Railways: surface track – Deadening noise
Reexamination Certificate
2000-08-31
2001-12-04
Le, Mark T. (Department: 3617)
Railways: surface track
Deadening noise
C238S283000, C238S338000, C238S342000, C238S345000, C238S349000
Reexamination Certificate
active
06325301
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention falls within the field of devices for mounting the rails of a railway track. It relates more particularly to a track support system to be affixed directly onto a bed or floor or onto sleepers.
Current devices for fixing track rails include fastener means and at least one pad made of elastic material which gives elasticity to the wheel-rail assembly so that there is obtained a degree of is of the environment with respect to the vibrations produced by the dynamic forces applied to the rails when a vehicle runs on the rails.
There is almost always an elastic device in the form of a relatively rigid pad directly beneath the rail. There is often a second, more flexible pad beneath a metal sole-plate or a sleeper. The latter pad provides anti-vibration isolation.
The first resonant frequency, in flexure, of the wheel-rail assembly depends on the dynamic stiffness of the pads. This resonant frequency is inversely proportional to the anti-vibration performance of the rail-fixing system: a low resonant frequency gives better anti-vibration isolation than a high resonant frequency. With pads which have a low dynamic stiffness, the first resonant frequency of the wheel-rail assembly is reduced, thereby giving rise to a good anti-vibration filter. The best filter is therefore obtained with the lowest dynamic stiffness of the pads.
However, there is a lower physical limit to this dynamic stiffness of the pads used in the current rail-fixing systems. The dynamic stiffness is directly proportional to the static stiffness of the pads. The static stiffness of the pads cannot be too low because of the fact that it has a direct influence on the deflection of the rails when a vehicle is running along the rails. This rail deflection is generally limited to approximately 3 mm. This static rail deflection limit imposes a minimum static stiffness, and thus a minimum dynamic stiffness of the anti-vibration pad. This phenomenon limits the anti-vibration isolation performance of the current rail-fixing systems. For most current fixing devices, the resonant frequency lies between 35 Hz and 60 Hz.
In order to obtain a superior isolation performance to that obtained with the current fixing systems, it is necessary for the fixing and isolation functions to be completely decoupled. This is realized in systems of the floating-slab type in which the rails are fixed onto a slab which is itself isolated from the environment by anti-vibration studs placed between the slab and the bed (or floor). In the case of a floating slab, the resonant frequency lies between approximately 10 Hz and 25 Hz, which gives a better anti-vibration filter. The latter systems are however very expensive and difficult to maintain.
BRIEF SUMMARY OF THE INVENTION
It is the primary object of the present invention to provide a rail support system for being fixed directly onto a bed or floor or onto sleepers anchored into a concrete bed or in the ballast, which has an anti-vibration isolation performance close to that obtained with a floating slab and which at the same time ensures good rail stability.
This object is achieved according to the invention by a rail support system which comprises a sole plate resting on an anti-vibration pad disposed on a supporting structure and at least one adjustable prestressing resilient device acting on the sole-plate to urge the sole-plate towards the supporting structure and apply a defined prestressing force to the anti-vibration pad so that the static deflection of the rail is limited to a defined value when a vehicle moves over the rail.
As a result of the prestress applied to it, the anti-vibration pad always works in the region of quasi-linear behaviour of its deflection curve. When a wheel passes on the rail in the region of the support device, the anti-vibration pad continues to operate in the region of quasi-linear behaviour. The prestress becomes very low when the wheel passes over the support device and the static deflection of the rail is limited while the desired anti-vibration isolation is provided. The system of the invention thus provides, for supporting the rail, a high apparent static stiffness together with a low dynamic stiffness. It is also useful in affixing two rails in a curve, whereby the invention provides a reduction in squeaking noise.
The rail support system according to the invention may be realized with or without a metal base-plate underneath the anti-vibration pad. In the first case, the sole-plate which carries the rail is fastened to the base-plate by means of the prestressing devices. In the second case, the sole-plate is anchored directly into the track bed by means of the prestressing devices.
A further object of this invention is to provide a sole-plate for supporting a rail, which is specially adapted for being anchored directly into the support structure of the track with an anti-vibration pad underneath sole-plate.
REFERENCES:
patent: 2421502 (1947-06-01), Hayes
patent: 4765538 (1988-08-01), Meyer
patent: 4844338 (1989-07-01), Bucksbee
patent: 5314115 (1994-05-01), Moucessian
patent: 6027033 (2000-02-01), Vanhonacker
patent: 6027034 (2000-02-01), Demmig et al.
patent: 296 19 480 (1997-02-01), None
patent: 2 737 511 (1997-02-01), None
patent: WO 97/42376 (1997-11-01), None
Le Mark T.
Lipsitz Barry R.
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