WO2011082823A1

WO2011082823A1 - Bogie axle box with damping interfaces

Info

Publication number: WO2011082823A1
Application number: PCT/EP2010/050088
Authority: WO
Inventors: Michaël DUGUET; Thierry Le Moigne
Original assignee: Aktiebolaget Skf
Priority date: 2010-01-07
Filing date: 2010-01-07
Publication date: 2011-07-14
Also published as: EP2521667A1

Abstract

An axle box (1) for a railway bogie comprises a core part (13) with an axle passage (2), comprises spring seats (3) for one or more springs, and comprises one or more friction surface elements (10). Each friction surface element defines a friction track for an end surface of a piston. The axle box (1) is adapted for supporting a bogie pedestal transmitting efforts to the axle box both through the springs and though the friction surface elements (10). Either the spring seats (3), or the friction surface elements (10), comprise an at least two layer damping plate (11-12, 7-9). The two layer damping plate comprises a first layer (11, 7) being a rigid sheet, on a first side of the plate facing one of the springs or facing one of the pistons, and comprises a second layer (12, 9) being made from an elastomeric material more flexible than the material of the first layer (11, 7), the second layer (12, 9) being placed on the second side of the plate.

Description

Bogie axle box with damping interfaces

The present invention relates to a railway bogie, especially the so called "Y25 " bogie of widespread use throughout Europe, and in particular to the noise reduction of such bogies used on freight wagons, to make them compliant with the more and more strenuous no ise regulations.

Such a bogie comprises a pair of pedestals on which a wagon can be assembled, each pedestal being supported by a pair of axle boxes through respective pairs of spring sets .

Friction damping arrangements are provided to damp, primarily, vertical and lateral movement between the axle boxes and pedestals . Each damping arrangement typically comprises a piston slidably mounted upon one of the pedestals and having an end face which can be brought into contact with a friction surface of the axle boxes, the piston being moveable by a drive member and a so called Lenoir link, connected between the pedestal and the drive member.

The Lenoir link is inc lined to the vertical such that the weight of the pedestal and the wagon applies a lateral force to the drive member and piston. The magnitude of the force applied to the piston is thus dependent upon the load. The degree of damping between the pedestal and the axle box thus increases with the load o f the wagon.

The mounting o f the piston is such that there is contact between the piston and the pedestal and, in use, between the end face of the piston and the axle box. As the piston, pedestal and axle box are usually made o f steel, such a friction contact generates vibrations which are transmitted both to the axle box and to the wagon. The deformation of the spring sets also may generate some contact vibrations. In addition to this, the vibrations generated by the wheel to rail contact are transmitted though the springs, and through the Lenoir system, to the pedestal and then to the wagon, which acts as a resonance chamber.

Such an Y25 bogie is described in patent application GB 2 401 844. In this document, the surface of the piston is coated with, or made of, a composite material, so as to avoid metal-metal friction o f the Leno ir system piston against the friction surface of the axle box. In addition to this, the piston, instead of being slidably mounted in a horizontal sleeve, is embedded in a deformable sleeve o f resilient material , to avoid friction vibrations at the sleeve level.

However, coating the pistons with a so fter material than steel makes the piston surface prone to early wear, and may later require costly replacements o f the pistons. Moreover, vibrations are still generated at the spring level.

The present invention aims at proposing an axle box with integrated anti-vibration equipment, which can be assembled to a standard "full metal" Lenoir system and pedestal. Production and maintenance of the axle box according to the invention should be cheaper and easier than with usual "metal -to metal" contacting bogies.

According to one aspect of the invention, an axle box for a railway bogie comprises a cast iron or cast steel core part with an axle passage, comprises spring seats for one or more springs, and comprises one or more friction surface elements. Each friction surface element defines a friction track for an end surface of a piston. The axle box is adapted for supporting a bogie pedestal transmitting efforts to the axle box both through the springs and though the frictio n surface elements. Either the spring seats, or the friction surface elements, comprise an at least two layer damping plate . The two layer damping plate comprises a first rigid layer being a rigid sheet, on a first side of the plate facing one o f the springs or facing one of the pistons, and comprises a second layer being made from an elastomeric material more flexible than the material of the first layer, the second layer being p laced on the second side o f the plate.

The second, elastomeric, layer thus faces either the cast steel/cast iron core part, or faces the pedestal if the damping p late is placed between the springs and the pedestal.

The material o f the first layer may be metal (such as steel) or may be a po lymer based compound. The material is chosen to have a higher Young's modulus than the material of the second layer, or at least will be designed to have a higher tensile strength (entailing higher flexural strength) . The second material is chosen for its damping properties, preferably among elastomeric compounds, though other damping materials can be envisaged (such as wood) . Required vibration damping properties usually go together with so fter structures and/or visco-elastic behaviour.

In a preferred embodiment, the spring seats and the friction surface elements each comprise a two layer damping p late.

In another embodiment, the spring seats and the frictio n surfaces each comprise at least one damping layer o f a po lymer material, either o f an elastomeric material or of a more rigid polymer.

