GB2033313A - Rail wheel - Google Patents

Abstract

A rail wheel is provided with a tire or running rim 242 made from a memory alloy, e.g. a memory alloy containing titanium and nickel. In addition a resilient layer 243 of a natural or synthetic polymeric material is provided between the tire or running rim 242 and the wheel body 241 so as to enhance wheel/rail adhesion, reduce mechanical shock and reduce noise. The tire or running rim 242 and the co-operating surface of the wheel body 241 are shaped and arranged so that the tire or rim 242 cannot slip off the body. Alternatively the resilient layer may be replaced by an arched metal spring or the memory alloy rim or tyre may itself be arched to provide resilience. In another construction the wheel body is integral with the rim and the whole is made of a memory alloy, a resilient layer being provided between the wheel body and hub. An embodiment is also disclosed in which the running rim or tyre is not of a memory alloy but is held in place on the wheel body by rings of memory alloy. <IMAGE>

Description

SPECIFICATION Improved rail wheel This invention relates to wheels, especially rail vehicle wheels.

It has been known almost since the beginning of the railroad era that the wheel/rail adhesion of steel wheels and steel rails is somewhat poor, especially under lubricated and/or wet conditions.

Whilst the adhesion has in general been tolerable in conventional railroad systems it has nonetheless been a major limitation on the design and operation of railroad and, more recently, of the modern rapid mass transit rail systems now being used for commuters in many urban areas.

Wheel/rail adhesion limits the maximum grades a rail vehicle can climb and descend. The level of adhesion currently available with steel wheels operating on steel rails limits acceptable grades on existing rapid mass transit systems to about 4 per cent. The civil engineering costs to construct railways with such gentle grades can easily be the most expensive part of building a new rail transit system. Clearly, higher wheel/rail adhesion means that new rail transit systems can be designed and built with steeper grades and lower cost than heretofore possible.

Moreover wheel/rail adhesion affects not only the speed with which a rail vehicle can travel under various conditions but also the time and distance within which the vehicle can be started and stopped. Mass transit vehicles must be reliably stopped and started quite frequently under various conditions and vehicle headway, that is the distance which must be maintained for safety reasons between consecutive trains, is, therefore, heavily dependent on acceleration and braking performance under conditions adverse to wheel/rail adhesion. Only by improving vehicle headway can service levels be increased while maintaining or increasing train speeds.

To achieve high service levels (consistent, of course, with not exceeding limitations imposed by human factors) designers of rapid transit systems would like to employ a maximum deceleration of 3.0 miles per hour per second. To achieve this level of deceleration the minimum coefficient of adhesion between rail and wheel must lie somewhere between 0.14 and 0.20. The term "coefficient of adhesion" is used rather than coefficient of static or dynamic friction because the contacting portions of the wheel and rail are continuously changing and some slippage between the wheel and the rail may or may not occur during braking. Unfortunately, water, oil, grease, rust and other contaminants and their various combinations all affect wheel-to-rail adhesion. For example, moisture and a small amount of rust are known to form a slurry which greatly reduces the coefficient of adhesion.Under some conditions the actual coefficient of adhesion between steel wheels and steel rails has been measured and found to be as low as 0.03.

Considerable research has accordingly been conducted to obtain improved wheel/rail adhesion but, whilst it has been shown that certain materials, including titanium, give improved adhesion to steel, no practical or commercially feasible means has been found for exploiting them.

In German Offenlegungschrift No. 2 816 099 there is described an claimed a wheel, especially a rail vehicle wheel, the tire or running rim which consists of or comprises a member made from a memory alloy. In general the memory alloy member advantageously forms the running rim itself but, in certain embodiments, it may be present as an auxiliary member which is used in conjunction with and co-operates with a separate running rim member. German Offenlegungschrift No. 2 81 6 099 also describes and claims a method of applying a tire or running rim to a wheel which comprises applying a memory alloy member in its deformed heat-unstable configuration to the wheel and heating it to cause it to recover and either to grip the wheel and form a running rim or else to secure a separate running rim member to the wheel.

