EP1197598A1

EP1197598A1 - Vibration damper for rails

Info

Publication number: EP1197598A1
Application number: EP01203593A
Authority: EP
Inventors: Hugo Sol; Patrick Carels
Original assignee: Composite Damping Material NV CDM
Current assignee: Composite Damping Material NV CDM
Priority date: 2000-10-10
Filing date: 2001-09-24
Publication date: 2002-04-17
Anticipated expiration: 2021-09-24
Also published as: DE60134707D1; BE1013746A3; EP1197598B1; ATE400699T1

Abstract

The invention concerns a vibration damper (1) for rails (3) of a railway, resting on sleepers (4) which are situated at a certain distance (10) from one another, which damper (1) is designed to be fixed to said rails between two successive sleepers (4), whereby said damper (1) comprises at least one damping element (7) which must be placed against the rail flange (3a) and/or the top side of the rail foot (3b) of the rail (3), so that the far end (6) of the damping element (7) which is turned away from the rail (3) can freely vibrate.

Description

The invention concerns a vibration damper for rails of a railway, resting on sleepers which are situated at a certain distance from one another.
Vibrations in rails are caused among others by the wheels of railway vehicles rolling over them. Most vibrations are strongly damped by the sleepers upon which the rails rest. With certain resonance frequencies, standing waves are created in the rails with nodes situated at the height of the sleepers, as a result of which the rails will vibrate independently of the latter and may cause considerable noise pollution.
According to the present state of the art, vibrations in rails are damped by applying for example vibration-isolating strips between the rails and the sleepers or against the flange and the foot of the rails over almost the entire length of the latter. Consequently, these techniques can only be applied before or during the mounting of the rails on the sleepers.
Another already known technique for damping vibrations in rails is described in patent number EP 0 761 879 and consists in fixing an active vibration damper between two successive sleepers, upon which rests a rail, at the rail foot of the rail.
With these active vibration dampers, the vibrations in the rails are damped by a non-deformable active mass which is surrounded by a deformable or elastic layer and which is situated in the above-mentioned vibration damper above the rail foot. In the damper, the mechanical energy of a vibration in the rail is transformed into thermal energy. This can be done in an optimal manner when the natural vibrations of the vibration damper are excited. Consequently, in order to obtain an effective damping, the resonance frequencies of the natural vibrations of the vibration damper must be adjusted to the resonance frequencies of the major natural vibrations of the rails resting on the sleepers.
A rail thus has different vibration modes which each correspond to a certain resonance frequency. The major vibration mode, also called the fundamental vibration mode, is a standing wave with a vertical vibration direction whose nodes coincide with the position of the sleepers. This wave has several higher harmonics, each corresponding to another resonance frequency of the rail. The first harmonic of this fundamental vibration mode is a standing wave with an additional node situated in the middle between two successive sleepers. However, there are also standing waves with a horizontal vibration direction, and there are torsion modes, each corresponding in turn with other specific resonance frequencies.
The existing vibration dampers as described in EP 0 761 879 have a solid active mass which is adjusted, together with a springy element, to the frequency of the fundamental vibration mode. Thus, these existing vibration dampers have little influence on the other vibration modes such as the higher harmonics of the fundamental vibration mode, the horizontal vibration modes and the torsion modes, so that practically only the wave with the fundamental vibration frequency is damped.
The invention aims to design an active vibration damper with a simple construction which makes it possible to damp practically all the vibration modes and which, as a consequence, does not restrict itself to damping the fundamental vibration mode.
To this aim, the vibration damper, which is designed to be fixed to the rails of a railway between two successive sleepers, contains at least one damping element with an evenly divided rigidity and mass, which must be applied against the rail flange and/or the top side of the rail foot of the rail. Thus, the side of this damping element which is turned away from the rail can freely vibrate. The vibration damper according to the invention preferably contains two damping elements which must be provided opposite to one another on either side of the rail.
The vibration damper according to the invention has an infinitely long series of vibration modes with a high density of resonance frequencies, including those frequencies which correspond to the resonance frequencies of the rails resting on the sleepers. This makes sure that for every resonance frequency of the rail, there is always a resonance frequency of the vibration damper which is very close to the latter or which even coincides with it entirely.
For an optimal interaction between the rail and the damper, the damping elements follow the geometry of the rail flange and/or the rail foot to perfection, such that the movement of the rail excites the resonance frequencies of the vibration damper.
Practically, said damping elements consist of vibration-damping elastic material, such as granules of recycled rubber in a matrix of polyurethane, and they are practically beam-shaped with a pre-formed far end, so that they can be fitted onto the rail flange and rail foot. This pre-formed far end must be fixed against the rail, so that the opposite far end remains free.
In an advantageous manner, the vibration damper further comprises a layered plate consisting of at least one relatively elastic layer and a vibration-damping viscoelastic layer, whereby the latter must be attached to the bottom side of the rail foot, so that the above-mentioned elastic layer is isolated from the rail.
