Improvements in bogie trucks for rail vehicles

Abstract: A bogie truck for a rail vehicle comprises a pair of spaced side frames (10), front and rear wheel and axle sets (17) extending transversely between the side frames and rotatable in bearing assemblies (20) which are connected by primary suspension means (23) to the side frames. A transverse bolster (11) is connected between the side frames and has a mounting, including secondary suspension means (32), for connection to the rail vehicle. The total vertical stiffness ofthe secondary suspension means (32) is greater than the total vertical stiffness of the primary suspension means (23).

Description: The invention relates to bogie trucks for rail vehicles, and particularly to bogie trucks of the kind comprising a pair of spaced side frames, front and rear wheel and axle sets extending transversely between the side frames and rotatable in bearing assemblies which are connected by primary suspension means to the side frames, and a transverse bolster connected between the side frames and having a mounting for connection to the rail vehicle body, said mounting including secondary suspension means. In bogie trucks of this type it is usual for the primary suspension to have significantly greater vertical stiffness than the secondary suspension, which may often be in the form of elastomeric "hourglass" springs. Such an arrangement provides the appropriate overall degree of vertical stiffness for the suspension of the bogie truck, while the hourglass springs allow the required lateral and longitudinal freedom of movement of the bogie truck relative to the rail vehicle. However, in view of the comparatively soft vertical stiffness of the hourglass springs it is usually necessary to provide vertical damping means between the bogie truck and rail vehicle. According to the present invention, this prior art arrangement is reversed, that is to say the vertical stiffness of the secondary suspension means is made significantly greater than the vertical stiffness of the primary suspension means. As well as providing operating advantages, such arrangement may allow vertical damping between the bogie truck and rail vehicle to be dispensed with, thus reducing the cost of the system. According to the invention, therefore, there is provided a bogie truck for a rail vehicle, comprising a pair of spaced side frames, front and rear wheel and axle sets extending transversely between the side frames and rotatable in bearing assemblies which are connected by primary suspension means to the side frames, and a transverse bolster connected between the side frames and having a mounting for connection to the rail vehicle, said mounting including secondary suspension means, the total vertical stiffness of the secondary suspension means being greater than the total vertical stiffness of the primary suspension means. The secondary suspension means may comprise at least one vertically resilient shear pad assembly for connection between the bolster and the vehicle body. The shear pad assembly may comprise bodies of resiliently flexible material for connection between the bolster and vehicle body at locations spaced symmetrically apart on either side of the central fore-and-aft axis of the rail vehicle. The resiliently flexible material may comprise natural or synthetic rubber or other suitable elastomer. Each body of resiliently flexible material may comprise a number of pads of such material stacked one above another and bonded to interleaved rigid plates. Such arrangement increases the vertical stiffness of the shear pad assembly. There may be provided a plurality of shear pad assemblies, including one or more main assemblies which are arranged to be vertically compressed after a predetermined vertical compression of one or more secondary assemblies. Thus in the tare, or unladen, condition of the vehicle, the stiffness is provided only, or mainly, by the secondary assemblies. In the laden condition, however, the main assembly comes into effect, thereby increasing the vertical and lateral stiffness. There may be provided a main shear pad assembly connected between the bolster and the rail vehicle in series with at least one secondary shear pad assembly, means being provided to limit the compression of the secondary shear pad assembly so that, after an initial degree of compression, the vertical stiffness is provided by the main shear pad assembly only. For example there may be provided a main shear pad assembly which is connected between the bolster and an intermediate element, and two secondary shear pad assemblies on either side of the central assembly, the secondary assemblies having upper ends which are engaged with the rail vehicle and lower ends which are engaged with said intermediate element, said intermediate element coming into contact with the rail vehicle, after a predetermined compression of the secondary assemblies, thereby preventing further compression of