Patent Abstract:
A damper ( 18 ) for a rail ( 10 ), includes a deformable material ( 20 ) and an elongate resonant member ( 20, 24 ), the resonant member being of a stiff material as compared to the deformable material and being sized to exhibit a resonant frequency in the range of vibration frequencies of the rail, wherein the resonant member includes a clip ( 26 ) extending therefrom so as to retain the resonant member and the deformable material in place on the rail. The clip preferably extends laterally of the resonant member to grip the underside of the rail. The clip can have an engagement formation on the end thereof, to engage with a like formation of a further damper located on the opposing side of the rail.

Full Description:
FIELD OF THE INVENTION 
     The present invention relates to a rail damper. 
     BACKGROUND ART 
     The noise emitted by moving rail vehicles is a major limitation on their use, in that it will limit the ability of operators to install new lines in populated areas, and will limit speeds and traffic volumes on existing lines. The noise tends to be dominated by rolling noise from the wheel/rail interface, which is caused partly by vibration of the wheels and partly by vibration of the track. 
     It is not possible to select alternative materials, etc, for these elements since they are subject to very high transient loads during use, and must withstand these. Materials that would be able to absorb vibration and hence reduce noise would be unable to survive in use for any appreciable time. Resilient rail fastenings have been employed to reduce track forces and thereby reduce component damage and structure-borne noise. However, they have an adverse effect on track noise, as they tend to reduce the attenuation of rail vibration. 
     EP628,660 A1 discloses a rail bar in which a body of high specific mass is arranged within a mouldable material of low specific mass. 
     Our previous application WO99/15732 discloses a rail damper adapted to absorb a wide range of resonant frequencies in the rail through the use of a damper with resonant members tuned to two frequencies in the spectrum of noise to be absorbed. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide a means for reducing the track noise emitted by a rail system, along the lines of the systems shown in EP628,660 A1 and WO99/15732 but which are more straightforward to install. 
     We therefore provide a damper for a rail, comprising a deformable material and an elongate resonant member, the resonant member being of a stiff material as compared to the deformable material and being sized to exhibit a resonant frequency in the range of vibration frequencies of the rail, wherein the resonant member includes a clip extending therefrom so as to retain the resonant member and the deformable material in place on the rail. 
     The clip allows the damper to be fitted to the rail in an extremely short time as compared to gluing and curing processes, and with greater confidence and less inventory as compared to clamping processes. 
     The relationship between the resonant member and the deformable material is not crucial to this invention. If desired, the resonant member can be embedded in the deformable material, either by being enclosed or with a surface exposed, or the deformable material can simply be sandwiched between the resonant member and the rail. 
     The resonant member is elongate and will usually extend alongside the rail. The clip then preferably extends laterally of the resonant member, meaning that it can grip the rail, preferably the underside thereof. The clip can have an engagement formation on the end thereof, to engage with a pre-formed engagement means or with a like formation of a further damper located on the opposing side of the rail. In this latter case, it is preferred that the engagement formation is symmetrical such that both clips are identical. 
     A further resonant member can be included, for example as taught in WO99/15732 (or otherwise). The further resonant member is thus preferably sized to exhibit a different resonant frequency in the range of vibration frequencies of the rail. To this end, it can have a different profile to the first resonant member. It can be embedded within the deformable material in the same manner as the first. 
     The deformable material is preferably in an elongate form and/or continuous. A deformable material that consisted simply of isolated islands supporting the resonant member might be less robust and may have inappropriate elastic properties for transmission of vibration, although these issues may be resolvable through materials selection. 
     The deformable member can be visco-elastic and/or rubber or rubber-like. It is preferably substantially uniform in composition. 
     The present invention also provides a rail, to which is attached a damper as defined above. In such a rail, the damper is preferably positioned on the rail so as to cover the junction between the web and the foot of the rail. This will be assisted if at least one (or the) resonant member is an elongate angled section, ideally with an angle that matches the angle between external surfaces of the rail head and foot. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which; 
         FIG. 1  shows a known rail damper held in place with a clamp; 
         FIG. 2  shows the damper of the present invention in section, in the process of assembly; 
         FIG. 3  shows a perspective view of the damper of the present invention, in place; 
         FIG. 4  shows a section of an alternative damper, in place; 
         FIG. 5  shows a perspective view of a damper according to the present invention; and 
         FIGS. 6   a  and  6   b  show interlocking parts of clips of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to  FIG. 1 , a known rail and damper are shown, in which the rail  10  consists of a wide foot  12 , a web  14  and an enlarged head  16 . On each side of the foot/web join there is a damper  18  constructed in accordance with WO99/15732. This comprises a body  20  of deformable material in which are embedded two elongate bars  22 ,  24  of a different sectional profile. These bars  22 ,  24  resonate at different frequencies within the range of vibration frequencies of the rail and the combined body  20  and bars  22 ,  24  forming the damper  18  absorb a wide range of vibration frequencies from the rail and thereby alleviate noise emissions. 
     It can however be difficult to attach the damper  18  to the rail  10 . One option is to glue the damper in place or to cure the deformable material in place on the rail. This approach gives a good attachment but takes some time to install. Another option also shown in  FIG. 1  is to use a C-clamp  26 , which urges the damper down onto the rail by compressing it in place. This clamp fixes onto the top surface of the damper  18  and the underside of the rail foot  12 . However, this is less secure and requires a wider range of parts to be stocked. 