As is known, certain alloys, commonly called memory alloys," can be used to make heatrecoverable articles, that is to say articles which have been deformed from an original configuration and which are capable of recovering towards that original configuration on heating. Amongst such memory alloys, there may be mentioned, for example, various alloys of titanium and nickel which are described, for example in U.S. Patents Nos.

3,174,851,3,351,463, 3,753,700, 3,759,552, British Patents Nos. 1,327,441 and 1,327,442 and NASA Publication SP 110, "55-Nitino-The.

Alloy with a Memory, etc." (US Government Printing Office, Washington D.C. 1972). The property of heat-recoverability has not, however, been solely confined to such titanium-nickel alloys. Thus, for example, various copper base alloys have been demonstrated to exhibit this property in e.g. N. Nakanishi et al, Script Metallurgica 5, 433-440 (Pergamon Press 1971) and such materials may be alloyed to lower their transition temperatures to cryogenic regimes by known techniques. Similarly, 304 stainless steels have been shown to enjoy such characteristics, E. Enami et al, id at pp. 663-68.

Likewise, certain alloys of titanium and niobium also exhibit memory. C. Baker, Metal Science Journal 5, 92-100 (1971) and J. P. Morniroli et al, C.R. ACD. SCI., C 275 (16) 869-871(1972).

In addition, certain zirconium based alloys such as those described in British Patent No.1,202,404 also exhibit memory characteristics.

In general, nickel-titanium alloys such as those mentioned above have a transition temperature below +1200C. Particularly useful alloys have a transition temperature from --1 96 OC to -700C (this being well below the lowest temperature they are liable to encounter during everyday use), and may be brought into their martensitic state by immersion in liquid nitrogen. However, more recently, it has been found possible to "precondition" memory alloys so as transiently to raise their transition temperature. This enables the articles made from such alloys to be kept at room temperature prior to use, so that they can be caused to recover by heating above room temperature to their artificially raised initial transition temperature.After recovery, the transition temperature reverts to a value below operating temperature so that there is not danger of a reverse transformation. Such preconditioning methods, which eliminate the need for refrigeration during storage, transportation, and installation are described, for example in German Offenlegungsschriften 2,603,878 and 2,603,911.

Memory metals have already found certain commercial applications in which their dimensional recovery and, in some cases, high strengths have been utilised in, for example, the formation of mechanical and electrical connections.

The invention described and claimed in German Offenlegungschrift No. 2 816 099 is based on the surprising observation that memory alloys, especially binary and ternary alloys of titanium and nickel, can advantageously be used to form running rims for rail vehicle wheels not only by virtue of their dimensional recovery properties but also be virtue of various other properties which, even if they had previously been noted, had never been fully evaluated or utilised in practical applications. As a result of this observation, it is possible to provide running rims which can readily be applied to the basic wheel by using the known heat-recovery properties of the alloys, but which also exhibit other surprising improvements with regard to wheel/rail adhesion and other relevant properties.

The present invention is based on our further observation that various properties of such wheels which are provided with a tire or running rim component made from a memory metal can surprisingly be enhanced by the incorporation of a resilient component, especially so as to provide improved resistance to mechanical shock and to reduction in noise during use.

The memory alloys especially preferred for use in the present invention in its application to rail vehicle wheels for rapid mass transport systems are the titanium-nickel alloys known generaliy in the art as the "55-Nitinol Alloys." These alloys, in general, contain from 43 to 48% by weight titanium, the remainder being comprised by nickel, and, sometimes, minor amounts of tertiary elements such as cobalt or iron which may be included to control the transition temperature.