In a preferred embodiment, the first layer o f a least one o f damping plates is made of steel, with a manganese mass content of the steel o f at least 8%

In a preferred embodiment, at least a damping plate of the axle box comprises a layer made o f a polyamide based compound , with either a po lymer matrix base of PA66 or a polymer matrix base o f PA6-G .

In this embodiment, the spring seats may comprise a two layer damping plate, whereas each friction surface facing the pistons may be the surface of a one piece polymer plate, directly leaning against the cast iron/cast steel core part . Preferably, the one piece polymer plate is made o f a po lyamide based compound, with either a po lymer matrix base o f PA66 or a polymer matrix base of PA6-G .

In an advantageous way, the spring seats each comprise a base plate adapted to support at least an end coil of a spring, and a guiding ring adapted to be inserted between two coaxial springs. Both base plate and guiding ring may be separated from the cast iron/steel core part by an elastomeric sole, and may be made of a same material, more rigid than the material o f the elastomeric so le.

In a different embodiment, spring guiding rings are welded to the cast iron/steel core part, an external damping washer and an internal damping washer being inserted respectively on the external side and on the internal side of the ring. Each washer constitutes a two layer damping plate comprising a first layer in the form o f a rigid sheet facing one o f the springs, and comprising a second layer in the form o f an elastomeric sheet made of a elastomeric material more flexible than the material o f the first rigid sheet, the second sheet being placed on the side o f the washer opposite to the spring.

Advantageously, at least one of the two-layer damping plates rests on a base surface of the cast iron/cast steel core part which is in rough cast state. This may be the case for the friction surface elements or for the spring seat cups, or for both.

In yet another embodiment, spring guiding rings may be welded to the cast iron/steel core part, an external damping washer and an internal damping washer being inserted respectively on the external side and on the internal side of the ring, each washer being made of a single damping material, such as an elastomeric compound.

In a preferred embodiment, the friction surface elements each comprise a polymer sheet with at least one roughly central protrusion, extending through, and further than, the depth of an elastomeric sheet, and the cast iron/steel core part is provided with recesses in which the tips of the protrusions can fit, so as to limit lateral movements, i . e. , movements within the friction plane of the piston end, between the friction surface element and the cast iron/steel core part.

Advantageously, the friction surface elements each comprise a polymer sheet with a central friction plate and two lateral plates both forming, in non assembled state, an angle of between 94° and 120° with the central plate, each central and lateral plate being provided with at least one protrusion adapted to fit in a corresponding recess of the cast iron part.

Some additional objects, advantages, and novel features of this invention shall be set forth in the description that fo llows. A preferred but non limiting form o f embodiment will now be described, with reference to the attached drawings, wherein:

-Figure 1 is an exploded perspective view o f an axle box according to the invention, -Figure 2 is a partial top view of an axle box according to the invention,

-Figure 3 is a partial top view of another embodiment of an axle box according to the invention,

-Figure 4 is a partial top view of yet another embodiment o f an axle box according to the invention,

-Figure 5 a is a side view of a liner front plate belonging to yet another embodiment of an axle box according to the invention,

-Figure 5b is a top view o f the liner front plate of fig 5 a, -Figure 5 c is a cross section view of an axle box according to the invention co mprising the front plate illustrated on figures 5 a and 5b,

-Figure 6 is a partial cross section view of another embodiment of an axle box according to the invention,

-Figure 7 is a partial cross section view o f yet another embodiment of an axle box according to the invention.

As it can be seen in FIG . 1 and in FIG. 5 c, an axle box 1 comprises a cast iron or cast steel core 1 3 with a cylindrical bore defining a horizontal axle passage 2, having a geometrical axis X-X ' . The cast core 13 comprises a right hand (according to fig. 1 ) vertical thrust base surface 14 and a left hand (according to fig. 1 ) vertical thrust base surfaces 14, on two opposite external faces of the cast core . The thrust base surfaces have horizontal normal directions, opposite to one another, and the normal directions are also perpendicular to the axis X-X ' of the axle passage 2. Each thrust base surface 14 is of overall rectangular shape and is limited on a front side and on a back side o f the rectangle, by a vertical lateral stop surface 1 5 , also of overall rectangular shape. The lateral stop surfaces 15 are perpendicular to the thrust base surfaces 14. Each thrust base surface 14 together with its lateral stop surfaces 1 5 defines a rectangular groove, in which groove the end o f the Leno ir system (not represented) can be inserted.

Thrust base surface 14 supports the pressure of the Leno ir system piston, whereas stop surfaces 15 limit the displacement of a front and of a back abutment element, both adj acent to the Lenoir piston, in order to prevent the pedestal from sliding away from the axle box in the X-X' direction.