       FIG. 2  shows an alternative design. The rail  10  is loosely fitted with a first damper  50  comprising a block of first deformable material  52  in which is embedded a first resonant member  54  in the form of an elongate steel rod. A second clamp-on resonant member  56  is provided, in the form of a second elongate rod of a different sectional profile. This has on one side a second strip  58  of deformable material and, extending from the opposing side, one or preferably a plurality of clips  60 . In this case, the clips are of a generally C-shaped profile and extend from the rod  56  at intervals. Alternatively, the clips could be continuous along the length of the resonant member. They are sized such that when the rod  56  rests on the upper face of the block  52 , the distal end of the C-clip  60  presses against the underside of the rail foot. In this way, once the rod  56  is in place, a two-resonator damper is formed which is already held in place by the clip or clips  60 . 
     As shown in  FIG. 2 , the first resonator  54  is embedded in the deformable material  52  with only one face of the first resonator being exposed. This is on the outer face of the deformable material  52  and thus there is a layer of deformable material between the first resonator  54  and the rail  10  and on the upper surface of the damper  50 . The layer on the upper surface thus lies between the first resonator  54  and the second clamp-on resonator  56  when the latter is in place. 
     Alternative arrangements are of course possible. For example, an extended layer of deformable material  58  could cover the underside of the second resonator  56 , instead of or in addition to the layer of deformable material on the upper surface of the first resonator  54 . 
       FIG. 3  shows a section of the elongate resonators  54 ,  56  and the two clips  60  which extend from the outer face of the second clamp-on resonator  56  and show a C-shaped configuration with the lower edge of the C extending beneath the rail foot  12 . As shown in  FIG. 3 , the clips have a profile which includes an outwardly extending part  62  to provide the necessary clearance of the rail foot  12 , a downwardly extending part  64  to cover the distance between the second resonator  56  and the attachment point, in this case the lower face of the rail foot  12 , and an inwardly extending part  66  to engage with the attachment point being the underside of the rail foot  12 . 
       FIG. 3  also shows the deformable material  58  attached to the second clamp-on resonator, with a part  68  extending over the upper surface of the second resonator  56 . This part of the deformable material is not expected to play a major part In the vibration absorption properties of the damper but may offer an decorative effect and provide a measure of environmental protection. 
       FIG. 4  shows a three-mass system  100  secured in place on one side of the rail  10 . First and second resonant members  102  and  104  of the three mass system are embedded in a deformable material  106 . A third or clamp-on resonant member  108  lies over the deformable material  106  and has one or more clamps  110  which extend beneath the rail foot  12 . These clamps resiliently urge the third clamp-on resonant member  108  towards the rail foot  12  and thus trap the first and second resonant members  102 ,  104  to hold the clamp-on damper  100  in place on the rail. A small clearance is provided between one end of the third clamp-on resonant member  108  and the rail  10  to allow the former to vibrate. This could of course be replaced by a layer of deformable material, but a manufacture step is avoided by using a clearance instead. Vibrations will still be transmitted to the third clamp-on resonator  108  via the deformable material  106  in which the first and second resonators  102 ,  104  of the three-mass system are embedded. 
     The three resonators  102 ,  104 ,  108  are all of a different cross-sectional profile and all thus generate a system with multiple resonant frequencies. In practice, some resonators could be matched, if desired, or if only a single or double frequency damper was required. 
     In  FIG. 4 , a standard single-mass damper  112  is provided on the second side of the rail. The frequency damped by this damper could be the same as one of those damped by the three-mass damper  100  or it could be a fourth frequency. This could of course be replaced with a single-, two- or three-mass damper as set out herein. 
       FIG. 5  shows a damper  120  comprising a resonator  122  embedded in a deformable material  124  and with (in this case) two clamps  126  extending from the resonator  122  to clamp the latter in place. The dimensions of the clamps can again be adjusted to suit the particular arrangement. A further block of deformable material (not shown) can be interposed beneath the resonator  122  to be clamped in place. This block can contain further resonators tuned to the same or to further frequencies. If there is no further block of deformable material then a layer of deformable material beneath the resonator  122  may be useful. 
       FIGS. 6   a  and  6   b  show a modified form of the clamp, applicable to any of the various dampers described above. The tip  128  of the clamp (see  FIG. 5 ) will normally lie beneath the rail foot. Where a clamped damper is fitted on either side of the rail, there will be two such tips facing each other. As shown in  FIG. 6   a , these tips can be formed with engagement formations  130   a ,  130   b  that are adapted to lock together. In  FIGS. 6   a  and  6   b , the clamps shown from above, are symmetrical and thus the two parts are identical to evident advantage. A wide range of engagement formations are suitable, including the half-dovetail cam profiles of  FIGS. 6   a  and  6   b.    
     The materials used for the above-described parts can be any suitable material exhibiting appropriate properties. A rubber or rubber-like material is preferred for the deformable material as this exhibits appropriate visco-elastic properties. The remaining parts are suitably of a ferrous material such as steel, although parts of the clip such as the downwardly extending part  64  could be of a less stiff material such as nylon or a composite such as a plastics/steel composite. 
     The damper according to the present invention has a number of advantages. In particular;
         the clamping arrangement substitutes for gluing and thereby reduces installation time   the tuned dampers can have 2 or more masses, as desired   the dampers can be removed when the life of the rail is expired   the dampers can be removed for rail maintenance   the dampers can be wider than known designs, to sit between the sleepers   the dampers can be higher than the existing design, since they could be removed for tamping operations, although clearance for other equipment such as the worn rail/worn wheel condition will still have to be taken into account       

     It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention.

Technology Classification (CPC): 4