GB2325909A - Bogie truck suspension - Google Patents

Abstract

A bogie truck for a rail vehicle comprises a pair of spaced side frames 10 and front and rear wheel and axle sets 17 extending transversely between the side frames and rotatable in axle boxes 26 which are connected by suspension means to the side frames. A transverse bolster 11 extends between the side frames 10, and "hourglass" spring bearings 14 are connected between the bolster and the rail vehicle body. Each side frame includes a central portion 15 connected to the bolster 11 and two cantilever leaf springs 16 extend forwardly and rearwardly respectively from the centre portion. The free end of each leaf spring 16 is connected to an axle box 26, the leaf springs thereby constituting primary vertical suspension means for the truck.

Description

"Improvements in bogie trucks for rail vehides" The invention relates to bogie trucks for rail vehicles, and in particular to bogie trucks ofthe 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, a transverse bolster connected between the side frames and having a mounting for connection to the rail vehicle body, and further suspension means for connection between the transverse bolster and the rail vehicle body.

In such a bogie truck the primary suspension allows each wheel and axle set to perform limited vertical movement relative to the side frames and, more importantly, to be twisted relative to the side frames in a yaw sense, and to be able to translate laterally.

Commonly the primary suspension includes a pair of vertical helical compression springs which are connected between an axle box at each end of the wheel and axle set and a part ofthe side frame. The axle boxes may be inboard or outboard ofthe wheels ofthe wheel and axle set, but the present invention relates particularly to arrangements where the axle boxes are located inboard.

While such bogie designs have been very successful over many years, the structure of the side frames, axle boxes and associated components is comparatively massive, resulting in comparatively high unsprung weight and substantial loads on the track and rail vehicle. The cost of the bogie may also be related to its weight. There would therefore be significant advantages in reducing the weight, and particularly the unsprung weight, of the bogie truck. The reduced overall weight may reduce the cost of manuflicture and allow an increased payload to be carried by the rail vehicle, whereas the reduction in unsprung weight may allow the rail vehicle to travel faster with less damage to the vehicle and track. The present invention therefore sets out to provide various improvements in bogie trucks which may, inter alia, provide the advantages of simplicity, lower cost and lower weight.

According to a first aspect ofthe invention 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 suspension means to the side frames, a transverse bolster connected between the side frames and having a mounting for connection to the rail vehicle body, and further suspension means for connection between the transverse bolster and the rail vehicle body, wherein each side frame includes a central portion connected to the bolster and two cantilever leafsprings extending forwardly and rearwardly respectively from the centre portion, the free end of each leaf spring being connected to the bearing assembly in which one end of a respective wheel and axle set is rotatable, the leaf springs thereby constituting primary vertical suspension means for the bearing assemblies.

The use of cantilever leaf springs as the primary vertical suspension means may enable both the overall weight and the unsprung weight ofthe bogie truck to be reduced, with the advantages referred to above.

As previously mentioned, the invention is particularly applicable to arrangements wherein said bearing assemblies are located inboard of the wheels of said wheel and axle sets. The use of cantilever leaf springs may allow a significant reduction in size of the bearing assemblies in which the wheel and axle sets are rotatable, thus allowing the bearing assemblies to be located closer to the wheels, on the inboard side thereof, than is possible with previous arrangements. This reduces the bending moment applied to the axle thus enabling a lightening ofthe axle structure, leading to further reduction in the unsprung weight.

Each cantilever leaf spring may be a two-rate, or variable rate, spring.

Each bearing assembly may comprise roller bearings disposed between an inner race extending around a part of the wheel and axle set and an outer race formed within surrounding bearing cups, and an axle box to which the bearing cups are coupled, a free end ofthe associated leaf spring being connected to the axle box. For example, the axle box may comprise an extension, and preferably a downward extension, which is connected to, or integral with, one ofthe bearing cups ofthe bearing assembly.

Preferably, the free end of the leaf spring is connected to the axle box by secondary suspension means.