Two flanges 16 extend horizontally to the left and to the right, in directions normal to the thrust base surfaces. Each flange 1 6 is provided with a mainly horizontal spring seat base surface 6. The normal direction (vertical direction on figs 1 and 5 c) o f the spring seat base surface 6 is perpendicular, both to the axle passage axis X-X ' and to the direction normal to the thrust base surfaces. A spring seat cup 3 is assembled to each spring seat base surface 6. The spring seat cup 3 can be assembled by any means such as riveting, screwing, gluing, or it can just be removably positioned onto each spring seat base surface 6, by complementary shapes between the spring seat cup 3 and the spring seat base surfaces 6.

Each spring seat cup 3 comprises a guiding ring 8 having the shape of a ho llow cylinder with a diameter such that it can be inserted between the outer diameter o f an inner spring 4 and the inner diameter of an outer spring 5 (inner spring 4 and outer spring 5 are not represented on figure 1 , but are visible on figure 5c) . Such a set of inner spring 4 and outer spring 5 constitutes a coaxial set of springs belonging to the suspension system of a railway bogie (not represented) . Each spring seat cup 3 also comprises a base plate 7 to which the guiding ring 8 is assembled. Base plate 7 and guiding ring 8 can be assembled or fabricated as one piece, for instance by injection of thermoplastic or thermoset polymer based compounds. Base plate 7 mainly consists of a flat washer whose outer diameter is larger than the diameter of the outer spring 5 , and whose inner diameter may have a value between zero and the inner diameter of the inner spring 4.

Between the base plate 7 and the spring seat base surface 6, an elastomeric so le 9 is assemb led. The base plate 7 p lus elastomeric so le 9 constitute a two layer damping plate. The elastomeric sole 9 is in the shape of a flat washer with an outer diameter preferably at least equal to the diameter of the base plate 7, or larger, and an inner diameter between zero and the inner diameter of the inner spring 4. The elastomeric so le 9 can be glued or overmoulded onto the spring cup 3 , or it can consist of a separate elastomeric sheet of material which is held in place by compression forces between the spring seat cup 3 , and the spring seat base surface 6, or possibly also held in place by the same assembling means which maintain the spring seat cup 3 onto the spring seat base surface 6. In another embo diment, base plate 7 and guiding ring 8 can be overmoulded onto the elastomeric so le 9 or vice- versa.

Each thrust base surface 14 is at least partly covered by a liner back plate 12 made of elastomeric material. The liner back plate 12 covers at least a major part of the thrust base surface 14 and can also cover partly or in whole the lateral stop surfaces 1 5. The liner back plate 12 is itself shielded from outer contacting elements by a liner front plate 1 1 . The liner front plate 1 1 is made of a more rigid material than the liner back plate 12. The liner front plate 1 1 can be made o f metal such as steel, or can be made of a polymer based compound. The liner front plate 1 1 covers a major part, or covers the whole thrust base surface 14, and also covers the lateral stop surfaces 15. The liner front plate 1 1 can be made in one piece, as a single sheet bent to form a U profile, or can be made in three sheet parts, one flat sheet covering the thrust base surface, and each other flat sheet covering a lateral stop surface 1 5. The liner back plate 12 can be overmoulded on, or glued to , the liner front plate 1 1 , or can be constituted by a separate sheet. The liner back plate 12 is held in sandwich between the cast iron or cast steel core 1 3 and the liner front plate 1 1 , in such a way that the liner front plate 1 1 does not contact the thrust base surface 14. According to the total size of the liner back plate 12 and to various embodiments of the invention, the liner front plate 1 1 may, or may not rest directly on the lateral stop surfaces 1 5.

The liner front plate 1 1 is assembled to the cast iron or cast steel core 13 by means of rivets or screws 1 8. Liner front plate 1 1 together with associated liner back plate 12 form a friction surface element 10, which provides an outer surface (central part of liner front plate 1 1 ) adapted to resist friction with the end surface o f a Lenoir system piston. The vibrations generated by the friction contact between the piston (not represented) and the liner front plate are partly dampened at the liner front plate level, by energy dissipation into the liner back plate 12. The residual vibrations may be transmitted to the cast iron or cast steel core 13 , but these vibrations will only be transmitted through limited areas o f contact between the liner front plate 1 1 and the cast iron steel core 13 , id est. areas where the liner front plate 1 1 contacts, and/or areas where the liner front plate 1 1 is riveted or screwed to the cast iron or cast steel core 13.

In the prior art, Y25 bogies friction surface element 1 0 usually consists in one or several steel sheets welded to the cast iron or cast steel core 13 , thus providing a friction surface without damping means, and with a high degree of transmission of the vibrations between the friction surface element and the cast iron or cast steel core.

As the liner back plate 12 o f the invention is not directly subj ected to friction, it can be made o f elastomeric materials including elastomeric composite materials of higher damping properties than the harder composite material covering or constituting the end of the piston of the prior art. As a matter of fact, materials with high damping properties also usually show a higher degree of viscoelastic flexibility, which is not a recommended feature to withstand repeated frictions from a harder part.

