Railways: surface track – Deadening noise
Patent
1997-12-30
2000-02-22
Oberleitner, Robert J.
Railways: surface track
Deadening noise
238 2, E01B 1900
Patent
active
060270330
DESCRIPTION:
BRIEF SUMMARY
The present invention falls within the field of devices for supporting the rails of a railway. It relates more particularly to a method for fixing a rail.
Current devices for fixing a rail include at least one pad made of elastic material which gives elasticity to the wheel/rail assembly so that a degree of vibratory isolation of the dynamic forces with respect to the environment is obtained.
There is almost always an elastic stage (a quite 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 vehicles are running along the rails. This rail deflection is generally limited to approximately 3 mm. For most current fixing devices, the resonant frequency lies between 35 Hz and 60 Hz.
This static rail deflection limit imposes a minimum static stiffness, and thus a minimum dynamic stiffness of the pad. This phenomenon limits the anti-vibration isolation performance of the current rail-fixing systems.
In order to achieve a superior isolation performance to that obtained with the conventional fixing systems, it is necessary for the fixing and isolating functions to be completely decoupled: this is realized in systems of the floating-slab type in which the rails are fixed to a slab which is itself isolated from the environment by anti-vibration studs 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.
The object of the present invention is to give the rail-fixing devices an anti-vibration isolation performance close to that obtained with a floating slab and at the same time to ensure good rail stability.
This objective is achieved according to the invention by a novel method for fixing a rail, as defined in the claims. The anti-vibration pad is subjected to a significant preload, this preload being such that the anti-vibration pad works in its region of linear behaviour. When a wheel passes over the rail above a fixing device, the load becomes greater, but the anti-vibration pad continues to operate in its region of linear behaviour. The static rail deflections are thus limited, while providing the desired anti-vibration isolation. The method according to the invention for fixing the rail thus provides a high apparent static stiffness with a low dynamic stiffness.
The invention is explained in more detail in the description which follows, with reference to the appended drawings.
FIG. 1 shows a typical rail-fixing device.
FIG. 2 shows a typical static deflection curve for an anti-vibration pad.
Referring to FIG. 1, a typical rail-fixing device, having two elastic stages, comprises the following members:
The anti-vibration pads have a static deflection curve as shown in FIG. 2. Three regions may be distinguished in this curve:
It is important for the product always to work in the linear region because of the fact that the actual load is quasi-static and rapid (the passage of wheels). This avoids passin
REFERENCES:
patent: 4266719 (1981-05-01), Ortwein et al.
patent: 4316578 (1982-02-01), Reynolds et al.
patent: 5203501 (1993-04-01), Vanotti
McCarry, Jr. Robert J.
Meroni, Jr. Charles F.
Oberleitner Robert J.
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