METHOD OF ASSEMBLING RAILS AND SLEEPERS AND TRACK FOR TRACKBOUND VEHICLES

Abstract: Method and track when assembling rails and sleepers, the assembly being carried out with different degrees of resilient softness between rail and sleeper. The degrees of resilient softness are selected on the basis of a PN sequence.

Description: METHOD OF ASSEMBLING RAILS AND SLEEPERS AND TRACK FOR TRACKBOUND VEHICLES The present invention relates to a method of assem¬ bling rails and sleepers, the assembly being carried out with different degrees of resilient softness. The inven¬ tion also concerns a track for trackbound vehicles, where rails and sleepers are assembled with different degrees of resilient softness. When a train moves along a railway track, large amounts of energy are released. Part of the released energy is spread as noise from the train, down into the ground, out in the air and into and along the track. This noise, of course, causes serious problems in built-up areas, and attempts are usually made to obviate these problems by means of embankments or other types of noise protection, which are costly. Attempts have also been made to solve the problem of noise by assembling rails and sleepers with more or less resilient softness. The resilient softness is determined by the properties of the elastic rail seat which is posi¬ tioned between rail base and sleeper and which usually consists of two steel plates with a rubber portion there¬ between. The resilience is determined by the quality of the rubber. Assembly with little resilient softness causes attenuation of the noise in the track, but not out in the air and down into the ground, whereas assembly with great resilient softness causes attenuation of the noise out in the air and down into the ground but hardly along the track, insofar as the noise effect directed along the rail is released in the first discontinuity in the rail, resulting in noise in this position. Finally, rails and sleepers have been assembled with alternatingly great and little resilient softness. In fact, this re¬ sults in the energy released by the train being distrib¬ uted in a somewhat more uniform manner to the surround- ings, but this is also no satisfactory solution to the noise problem. One object of the present invention is to improve the above-described prior art technique of assembly and select the resilient softness in the assembly such that a more efficient attenuation of noise is achieved. A fur¬ ther object is to provide a track with improved noise attenuation properties. The objects are achieved by the method and the track according to claims 1 and 4, respectively. The invention is based on the knowledge that a PN sequence spreads the frequency content of a signal, which is a well-known phenomenon in signal processing. A PN sequence, a pseudonoise sequence, is a random sequence which can be generated by means of a feedback filter, The length of the filter, i.e. the number of delay steps, de¬ termines the frequency properties of the generated se¬ quence. The longer the filter the more the frequency content is spread, or smeared. According to the inven- tion, the emitted effect of the train is spread in fre¬ quency by the sleepers being assembled with the rails with at least two different degrees of resilient softness according to a PN sequence. In addition to the achieve¬ ment of a frequency spread, which results in a consider- able decrease of the noise level, the possibility of dis¬ tributing the emitted effect more uniformly is main¬ tained. The inventive method means that first a PN sequence having at least two levels is generated by means of a suitable filter. The length of the filter is deter- mined according to the desire of spreading the energy in frequency in the surroundings where the sleepers are to be located. Subsequently, each level of the PN sequence is allowed to represent its degree of resilient softness. Then, by assembling rails and sleepers according to this representation, with different resilience, in the same relative order as the levels of the generated PN se¬ quence, a smearing of the noise frequency content of the train is achieved. In a preferred embodiment, the PN sequence is given two levels, use being made of two different degrees of resilient softness when assembling the sleepers and the rails along the track. In another preferred embodiment, use is made of more than two different degrees of resilient softness in the assembly in order to further optimise the controlling of the effect. This embodiment means that first a PN sequence is generated, which has preferably two levels and which is allowed to pass through a digital optimisation filter. The digital optimisation filter is designed according to certain optimisation criteria, such as the desired number of different degrees of resilient softness and the de¬ sired frequency response of the specific case. What fre- quency response is desired depends on in what surround¬ ings the sleepers are to be arranged. In areas of, for instance, clayey ground it is not suitable to let the effect be spread in low-frequency form, and therefore the optimisation filter is in this case given a design which shifts the effect from low frequencies to high frequen¬ cies. After having generated a sequence with desired properties by means of the digital optimisation filter, each level of this sequence is allowed to represent a degree of resilient softness, such that each of the different degrees of resilient softness is represented in the sequence in assembly. According to this representa¬ tion, the sleepers and rails are then assembled with different resilience along the track in the same relative order as the levels of the generated sequence. The invention will now be described in more detail with reference to the accompanying drawings, in which Fig. 1 is a flow diagram which describes the steps that are to be carried out when using an embodiment according to the present invention, Fig. 2 shows an arrangement of sleepers and rails assembled with different resilient softness, which arrangement is the result when the embodiment in Fig. 1 is used. Fig. 3 is a flow diagram which describes the steps that are to be carried out when using a different embodi- ment according to the invention. Fig. 1 shows the steps that are to be carried out in one embodiment according to the present invention. In this embodiment, use is made of two different degrees of resilient softness when assembling sleepers and rails along a track. In step A, a PN sequence of a suitable length and having two different levels is generated. Then in step B, each of the levels of the generated PN se¬ quence is allowed to represent a degree of resilient softness. Finally, in step C the sleepers and rails are assembled with different resilient softness in the same relative order as the levels of the generated PN se¬ quence, according to the representation in step B. Fig. 2 illustrates an example of an arrangement which may result when the embodiment according to the flow diagram in Fig. 1 is used. The dark sleepers are assembled with the rails having little resilience and the light sleepers are as¬ sembled with the rails having great resilience. Fig. 3 shows the steps that are to be carried out in another embodiment according to the present invention. In this embodiment, use is made of more than two different degrees of resilient softness when assembling sleepers and rails along a track. In step A, a PN sequence, or the like, of a suitable length is generated. Then in step B, the PN sequence is allowed to pass through a digital optimisation filter, the properties of which are selected on the basis of given optimisation criteria, such as the desired frequency response and the number of levels that is desirable in the output sequence of the optimisation filter. The number of levels is preferably selected to be equal to the number of different degrees of resilient softness. In step C, each level of the output sequence from the optimisation filter is allowed to represent a degree of resilient softness, such that each of the different degrees of resilient softness is represented in this output sequence in the assembly. Finally, in step D, the sleepers and rails having different resilient soft- ness are assembled in the same relative order as the levels of the generated output sequence, according to the representation in step C. Several modification of the invention are, of course, possible within the scope of the invention. For instance, the PN sequence can be replaced by other types of random sequences, such as a PBR sequence that is well-known from signal processing. Also maximum-length sequences can ad¬ vantageously be used for the purposes of the invention.