Thus, for example, the transition temperature for the stoichiometric binary alloy, TiNi, is about 800 C. However, this transition temperature can be depressed towards absolute zero by adding a selected tertiary element such as one of those mentioned. The alloy used in "Cryofit" parts sold by Raychem Corporation has a transition temperature of about -1 200C which makes it especially suitable for use in all environmental conditions. For convenience, therefore, the present invention will now be described with reference to such alloys.

In accordance with the preferred method of applying the tire or running rim component an annular member of a titanium-nickel alloy is iowered in temperature to below the transition temperature of the alloy, i.e. that in which the alloy exists in its martensitic state. The annular member is then expanded in the martensitic state so as to make it radially heat-shrinkable.In order to apply the annular member it is placed circumferentially about the bearing surface of the wheel (which is usually, at this stage, provided with the resilient component, as will be apparent from the ensuing description) and is then heated to, or, more usually allowed to warm to, a temperature above the transition temperature whereby the annular member contracts towards its original diameter and thereby grips the bearing surface with compressive force, a stress of up to about 413,700 kPa (60,000 psi) being developed in the alloy depending upon the amount of unresolved shrinkage.

In general the dimensions of the annular member relative to the wheel will be chosen so that a radial expansion of about 8% will enable the annular member to be positioned properly about the wheel. Some unresolved recovery may remain after the annular member has been shrunk and is firmly seated on the bearing surface.

As mentioned above, the transition temperature (or, more correctly, the transition temperature range) will depend upon the precise constitution of the titanium-nickel alloy. It will be appreciated, however, that the transition temperature should desirably be chosen to be less than the minimum temperature to which the running rim may be exposed during use and, for this reason, the transition temperature preferably lies beiow -600C and, more preferably, below -11 1 50C. Preferred alloys comprise from about 43 to 45% by weight titanium, preferably from about 43.4 to 44.4% by weight.The alloy consisting essentially of from about 43 to 45% by weight titanium, from about 2 to 5% iron, not more than 1% by weight of other elements, the balance being nickel, is especially suitable because it can easily be maintained in its martensitic phase prior to application by storage in liquid nitrogen (or, possibly, in dry ice), but once it has returned to its austenitic phase it can safely be used in the most extremely cold climates.

In other embodiments the running rim may be made from any material possessing the desired adhesion and other properties relevant to the problems discussed above and one or more memory alloy members may be used to retain the running rim in position (including the case where the memory alloy member(s) forms at least part of the running surface). For example, the running rim may be retained in position by two flanged heatshrinkable alloy rings provided at each side thereof. In another embodiment a heat-shrinkable memory alloy hoop may act to retain a separate annular running rim in position by the force which it generates when its thickness increases on recovery, the hoop being positioned as in intermediate member between the rim and the wheel bearing surface. Other variations will, of course, be apparent to those skilled in the art.

In all embodiments, it will in general be preferred for the rail-contacting annular rim member to be formed as an integral part.

However, in certain applications, the annular rim may be split at one or more points around its circumference, preferably at an angle, so as to facilitate installation and subsequent removal for repair, etc.

Whilst in many embodiments it will be preferable to provide the running rim as a simply annular member it may in other embodiments be advantageous to provide the rim with an annular flange extending radially outward from one of its edges. Such a flange, which may or may not be in contact with a flange on the wheel itself, may further enhance wheel to rail adhesion, may help further to eliminate noise. In any event, such a running rim may also help further to reduce wear on both rails and wheels because the rail can be lubricated on curves without losing adhesion.

One advantage of these embodiments of the present invention is that the rim members and assemblies may readily be removed and repaired or replaced without unnecessary damage to themselves or to other components of the wheel.

For example, a heat-shrunk Nitinol running rim may be caused to expand to an extent which will allow its removal from the wheel simply by cooling it below the transition temperature, for example by spraying it with liquid nitrogen, see U.S. Patent No. 4,035,007. Yet another advantage is that the radical contraction of the annular member is accompanied by an increase in its width which may be used to locate the running rim tightly within a groove in the wheel by virtue of the lateral recovery forces.