the secondary assemblies, as the vehicle is loaded. The total vertical stiffness of the secondary suspension means is preferably at least twice the total vertical stiffness of the primary suspension means, in both the unladen and laden conditions, and is more preferably at least three times the total stiffness of the primary suspension means. In a preferred arrangement the total stiffness of the secondary suspension means is in the range of three to four times the total stiffness of the primary suspension means. According to another embodiment of the invention, each primary suspension means may comprise a pair of vertical two-rate spring assemblies connected between the bearing assembly and the associated side frame, the two spring assemblies being disposed on either side of the bearing, an hydraulic damper connected between the bearing assembly and the side frame, and a traction rod extending in a generally fore-and-aft direction between the bearing assembly and the side frame. Resilient restraining means may be disposed between a part of each bearing assembly and a part of the associated side frame to increase the lateral stiffness of the primary suspension. The resilient restraining means may comprise a body of resiliently flexible material disposed between a part on the bearing assembly and a part on the side frame. For example, the body of resiliently flexible material may comprise a flexibly resilient bush mounted on the side frame and surrounding an upwardly extending spigot on the bearing assembly. Alternatively, the resilient restraining means may comprise any other form of spring means. According to another embodiment of the invention, the mounting for connection to the rail vehicle body may comprise at least one vertically resilient shear pad assembly connected between the bolster and the vehicle body, and buffers for limiting lateral relative movement between the vehicle body and bolster. Preferably, a generally fore-and-aft extending secondary traction rod, and a laterally extending damper, are connected between the bolster and the vehicle body. The shear pad assembly may comprise bodies of resiliently flexible material connected between the bolster and vehicle body at locations symmetrically spaced on either side of the central fore-and-aft axis of the rail vehicle. Each body of resiliently flexible material may comprise a number of pads of such material stacked one above another and bonded to interleaved rigid plates. Such arrangement increases the vertical and lateral stiffness of the shear pad assembly. There may be provided a plurality of shear pad assemblies, including one or more secondary assemblies which are arranged to be vertically compressed only after a predetermined vertical compression of one or more primary assemblies. Thus in the tare, or unladen, condition of the vehicle, the stiffness is provided only by the primary assemblies. In the laden condition, the secondary assemblies also come into effect, thereby increasing the vertical and lateral stiffness. The lateral buffers between the bolster and the vehicle body may comprise a body of elastomer fixedly mounted on one part and engageable by a fixed abutment on the other part upon a predetermined extent of relative lateral movement between the bolster and vehicle body. The following is a more detailed description of embodiments of the invention, by way of example, reference being made to the accompanying drawings in which: Figure 1 is a plan view of a bogie truck in accordance with the present invention, Figure 2 is a side elevation of the bogie truck, Figure 3 is an end view of the bogie truck, Figure 4 is an elevation of one form of secondary suspension means used in the bogie truck of Figures 1-3, Figure 5 is a section on the line 5-5 of Figure 4, Figure 6 is a plan view of the suspension means, Figure 7 is a part-side elevation of a bogie truck, similar to Figure 2, showing an alternative form of primary suspension, Figure 8 is a similar view to Figure 7 of a further form of primary suspension, Figure 9 is a plan view of another form of bogie truck in accordance with the present invention; Figure 10 is a side elevation of the bogie truck of Figure 9, Figure 11 is an end view of the bogie truck of Figure 9, Figure 12 is a similar view to Figure 9 of a further arrangement showing the provision of an optional resilient bush between each axle box and the side frame of the bogie truck, and Figure 13 is an end view of part of a bogie truck in an alternative arrangement, showing a different form of mounting between the bolster and the vehicle body. Referring to Figures 1-4 ofthe drawings: the bogie truck comprises two spaced side frames 10 connected by a transverse bolster 11 to provide a generally H-shaped frame. The bolster 11 is connected to the underside of the rail vehicle body 9 (not shown) by an assembly 12 comprising a downwardly projecting component 13 which engages within a corresponding socket component