In a particularly advantageous manner, the elastic layer is made of steel, and the layered plate is fitted onto the bottom side of the rail foot, whereby this plate forms a connecting piece between the two damping elements situated opposite to one another.
Another major characteristic of the invention is that the resonance frequencies of this layer of steel, together with the vibration-damping viscoelastic layer, is adjusted to the frequency of the fundamental vibration mode and possibly also to its first harmonic. Thus, the layered plate has one or several resonance frequencies which correspond to the frequencies of the vibrations to be damped in the rails resting on the sleepers, and apart from being a connecting piece, it also has a major active function in the operation of the vibration damper.
More specifically, the resonance frequencies of said layered plate in the vibration damper according to the invention are adjusted to the resonance frequencies of the fundamental vibration mode and its first harmonic on the one hand, between more or less 800 and 1000 Hz and between more or less 1600 and 2000 Hz respectively, and use is made on the other hand of two damping elements with a high density of resonance frequencies of some 0 Hz to 3000 Hz in order to damp additional resonances of the rail.
The invention also concerns a method for damping vibrations caused by railway vehicles in the rails of a railway. These rails rest on sleepers, situated at a certain distance from one another, whereby a vibration damper is attached to the rails between two successive sleepers.
This method is characterised in that said vibration damper is fixed to the rails between two successive sleepers in a position between the vibrating point of the rails on the one hand, with the largest vertical divergence for the vibration according to the fundamental vibration mode, and one of either vibrating points of the rails with the largest vertical divergence for the vibration according to the first harmonic of the fundamental vibration mode on the other hand.
In an advantageous manner, for an optimal damping, this vibration damper is fixed to said rail at a distance from the nodes of the fundamental vibration mode which is equal to three eighth of the distance between two successive nodes. In that particular place, the sum of the vertical divergence from the fundamental vibration mode and its first harmonic vibration is maximal.
Other particularities and advantages of the invention will become clear from the following description of specific embodiments of the method and the device according to the invention; this description is given as an example only and does not restrict the scope of the claimed protection in any way; the reference figures used hereafter refer to the accompanying drawings.
Figure 1 is a schematic side view of a railway with a rail onto which are attached vibration dampers according to the invention.
Figure 2 is a cross section of a rail and a vibration damper according to a first embodiment of the invention.
Figure 3 is a schematic top view to a smaller scale of a rail with a vibration damper according to this embodiment of the invention.
Figure 4 is a cross section of a rail with a vibration damper according to a second embodiment of the invention.
Figure 5 is a schematic top view to a smaller scale of a rail with vibration dampers according to this second embodiment of the invention.
Figure 6 is a schematic representation of the fundamental vibration mode and its first harmonic in a rail.
In the different drawings, the same reference figures refer to identical or analogous elements.
The invention concerns vibration dampers 1 designed to be attached to rails 3 of an existing railway, in discrete places between sleepers 4 upon which said rails 3 are mounted, as is represented in figure 1. The sleepers 4 rest on a conventional railway bed 5, preferably at a regular distance from one another, which is for example made of shingle. The rails 3 have a rail foot 3b and a rail surface 3c which are connected by means of a standing rail flange 3a.
The vibration dampers 1 are preferably attached to the rails 3 in such a manner that there is no direct contact between them and the railway bed 5, and thus they are freely suspended to the rails 3. This makes sure that the vibration dampers 1 can freely vibrate on their far ends 6 turned away from the rails 3.
In a first embodiment of the vibration damper 1 according to the invention, as is represented in figures 2 and 3, it contains two elastic, practically beam-shaped elements 7, with a length of almost 18 cm according to a direction across the rail 3, a height of almost 8 cm, a width of almost 8 cm according to the longitudinal direction of the rail 3 and a mass of almost 2 kg. Both beam-shaped elements 7 are fixed crosswise to the rail 3. One far end 6' of the above-mentioned elements 7 is placed against the rail 3 and has such a shape that it fits almost perfectly to the rail flange 3a and the rail foot 3b. The other far end 6 is not fixed and thus can vibrate freely. Said elements 7 consist for example of granules of recycled rubber in a matrix of polyurethane having a density of some 1000 kg m^-3 and a modulus of elasticity (E) of some 14 10⁶ N m^-2.
According to this embodiment, the damper 1 also contains a layered plate 8 consisting of a steel plate 8b which is covered on either side with a layer 8a and 8c made of a conventional damping viscoelastic material, whereby said steel plate 8b has a width of some 8 cm, a density of some 7850 kg m^-3 and a modulus of elasticity (E) of some 21.10¹⁰ N m^-2, whereas the above-mentioned viscoelastic layers 8a and 8c have a density of some 1000 kg m^-3 and a modulus of elasticity (E) of some 20.10⁶ N m^-2.
This layered plate 8 must be fixed against the bottom side of the rail foot 3b. On either side of the rail 3, the layered plate 8 is also connected to the part of the bottom side of said elements 7 which is situated at the rail foot 3b. The plate 8 thus forms a connecting piece between the elements 7, however without hindering the far ends 6 of the elements 7 which are turned away from the rail 3 to freely vibrate.
