WO2011073826A1

WO2011073826A1 - Rail vibration absorber and fastening mechanism

Info

Publication number: WO2011073826A1
Application number: PCT/IB2010/055290
Authority: WO
Inventors: Wai Lun Ho
Original assignee: Wilson Acoustics Limited
Priority date: 2009-12-14
Filing date: 2010-11-19
Publication date: 2011-06-23
Also published as: CN102713066A; CN102713066B; EP2513374A1; EP2513374A4

Abstract

A rail vibration absorber and a fastening mechanism are provided. The rail vibration absorber to absorb the vibration from the rail based on a tuned mass damping mechanism. The apparatus comprises at least one vibration absorber (12) adapted to couple to a rail (3, 4), at least one fastening module and at least one mounting module. The mounting module is coupled to the fastening module and also adapted to secure the vibration absorber (12) to the rail (3, 4) at a first location and at a second location substantially different from the first location. When the natural frequencies of the damping system are tuned to the rail vibration frequencies, most of the vibration energy from the rail would be taken up by the absorber.

Description

Rail Vibration Absorber and Fastening Mechanism

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application having Serial No. 61/286,031 filed Dec. 14, 2009, which is hereby incorporated by reference herein in its entirety.

FIELD OF INVENTION

[0002] This invention relates to a vibration absorber for reducing vibration and noise radiation from rail, and the fastening mechanism to attach the absorber to the rail.

BACKGROUND OF INVENTION

[0003] Railway noise impact on nearby residents has drawn increasing environmental concerns as railway lines extending into urban centers. Erection of wayside noise barriers in existing railway lines is usually restricted in many cases owning to structural loading and artistic concerns. In recent years, more efforts were developed to control rail noise radiation at source by attaching vibration absorbers onto rails.

[0004] Conventional methods of fastening rail vibration absorbers by gluing or clamping would allow tiny movement gaps to be generated at the attachment interface after repeated train passage. At critical noise radiating frequencies (>300Hz), rail vibration displacement is less than a few microns. At such small amplitude, vibration energy transfer from the rail to the absorbers would be significantly hindered by the tiny gaps at the attachment interface even if the gaps are less than a micron. A persistent mounting method with rigid interface connection is vital for rail vibration absorber performance.

SUMMARY OF INVENTION

[0005] In the light of the foregoing background, it is an object of the present invention to provide an alternative method and apparatus to mount the vibration absorbers onto the rail. [0006] The invention is a vibration absorber based on tuned mass damping mechanism, comprising oscillation mass, shear resilient layers and holding plates stacked alternatively to form discrete mass-spring-systems. When the natural frequencies of these mass- spring-systems are tuned to the rail vibration frequencies, most of the vibration energy from the rail would be taken up by the absorber, and dissipated in the shear resilient layer by hysteresis.

[0007] To minimize the aforementioned movement gaps at the mounting interface and maximize energy transfer to the absorber, the present invention provides a persistent mounting method with rigid connection at the mounting interface for high frequency vibration. [0008] The absorber is mounted to the rail by compressive force provided by a mounting bolt beneath the rail. An inclined plane is used to provide simultaneous clamping forces in both vertical and lateral directions. At the mounting points, thin layer of gap filing material having high viscosity and low compressibility are applied. The gap filling material aims to solidify any movement gaps for high frequency (>300Hz) vibration transmission.

[0009] Resilient buffer layer is inserted above the inclined plane. For typical rail vibration of less than lOOg (gravitational acceleration), the resilient buffer provides rigid connection for effective energy transfer to the vibration absorbers. In extreme events of high vibrations, these resilient buffers prevent structural damage to mounting components. After the event, the mounting members would be automatically restored to its original position by the resilient buffer compression force.

[0010] Other features of the invention are revealed in the detailed description.

BRIEF DESCRIPTION OF FIGURES

[0011] Fig. 1 shows the cross sectional view of an exemplary embodiment of the vibration absorber being attached to the rail. [0012] Fig. 2 shows the isometric view of an exemplary embodiment of the vibration absorber being attached to the rail.

[0013] Fig. 3 shows the 3-dimensional view of an exemplary embodiment of the vibration absorber being attached to the rail, as viewed from the bottom.