Liner front plate 1 1 can be made o f steel, preferably manganese alloyed steels, i. e. steels with a manganese mass content higher than 10%, typically between 1 1 % and 14% , with a main composition

Table 1 : typical manganese alloyed steel

Such steels are highly wear resistant but can be subj ected only to limited deformation. A liner front plate made o f such manganese steel can be fabricated in three separate sheets each assembled to the cast iron or cast steel core 13 , if a well defined angle is needed between the frict ion surface facing the piston and sheets covering lateral stop surfaces 15.

If a sharp angle is not needed between the friction surface facing the piston and the lateral stop surfaces 15 , for instance because the piston is not as wide as the friction surface, the liner front plate 1 1 may be made o f a single sheet of steel with bending regions between the friction surface and the lateral stop surfaces so designed, as to have a large enough curvature radius to be consistent with the deformat ion ability o f the steel. In other embodiments, the liner front plate 1 1 can be inj ected as one piece with either a thermoplastic or a thermoset compound .

Thermoplastic compounds will be preferred over thermosets because they are less brittle than thermo sets, and they will better withstand stress concentrations along the edges o f the piston. PA66 compounds are a preferred option because o f their good abrasio n resistance at still affordable price.

To enhance their sliding abilities, these compounds can contain fluorinated lubricants such as perfluoropolyether (PFPE) molybdenum di sulphide (MoS₂), aramid or carbon fibres and/or glass fibres to limit their wear rate.

In yet another embodiment, the liner front plate 1 1 could be made o f three separate plates made of cast PA6-G or PA6/ 12-G, which are highly resistant polyamides having to be manufactured as cast shapes, in order to obtain optimal mechanical properties. Solid or liquid lubricants can also be added to these cast polyamides.

As the central part of the liner front plate 1 1 is subj ected to the highest friction stresses, mixed so lutions can also be envisaged to combine ease of assembly (three-sided liner front plate), and optima l abrasion resistance (over the central sheet part) such as overmoulding a central plate made of manganese alloyed steel or made of cast po lyamide, with for instance an inj ected PA66 compound which will cover the back o f the liner front p late and constitute the lateral sides of the liner front plate.

In such an embodiment, the steel sheet or the cast polyamide sheet could be provided with through holes to be filled by the other material, to enhance mechanical bonding between the two types of material.

The liner back plate 12, whether it covers only the thrust base surface 14 or whether it covers both the thrust base surface 14 and the lateral stop surfaces 15 , is made as a single part either bonded (glued or overmoulded) to the liner front plate 1 1 , or assembled as a separate sheet. In some embodiments, the liner front plate 1 1 can be moulded over liner back plate 12. The liner back plate 12 is made o f an elastomeric material (natural rubber, synthetic rubber such as polyurethane, silicones, thermoplastic elastomers). The elastomeric material can contain continuous or non-continuous fibres to enhance its shear resistance (aramid or glass or carbon fibres, nylon, po lyester, cotton, steel, as chopped fibres or as woven/non woven mats) .

One further advantage of replacing a conventional friction surface element 1 0 welded onto the cat iron or cast steel core, by a removable friction surface element 10, is to facilitate not only the assembly but also the replacement of this wear element when needed . In addition to this, if the liner front plate 1 1 is const ituted of a polymeric material, so fter than steel, whereas the end of the Lenoir system piston remains a steel surface, mo st of the wear in time is likely to occur on the liner front plate 1 1 rather than on the end piston side . One will thus avoid a more costly replacement o f the piston.

Coming back to the spring seat cup 3 , the guiding ring 8 can be made o f ro ll-bended steel, welded to another sheet of steel constituting the base plate 7. Guiding ring 8 and base plate 7 can also be moulded as a single part out of wear resistant thermoplastics such as PA66 reinforced with glass fibres.

Other thermoplastics could also be used as a basis for the polymer compound used for inj ect ing the guiding ring plus base plate washer, such as po lyacetal (POM) or polyethylene terephtalate (PETP) . Other reinforcements as well as lubricants can be used such as aramid or glass or carbon fibres as reinforcements, fluorinated lubricants or mo lybdenum disulphide.

Inj ecting a spring seat cup 3 out of a polymer compound, instead of conventionally welding a steel guiding ring to a steel base plate, will on one hand, result in an easier fabricat ion process and, on the other hand, generate less risks of damaging the surfaces of the springs, which can sometimes result in early breakage of the springs. Mixed material solutions are also possible when fabricating the spring seat cups 3 , such as overmoulding a polymer guiding ring onto a steel base plate.

The elastomeric so le 9 overmoulded on base plate 7, or fabricated as a separate sheet, can be made of the same type o f elastomeric materials or elastomeric compounds, as those listed above for the liner back plate 12.

The presence of the elastomeric sole 9 can further compensate for differences in flatness between the base plate 7 and the spring seat base surface 6. Expensive and time consuming machining operations otherwise necessary to reach a high degree of flatness can thus be avoided either on base plate 7 or on spring base surface 6, or on both. To this purpose, according to the amplitude of deformations to be accommodated, the elastomeric sole may be manufactured as a constant thickness sheet, or may be manufactured as a variable thickness sheet if, for instance, a draft angle of the cast core 13 is to be compensated for.