The plate 8 has a resonance frequency of some 800 Hz. As a result, a vibration in the rail 3 with a frequency of some 800 Hz will create a resonance in the plate 8. Due to the vibration of this resonance frequency, the plate 8 will bend around an axis which is parallel to the rail 3. This mechanical energy which is transmitted to the plate 8 is thus transferred in thermal energy.
By means of fixing means, consisting of bolts 9 and pressure plates 13, the elements 7 and the layered plate 8 are tightened against the rail 3. The bolts 9 are provided on either side of the rail 3, right through the elements 7 and the layered plate 8. The pressure plates 13 extend in a recess provided to this end in the top surface of the elements 7.
In order to provide for a good connection of the elements 7 against the rail flange 3a and the rail foot 3b, the far end 13' of the pressure plates 13 in the vicinity of the rail flange 3a is directed somewhat slantingly upward, and it thus pushes against a correspondingly inclined part of the elements 7. By tightening the bolts 9, the elements 7 are pushed laterally against the rail 3 via the pressure plates 13 and they are fitted close onto the latter. Consequently, the bolts 9 provide for a perfect fit of the elements 7 and the plate 8 onto the rail 3 on the one hand, and they provide for a certain pre-stress between the elements 7, the plate 8 and the rail 3 on the other hand. Said pre-stress is adjusted by tightening the bolts 9.
By thus fixing the vibration dampers 1 to the rails 3, vibrations occurring in the latter are almost entirely transferred to the vibration dampers 1.
Consequently, no changes have to be made to the rails 3 when fixing the vibration dampers 1.
A second embodiment of the vibration damper 1 according to the invention is represented in figures 4 and 5.
This embodiment differs from the preceding embodiment in that the damper 1 comprises two elastic L-shaped elements 7, having a length of some 18 cm according to a direction across the rail 3, a height of some 8 cm, a width of some 8 cm on the side 6' which is fitted to the rail 3, a width of some 20 cm on the side 6 turned away from the rail 3, and a mass of 4 kg. These elements 7 can also be formed of granules of recycled rubber in a matrix of polyurethane.
Further, this second embodiment differs from the preceding embodiment in that the layered plate 8 has a first resonance frequency of some 890 Hz on the one hand, and a second resonance frequency of some 2090 Hz on the other hand. These two resonance frequencies of 890 Hz and 2090 Hz practically coincide with the frequencies of the rail 3 for the fundamental vibration mode 12 and its first harmonic 11, as is schematically represented in figure 6.
A resonance is created in the plate 8 as soon as the rail 3 starts to vibrate with the first resonance frequency. Just as in the first embodiment, this results in a bending movement of the plate 8 over an axis which is parallel to the rail 3. In this second embodiment as well, a resonance is created in the plate 8 as soon as the rail 3 starts to vibrate with the second resonance frequency. This results in a bending movement of the plate 8 over an axis which is perpendicular to the rail 3.
In this second embodiment, the fixing means contain additional pressure plates 19 which, with a slantingly downward directed far end 19', push against the underlying pressure plates 13 when the corresponding bolt 9 is tightened. Thus, it is possible to exert a pressure force on the pressure plates 13 via the far end 19' of the pressure plates 19, so that the far end 6' of the elements 7 is slightly deformed and thus almost perfectly fit onto the rail flange 3a and the top side of the rail foot 3b.
The invention also concerns a method for fixing said vibration dampers 1 to the rails 3 between the sleepers 4 situated at a certain distance 10 from one another upon which these rails 3 rest (Figure 1).
As a railway vehicle rides over the rails 3, vibrations in the shape of standing waves 11 and 12 are created therein, in particular the fundamental vibration mode and its first harmonic with the corresponding resonance frequencies of the rails 3. As described above, the rails 3 vibrate independently of the sleepers 4 with these resonance frequencies. This is schematically represented in figure 6.
With a vibration 12 according to the fundamental vibration mode, the rail 3 will show a maximum divergence at a point 15 which is situated almost in the middle between two successive sleepers 4. The first harmonic of this fundamental vibration mode corresponds to a vibration 11 whereby two points 14 with a maximum divergence of the rail 3 are obtained. These points 14 are situated at a distance from the attachment of the rail 3 to the sleepers 4 which is equal to one fourth of the total distance between two successive sleepers 4.
In order to obtain a damping of the vibration of the rail 3 which is as large as possible, the vibration damper 1 is preferably attached on the rail 3 in a position in which the total divergence of the rail 3 resulting from the fundamental vibration mode and the first harmonic thereof is maximal.
In particular, according to the method of the invention, the vibration dampers 1 are attached to said rail 3 at a distance 2 from the sleepers 4 which amounts to some three eighth of the distance 10 between two successive sleepers 4.
In certain cases, it is sufficient to maximally dampen the fundamental vibration mode only. The vibration damper 1 is then attached to the rail 3 in the middle between two successive sleepers 4 where the divergence of the rail 3 is thus maximal.
Naturally, the invention is not restricted to the above-described method and the vibration damper represented in the accompanying figures. Thus, it is possible to fix more than one vibration damper between two successive sleepers. Further, it is also possible for the vibration damper 1 according to the invention to have a damping element 7 on one side of the rail 3 only.
The device and the method according to the invention cannot only be applied to conventional railways, they can also be used in all sorts of applications where a discrete bearing of rails results in annoying vibrations and the accompanying noise pollution.