Claims: CLAIMS 1. A method of assembling rails and sleepers when laying a track for trackbound vehicles, the assembly being carried out with different degrees of resilient softness, c h a r a c t e r i s e d in that the degrees of resilient softness are selected on the basis of a PN sequence. 2. A method as claimed in claim 1, c h a r a c ¬ t e r i s e d in that two different degrees of resilient softness are selected; a PN sequence having two different levels is selected; the two levels of the PN sequence are each made to represent a degree of resilient softness; and the sleepers and rails are assembled along the track with degrees of resilient softness in a relative order conforming with the levels of the PN sequence. 3. A method as claimed in claim 1, c h a r a c ¬ t e r i s e d in that more than two different degrees of resilient soft¬ ness are selected; the PN sequence is emitted through such a digital optimisation filter as converts the PN sequence to a new sequence having a selected number of levels which is equal to the number of different degrees of selected resilient softnesses; each level of the new sequence is selected to repre¬ sent a degree of resilient softness, such that each of the different degrees of resilient softness is repre¬ sented in the new sequence; and the sleepers and rails are assembled along the track with degrees of resilient softness in a relative order conforming with the levels of the new sequence. 4. A track for trackbound vehicles, where rails and sleepers are assembled with different degrees of resil¬ ient softness, c h a r a c t e r i s e d in that the degrees of resilient softness are selected on the basis of a PN sequence. 5. A track as claimed in claim 4, c h a r a c ¬ t e r i s e d in that the sleepers and rails are assembled along the track with differently resilient assembly in a relative order conforming with a PN sequence having two levels, one level of the PN sequence representing a more resilient degree of assembly and the other level of the PN sequence representing a less resilient degree of assembly. 6. A track as claimed in claim A, c h a r a c - t e r i s e d in that the sleepers and rails are assem¬ bled along the track with different degrees of resilient assembly in a relative order conforming with a generated new sequence, which is obtained by the PN sequence being emitted through a digital optimisation filter and which has a number of levels which is equal to the number of different degrees of resilient softness, each level of the new sequence representing a degree of resilient soft¬ ness, such that each of the different degrees of resil¬ ient softness is represented in the new sequence.

Inventors: LAGOE THOMAS, LAGOE, THOMAS
Applicants: LAGOE THOMAS, LAGOE, THOMAS
Application year: 1997
Main classification: E01B19
IPC codes: E01B9, E01B19