Assembly means between the spring seat cups 3 and the cast iron or cast steel core 13 are mainly needed, first to permit a good initial positioning of the springs 4 and 5 and secondly, to permit handling of the axle box as a single part. Traditional assembly means such as rivets or screws can be envisaged, but gluing may be suffic ient if other centering means (than rivets or screws) are provided. Spring seat cups 3 could also be designed without any assembly means to the iron or cast steel core 13. In this case, a centering mean should preferably be provided, such as a moulded boss 35 on the spring seat base 6 fitting in a central ho le 36 o f the spring seat cup 3 (see fig. 5 c) , or a protrusion (not represented) of a plastic moulded base plate 7 into a recess (not represented) of the spring seat base 6.

Base plate 7 has a function of providing a wear resistant surface to face the end coils of springs 4 and 5 , and also a function o f distributing the linear co ntact forces o f the end coils over a larger surface of contact between base plate 7 and elastomeric sole 9. The vibrations generated by or transmitted through the springs can thus be more easily dissipated within a larger vo lume o f material, mainly constituted by the elastomeric sole 9. Liner front plate 1 1 also ensures, to a lesser extend, the same "stress diluting" functio n, so that vibrations generated by the contact with the Lenoir piston can be better dampened by the liner back plate 12.

By isolating the guiding ring 8 from the spring seat base surface 6 by means o f the elastomeric sole 9, vibrations cannot (or can to a much lesser extent) be transmitted to the guiding ring from the springs to the cast iron or cast steel part 13.

Fig. 2 is a half top view o f the axle box on Figure 1 . Features common to Figure 1 have been designated by same reference numbers as on Figure 1 . As it can be seen on both Figure 1 and Figure 2, in this embodiment, the spring seat cups 3 are assembled to the flanges 16 by four rivets 1 8 distributed around the external part of the base plate 7, i.e. the part of the base plate protruding from the guiding ring 8. The liner back plate 12 is held by compression between the liner front plate 1 1 and the thrust base surface 14. The liner front plate 1 1 is a steel sheet, bent so as to form three planar surfaces, one surface covering the thrust base surface 14 and two surfaces covering each of lateral stop surfaces 15. The steel sheet is further bent to form two lateral flanges 1 9 perpendicular to the lateral stop surfaces. Each flange 19 rests directly on the cast iron/cast steel core 13 , and is assembled to the cast core by screws or rivets 1 8 , or by other assembly means (flanges 1 9 could for instance be inserted into corresponding slots (not represented) machined in lateral surfaces 15) . Along the entirety o f the thrust base surface 14 and the entirety o f lateral stop surfaces 1 5 , the liner front plate 1 1 is separated from the cast iron or cast steel core 13 by the liner back plate 12, thus preventing (or reducing) vibration transmission through these three surfaces between the liner front plate 1 1 and the cast iron or cast steel core 1 3. On the contrary, lateral flanges 1 9 of the liner front plate 1 1 rest directly on a rib edge surface 20 adj acent to the lateral stop surface 15. The direct, non deformable contact, between lateral flanges 19 and rib edge surface 20 make the screw assembly more reliable, than screws ho lding a variable thickness two-layer plate, which may subj ect the screws to vibratio ns o f higher amp litude.

The main vibration cause o f the friction surface element 10 is the contact between the Lenoir piston and the central part 23 of the liner front plate 1 1 . These vibrations have to propagate through the lateral sides 24 of the liner front plate 1 1 , before they can reach the metal-metal contact, at the flanges level 19, between liner front plate 1 1 and cast core 13. As the vibrations of lateral sides (24) of the liner front plate 1 1 are also dampened by the contact between front plate 1 1 and liner back plate 12 along the lateral stop surfaces 15 , only a limited amplitude of vibrations finally reaches the cast iron or cast steel core 1 3.

Figure 3 is a top view of another embodiment of an axle box according to the invention, with a different shape of the liner front plate 1 1 and a different shape of the liner back plate 12, as well as different assembly means between liner front plate 1 1 and cast steel or cast iron core 1 3. Features common to Figures 1 and 2 have been designated by same reference numbers as on previous figures. As on Figure 2, liner front plate 1 1 defines three planar surfaces, one surface 23 covering the thrust base surface 14 and two lateral surfaces 24 covering the stop surfaces 1 5. For assembly purposes, additional flanges 21 are provided on the upper and lower edges of each surface covering the lateral stop surfaces 15. These additional flanges are riveted or preferably screwed to the cast iron or cast steel core 13. In this embodiment, the liner back plate 12 only covers the thrust base surface 14, and does not extend further than this thrust base surface 14. In this manner, the central part of the liner front plate 1 1 is dampened by the presence o f the liner back plate 12. At the same time, vertical movements of lateral surfaces 24 are strongly reduced compared to a so lution where the liner front plate 1 1 is only assembled along extremally located flanges 1 9 as on Figure 2. On the other hand, vibrations generated in lateral parts 24 of liner front plate 1 1 are not dampened to the same extent as in the embodiment of Figure 2.