It will be appreciated that the dimensional recovery properties of memory metals can readily be used to advantage in securing the running rim to the wheel. It has further been found, however, that, especially when a resilient component is incorporated in the wheel structure in accordance with the present invention, various other very important advantages can be obtained by their use. Perhaps the most surprising and significant of these is the greatly improved adhesion shown by a Nitinol running rim as compared with steel. The following Table summarises the average dynamic coefficients of friction obtained during recent tests under different conditions by using Nitinol and steel running rims.

Test condition Nitinol wheel Steel wheel on steel rail on steel rail Clean and Dry > .5 Water > .4 < .2 Diesel Fuel Oil > .4 < .08 Lubricating Oil > .08 < .005 To some extent the improvement may be attributed to the fact that the relatively low modulus of elasticity of Nitinol, from 12 to 14 x 106 psi (which is less than half that of steel), results in a larger area of contact with the rail and, in turn, leads to greater adhesion, the Nitinol/steel: steel/steei contact area ratio being about 1.4: 1. A residual benefit of this greater contact area and a more compliant wheel is noise reduction as exemplified by a significant decrease in the roar caused by microsurface imperfections.

Preliminary wear tests comparing rail wear and wheel wear of Nitinol wheels on steel rail and steel wheels on steel rail indicated that under various conditions the rail wear with Nitinol wheels is up to 10 times less than with steel wheels and wheel wear is up to 5 times less on Nitinol wheels compared to steel wheels.

A further surprising and significant point is that the adhesion versus slip behaviour of Nitinol constitutes another useful characteristic of this material in rail wheel applications. In contrast to steel, which displays a peak adhesion at about 7% slip, followed by decreasing adhesion with increasing slip, Nitinol adhesion monotonically increases with increasing slip over the entire range of slip. This attribute of Nitinol wheels may be used as a passive control device to improve slipspin control system performance and may potentially eliminate the requirement for slip-spin control completely. Another important result of this attribute of Nitinol wheels is the reduced stopping distance in emergency situations as compared to conventional steel wheels.Thus, whilst with a steel wheel on a steel rail a braking control system faces an inherently unstable condition as slip begins to occur, and this has led to the need for very sensitive and responsive slip spin control systems, with a Nitinol running rim the system may be inherently stable and selfcorrecting. If so, this will reduce the requirement for sensitive slip-spin systems or else enhance the slip-spin performance in existing systems.

It is believed that the frictionai characteristics of Nitinol alloys have never been studied before and it follows, therefore, that these surprising advantages could not have been foreseen. Other properties of Nitinol alloys which are advantageous in this application are their fatigue and corrosion resistance, which give them a long and reliable life and their relative insensitivity to commonly encountered adhesion reducing contaminants. These properties combined with the larger wheel/rail contact area give rise to reliable low electrical impedance at the wheel-torail interface, which is important for the efficient working of the control and detection methods used in modern rail systems.

It will also be appreciated that the improved adhesion coefficient and other properties shown by the Nitinol alloys may, in some applications, be utilised without at the same time using the memory characteristics of the alloy. In such applications it will be sufficient to affix the annular member to the wheel by conventional methods.

Alternatively, the wheel body itself may be fabricated from such alloys, if so desired, in which case a separate and discrete tire or running rim component may be unnecessary.

Whilst the present invention has been particularly described with reference to titanium nickel alloys it will be appreciated that similar advantages may be obtained by using other memory alloys, and, in particular, titanium memory alloys, which exhibit a coefficient of adhesion with steel rail of at least 0.14 preferably at least 0.20, and, in any case, that those and other memory alloys may have application to other rail systems, e.g. freight rail systems, where noise reduction, rail wear and wheel wear are specially important.

It will be appreciated that the present invention is applicable in principle, to any type of wheel and that the wheels may themselves be provided with other features intended to improve their performance, including, for example, those designed to reduce or eliminate impact loading of vehicle chassis components and unwanted noise such as curve squeal, rail joint impact noise and roar or tangent track rolling noise.