Claims

Vibration damper (1) for rails (3) of a railway, resting on sleepers (4) which are situated at a certain distance (10) from one another, which damper (1) is designed to be fixed to said rails between two successive sleepers (4), characterised in that said damper (1) comprises at least one damping element (7) which must be placed against the rail flange (3a) and/or the top side of the rail foot (3b) of the rail (3), whereby the far end (6) of the damping element (7) which is turned away from the rail (3) can freely vibrate.
Damper (1) according to claim 1, characterised in that said damping element (7) fits to the rail flange (3a) and the top side of the rail foot (3b).
Damper (1) according to any of claims 1 or 2, characterised in that said damper (1) comprises two elements (7) which must be placed opposite to one another on either side of the rail (3).
Damper (1) according to any of claims 1 to 3, characterised in that said damping element (7) has a high density of resonance frequencies, including those frequencies which correspond to the resonance frequencies of the rails (3) resting on the sleepers (4)
Damper (1) according to any of claims 1 to 4, characterised in that said damping elements (7) are practically beam-shaped and are made of vibration-damping elastic material, such as granules of recycled rubber in a matrix of polyurethane.
Damper (1) according to any of claims 1 to 5, characterised in that said damper (1) further has a layered plate (8) having at least one elastic layer (8b) and a vibration-damping viscoelastic layer (8a), whereby the latter must be fixed to the bottom side of the rail foot (3b) so as to isolate said elastic layer (8b) from the rail (3).
Damper (1) according to claim 6, characterised in that said elastic layer (8b) is made of steel.
Damper (1) according to claim 6 or 7, characterised in that said layered plate fits to the bottom side of the rail foot (3b).
Damper (1) according to any of claims 6 to 8, characterised in that said layered plate (8) forms a connecting piece between two damping elements (7) situated opposite to one another, whereby said elastic layer (8b) and/or vibration-damping viscoelastic layer (8a) makes contact with the bottom side of said elements (7).
Damper (1) according to any of claims 6 to 9, characterised in that said layered plate (8) has one or several resonance frequencies which correspond to resonance frequencies of the rails (3) resting on the sleepers (4)
Damper (1) according to any of claims 6 to 10, characterised in that said layered plate (8) has resonance frequencies which correspond to the resonance frequencies of the fundamental vibration mode with a divergence in the vertical direction and its first harmonic.
Damper (1) according to any of claims 1 to 11, characterised in that it has means, in particular bolts (9) and pressure plates (13), to push said damping elements (7) with an adjustable tension against the rails (3).
. Damper (1) according to any of claims 6 to 12, characterised in that it comprises means, such as bolts (9) and pressure plates (13), to push said layered plate (8) with an adjustable tension against the rails (3).
Method to dampen vibrations created by railway vehicles in the rails (3) of a railway, which rails (3) rest on sleepers (4) situated at a certain distance (10) from one another, whereby a vibration damper (1) is attached to said rail (3) between two successive sleepers (4), in particular a vibration damper (1) according to any of claims 1 to 13, characterised in that said damper (1) is fixed to said rails (3) in a position between the point (15) of the rails (3) with the largest divergence for the vibration with the resonance frequency which results in the standing wave (12) of which all nodes (17) are situated at the height of the attachment of said rails (3) onto said sleepers (4) on the one hand, and one of the vibrating points (14) of the rails (3) with the largest divergence for the vibration with the resonance frequency which results in the standing wave (11) with an additional node situated in the middle between two sleepers (4) on the other hand.
Method according to claim 14, characterised in that said damper (1) is fixed to said rail (3) at a distance (2) from the sleepers (4) which amounts to practically three eighth of the distance (10) between two successive sleepers (4).
Railway with one or several rails (3) characterised in that said rails (3) are provided with vibration dampers (1) according to any of claims 1 to 13.