Figure 4 is a partial top view of yet another embodiment of an axle box according to the invention. Figure 4 only differs from Figure 3 in that the central part of the liner front plate 1 1 is provided with extra upper and lower flanges 22, which limit the vertical displacements of the central part of the liner front plate 1 1 and thus also limit shear strain in the liner back plate 12.

These extra flanges 22 also act as means for maintaining the liner back plate 12 between the liner front plate 1 1 and the cast iron or cast steel core 13. Still, these extra flanges 22 may limit the damping effect of the liner back plate 12 , as vibrations can be transmitted from the friction surface area 23 o f the front plate 1 1 through these flanges 22 into the cast iron or cast steel core 1 3.

Other embodiments can be derived from Figure 4, such as a liner front plate 1 1 made in three separate parts, each comprising a planar vertical surface assembled by an upper and a lower horizontal flange 2 1 or 22. One could also envisage a one-piece liner front plate whose central part 23 is assembled to the cast iron or cast steel core by horizontal flanges 22 as on Figure 4, and whose lateral sides 24 are assembled to the cast iron or cast still core 13 by vertical flanges 19 as on Figure 2.

In some embodiments, horizontal flanges may be present only on the upper side o f the cast iron or cast steel core 13. Liner front plate 1 1 depicted on Figures 1 , 2, 3 , 4 can be made either of metallic materials such as steel, or can be made o f an inj ectable polymer based compound such as PA66 based compounds.

Figures 5 a, 5b and 5 c show another shape of liner front plate 1 1 , which is specially adapted for inj ection moulded front plates. Features common to previous figures can be seen on figs. 5 a to 5c , which have been designated by same reference numbers as on previous figures. Liner front plate 1 1 comprises a central friction plate 23 and two lateral plates 24 forming an angle o f between 90 and 120° , preferably between 95 and 1 1 5 ° . These angles a are defined in an unconstrained, as moulded state, and are intended to be brought back to a 90° value when the liner front plate 1 1 is inserted in its final assembled position between the two lateral stop surfaces 15 of a cast iron/cast steel core 1 3. Each lateral plate 24 is provided, on its side facing the lateral surfaces 15 , with a protrusion 25 whose height above the surface of the plate 24 is of the same range as the thickness o f plate 24.

"Of the same range" here means of the same order o f magnitude, for instance comprised between half the thickness of plate 24 and three times the thickness of plate 24. The protrusion 25 extends in the vertical direction of the liner front plate 1 1 , defining a lo cking strip 28 whose surface is more or less perpendicular to the external surface of p late 24 (i. e. , the surface facing the lateral stop surface 15) . Central plate 23 is provided with a protrusion 26 which extends above the surface of plate 23 , to a value which is at least as much as the thickness of the liner back plate 12 in a non-compressed state.

Preferably, the height of the protrusion 26 should be at least double o f the thickness of plate 23 , and could be up to five t imes the thickness of plate 23. Protrusions 25 and 26 may be solid volumes or may be ho llow vo lumes . An open passage 27 may even run through these protrusions, especially protrusion 26, crossing the liner front plate 1 1 from one face to the other. The liner front plate 1 1 of figs 5 a, 5b and 5 c can be inj ected in thermoplastic materials already stated above. This liner front plate 1 1 is associated with a liner back plate 12 (not represented) covering only the thrust base surface 14, and provided with one or several through holes, with shapes corresponding to the outlines of protrusions 26 present on the central plate 23 of liner front plate 1 1 . The liner back plate 12 can also be glued to, or overmoulded on, the liner front plate 1 1 . The liner back plate 12 can thus be assembled to the liner front plate 1 1 by sliding ho les of liner back plate 12 around protrusions 26 of liner front plate 1 1 . Liner front plate 1 1 can then be assembled to the cast iron or cast steel core 1 3 by placing tips o f protrusions 26 into corresponding recesses 37 of the thrust base surface 14, and by inserting protrusions 25 into corresponding recesses (not represented) of lateral stop surfaces 1 5. This is done by pressing the liner front plate 1 1 with already assembled liner back plate 12 onto it, against thrust base surface 14, thus generating a reduction o f both angles a between the central and the lateral plates of the liner front p late 1 1 , from their initial value, to an assembly value o f 90° or less, necessary to enable protrusions 25 to sl ide into their corresponding recesses . Once protrusions 25 are inserted in corresponding recesses, angles a acquire then maintain a constant value of 90° . This 90° angle is ensured by an e lastic deformation o f lateral p lates 24 o f the liner front plate 1 1 , which deformation keeps plates 24 pressed against the lateral stop surface 1 5 , and keeps protrusions 25 inserted into their corresponding recesses o f the cast iron/cast steel core 13.

