A RAILWAY WHEEL/RAIL NOISE AND WEAR REDUCTION ARRANGEMENT

Abstract: A railway wheel/rail squeal suppression, wheel/rail noise reduction and wear reduction arrangement includes a separate structure (14) carried by a rail. The separate structure has a saddle-like profile including a web portion (15) defining a running surface for supporting the wheel, and two flange portions (16a, 16b). The saddle-like profile is shaped substantially in conformity with the shape of the railhead, is located on top it and is mechanically de-coupled therefrom. Resilient means (17) is interposed between the web portion and the railhead (13). The web portion (15) has a thickness not less than about twice the thickness of the flange portions so as to resist detrimental compression of the resilient means (17) and transfer only a portion of wheel load to the rail, and the flange portions (16a, 16b) are connected to the rail so as to transfer a remaining wheel load thereto.

Description: A railway wheel/rail noise and wear reduction arrangement. The present invention concerns a railway wheel/rail squeal suppression, wheel/rail noise reduction and wear reduction arrangement . It is well known that railway wheels may cause loud screeching or squealing noises particularly when running on a curved rail due to bogie crabbing and wheel flange-to-rail contact. The noise is normally composed of one or more tonal components that could alter its sound levels with time in a very annoying way. Such a noise is usually referred to as wheel/rail squeal and is a problem in most traffic systems employing track-bound vehicles, such as trams/streetcars, underground/subway cars and the like. Various attempts have been made in the past to reduce vibrations and structureborne sound associated with wheel/rail systems, both to reduce noise emissions and to prevent the formation of ripples in the rail which in turn lead to disturbing noise, involving measures both on the wheels (U.S. Patent No. 4,358,148) and the rail (U.S. Patents Nos . 3,974,963 and 4,203,546). Most prior art vibration reduction systems employ masses, springs and dampeners or visco-elastic layers attached to a wheel and/or a rail. One object of the present invention is to reduce the wheel /rail squeal and simultaneously reduce the wear of both the wheel and the rail by measures on the rail. This aspect of the present invention is based on earlier studies performed by the inventor utilising non-linear lumped parameter models. These studies reveal that a reduced rail mass will affect the non-linear stick-slip process in such a way that the wheel/rail squeal is most likely to be totally abolished. The inventive idea, thus, as regards the wheel/rail squeal reduction, resides in reducing the dynamically participating mass of the rail, and, more precisely, a portion of a rail excited by a wheel travelling on it. It is also well known that railway wheels may cause high sound levels even when running on a welded straight track. Such a noise is usually referred to as wheel/rail roar noise and is a problem in most transportation systems employing rail carried vehicles, such as trams/streetcars, underground/subway cars high-speed trains and the like. Various attempts have been made in the past to reduce radiation of airborne sound, vibrations and structureborne sound associated with wheel/rail systems. These attempts have been targeting to reduce noise emissions e.g. by screens, by special wheel designs etc. Instead, another object of the present invention is to reduce the wheel/rail roar noise by measures on the rail and simultaneously reduce wear of both the wheel and the rail. This aspect of the present invention is based on various studies which reveal that an increased compliance in the wheel/rail contact patch as well as making the contact patch longer, such as occurring when the wheel or rail is made more compliant, both will work to reduce the emitted noise level from the wheel/rail system. The increased compliance will cause the existing roughness in the running surfaces of the wheel and the railhead to generate smaller (reduced) forces when the wheel is rolling on the rail, and, consequently, less noise. The extension of the length of the contact patch will cause the roughness wavelength, which is small compared to the length of the contact patch, to be filtered out. Thereby the excitation forces onto both the wheel and the rail will be significantly reduced, and, as a consequence, the noise emitted as well as wear of the wheel and of the rail will be correspondingly reduced. The inventive idea, thus, as regards the wheel/rail roar noise reduction, resides in increasing the mechanical compliance of the rail and, more precisely, a portion of a rail excited by a wheel travelling on it, thereby making the contact patch longer and the roughness virtually softer thereby reducing the roughness induced rolling forces onto both the rail and the wheel . The reduced forces will also