Patent Publication Number: US-7900563-B2

Title: Reinforcing assembly for a tubular cross member of a rail and tram car bogie

Description:
TECHNICAL FIELD 
     The present invention relates to a reinforcing assembly for a tubular cross member of a rail and tram car bogie, and in particular for a tubular cross member of an underground train motor-driven bogie. 
     BACKGROUND ART 
     As is known, the motor-driven bogie of a rail and tram car comprises a frame defined by two side members, and by two cross members spaced apart in the longitudinal travelling direction of the train. The side members support a rotary front and rear axle, each fitted with two wheels mounted to run along rails, and the cross members support two motor reducers and two brake assemblies for driving and braking the axles. 
     The cross members have a tubular structure, and ends extending inside respective holes in the side members and welded to the side members. When running, fatigue failure sometimes occurs at the weld connection between the tubular cross member and the side member, and is presumably caused by a combination of technological weld defects (e.g. irregular weld bead, stuck welds, solid inclusions, lack of fusion, relative positioning errors between the cross member and the hole in the side member) and anomalous stress conditions not covered in standard tests and current regulations. 
     Fatigue cracks, in particular, are found to substantially originate in a horizontal plane corresponding to the mid-plane of the cross members, and are therefore presumably caused by bending moments having an approximately vertical axis and so produced by fatigue loads acting longitudinally on the side members. In-service strain gauge readings actually tend to show, particularly when the train is travelling along curves, anomalous stress on the frame caused by so-called “rhombusing” of the side members of the bogie, i.e. stress caused by a longitudinal load acting on each wheel in opposite directions on the two sides of the bogie. 
     A need is therefore felt to reinforce the tubular cross members of existing bogies, by performing repair and/or updating work at ambient temperature, without dismantling the bogies, and with no need for machining the cross members. 
     DISCLOSURE OF INVENTION 
     It is an object of the present invention to provide a reinforcing assembly for a cross member of a rail and tram car bogie, designed to meet the above demand in a straightforward, low-cost, reliable manner, preferably by permitting fast repair and maintenance work. 
     According to the present invention, there is provided a reinforcing assembly for a tubular cross member of a rail and tram car bogie; the assembly being characterized by comprising:
         a liner elongated along an axis, deformable radially, and insertable axially inside one end of said tubular cross member to line an inner cylindrical surface of said end; and   radial forcing means insertable axially inside said liner, and which are activated to force said liner radially outwards to lock the liner, in use, against said inner cylindrical surface.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A non-limiting embodiment of the invention will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  shows a partial plan view of a rail and tram car bogie; 
         FIG. 2  shows a section along line II-II in  FIG. 1 , and a preferred embodiment of a reinforcing assembly for a tubular cross member of a bogie in accordance with the present invention; 
         FIG. 3  shows a section along line III-III in  FIG. 2 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Number  1  in  FIG. 1  indicates a motor-driven bogie (shown partly) of a rail and tram car (not shown). Bogie  1  comprises a frame  2 , in turn comprising two side members  3 , and two cylindrical tubular cross members  4  spaced longitudinally apart and extending along respective horizontal axes  5  perpendicular to the longitudinal travelling direction A of bogie  1 . Side members  3  comprise respective intermediate portions  6  having a substantially U-shaped lateral profile, and terminate with respective opposite longitudinal arms  7  supporting a front axle and a rear axle, both indicated  8 . Axles  8  rotate about respective fixed horizontal axes  9 , are fitted with wheels  11  mounted to run on rails (not shown), and are located on opposite sides of cross members  4 . 
     With reference to  FIGS. 1 and 2 , the bogie also comprises two brake assemblies  12 , which are fitted to respective supports—not described in detail, and each welded circumferentially to a relative cross member  4 —and cooperate frictionally with respective disks  13  fixed to axles  8 . 
     Each cross member  4  has three connecting points defined by respective sleeves  15  spaced apart axially, and extending vertically through, and welded to, cross member  4 . The six sleeves  15  support—in known manner not described in detail—two motor reducers  16  for driving axles  8 , and each defined by a relative electric motor  17  and a relative reducer  18 . 
     With reference to  FIG. 2 , the ends  19  of cross members  4  engage respective holes  20  in side members  3 , and are welded to side members  3  in known manner not described in detail. To increase the rigidity, and therefore reliability, of the weld connections between side members  3  and cross members  4 , each end  19  is provided with a respective reinforcing assembly  21 , which, at the assembly stage, is inserted axially inside end  19 , working from the outer side of bogie  1 . 
     With reference to  FIGS. 2 and 3 , assembly  21  comprises a liner  22 , which is elongated along an axis  23  (substantially coinciding, in use, with axis  5 ) and defined by a cylindrical metal wall made of steel and having an open section along a longitudinal opening  24  defined by a cut along the whole axial length of liner  22 . 
     Liner  22  is elastically deformable radially along its whole axial length by virtue of opening  24 , is formed by cutting along a generating line of a cylindrical tube (not shown), and, when not deformed, has an outside diameter equal to the inside diameter of end  19  plus roughly 2 millimeters, and an inside diameter equal to the inside diameter of end  19  minus roughly 5 millimeters. More specifically, the inside diameter of ends  19  is measured directly on the cross members  4  requiring maintenance and reinforcement by means of assemblies  21 . 
     Liner  22  therefore has a radial thickness of about 7 millimeters, lines an inner cylindrical surface  25  of end  19 , extends at most up to about 15 millimeters short of sleeve  15  (i.e. up to about 45 millimeters from the sleeve axis), and has an outer lateral surface  26  which is cylindrical, except for opening  24 , for two axially spaced outer circumferential recesses  27 , and for a conical end portion  28  tapering towards axis  23  and defining a lead-in portion by which to insert liner  22  inside cross member  4 . 