Liner front plate 1 1 thus remains locked against horizontal movements, held between the thrust base surface 14 on which it rests through the liner back plate 12, and between the locking strips 28 which abut against a corresponding surface of the recess in which the protrusion 25 is inserted. In vertical direction, the liner front p late 1 1 is prevented from moving by abutment of upper and lower sides o f protrusion 26, abutting against corresponding walls of the recess 37 in which the protrusion is inserted.

An inj ected liner front plate 1 1 with integrated assembly means 25 and 26 as described on figures 5 a to 5 c, is easier to assemble and to disassemble, and is less sensitive in time to a loosening of assembly means than riveted or screwed assemblies.

Figure 5 c is a cross section view o f an axle box according to the invention, comprising the front plate 1 1 illustrated on Figures 5 a and 5b. The axle box o f Figure 5c is provided with the similar type o f spring seat cups 3 as those depicted on Figure 1 , i. e. cups comprising a one piece guiding ring 8 plus base plate 7, and supported by an elastomeric so le 9. But contrary to fig. l , spring seat cups 3 of fig.5 are provided without any assembly means to the iron or cast steel core 13. Centering of the cups 3 is made possible by a moulded boss 35 of the spring seat base 6, fitting in a central ho le 36 of the spring seat cup 3.

As can be seen on Figure 5 c, the central protrusion 26 o f liner front plate 1 1 is inserted in a corresponding through hole 38 o f the liner back plate 12 and in a corresponding recess 37 -which is here defined as an open through hole 37- o f the cast iron or cast steel core 13. The lock const ituted by protrusion 26 and corresponding recess 37 not only is a means for globally maintaining liner front plate 1 1 in position, but it also limits the displacement of liner front plate 1 1 in the region around protrusion 26, thus limiting maximum shear strain, both in liner front plate 1 1 and liner back plate 12.

Figure 6 is a part ial section view o f another embodiment of an axle box according to the invention. Features common to previous figures can be seen on Figure 6, which are then designated by same reference numbers as in previous figures. The spring seat cups 3 o f Figure 6 are similar to those depicted on Figure 1 , except that they are assembled to the cast iron or cast steel core 1 3 by a central screw 1 8 instead of being assembled by several screws or rivets distributed around the external part of the base plate washer.

Liner front plate 1 1 is here a polymer injected liner, this time with a so lid central protrusion 29 inserted in a corresponding recess 37 of the cast iron or cast steel core 13 , which recess is a blind ho le instead of being an open ho le 37 as on Figure 5 c.

Figure 7 is a partial cross-section view o f yet another embodiment of an axle box according to the invention. Features common to previous figures can also be seen on Figure 7, designated by same reference numbers as on previous figures . The axle box o f Figure 7 is equipped with the same type of liner front plate and liner back plate as on Figure 6. This time, the spring seat cup comprises a metallic guiding ring 8 whose lower circumference is welded into a corresponding circular groove 30. Base plate 7 and elastomeric sole 9 are replaced by four washers designed at separate parts from the guiding ring 8. One elastomeric washer 3 1 and one rigid washer 32 made of metal or plastic have an inner diameter which is little more than the external diameter of guiding ring 8 , and an outer diameter which is more or less equal to the outer diameter of the outer spring 5. Another elastomeric washer 33 , and another rigid washer 34 made o f plastic or steel, have an outer diameter which is little less than the inner diameter of the guiding ring 8 and have an inner diameter which may be roughly equal to the inner diameter of the inner spring 4, but which can also be less, down to a value of zero for a solid surface washer.

Outer washers 3 1 and 32 may be independent from each other or may be bonded by gluing, overmoulding or other means, and the same applies foe inner washers 33 and 34. Elastomeric washers 3 1 and 33 lay against a machined, or against an as cast surface o f the cast iron or cast steel core 13 , and rigid washers 32 and 34 support the Hertzian contact of the end coils o f springs 4 and 5. To avoid Hertzian types stress concentrations in rigid washers 32 and 34, in so me embodiments only elastomeric washers 3 1 and 33 may be provided, with a thickness sufficient to accommodate deformations around the spring wire and to ensure sufficient damping. Still, with a two-layer washer, due to the stress distribution ensured by the rigid washers, a lesser thickness o f elastomer will be needed, and the elastomer may be chosen more according to its damping properties than considering its compression set or its shear resistance. In this embodiment, where two separate damping washers for the internal spring 4 and for the external spring 5 of each spring set, the thickness and type of elastomeric material may be different for each washer, so as to take into account the difference in forces exerted and the difference in vibration amplitude of each spring.