The secondary suspension means may comprise bodies of flexibly resilient material connected between abutments on the free end of the leaf spring and on the axle box respectively. Preferably said bodies of flexibly resilient material are orientated to resiliently oppose both longitudinal and lateral movement between the axle box and leaf spring. For example, said bodies of resiliently flexible material may comprise chevrons of elastomer or other resilient material secured between the axle box and leaf sprin & the apex ofthe chevron facing downwardly and extending generally parallel to the axle of the associated wheel and axle set. Many other arrangements can be envisaged for achieving a similar effect.

In any ofthe above arrangements, said further suspension means may comprise tertiary suspension means in the form of a solid body of elastomer for connection between the transverse bolster and the rail vehicle body. For example, the tertiary suspension means may be a so-called "hourglass" bearer spring. Each such spring may comprise a lower support plate for mounting on the bogie frame, an upper support plate for mounting on the under frame of the rail vehicle, and two bodies of elastomer sandwiched between the support plates and separated by an intermediate plate structure to which the bodies of elastomer are also bonded. Each elastomer is in the form of a body of revolution, and the two bodies together have an overall configuration reminiscent of an hourglass.

Any other suitable arrangement may be employed. For example, a single body ofelastomer of suitable shape may be encircled by a rigid metal band, so that as the body is compressed vertically its radial expansion is restricted by the band so as to increase the stiffness.

According to a second aspect ofthe invention 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, a transverse bolster connected between the side frames and having a mounting for connection to the rail body, and further suspension means for connection between the transverse bolster and the rail vehicle body, wherein the axle of each wheel and axle set includes a hollow tubular outer portion through which extends a separate inner portion of smaller diameter than the internal diameter of the outer portion, said inner portion being tensioned to place the outer tubular portion under compression.

Such arrangement may reduce the mass of the axle and hence also reduce the unsprung weight. Also, the fact that the outer tubular portion of the axle is under compression tends to inhibit crack propagation as a result of impact or other damage on the outer surface of the axle.

As in the first aspect ofthe invention, each bearing assembly may comprise roller bearings disposed between an inner race extending around part of the wheel and axle set and an outer race formed within surrounding bearing cups, the inner race being formed on bearing cones coaxially disposed between one end of said tubular axle portion and an abutment on another part of the wheel and axle set, whereby said bearing cones are axially compressed when the tubular axle portion is compressed.

The bearing cone adjacent the end of the tubular axle portion may be formed with an annular rebate in which the end edge ofthe tubular axle portion is received and located.

The bearing cones may surround an axial hub extension of the wheel, the aforesaid abutment being formed on said hub extension.

As in the first aspect ofthe invention, said bearing assemblies may be located inboard ofthe wheels ofthe bogie truck.

A third aspect of the invention relates to the construction of the wheels on a bogie truck of the kind first referred to. Each wheel will normally comprise a hub, an outer tread having a flange at one side thereof, and a web between the hub and tread.

One form of braking arrangement for such a wheel is a disc brake in which a brake pad is applied either directly to the web of the wheel or to a separate braking component mounted on the web. Application ofthe brakes to the wheel may generate a substantial amount of heat and it is desirable that the transfer of heat from the wheels to the bearing assemblies in which the wheel sets are rotatable is minimised as far as possible. The third aspect of the present invention sets out to provide an arrangement whereby this may be achieved.

According to the third aspect of the invention, therefore, there is provided a railway wheel comprising a hub, an outer tread having a flange at one side thereof, and a web between the hub and the tread, wherein the web comprises an annular braking portion adjacent the tread, having a surface for engagement by a brake pad, and an annular connecting portion between the braking portion and the hub, the thickness of the connecting portion, in the axial direction, being less than the thickness of the braking portion.

The reduction in thickness ofthe connecting portion, in relation to the braking portion, reduces the cross-sectional area of the flowpath available for the flow of heat generated by braking inwardly to the hub of the wheel and hence to the associated bearing assembly.