     More specifically, recesses  27  have a radial depth of about 0.2 of a millimeter, and are formed in axial positions corresponding to those of relative recesses  29 , of the same radial depth, formed on an inner cylindrical surface  30  of liner  22 . 
     Assembly  21  also comprises a number of radial forcing devices  31 ; and a cylindrical tubular body  32 , or so-called “plug”, coaxial with liner  22  and interposed between liner  22  and devices  31 . 
     Body  32  comprises an intermediate portion  33  having a number of straight longitudinal slits  34 , which divide portion  33  circumferentially into radially deformable sectors  35 , and are closed axially at the end of body  32  by a continuous annular portion  36 . Body  32  also comprises an end portion  37  opposite portion  36  and having a number of straight longitudinal slits  38 , which are aligned with slits  34 , are open axially at the end of body  32 , and divide portion  37  circumferentially into radially deformable sectors  39 . 
     Slits  38 ,  34  are separated axially by respective plate portions  40 , which are thinner radially than sectors  39 ,  35  and flush with an inner cylindrical surface  41  of body  32 . Towards the end defined by portion  36 , surface  41  terminates with an outwardly-flared conical portion  42 , on which the ends of slits  34  are formed. 
     Body  32  also has an outer cylindrical surface  43 , which, at sectors  35 ,  39 , is forced onto surface  30  by the radial thrust exerted by devices  31 . 
     Devices  31  are arranged along axis  23 , are located along portions  33 ,  37 , in positions spaced axially apart from recesses  27 ,  29 , and are defined by shaft fitting devices, e.g. of the type known by the trade name “Tollok” (registered trademark). More specifically, each device  31  is mounted on a respective central supporting pin  45  having a threaded axial hole by which to position and extract pin  45  by means of a threaded bar (not shown). Each device  31  comprises a respective pair of rings (not shown), which are slid axially along pin  45  with respect to each other by a screw-nut screw coupling (not shown); and a respective radially-expandable outer member (not shown), which is fitted to the outer periphery of said rings by a wedge coupling, and is movable radially outwards, when the rings are moved towards each other by axially tightening the screw-nut screw coupling, to force sectors  35 ,  39  against liner  22  and so frictionally lock liner  22  against surface  25 . 
     To assemble assembly  21 , firstly, surface  25  of cross member  4  is degreased, any surface roughness is removed from surface  25 , the edges of opening  24  are ground, and liner  22  is degreased. 
     Next, liner  22  is inserted axially inside end  19  by forcing portion  28  axially and by radially and elastically compressing liner  22 , so that opening  24  is positioned upwards “at twelve o&#39;clock” ( FIG. 3 ). 
     Next, surface  43  of body  32  is turned to achieve a maximum radial clearance of 0.2 of a millimeter with respect to the inside diameter of liner  22  measured when the liner is deformed and located inside cross member  4 . 
     Once surface  43  is degreased, body  32  is inserted inside liner  22  and locked by successively assembling devices  31 . 
     Finally, a cover  50  is fitted on to close end  19 , and is fixed to body  32 , e.g. by means of screws. 
     Once assembled, assembly  21  greatly increases the rigidity of cross member  4 , thus reducing fatigue stress levels, by increasing the flexural inertia of cross member  4  where it contacts, and therefore is joined to, side member  3 . More specifically, the increase provides for a roughly 30% theoretical reduction in local stress, as compared with a non-modified cross member  4 , thus increasing fatigue endurance. 
     At the same time, assembly  21  defines an alternative route for the stress flow at the joint, in accordance with a so-called “Damage Tolerance” concept. That is, as opposed to being related to the critical length of the weld crack, fatigue failure of cross member  4  now coincides with fatigue failure of body  32 , which is capable of transferring the bending moment from cross member  4  to side member  3 , even in the event of complete splitting of the weld, provided devices  31  ensure the frictional connection described above. Though subjected to greater nominal stress than cross member  4 , body  32 , not being cut and having no welds, may be designed for practically infinite fatigue endurance. 
     Assembly  21  also obviously permits in-shed modification of existing bogies, with no need to dismantle any parts of bogie  1 , and provides for a high degree of reliability of the cross member  4 /side member  3  connection, with more or less constant, predictable, and therefore programmable maintenance procedures and schedules. 
     Given the quality, simplicity, and speed of the maintenance work involved, train downtime is minimum. In fact, work is only carried out inside both axial ends of cross member  4 , working from the outer side of frame  2 , and involves no machining of cross member  4 , no reinforcing welds about the existing weld, and no hot forcing. 
     Slightly conical portion  28  and the undercutting defined by recesses  27  facilitate insertion of liner  22  inside cross member  4 , with relatively little axial force required, and at any rate compatible with a straightforward portable hydraulic tool. The solution provided also reduces possible fretting problems in the cross member  4 /liner  22  connection, and provides for gradual passage of rigidity to the end of liner  22  defined by portion  28 , so as to reduce the notching effect. 
     Since the inside and outside diameters are defined, bodies  32  are the same for all cross members  4  and all bogies  1 , and can therefore be produced on a small scale. 
     Moreover, using assembly  21 , the time lapse between inspections of modified bogies  1  may be extended, thus reducing routine inspection time and cost. 
     Clearly, changes may be made to assembly  21  as described herein without, however, departing from the scope of the present invention. 
     In particular, liner  22  may be forced radially and locked against inner surface  25  of cross member  4  using systems other than devices  31  described by way of example; and/or radial deformability of body  32  may be achieved by other than slits  34 ,  38  and sectors  35 ,  39  as described and illustrated; and/or body  32  may even be deformed permanently outwards, as opposed to only elastically, to lock liner  22  in place. 
     Finally, reinforcing assembly  21  may be applied to bogies of any type, not just motor-driven bogies.