The resilient components used in the present invention may be provided at various locations in the wheel structures according to desired design considerations but, in preferred embodiments, they are provided between the tires or running rims made from the memory alloy and the wheel bodies. They are typically provided to enhance adhesion, especially at high speeds, to reduce shock and thereby enhance comfortable travel, and to reduce noise.

The resilient component may advantageously comprise a layer of a resilient material such as a natural or synthetic polymer. Amongst suitable polymeric materials there may be mentioned, for example, natural and synthetic rubbers; fluorocarbon elastomers such as those sold under the names "Viton" by DuPont and "Fluorel" by 3 M Corporation: ethylene/propylene copolymers and ethylene/propylene/conjugated dione terpolymers; chlorosulphonated polyethylenes such as those sold under the name "Hypalon" by DuPont; "Neoprene" rubbers sold by DuPont, vinyl acetate/ethylene copolymers having a high vinyl acetate content, for example those sold by Wacker Chemie; polysulphide resins; polyacrylates; polybutadienes; butadiene/styrene copolymers; polyisobutylene; polyisoprene; flexible epoxy resins, high density polyethylene and polyurethanes.

The resilient layer may either be electrically conductive or non-conductive as so desired.

Where it is desired that the layer be electrically conductive, conductive polymer materials, such as those filled with carbon black or metal particles, are especially preferred.

In yet other embodiments, a resilient spring member made for example from a phosphor bronze, steel or beryllium copper may be incorporated between the running rim and the wheel. Such spring members may be used together with the rubber-like and other materials discussed above. In som embodiments the tire or running rim may itself be resilient.

In all such cases, and indeed in all preferred embodiments of the present invention, the tire or running rim, on the one hand, and the wheel, on the other hand, are preferably shaped so that the tire or running rim cannot slip off the wheel, for example upon destruction or degradation of the resilient layer; the need for further engaging components such as rivets and bolts etc. is thereby obviated. This can be achieved, for example, by providing co-operating protuberances and grooves on the communicating surfaces of the components, typically by providing a V-shaped inner suface on a tire and a V-shaped groove on the outer surface of the wheel.Thus the tire or running rim is held captive on the wheel and the resilient material is positioned in the zone of captivation, thus positively assisting in the necessary mechanical interference between the tire or rim and the wheel whilst at the same time providing a resilient cushion whereby the "footprint" of the wheel on a rail may be increased.

The wheel itself may be solid, such as for example a conventional aluminium or steel wheel, or may be spoked, in which case the spokes themselves may advantageously be made from a memory alloy further to facilitate the assembly of the tire or running rim and the wheel.

Various embodiments according to the present invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an isometric flow diagram showing the steps in a method for securing a memory alloy running rim to a rail vehicle wheel; and Figures 2 to 1 7 are partial sectional views illustrating different rail vehicle wheels in accordance with the present invention.

Referring now to Figure 1, there is shown a rail vehicle wheel 111 having a bearing groove 112 positioned between an inside flange 11 3, which is provided to prevent laterai motion of the wheel relative to a track rail, and a keeper flange 114. In accordance with the present invention the bearing groove 112 is provided with a running rim 11 6 made of a memory alloy, preferably a 55-Nitinol alloy.

Running rim 11 6 may be made, for example, by a rolling process so as to have an inside diameter which is less than the diameter of the cylindrical bearing surface of groove 112. The degree of difference between the inside diameter of the running rim and the bearing surface diameter will depend upon the amount of internal stress it is desired to develop within the memory alloy when the rim compressively grips the bearing surface.

Generally, however, satisfactory results are obtained when the running rim 11 6 has an inside diameter which is from about 0.25 to 2% less than the diameter of the bearing surface.

