) the stem of the spoke is subject to bending stresses to compensate for this misalignment. This bending generates uneven stresses creating overloading particularly in the outermost parts, furthest from the axle, in the cross-section of the spoke. 
   In the case of spokes with light alloy stems, the effect is increased due to the larger diameter of the spoke. To eliminate this disadvantage, in the example in  FIG. 10  provision is made for the larger diameter part, of aluminium alloy, of the stem  108  of the spoke  104  not to abut against the facing surface  109  of the nipple  105  but to be held apart from it by a space  102  and joined only by the stem  103  of the stud  110 . To prevent the ingress of water into the space  102 , provision is made for a deformable elastomer seal  111  to be inserted into it, functioning both as a compensating rubber washer and as a deformable sealing element closing off the space  102 . 
   With reference to  FIGS. 11 to 22 , other examples of embodiment of spoked wheels according to the invention provide for the nipple to be connected to the spoke by a pivoting attachment. In  FIG. 11 , a pivot  201  is produced by providing a partially spherical swivel head  202  at the end of the stud  210  which is fitted into a rounded seating  211  in an axial cavity  212  of the nipple  205 . The partially spherical swivel head can also be made directly on the stem of the spoke where the spokes are of steel or materials of corresponding strength ( FIG. 12 ). 
   The partially spherical swivel head, as can be seen from the examples in  FIGS. 13 to 21 , may also have a marked curvature which allows the hole  21  in the rim receiving the nipple  205  to be made with an axis radial to the rim, leaving the offset to be taken up entirely by the spherical swivel  202 . The joint between the spherical swivel  202  and the stem of the spoke may be obtained by means of a head  213  on the stud  210  ( FIG. 13 ), by a threaded joint  214  ( FIG. 14 ) or, in a similar manner, directly by the stem of the spoke ( FIGS. 15 and 16 ). 
   With reference to  FIGS. 17 to 22  provision is also made for the nipple  305  to have a seating  306  open towards the channel in the rim  2  with closure provided by means of a cover  307  fitted by pressing onto the nipple  305  or using a threaded joint. In another variant of the invention, illustrated in  FIGS. 21 and 22 , provision is made for the nipple  405  to be inserted into the hole  421  in the rim and locked bidirectionally in it by upsetting  422  or other mechanical securing operation. In  FIG. 22 , provision is made for the seating for the partially spherical swivel to be machined at an angle in line with the spoke. 
   In  FIG. 23 , the spoke  4  has one end, housed in a nipple  500 , in the form of a flared head  501  held so as to allow slight axial movement in a chamber  502  of the nipple  500  by means of a sleeve  503  which is screwed into a blind axial hole in the nipple  500 . The sleeve  503  is locked by a shoulder  504  abutting against the end of the nipple facing towards the wheel hub. The nipple  500  is in turn screwed into the hole  505  in the rim and locked axially relative to it so as to be airtight with a seal  506  fitted between them. 
   The example in  FIG. 24  has a nipple shown as  600 . It is substantially similar to the previous one and therefore has identical reference numbers to indicate identical parts. It differs from the previous example in that the nipple  600  can be opened at the end facing the spoke  4 , where it has a removable airtight closure formed by a screw cover with a seal  602  inserted. The sleeve  503  is omitted. 
   The nipple in the example in  FIG. 25  is shown as  700 . It is substantially similar to the previous one and therefore has identical reference numbers to indicate identical parts. It differs from the example in  FIG. 24  in that the spoke  4  terminates in a threaded length  701  onto which is screwed a conventional nipple of the type with a cylindrical shank  702  widened into a flared portion  703  and locked by pouring in thread locking resin  704 . 
   The invention thus achieves the proposed purpose and secures numerous advantages compared with the known technology. In particular, it allows the production of lightweight wheels, with reduced rotating mass, safe both in use at high speed and in case of accidental impacts.