on the bolster 11. The assembly 12 allows the bogie to tilt relative to the rail vehicle when the vehicle is passing over undulating track. Each side frame 10 is secured to the end of the bolster 11 by Huck bolts 16. Between the side frames 10, fore-and-aft of the bolster 11, there extend wheel sets 17 each comprising an axle 18 on which are rigidly mounted flanged wheels 19. Outboard of each wheel 19 the wheel set comprises a journal which is rotatable in a bearing in a bearing assembly 20. As best seen in Figure 2, each bearing assembly 20 comprises an axle box, containing the bearing, mounted at one end of a radial arm 21 which is pivotally mounted at 22 on a lower part of the side frame 10, so as to be capable of limited up-and-down swinging movement relative to the side frame. A vertical helical compression spring assembly 23 is disposed above the axle box with its tower end engaging in a recess on the end of the radial arm 21 and its upper end connected to the underside of the side frame 10. In known manner the spring assemblies 23 are two-rate assemblies so as to provide different vertical stiffnesses for the unladen and laden conditions of the vehicle. The helical compression spring assemblies 23 constitute the primary suspension of the bogie truck and also provide lateral stiffness. A vertical hydraulic damper 24 is disposed outboard of the axle box and is pivotally connected between brackets 25, 26 on the radial arm 21 and the side frame 10 respectively. Associated with each wheel is a brake pad 27 which is mounted on a pair of links 28 suspended from a bracket on the bolster 11, so that the brake pad may be swung into and out of engagement with the peripheral surface of the wheel 19. The brake assemblies 27, 28 are all operated by a main operating linkage mounted on the bolster 11. The operating linkage comprises two operating cross members 29, 30 which are slidable towards and away from one another along the fore-and-aft axis of the bogie truck. The cylinder of an air cylinder assembly 31 is fixed to the operating member 30 and is connected by a rigid link 232 to one end of a double-ended lever arm 234 which is pivotally mounted at 235 on the other operating member 29. The opposite end of the lever arm 234 is pivotally connected at 236 to one end of an elongate slack adjuster 237. The opposite end of the slack adjuster 237 is pivotally connected at 238 to a further double-ended lever 239 which is pivotally mounted at 240 on the first operating member 30. The opposite end of the lever 239 is pivotally connected at 241 to the end of the piston of the air cylinder assembly 31. In order to apply the brakes, the air cylinder assembly 31 is actuated so as to extend the piston. The extension of the piston alters the geometry of the linkage provided by the four links 232, 234, 237 and 239 in a manner to move the operating members 29 and 30 away from one another, thereby urging the brake pads 27 against the wheels 19. 'Conversely, operation of the air cylinder assembly 31 to retract the piston moves the operating members 29, 30 towards one another again, swinging the links 28 towards the bolster 11 so as to disengage the brakes. The slack adjuster 237 is of a well known kind in which the effective length of the adjuster is automatically varied, during operation of the linkage, to take up any slack in the linkage or to compensate for wear of the brake pads 27. Secondary suspension means are provided between the bolster 11 and the underside of the vehicle body as indicated at 32 in Figures 1 and 3. Each secondary suspension means is shown in greater detail in Figures 4-6. As best seen in Figure 4, each suspension means comprises a main central vertically resilient shear pad assembly 33, known as a multi-leaf spring, the lower end of which is permanently connected to the upper side of the bolster 11. Two secondary shear pad assemblies, or multi-leaf springs, 34 are disposed on either side of the central spring 33. Each spring comprises a number of rectangular pads 35 of rubber or other elastomeric material stacked one above another and bonded to interleaved rigid metal plates 36. A metal saddle 37 has a central part 38 which sits on the top of the central assembly 33 and extends outwardly and downwardly to outer platforms 39 on which the lower ends of the secondary assemblies 34 sit. The upper ends of the outer assemblies 34 are connected to, or otherwise engage, the underside of the vehicle body 9, and the central part 38 of the saddle is spaced about 5mm below the vehicle body. The lower surfaces of the platforms 39 of the saddle 37 are spaced a short distance above the surface of the bolster. In the unladen condition of the vehicle the outer assemblies 34 are in series with the central assembly 33, and the spring suspension is mostly provided by the outer secondary assemblies which are less stiff than the central assembly 33. As the vehicle is loaded, however, the outer assemblies 