After running rim 116 is formed with such an original diameter it is cooled to a temperature below the transition temperature zone or at least between the austensitic and martensitic phases of the memory metal, for example by immersion in liquid nitrogen. It is then expanded by using, for example, a radially expanded collett so that its inside diameter becomes greater than the diameter of the bearing surface. Of course, when a keeper flange 114 is provided, as shown, the expanded inside diameter of running rim 116 must be sufficient to allow the rim to clear the flange.In general, it will be appreciated that the dimensions of the flange 114 and the groove 112 should preferably be such that with about 8% ring expansion the flange 114 may be cleared in the expanded state and yet that from 0.25 to 2% of unresolved recovery will remain preferably uniformly distributed around the running rim when it is firmly seated in groove 11 2. However, the relatively large diameter of the wheel, i.e. about 76.2 cm (30 inches), ensures that such design requirements may be met.

Once it is expanded the running rim 116 is maintained in its martensitic phase until it is desired that the rim be applied to the wheel 111.

The rim 11 6 will remain in the martensitic phase as long as it is kept below its transition temperature, e.g. by being stored in liquid nitrogen.

When it is desired to apply the running rim 116 to the wheel 111, the rim 116 may be removed from its cold storage and placed circumferentially over the bearing groove 112 under ambient conditions at which time it will attempt to recover to its original diameter. However, it is only able to contract to the point when its inner surface engages the bearing surface of groove 11 2 with the result that the running rim 11 6 grips the bearing surface with compressive force.

For convenience of illustration, no resilient component is shown in the embodiment of Figure 1. However, it will be appreciated that the abovedescribed method can be utilized in connection with the embodiments of Figures 2 to 17, in which Figures 2 to 14 show various wheels in which a layer of resilient material, such as mentioned above, is provided in order to improve resistance to mechanical shock and noise reduction properties. In these drawings the wheel is numbered 121, 131 231,241, respectively, the memory alloy tire or running rim is numbered 122, 132... 232, 242, respectively, and the resilient layer is numbered 123, 1 33... 233, 243, respectively.It will be seen that various geometries are possible within the basic concept of providing a resilient layer and it will also be seen that, for example, in the preferred embodiments shown in Figures 2, 9, 10, 12, 1 3 and 14 that the running rim or the tire, on the one hand, and the load bearing surface of the wheel, on the other hand, are preferably so shaped and arranged that the tire or rim is positively restrained from slipping off from the wheel, even were the resilient layer to become damaged or degraded.

For example, in the especially preferred embodiment shown in Figure 14, the lower surface of the tire 242 is V-shaped and cooperates with a correspondingly shaped groove in the outer surface of the wheel 241.

Jn the embodiment shown in Figure 1 5 a spring steel member 254 is provided between the running rim 252 and the wheel 251 in order to give the desired resilience. Resilient material 253 may optionally also be provided.

In Figure 16 there is shown a wheel 261 in which the desired resilience is, in this case, provided by the memory metal running rim 262 itself. As shown, the running rim 262, made, for example, from a Nitinol alloy is arched away from the surface of the wheel in order to provide the desired spring characteristics. A layer of resilient material 263 is optionally provided.

Finally, in Figure 1 7 there is shown a further form of wheel 271 according to the present invention in which a resilient layer 273 is provided between the hub 274 and the outer body of the wheel 272, which is made from a memory alloy.

The terms "tire" and "running rim" as used in this specification generally include all members having a running surface thereon which contacts the rail. Thus whilst some members may more commonly be regarded as tires by those skilled in the art and other members as running rims, each of said terms in the present specification is meant to include the other.