In all described embodiments, adding easily removable spring seat cups or spring seat washers, makes it easier to cope with the wear entailed by the springs, than when the wear occurs directly on the cast iron/cast steel core surface. The invention is not limited to the embo diments described and illustrated above, which are to be regarded as mere examples of a wider range of embo diments. For instance, spring seat cups with elastomeric so les could be provided at both ends of each spring set, or could be provided only at the upper end of each spring set, in order to isolate the pedestal and the wagon supported by the pedestal, from the vibrations generated by the springs themselves. Different shapes and different assembly means could be proposed, especially for the liner front plate 1 1 and liner back plate 12. Spring seat cups could be provided without any assembly means . The axle box could be provided with two-layer spring seat cups with an elastomeric so le/washer plus harder base plate/washer, so as to ensure maximum damping o f vibrations passing through a spring and, on the other hand, be provided with a mono lithic friction surface element, inj ected in a wear resistant polymer, with better damping properties than the current metal liner plate, but still with less damping properties than a two- layer friction surface element. The axle box could then be devoid o f elastomeric liner back plate, which would offer an opportunity for placing more lo cking protrusions on the liner front plate.

Each spring set could be constituted by a so le spring or by non concentric springs, in which case spring seats could be provided with other centering means than a guiding ring.

The axle box according to the invention helps to reduce vibrations generated between the spring sets and the cast core, or the spring sets and the bogie pedestal, and helps to reduce vibrations generated by the contact of the Lenoir system piston with its corresponding friction surface, and also helps reducing transmission o f vibrations generated by contact of the wheel set with rail, to the pedestal and then to the wagon. The axle bo x according to the invention may thus be thoroughly helpful when developing new freight wagons which have to adhere to severe noise reduction specifications.

The axle box according to the invention may also be used in passenger trains or tramways . Also, the core of the axle box, could be made of another metallic material than cast iron or cast steel, for instance from aluminium alloy. The core of the axle box might also be made from a non metallic material.

Claims

1. Axle box (1) for a railway bogie, comprising a core part (13) with an axle passage (2), comprising spring seats (3) for one or more springs (4,5), and comprising one or more friction surface elements (10), each friction surface element defining a friction track for an end surface of a piston, wherein the axle box (1) is adapted for supporting a bogie pedestal transmitting efforts to the axle box both through the springs (4,5) and though the friction surface elements (10), characterized in that either the spring seats (3), or the friction surface elements (10), comprise an at least two layer damping plate (11-12, 7- 9), comprising a first layer (11, 7) being a rigid sheet, on a first side of the plate facing one of the springs (4,5) or facing one of the pistons, and comprising a second layer (12,9) being made from an elastomeric material more flexible than the material of the first layer (11, 7), the second layer (12,9) being placed on the second side of the plate.

2. Axle box according to claim 1, where the spring seats (3) and the friction surface elements (10) each comprise a two layer damping plate (7-9, 11-12).

3. Axle box according to any of the preceding claims, where the first layer (11, 7) of a least one of damping plates is made of steel, with a manganese mass content of the steel of at least 8%.

4. Axle box according to any of the preceding claims, comprising at least a damping plate (10, 3) comprising a layer (11, 7) made of a polyamide based compound, with either a polymer matrix base of PA66 or a polymer matrix base of PA6-G.

5. Axle box according to claim 4, where the spring seats (3) comprise a two layer damping plate (7-9), whereas each friction surface facing the pistons is the surface of a one piece polymer plate directly leaning against the core part (13).

6. Axle box according to any of the preceding claims, where the spring seats (3) each comprise a base plate (7) adapted to support at least an end coil of a spring (4, 5), and a guiding ring (8) adapted to be inserted between two coaxial springs (4, 5), both base plate and guiding ring being separated from the core part (13) by an elastomeric sole (9), and being made of a same material, more rigid than the material of the elastomeric sole.

7. Axle box according to any of claims 1 to 5, where spring guiding rings (8) are welded to core part (13), an external damping washer (31-32) and an internal damping washer (33-34) being inserted respectively on the external side and on the internal side of the ring (8), each washer constituting a two layer damping plate comprising a first layer in the form of a rigid sheet (32, 34) facing one of the springs (5, 4), and comprising a second layer in the form of an elastomeric sheet (31, 33) made of an elastomeric material more flexible than the material of the first rigid sheet, the second sheet being placed on the side of the washer opposite to the spring.

8. Axle box according to claim 1, where at least one of the two- layer damping plates (10, 3) rests on a base surface (6, 14, 15) of the core part (13) which is in rough cast state.

9. Axle box according to any of claims 1 to 4, or 6 to 8, where the friction surface elements (10) each comprise a polymer sheet (11) with at least one roughly central protrusion (26, 29), extending through, and further than, the depth of an elastomeric sheet (12), and where the core part (13) is provided with recesses (37) in which the tips of the protrusions can fit, so as to limit lateral movements, i.e., movements within the friction plane of the piston end, between the friction surface element (10) and the core part (13).

10. Axle box according to any of the preceding claims, where the friction surface elements (10) each comprise a polymer sheet (11) with a central friction plate (23) and two lateral plates (24) both forming, in non assembled state, an angle (a) of between 94° and 120° with the central plate (23), each central and lateral plate being provided with at least one protrusion (26, 29, 25) adapted to fit in a corresponding recess (37) of the core part.

11. Axle box according to any of the preceding claims, where its core part is made from aluminium alloy, cast iron, or cast steel.