The braking portion may comprise an integral portion of the wheel web itself: or may comprise a separate braking component mounted on the web.

The following is a more detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawings in which: Figure 1 is a plan view of one form of 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 a longitudinal sectional view through one end of a wheel and axle set of the bogie truck, Figure 5 is a similar view to Figure 4 of an alternative arrangement, and Figure 6 is a similar view of a further alternative arrangement.

Referring to Figure 1 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 ofthe rail vehicle body, indicated diagrammatically at 12 in Figure 3, by a traction rod 9. A downwardly projecting assembly 13, mounted on the underside of the vehicle body, is engageable between inclined rubber bumpers 13a on the bolster 11, so as to increase the stiffness of the suspension when the vehicle is laden. Tertiary suspension means, in the form of elastomeric "hourglass" spring bearings 14, are connected between the ends of the transverse bolster 11 and the underside ofthe vehicle body.

Each side frame comprises a central portion 15 which is integral with the end of the bolster 11 and a leaf spring suspension assembly comprising two cantilever leaf springs 16 which extend forwardly and rearwardly from the central portion 15 ofthe side frame. The leaf springs 16 constitute the primary vertical suspension means of the system. As best seen in Figure 1, the leaf springs 16 are located inboard and below the cental portion 15 ofeach side frame. Each leaf spring 16 may be a two-rate or variable rate spring.

Telescopic dampers 30, 31, angled to the vertical, as best seen in Figure 3, are connected between the central portion 15 of each side frame and the underside ofthe rail vehicle body 12. A fixed bracket 8 onthe central portion 15 ofthe side frame has a part 9 which underlies the leaf spring 16 so as to limit the downward movement thereof relative to the rest ofthe side frame.

Each wheel and axle set 17 of the bogie truck comprises an axle 18 to each opposite end of which a flanged wheel 19 is rigidly connected. The axles 18 are rotatable in bearing assemblies 20 which are connected to the ends ofthe leaf springs 16.

The construction of each bearing assembly 20 is shown in greater detail in the sectional view of Figure 4.

Referring to Figure 4, each bearing assembly comprises roller bearings 21 disposed between an inner race 22 extending around a hub extension 23 which is integral with the rear face ofthe wheel 19, and an outer race 23 formed within upper and lower semi-circular bearing cups 24, 25.

The bearing cups 24, 25 have mounted thereon a separate casting 26, which extends downwardly from the lower bearing cup 25 to provide an axle box for connection to the end ofthe associated leaf spring 16. Alternatively the casting 26 might be integral with the lower bearing cup. As best seen in Figure 2, the end of each leaf spring 16 has a shaped end portion 27 which projects into an aperture 28 in the axle box 26. The end portion 27 ofthe leaf spring is secured within the aperture 28 by secondary suspension means in the form of a chevron-sectioned block 29 of a suitable elastomer bonded to correspondingly shaped surfaces on the underside of the leaf spring portion 27 and the bottom surface of the aperture 28 in the axlebox. Since the chevron blocks 29 are ofrt from the axle 18, they can accommodate relative rolling between the wheel and axle set and the vehicle body.

As may be seen from Figure 4, the simple connection arrangement between the ends of the leaf springs 16 and the bearing assemblies 20 means that the axle box 26 is very compact and may thus be located very close to the inboard side ofthe wheel 19, thus keeping to a minimum the bending moment exerted on the axle 18 by the weight ofthe rail vehicle. Since the bending moment is reduced the bearings can be smaller and this again enables them to be located closer to the inboard face ofthe wheel 19. The reduction in bending moment also allows reduction in the size ofthe axle 18 itself.

As also best seen in Figure 4, the axle of each wheel and axle set includes a hollow tubular outer portion 32 each end of which is received in an annular rebate 33 in the end face of one of the two cones 34 which encircle the hub portion 23 of the wheel 19 and support the rollers 21.