It will be appreciated that the present invention provides a wheel which is especially suited to the modern rapid mass transit systems. However, it may also be advantageously utilised in other railroad systems and may be used, for example, on freight trains, locomotives, freight car trucks and other railroad vehicles. The larger wheel/rail contact areas and attendant lower contact stresses encountered when the present invention is employed provide lower wheel and rail wear for any given level of wheel loading. Additionally, one further significant advantage of the present invention is that it provides a lighter wheel assembly than has hitherto been possible using steel tires and running rims. This leads to a significant improvement in wheel dynamics because the lower unsprung mass constituted by the wheel may more readily be forced back on to the rail by the springs of the vehicle when an imperfection in the rail surface causes the wheel to jump upwards.

Other modifications and variations in accordance with the present invention will be apparent to those skilled in the art.

Claims (17)

1. A wheel which is provided with a tire or running rim component made from a memory alloy and which comprises a resilient compound so as to provide improved resistance to mechanical shock and to reduce noise during use.

2. A wheel as claimed in claim 1, which is a rail vehicle wheel.

3. A wheel as claimed in claim 1 or claim 2, wherein said resilient component is positioned between said tire or running rim and the wheel.

4. A wheel as claimed in any one of claims 1 to 3, wherein the tire or running rim and the cooperating surface of the wheel are so shaped and arranged that the tire or rim is positively captured and retained by the wheel and the layer of resilient material is positioned in the zone of mechanical interference of said tire or rim and said wheel which occasions said capture.

5. A wheel as claimed in claim 4, wherein the inner surface of the tire or rim is V-shaped and the co-operating surface of the wheel is provided with a corresponding V-shaped groove.

6. A wheel as claimed in any one of claims 1 to 5, wherein said resilient component comprises a layer or a resilient natural or synthetic polymeric material.

7. A wheel as claimed in claim 6, wherein said polymeric material is selected from the group consisting of a natural or synthetic rubber, a fluoro carbon elastomer, an ethylene/propylene copolymer, an ethylene/propylene conjugated diene terpolymer, a chloro sulphonated polyethylene, neoprene, a vinyl acetate ethylene copolymer, a polysulphide resin, a polyacrylate, a polybutadiene, a butadiene styrene copolymer, polyisobutylene, polyisoprene, a flexible epoxy resin, high density polyethylene or a polyurethane.

8. A wheel as claimed in claim 7, wherein said polymeric material contains an electrically conductive filler.

9. A wheel as claimed in claim 8, wherein said filler is selected from the group consisting of carbon black and metal particles.

10. A wheel as claimed in any one of claims 1 to 5, wherein the resilient component comprises a spring member made from a metal.

11. A wheel as claimed in claim 10, wherein the spring member is made from a phosphor bronze, steel or beryllium copper.

12. A wheel as claimed in any one of claims 1 to 5, wherein the memory metal tire or running rim is itself resilient and acts as the resilient component.

13. A wheel as claimed in any one of claims 1 to 12, wherein the memory alloy is a binary or ternary alloy of titanium and nickel containing about 43 to 48% by weight titanium.

14. A wheel as claimed in claim 13, wherein the alloy consists essentially of 43 to 45% by weight titanium, 2 to 5% by weight iron, not more than 1% by weight of other elements, the balance being nickel.

1 5. A wheel as claimed in any one of claims 1 to 14, wherein the tire or running rim has been applied by expanding it diametrically whilst the memory alloy was in its martensitic state, positioning it about a bearing surface of the wheel, and causing it to warm to the austenitic state to contract and grip the wheel with compressive force.

1 6. A rail wheel which is provided with a tire or running rim made from a binary or ternary alloy of titanium and nickel containing about 43 to 48% by weight titanium, the inner surface of the tire or rim and the outer body of the wheel being so shaped that said tire or rim cannot slip off sideways from said wheel because of mechanical interference between said tire or rim and said wheel, a layer of resilient polymeric material being positioned in the region of mechanical interference.

17. A wheel as claimed in claim 16, wherein said tire or running rim has been placed on said wheel by using the shape memory properties of the alloy.

1 8. A wheel as claimed in claim 1, substantially as described herein with reference to, and as illustrated in, Figures 2 to 1 7 of the accompanying drawings.