significantly reduce the wheel and rail wear. The inventive idea is realised by providing a running surface on a separate structure disengaged from the railhead on which a wheel is normally running. In practice, there are different ways of embodying this: a) A separate structure, preferably a saddle profile structure, extending in the longitudinal direction of the rail, is added onto the top, or, head portion of an original rail section; b) A longitudinal groove is cut into a railhead and an inlay structure is placed in the groove; c) An ordinary rail is machined to remove exterior portions of its head portion, and a separate structure, preferably a saddle profile structure having exterior dimensions corresponding to the removed portions is prepared to substitute the removed portion; d) A special rail profile and an associated separate structure, preferably a saddle profile structure, are prepared having together the profile and dimensions of an ordinary rail section. In either case, the mass of the separate structure shall be small in relation to the mass of the rail and be mechanically de-coupled from the rail, preferably by the interposition of resilient materials between the rail and the separate structure. Particularly, at the squeal frequency the co-oscillating mass of the separate structure shall be small in relation to the co-oscillating mass of the rail, typically in the range of 1:5-20. Also, the mass per length unit of the separate structure shall be very small in relation to the mass per length unit of the remainder of the rail, including possible attachments other than the separate structure. Since the dynamically disengaged structure resting on the railhead will also reduce the forces generated by the wheel/rail contact both in the vertical, lateral and longitudinal direction, also a significant reduction of the wear of the wheel and the rail will result. Japanese Patent Document 2-35102 (A) discloses a rail having its head crowned with a first layer of a material having sound absorbing or vibration isolating properties, such as a polymer material. Outside the first layer there is a damping member formed by a layer of uniform thickness of a damping alloy such as a Co-group or a Mn-Cu alloy. The shapes of the layers shown are such that mounting thereof inevitably involves bending of the layers to fit the profile of the railhead and, in one embodiment, an upper portion of the rail web. This, in turn, means that the outer layer, the damping member, is comparatively weak and not capable of resisting wheel loads to the extent necessary to avoid overload of the polymer material. Furthermore, in the embodiment where the two layers extend downwards along a portion of the rail web and are attached thereto by means of bolts, there is no possibility that the wheel loads can be transmitted to the rail by means of the damping member . Embodiments of the present invention will now be described, reference being made to the accompanying drawings, wherein: Fig. 1 is a cross section through a rail provided with a wheel/rail squeal suppression arrangement including a separate structure added onto the head portion of the rail according to a first embodiment; Fig. 2 is a perspective view of a section of an arrangement according to Fig. 1; Fig. 3 is a cross section through a variant of the first embodiment according to Figs . 1 and 2 ; Fig. 4a shows a cross section through an upper portion of a normal railhead; Fig. 4b shows a cross section through a rail having portions of its railhead removed and replaced by a separate saddle profile structure according to a third embodiment of the present invention; Fig. 5 shows a cross section through a rail including a special rail profile and a saddle profile structure according to a fourth embodiment of the present invention. The rail shown in Figs. 1 - 3 is an ordinary rail used for trams and trains and having a foot portion 11, a web portion 12 and a head portion 13. In the first embodiment of the invention shown in Figs. 1 and 2, a separate saddle profile structure 14 is added onto the top of the railhead 13 to extend in its longitudinal direction. This separate structure substantially has the section of an inverted U having a web portion 15 and two leg portions 16a, 16b. The separate structure is suitably an extruded or continuously cast profile of aluminium or a forged or hot rolled profile of wrought steel . As seen particularly in Fig. 1, the curvature of the surface of the separate structure 14 facing the railhead is adapted to the curvature of the railhead 13 such that these curvatures are substantially uniform. A supporting layer 17 of a resilient material, such as rubber, is interposed between the top surface of the rail head and the separate structure, thus keeping the latter at a substantially uniform distance a from the rail head. A typical thickness of the layer 17 is 1 - 6 mm, preferably 2 - 3 mm, in a squeal suppression embodiment, and 1 - 8 