34 compress until the underside of the vehicle 9 engages the central part 38 of the saddle 37 so that no further compression of the assemblies 34 is possible. Further compression of the suspension means is then resisted solely by the central assembly 33. In accordance with the present invention the combined stiffness of the secondary suspension means 32 is greater than the combined vertical stiffness of the primary suspension means 23, both in the laden and unladen condition. For example the vertical and lateral stiffnesses of the primary and secondary suspension may be as follows: Primary Suspension Per axlebox Total Vertical Stiffness (KN/mm) Unladen 1.00 4.00 Laden 4.00 16.00 Lateral Stiffness (KN/mm) Unladen 1.00 4.00 Laden 3.00 12.00 Secondary Suspension Per unit Total Vertical Stiffness (KN/mm) Unladen 6.00 12.00 Laden 20.00 40.00 Lateral Stiffness (KN/mm) Unladen 0.50 1.00 Laden 1.00 2.00 Thus, by making the stiffness of the secondary suspension significantly greater than the stiffness of the primary suspension, it is possible to avoid the necessity, and hence expense, of providing vertical damping for the secondary suspension, while maintaining the overall required vertical stiffness. At the same time, with the arrangements shown, the secondary suspension can still provide sufficient freedom in the lateral and longitudinal directions to permit the necessary rotational and translational movement of the bogie truck relative to the vehicle body. Although Figures 1-3 show the bearing assemblies 20 mounted on pivoted radial arms 21 on the side frames 10, it will be appreciated that this is only one example of a number of possible alternative arrangements for providing for vertical movement of each bearing assembly relative to the side frame 10. Figures 7 and 8 show possible alternative arrangements. In the arrangement of Figure 7 the bearing assembly 20 is constrained by the coil springs 23 to move vertically with respect to the side frame 10 and is located by a track rod 40 which extends in the fore-and-aft direction and is pivotally mounted at one end, as indicated at 41, to a lower part of the side frame 10, for pivotal movement about a horizontal axis. The rod is pivotally mounted at its opposite end to the bearing assembly 20, as indicated at 42, for pivotal movement about a vertical axis. Each pivotal connection incorporates a resilient bush. In the further arrangement shown in Figure 8 the bearing assembly 20 is restrained for vertical movement by sockets 43 which slidably receive bearing elements 44 on the lower ends of guide posts 45 which are mounted at their upper ends on the side frame 10 and extend downwardly through the centres of the coil springs 23. Referring to Figures 9 to 11: the bogie truck comprises two spaced side frames 110 connected by a transverse bolster 111. The bolster 111 is connected to the underside of the rail vehicle body by an assembly 112 comprising a downwardly projecting part-spherical component 113 which engages within a corresponding socket component 114 on the bolster 111. Each side frame 110 comprises a central portion 115 which is secured to the ends of the bolster 111 by Huck bolts 116. The ends of the bolster 111 are provided with accurately machined surfaces which mate with corresponding accurately machined surfaces on the side frames 110 so that each side frame, when such surfaces are brought into engagement, is accurately located in the required orientation with respect to the bolster. Not only does this ensure that the H-frame of the bogie will be square when assembled, with a minimum of jigging, but it greatly facilitates the replacement of a side frame, or the bolster, since the replacement component will also be formed with the appropriate accurately machined surfaces so that, again, the components will fit together with a minimum of accurate jigging. The bolster 111 is of generally I-section, comprising a central vertical web 111a and upper and lower flanges 111b and 111c. Between the side frames 110, fore-and-aft of the bolster 111, there extend wheel sets 117 each comprising an axle 118 on which are rigidly mounted flanged wheels 119. Outboard of each wheel 119 the wheel set comprises a journal which is rotatable in a bearing in a bearing assembly 120. As best seen in Figure 10, each bearing assembly 120 comprises an axle box 121, containing the bearing, mounted on a lower support frame 122. A vertical helical compression spring assembly 123 is disposed on each side of the axle box 121 with its lower end engaging in a recess in the lower frame 122 and its upper end connected to the underside of the side frame 110. In known manner the spring assemblies 123 are two-rate assemblies so as to provide different vertical stiffnesses for the tare and laden conditions of the vehicle. The helical compression spring assemblies 123 constitute the primary suspension of the bogie truck. The spring assemblies 123 also provide the lateral stiffness