In order to maintain the tubular axle portion 32 under compression, the axle also comprises a central longitudinal shaft or bolt 35 which passes axially through the centre of the tubular portion 32 and through a bore in the hub portion 23 of the wheel 19.

Tension is applied to the shaft 35 by screw nuts 36 at each end and, as the nuts are tightened, increasing tension in the shaft 35 applies compression to the tubular portion 32 ofthe axle which also serves to clamp the cones 34 firmly into an annular rebate on the hub portion 23 in which the cones are located.

As previously mentioned, the compressive stressing of the outer portion 32 of the axle increases the stresses which it can bear and also tends to inhibit the propagation of any cracks which might be initiated in the axle as a result of impact or other damage.

The extent ofthe compression ofthe axle 32 is such that it remains under compression under all temperature conditions to which the components are likely to be subject in use.

The use of a hollow axle may result in a significant reduction of the unsprung weight of the bogie truck and, in addition, the hollow axle allows the insertion of an ultrasonic probe along and within the axle to check for flaws in the structure of the outer tubular portion.

Referring again to Figure 4, each wheel 19 comprises the hub portion 23, an outer tread 36 having a flange 37 at the inner side thereon and a web 38 between the hub and the tread 36. Annular braking rings 39 are secured to opposite sides ofthe web 38.

As best seen in Figure 2, arcuate brake pads 40 are located on each side of each wheel 19 and are engageable with the surfaces ofthe braking rings 39. The brake pads 40 are supported from Y-shaped brackets 41 which extend upwardly at an angle from the central portion 15 of the side frame. Mechanisms indicated generally at 42 serve to operate the brakes by swinging the brake pads 40 into and out of clamping engagement with the wheel.

Figure 5 shows a modification of the wheel arrangement of Figure 4, whereby the transfer of heat from the braking surfaces to the bearing assembly 20 is minimised.

In this case the separate annular braking rings 39 are omitted and the brake pads bear directly on the surfaces on opposite sides of a braking portion 43 of the web 38 of the wheel. Adjacent the outer tread 36 a small annular undercut 44 is provided at the outer periphery ofthe portion 43 to allow for wear ofthe braking surfaces.

Radially inwards of the braking portion, the web is reduced in thickness, as indicated at 45, the reduced thickness portion connecting the outer brake portion to the hub 23. The radial extent ofthe annular connecting portion 45 may be greater than half the radial extent of the braking portion 43 and, in the arrangement shown in the drawings, the actual width of the connecting portion 45 is in fact substantially equal to the axial width of the braking portion.

The thickness of the braking portion 43 is chosen so as to be suitable to accommodate the thermal stresses which are likely to be induced in the web during braking. The connecting portion 45 is however reduced in width so as to reduce the thermal path between the braking portion 43 and the wheel hub 23 so as to reduce the flow of heat inwards to the associated bearing assembly 20.

Figure 6 shows a modified version of the arrangement of Figure 4, where the compressed tubular axle 32 and shaft 35 are replaced by a more conventional solid axle 46.

Claims (24)

1. 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 suspension means to the side frames, a transverse bolster connected between the side frames and having a mounting for connection to the rail vehicle body, and further suspension means for connection between the transverse bolster and the rail vehicle body, wherein each side frame includes a central portion connected to the bolster and two cantilever leaf springs extending forwardly and rearwardly respectively from the centre portion, the free end of each leaf spring being connected to the bearing assembly in which one end of a respective wheel and axle set is rotatable, the leaf springs thereby constituting primary vertical suspension means for the bearing assemblies.

2. A bogie truck according to Claim 1, wherein said bearing assemblies are located inboard of the wheels of said wheel and axle sets.

3. A bogie truck according to Claim 1 or Claim 2, wherein each cantilever leaf spring is a two-rate, or variable rate, spring.

4. A bogie truck according to any of the preceding claims, wherein each bearing assembly comprises roller bearings disposed between an inner race extending around a part ofthe wheel and axle set and an outer race formed within surrounding bearing cups, and an axle box to which the bearing cups are coupled, a free end of the associated leaf spring being connected to the axle box.