mm, preferably 2 - 5 mm, in a roar noise reduction embodiment. It is designed to resist vertical loads and to ensure lateral flexibility of the separate structure. To achieve this, the material shall have a high bulk modulus to avoid "polymer crushing" (less than 30% compression of the rubber material) , and a low modulus of shear to give the important lateral flexibility. Further, its material properties shall not change significantly with temperature changes. It is advantageous that the rubber material exhibits a high material loss factor, typically η m = 0.3 - 0.9 or more in a squeal suppression embodiment, and 0.3 - 0.8 in a roar noise reduction embodiment. A useful material would be butyl rubber. Between the opposed inner sides of the legs 16a, 16b of the saddle profile structure and the respective sides of the rail head there may be provided lateral cushions 18a, 18b of a flexible material soft enough to enable lateral movement of the separate structure relative to the rail head. In order to firmly hold the separate structure 14 in place, its leg portions 16a, 16b are provided with flanges 19a, 19b adapted to be located in a common, substantially horizontal plane when the separate structure is mounted onto a rail. Angle irons 20, 21 having substantially perpendicular legs 20a, 20b and 21a, 21b, respectively, are firmly attached to the web portion 12 of the rail by means of horizontally spaced bolts 22 extending through the legs 20b, 21b and the web portion 12 and having nuts 22a and bolt heads 22b. The legs 20a, 21a are substantially horizontally aligned and spaced a small distance b from the flanges 19a, 19b, respectively. Resilient layers 23a, 23b are interposed between the respective facing flanges 19a, 19b and legs 20a, 21a to ensure lateral flexibility of the separate structure relative to the rail head. Bolts 24, 25 having nuts 24a, 25a and bolt heads 24b, 25b, respectively, vertically extend through the respective opposed flanges 19a, 19b and legs 20a, 21a to connect the separate structure 14 to the angle irons. Besides keeping the separate structure to the rail, the bolts 24, 25 serve to reinstate the galvanic connection between the wheel of a train and the rail that has been lost by the interposition of the layer 17 between the mass structure and the railhead. It is imperative, thus, that the heads and nuts of the bolts 24, 25 have good electrical contact with the flanges 19a, 19b and the legs 20a, 21a to ensure galvanic contact to the angle irons and further into the rail web by means of the bolts 21. In order to attenuate vibrations propagating along the web portion, layers 26a, 26b of a visco-elastic material, such as polyurethane, may be applied between the web portion 12 and the legs 20b, 21b, respectively. The arrangement shown in Fig. 3 differs from the one according to Figs. 1 and 2 only in that the separate structure 14' is asymmetrical as concerns the thickness of its web portion 15'. It will be seen thus, that in order to better withstand the load of a wheel, the web portion 15' has a thickened portion 15 'a which is the portion of the rail on which a wheel is to roll. It will further be seen, that the adjoining leg portion 16 'a is also somewhat thickened in relation to the opposed leg portion 16'b. Although the embodiment according to Figs. 1 - 3 will provide a solution to the noise problem, it involves the drawback that at least one of a pair of rails will have to be laterally displaced since adding a structure to a normal rail will influence the track width. The second embodiment of the present invention shown in Figs. 4a and 4b sets this drawback aside. Fig. 4a shows a section through a railhead 13 of a normal rail and the upper portion of its web portion 12. A cross-hatched portion 13' defined by a dash-dotted line indicates portions of the railhead to be removed in order to reduce the railhead section to an extent enabling a saddle profile structure having substantially the exterior dimensions of the original railhead to be mounted onto the reduced railhead 13'' as shown in Fig. 4b. Thus, the second embodiment of the present invention shown in Fig. 4b does not involve a change of the cross section of a normal rail. As mentioned, this has been accomplished by machining a normal railhead 13 so as to remove material 13' from the top and at least one side of the railhead (the one against which the flange of a railcar wheel bears, although Figs. 4a and b show both sides being reduced) leaving a reduced railhead 13'', and in that the removed material has been replaced by a saddle profile structure 14' resembling that shown in Fig. 1, and an interposed elastic layer 17, substantially according to Fig. 1, although the saddle profile structure 14' has exterior dimensions corresponding to those of the non-machined railhead shown in Fig. 4a. The saddle profile structure 14' is kept attached to the remaining rail by equal means as shown in Fig. 1, including flanges 19a, 19b, angle