for the bogie truck. A vertical hydraulic damper 124 is disposed outboard of the axle box 121 and is pivotally connected between brackets 125, 126 on the lower frame 122 and the side frame 110 respectively. A fore-and-aft extending track rod 127 is pivotally connected between each bearing assembly and a mounting 128 on the lower part of each side frame 110. As best seen in Figure 9, associated with each wheel 119 is a brake assembly 129 comprising two calipers 130 which overlie opposite sides of the wheel 119 and are pivotally connected to a cross link 131. The ends of the calipers 130 have brake pads 132 mounted thereon which are engageable with annular braking surfaces 133 which are coaxial with the wheel on opposite side faces thereof. The braking surfaces 133 may be integrally formed on the wheel or may comprise separate annular components which are secured to the wheel. The calipers 130 are operated through a mechanical linkage. One end of each inboard caliper 130 is pivotally mounted to a fixed bracket 134 on the bolster 111. The outboard caliper 130 is pivotally connected to one end of a cross link 135 which is movable longitudinally of the bolster 111. The cross link 135 is connected by a short link 136 to one arm of a bell crank 137 which is pivotally mounted on the side frame, as indicated at 138. The opposite arm of each bell crank 137 is pivotally connected to a fore-and-aft extending link 139 and the two links 139 are connected by a further cross link 140. A further linkage 141 connects the cross link 140 to a driving device, such as an air cylinder, located away from the bogie, for example in the bottom part of the rail vehicle body. In order to operate the brakes, the air cylinder or other device is actuated causing retraction of the links 139 to the left in Figure 9 which in turn pivots the bell cranks 137 so as to move the cross links 135 away from their associated fixed brackets 134. This operates the calipers 130 so as to close the brake pads 132 on to the annular braking surfaces on the wheels 119. In any of the arrangements described above resilient restraining means may be provided between each bearing assembly and the side frame to control the lateral stiffness of the primary suspension, and Figure 12 shows such an arrangement diagrammatically. In this arrangement the axle box 121 of the bearing assembly is provided at the top with an upwardly extending spigot 142 which extends into a resilient elastomer bush 143 which is mounted in a housing in the side frame. The spigot and bush arrangement 142, 143, to control the lateral stiffness of the primary suspension, may be provided in any of the arrangements according to the present invention, or may be omitted. Figure 13 shows an arrangement for mounting the bolster 144 of the bogie truck on the vehicle body 145, as an alternative to the arrangement shown in Figure 11. In this arrangement the bolster 144 is connected to the vehicle body 145 by two shear pad assemblies 146, 147 symmetrically disposed on opposite sides of the central fore-and-aft axis of the vehicle. Each shear pad assembly comprises two stacks of elastomeric shear pads 148 interleaved with rigid metal plates 149 to which the shear pads are bonded. The shear pad assemblies 146, 147 resist, through shear, relative lateral movement between the bolster and vehicle body. Each assembly might alternatively comprise simple blocks of elastomer, but the multi-layer arrangement shown increases the vertical and lateral stiffness of each assembly. As may be seen from Figure 13, each shear pad assembly 147 is permanently connected between the bolster 144 and the underside of the vehicle body 145. These constitute the aforementioned primary shear pad assemblies. However, the upper surfaces of the secondary shear pad assemblies 146 are, in the tare, or unladen, condition of the vehicle slightly spaced from the underside of the vehicle body, as indicated at 155 in Figure 13. Accordingly, in the tare condition only the assemblies 147 are operative to provide comparatively low vertical and lateral stiffness. However, in the laden condition the primary assemblies 147 are compressed, closing the gaps 155 and bringing the secondary assemblies 146 into operation. The vertical and lateral stiffness is thereby increased in the laden condition. In order to limit the permitted relative lateral movement between the bolster 144 and vehicle body 145, rubber buffers 150 are fixedly mounted on the upper side of the bolster 144, on opposite sides of the central longitudinal axis of the vehicle, and are engageable by abutments 151 fixed to the underside of the vehicle body. To provide longitudinal stiffness, a secondary traction rod 152 is pivotally connected between the bolster 144 and a downwardly extending bracket 153 mounted on the underside of the vehicle body 145. Lateral damping is provided by an hydraulic damper 154 pivotally connected between the bolster 144 and the bracket 153.