5. A bogie truck according to Claim 4, wherein the axle box comprises an extension which is connected to, or integral with, one of the bearing cups of the bearing assembly.

6. A bogie truck according to Claim 5, wherein the extension of the axle box is a downward extension.

7. A bogie truck according to any of Claims 4 to 6, wherein the free end of the leaf spring is connected to the axle box by secondary suspension means.

8. A bogie truck according to Claim 7, wherein the secondary suspension means comprise bodies of flexibly resilient material connected between abutments on the free end of the leaf spring and on the axle box respectively.

9. A bogie truck according to Claim 8, wherein said bodies of flexibly resilient material are orientated to resiliently oppose both longitudinal and lateral movement between the axle box and leaf spring.

10. A bogie truck according to Claim 9, wherein said bodies of resiliently flexible material comprise chevrons of elastomer or other resilient material secured between the axle box and leaf spring, the apex of the chevron facing downwardly and extending generally parallel to the axle of the associated wheel and axle set.

11. A bogie truck according to any of the preceding claims, wherein said further suspension means comprise tertiary suspension means in the form of a solid body of elastomer for connection between the transverse bolster and the rail vehicle body.

12. A bogie truck according to Claim 11, wherein the tertiary suspension means comprises a generally hourglass-shaped bearer spring.

13. A bogie truck according to Claim 12, wherein said bearer spring comprises a lower support plate for mounting on the bogie frame, an upper support plate for mounting on the under frame of the rail vehicle, and two bodies of elastomer sandwiched between the support plates and separated by an intermediate plate structure to which the bodies of elastomer are also bonded.

14. A bogie truck according to Claim 13, wherein each elastomer is in the form of a body of revolution.

15. A bogie truck according to Claim 11, wherein said tertiary suspension means comprise a single body of elastomer of encircled by a rigid metal band, so that as the body is compressed vertically its radial expansion is restricted by the band so as to increase the stiffness.

16. 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, a transverse bolster connected between the side frames and having a mounting for connection to the rail body, and further suspension means for connection between the transverse bolster and the rail vehicle body, wherein the axle of each wheel and axle set includes a hollow tubular outer portion through which extends a separate inner portion of smaller diameter than the internal diameter of the outer portion, said inner portion being tensioned to place the outer tubular portion under compression.

17. A bogie truck according to Claim 16, wherein each bearing assembly comprises roller bearings disposed between an inner race extending around part ofthe wheel and axle set and an outer race formed within surrounding bearing cups, the inner race being formed on bearing cones coaxially disposed between one end of said tubular axle portion and an abutment on another part of the wheel and axle set, whereby said bearing cones are axially compressed when the tubular axle portion is compressed.

18. A bogie truck according to Claim 17, wherein the bearing cone adjacent the end of the tubular axle portion is formed with an annular rebate in which the end edge of the tubular axle portion is received and located.

19. A bogie truck according to Claim 17 or Claim 18, wherein the bearing cones surround an axial hub extension of the wheel, the aforesaid abutment being formed on said hub extension.

20. A bogie truck according to any of Claims 16 to 19, wherein said bearing assemblies are located inboard of the wheels of the bogie truck.

21. A railway wheel comprising a hub, an outer tread having a flange at one side thereof; and a web between the hub and the tread, wherein the web comprises an annular braking portion adjacent the tread, having a surface for engagement by a brake pad, and an annular connecting portion between the braking portion and the hub, the thickness of the connecting portion, in the axial direction, being less than the thickness of the braking portion.

22. A railway wheel according to Claim 21, wherein the braking portion comprises an integral portion of the wheel web itself.

23. A railway wheel according to Claim 21, wherein the braking portion comprises a separate braking component mounted on the web.

24. A bogie truck for a rail vehicle, substantially as hereinbefore described with reference to the accompanying drawings.