[0014] Fig. 4 shows another exemplary embodiment of the vibration absorber, in which one oscillation mass is split to form a 2 degree of freedom system. Each labeled component is described below:

1 : Mounting Bar

2: Gap Filler

3: Rail Foot Tip

4: Rail Web

5 : Damper Mountin

6: Inclined Plane

7: Force Orientation Bar

8: Oscillation Mass Mounting Bolt

9: Resilient Buffer Layer

10: Viscous Layer Constraint Bar

1 1 : Force Transmission Member

12: Oscillation Mass

13: Oscillation Mass Holding Plate

14: Oscillation Resilient Layer

15: Resilient Buffer Holding Plate

16: Nylon Nut

17: Viscous Damping Layer DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] As used herein and in the claims, "comprising" means including the following elements but not excluding others. "Couple to" means physically contacting, either directly or indirectly.

[0016] While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those skilled in the art with access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the invention would be of significant utility.

Vibration Absorber Components

[0017] Referring to Figs. 1 to 3, the vibration absorber is attached to the rail web 4 and foot tip 3 via the mounting bars 1. Gap filling material 2 is applied at the interfaces between the mounting bars and the rail surface. Viscous damping material 17 is applied at the mounting interface between viscous layer constraint bar 10 and the bottom surface of the foot tips 3. Lateral compression force is exerted by a damper mounting bolt 5 underneath the rail. Force orientation bar 7 with an inclined plane 6 is used to change the orientation of the compression force thus allow the device to provide both lateral and vertical mounting force simultaneously. The vertical clamping force generated from the force orientation bar would be transferred to the foot tip via the resilient buffer layer 9, its holding plate 15, the viscous layer constraint bar 10 and the viscous damping layer 17. The lateral clamping force is transferred to the rail web via the force transmission members 11, oscillation mass holding plates 13 and mounting bars 1. An oscillation mass mounting bolt 8 is inserted through the holding plates 13, oscillation resilient layers 14 and oscillation masses 12 alternatively. Nuts are tightened to a specific torque at the two ends of the bolt so as to provide adequate holding force for the oscillation masses to oscillate at prescribed frequencies. Nylon nuts 16 are then tightened onto the top of conventional nuts to prevent them from loosening.

Mounting Force Orientation [0018] The invention uses a Force Orientation Bar with an inclined plane. The inclined plane transfers the horizontal compression force from the Damper Mounting Bolt to mounting forces in both vertical and horizontal directions. Therefore simultaneous mounting forces can be provided at all mounting points by tightening the Mounting Bolt.

Gap Filling Material

[0019] Vibration displacement of rails at noise radiation frequency is less than a few microns. Movement gaps at the attachment interface would be significantly hinder vibration energy transfer from the rail to the vibration absorbers. Existing vibration absorber mounting methods such as clamping and gluing cannot provide satisfactory mounting rigidity. For gluing fixation, sub-micron size gaps in the glue layers are inevitable especially in rusted and greasy operating rails. For clamping fixation, gaps are gradually generated and enlarged at the mounting interfaces by vibration from repeated train passage.

[0020] To solidify the mounting interface gaps, the present invention uses gap filling material (adhesive material with high viscosity and low compressibility) at the mounting points. Under static compressive force, the material behaves as flexible solid and deformed to fill up the movement gaps at the mounting points. Under high frequency dynamic train excitation force, it behaves as stiff solid which allow vibration energy to be effectively transferred to the absorber.

Viscous Damping Material

[0021] Viscous damping material is applied at the interface between the foot tip bottom face and the viscous layer constraint bar to provide viscous damping to the bending waves along the rails.

Persistent Mounting Force

[0022] For rails which are subjected to severe vibration due to repeated train passage, the mounting structure may fatigue and the mounting nuts may be loosened, and then the mounting rigidity would be substantially reduced. Resilient buffer layers are introduced to provide persistent mounting.

[0023] The nylon nuts have high friction at threads. They are screwed onto the top of conventional steel nuts to prevent loosening of the conventional nuts. Resilient buffer layers are inserted above the inclined plane. These resilient layers are pre-compressed to specified ratio (e.g.5 to 25%) by tightening their mounting bolts. For typical rail vibration of less than lOOg, the resilient layer provides rigid connection. In extreme events of high vibrations (>100g), these resilient layers act as a spring buffer to prevent structural damage of mounting components. After the event, the mounting components would be automatically restored to its original position by the resilient buffer layer force.