Claims: A substantially H-shaped bogie truck for a rail vehicle, comprising a pair of spaced side frames (10), front and rear wheel and axle sets (17) extending transversely between the side frames and rotatable in bearing assemblies (20) which are connected by primary suspension means (23) to the side frames (10), and a transverse bolster (11) connecting the side frames together and having a mounting for connection to the rail vehicle, the bolster (11) being connected to the underside of a vehicle body by an assembly (12) comprising a downwardly projecting component (13) which engages with a corresponding socket component on the bolster (11), so as to allow the bogie to tilt relative to the body vehicle said mounting consisting of secondary suspension means (32), characterised in that the total vertical stiffness of the secondary suspension means (32) is greater than the total vertical stiffness of the primary suspension means (23). A bogie truck according to Claim 1, wherein the secondary suspension means (32) comprise at least one vertically resilient shear pad assembly (33) for connection between the bolster (11) and the vehicle body. A bogie truck according to Claim 2, wherein the shear pad assembly (33) comprises bodies of resiliently flexible material for connection between the bolster (11) and vehicle body at locations spaced symmetrically apart on either side of the central fore-and-aft axis of the rail vehicle. A bogie truck according to Claim 3, wherein the resiliently flexible material comprises natural or synthetic rubber or other suitable elastomer. A bogie truck according to Claim 3 or Claim 4, wherein each body of resiliently flexible material comprises a number of pads (35) of such material stacked one above another and bonded to interleaved rigid plates (36). A bogie truck according to any of Claims 2 to 5, wherein there are provided a plurality of shear pad assemblies (33, 34), including one or more main assemblies which are arranged to be vertically compressed after a predetermined vertical compression of one or more secondary assemblies. A bogie truck according to Claim 6, wherein there is provided a main shear pad assembly (33) connected between the bolster and the rail vehicle in series with at least one secondary shear pad assembly (34), means being provided to limit the compression of the secondary shear pad assembly so that, after an initial degree of compression, the vertical stiffness is provided by the main shear pad assembly only. A bogie truck according to Claim 7, wherein there is provided a main shear pad assembly (33) which is connected between the bolster (11) and an intermediate element, and two secondary shear pad assemblies (34) on either side of the central assembly, the secondary assemblies having upper ends which are engaged with the rail vehicle and lower ends which are engaged with said intermediate element, said intermediate element coming into contact with the rail vehicle, after a predetermined compression of the secondary assemblies, thereby preventing further compression of the secondary assemblies, as the vehicle is loaded. A bogie vehicle according to Claim 1, wherein the mounting for connection to the rail vehicle body comprises at least one vertically resilient shear pad (33) assembly connected between the bolster (11) and the vehicle body, and buffers for limiting lateral relative movement between the vehicle body and bolster. A bogie truck according to Claim 9, wherein a generally fore-and-aft extending secondary traction rod (127), and a laterally extending damper, are connected between the bolster and the vehicle body. A bogie truck according to Claim 9 or Claim 10, wherein the shear pad assembly (146, 147) comprises bodies of resiliently flexible material (148) connected between the bolster and vehicle body at locations symmetrically spaced on either side of the central fore-and-aft axis of the rail vehicle. A bogie truck according to Claim 11, wherein each body of resiliently flexible material comprises a number of pads of such material stacked one above another and bonded to interleaved rigid plates (149). A bogie truck according to any of Claims 9 to 11, wherein there are provided a plurality of shear pad assemblies, including one or more secondary assemblies which are arranged to be vertically compressed only after a predetermined vertical compression of one or more primary assemblies. A bogie truck according to any of Claims 9 to 13, wherein the lateral buffers (150) between the bolster and the vehicle body comprise a body of elastomer fixedly mounted on one part and engageable by a fixed abutment on the other part upon a predetermined extent of relative lateral movement between the bolster and vehicle body. A bogie truck according to any of the preceding claims, wherein each primary suspension means comprise a pair of vertical two-rate spring assemblies connected between the bearing assembly and the associated side frame, the two spring assemblies being disposed on either side of the bearing, an hydraulic damper connected between the bearing assembly and the side frame, and a traction rod extending in a generally fore-and-aft direction between the bearing assembly and the side frame. A bogie truck according to Claim 15, wherein resilient restraining means are disposed between a part of each bearing assembly and a part of the associated side frame to increase the lateral stiffness of the primary suspension. A bogie truck according to Claim 16, wherein the resilient restraining means comprise a body of resiliently flexible material disposed between a part on the bearing assembly and a part on the side frame. A bogie truck according to Claim 17, wherein the body of resiliently flexible material comprises a flexibly resilient bush mounted on the side frame and surrounding an upwardly extending spigot on the bearing assembly. A bogie truck according to any of the preceding claims, wherein the total vertical stiffness of the secondary suspension means is at least twice the total vertical stiffness of the primary suspension means, in both the unladen and laden conditions. A bogie truck according to Claim 19, wherein the total vertical stiffness of the secondary suspension means is at least three times the total vertical stiffness of the primary suspension means, in both the unladen and laden conditions. A bogie truck according to Claim 20, wherein the total vertical stiffness of the secondary suspension means is in the range of three to four times the total vertical stiffness of the primary suspension means, in both the unladen and laden conditions. means.

Inventors: HARDING ALAN, KIBBLE MICHAEL, LATHAM JOSEPH, SMITH BRIAN, HARDING, ALAN, KIBBLE, MICHAEL, LATHAM, JOSEPH, SMITH, BRIAN
Applicants: POWELL DUFFRYN RAIL LTD, POWELL DUFFRYN RAIL LIMITED
Application year: 1998
Main classification: B61F5
IPC codes: B61F5