irons 20, 21, bolts 22, 24, 25, and interposed resilient layers 23a, 23b. Supplementary lateral cushions 18a, 18b may be interposed between the flanges 16a, 16b of the saddle profile structure and the lateral sides of the reduced railhead 13' ' . The third embodiment of the present invention shown in Fig. 5 utilises a rail section particularly manufactured for the purpose of enabling mounting thereon of a saddle profile structure . Thus, the portion of the rail section where its web portion 12 merges with the railhead has been widened to provide two opposed shoulders 30a, 30b having flat upper surfaces 31a, 31b, respectively, corresponding to those of the legs 20a, 20b, respectively, of the angle irons 20, 21 of Fig. 1. The shoulders 30a, 30b merge with a reduced railhead 13a having substantially the shape of the remaining railhead 13 ' ' of Fig. 4b. A saddle profile structure 14'', shaped and dimensioned substantially as the one according to Fig. 4b, is mounted onto the railhead 13a by means of bolts 24, 25 extending through flanges 19a, 19b of the saddle profile structure 14'' and the shoulders 30a, 30b, respectively. As before, a resilient layer 17 is interposed between the saddle profile structure 14'' and the diminished railhead 13a, and supplementary lateral cushions 18a, 18b may be interposed between the flanges 16a, 16b of the saddle profile structure and the lateral sides of the reduced railhead 13a. As can be seen in the Figures, the web portion 15 of the separate structures is substantially thicker than its flange portions. This is to make the web portion stiff enough not to cause polymer crushing. The ultimate stress limit for useful polymers is at about 30% compression. In operation, thus, a limit of about 20% compression should not be exceeded. Under such circumstances, it is preferred to make the web portion not less than about twice as thick as the flange portions. This, in turn, means a reduced deflection of the web portion and, consequently, that only a portion of the wheel load is absorbed by the resilient layers 23a, 23b so as not to risk causing detrimental polymer crushing, whereas a remaining portion of the load is transferred from the web portion through the flange portions to the rail by means of the angle irons 20, 21 and its attachment bolts 22 in the embodiments of Figs. 1 - 4b, and straight into the shoulders 30a, 30b in the embodiment of Fig. 5.

Claims: CLAIMS 1. A railway wheel/rail squeal suppression, wheel/rail noise reduction and wear reduction arrangement including a separate structure (14; 14'; 14'') carried by a rail having a foot portion (11) , a web portion (12) and a head portion (13) normally supporting a wheel, the separate structure having a saddle-like profile including a web portion (15; 15 'a) defining a running surface for supporting the wheel, and two flange portions (16a, 16b), the saddle-like profile being shaped substantially in conformity with the shape of the head portion, being located on top of it and being mechanically decoupled from the head portion, and resilient means (17) being interposed between the web portion and the head portion (13) , c h a r a c t e r i z e d i n that the web portion (15; 15 'a) has a thickness not less than about twice the thickness of the flange portions so as to resist detrimental compression of the resilient means (17) and transfer only a portion of wheel load to the rail, and that the flange portions (16a, 16b) are connected to the rail so as to transfer a remaining wheel load thereto. 2. An arrangement according to claim 1, c h a r a c t e r i z e d by fastening and load transmitting means (19, 20, 21, 22; 19, 30) between the separate structure and the rail. 3. An arrangement according to claim 2, c h a r a c t e r - i z e d i n that a viscoelastic layer (26a, 26b) is arranged between said fastening and load transmitting means and said rail . 4. An arrangement according to claim 1, c h a r a c t e r i z e d i that the mass of the separate structure is small in relation to the mass of the co-oscillating mass of the rail . 5. An arrangement according to any one of the preceding claims, c h a r a c t e r i z e d i n that the railhead (13'') has reduced cross sectional dimensions and that the separate structure (14') has external dimensions corresponding to those of a railhead having non-reduced dimensions. 6. An arrangement according to any one of the preceding claims, c h a r a c t e r i z e d i n that the separate structure includes means (19a, 19b) for attachment to the fastening and load transmitting means (20, 21; 30a, 30b) carried by the rail. 7. An arrangement according to claim 2, c h a r a c t e r i z e d i n that the rail includes integrated means (30a, 30b) for the attachment of the separate structure.

Inventors: NILSSON NILS-AAKE, NILSSON, NILS-AAKE
Applicants: ACOUSTIC CONTROL AB, NILSSON NILS AAKE, NILSSON, NILS-AAKE
Application year: 2001
Main classification: E01B19
IPC codes: E01B5, E01B19