Absorber Resonance Frequency Design

[0024] The vibration absorber is a tuned mass damper. It comprises of a plurality of oscillation masses. Each oscillation mass in the vibration absorber acts as a discrete single order of freedom (SDOF) mass-spring-system. Their natural frequencies can be independently tuned to match rail vibration at multiple frequencies. Such feature allows design flexibility for absorption of rail vibration at multiple frequencies, as there is no limitation on the frequency tuning for individual oscillation masses. As vibration bending waves propagate along the rail, the vibration energy is transferred to the oscillation masses and dissipated in the oscillation resilient layers by hysteresis.

[0025] Apart from absorbing rail vibration energy by tuned mass damping, the vibration absorber also indirectly reduces rolling noise by reducing rail corrugation growth rate, as observed in field tests.

[0026] There are alternative embodiments of the oscillation masses. The SDOF system can be converted to multiple degree of freedom (MDOF) systems by splitting the oscillation mass and inserting a resilient layer in between, without the need to alter other components. Fig. 4 shows another exemplary embodiment of the vibration absorber having a 2 DOF system. The natural frequencies are given by eqt(l).

where G is dynamic shear modulus of the resilient layers

A is the contact area between the resilient layer and the oscillation mass

b is the thickness of the resilient layer

M is the oscillation mass

K is a constant depends on the splitting geometry and properties of the additional resilient layer Frequency Tuning at Vertical and Lateral Directions

[0027] The present invention allows the oscillation masses to have different vertical and lateral natural frequencies by using anisotropic resilient layers. Such anisotropy may be achieved by introducing wavy patterns at the resilient layer surfaces along one direction.

[0028] The exemplary embodiments of the present invention are thus fully described. Although the description referred to particular embodiments, it will be clear to one skilled in the art that the present invention may be practiced with variation of these specific details. Hence this invention should not be construed as limited to the embodiments set forth herein.

Claims

What is claimed is:

1. An apparatus for reducing noise and vibration of rail and reduce rail corrugation growth rate, comprising:

a) at least one oscillation mass, said oscillation mass being exerted a first compression force by a force transmission member connected to said oscillation mass such that said oscillation mass is coupled to said rail in a first direction at a first location;

b) a force orientation bar indirectly connecting to said oscillation mass; said force orientation bar further transforming a part of said first compression force to a second compression force in a second direction substantially different from said first direction; wherein said oscillation mass being coupled to said rail by said second compression force substantially parallel to said second direction at a second location;

whereby said oscillation mass absorbs a first part of said vibration from said rail at said first location and a second part of said vibration at said second location.

2. The apparatus of claim 1 wherein said at least one oscillation mass comprises a pair of oscillation masses coupled to said rail at said first location and an opposite side of said first location respectively; wherein said first location is a web of said rail and said second location is a foot tip of said rail.

3. The apparatus of claim 1 further comprising oscillation holding plates, oscillation resilient layers and mounting bars ; each said oscillation mass being attached to at least one said oscillation holding plate via at least one oscillation resilient layer and at least one said mounting bar whereby said oscillation mass being coupled to said rail.

4. The apparatus of claim 3, wherein the surface of said resilient layers are aligned perpendicularly to the rail alignment, such that each of the said oscillation mass can simultaneously vibrate along shearing direction of said resilient layers, in both vertical and lateral directions of the rail.

5. The apparatus of claim 1, wherein said force orientation bar is in contact with two said force transmission members; said second compression force being exerted to the bottom of said foot tip of said rail such that said foot tip of said rail is coupled to said oscillation masses.

6. The apparatus of claim 4, wherein said force orientation bar comprises an inclined plane such that said part of said first compression force is transformed to said second compression force via said inclined plane.

7. The apparatus of claim 5, wherein said force orientation bar is connected to the bottom of said foot tip of said rail via at least one viscous layer constraint bar, said viscous layer constraint bar further comprising a resilient buffer layer and a viscous damping layer; whereby said second compression force being transferred to said foot tip of said rail via said resilient buffer layer, said viscous layer constraint bar and said viscous damping layer.

8. The apparatus of claim 6, wherein said resilient buffer layer is pre-compressed to a predetermined ratio by tightening said mounting bar; said resilient buffer layer acting as a spring buffer when said rail is vibrating at a force larger than a 1 OOg, where g is the gravitational acceleration.

9. The apparatus of claim 1 further comprising a damper mounting bolt having two nuts at opposite ends of said damper mounting bolt; said nuts creating said first compression force to said force transmission members.

10. The apparatus of claim 1 further comprising a gap filling material; said gap filling material filling a gap between said rail and said mounting bar for preventing creation of a movement gap between said rail and said oscillation mass when said rail is vibrating at a frequency larger than 300Hz.