GB2145797A

GB2145797A - A twist beam

Info

Publication number: GB2145797A
Application number: GB08418614A
Authority: GB
Inventors: Dr Dudley Stuart Hoddinott; Stephen Charles Sutton
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1983-08-17
Filing date: 1984-07-20
Publication date: 1985-04-03
Also published as: GB8322114D0; GB2145797B; GB8418614D0

Abstract

A twist beam 12 of tubular form comprises fibre-reinforced plastics material. In order to increase the torsional flexibility of the twist beam, at least one slit is cut along the twist beam. The twist beam may be joined at each end to a fibre-reinforced plastics, tubular trailing arm 14, to form an H-frame of a rear suspension unit of a vehicle. <IMAGE>

Description

SPECIF < ICATION A twist beam This invention relates to a support member in the form of a beam likely to be subjected in use to bending and twisting loads (hereinafter referred to as a "twist beam"), and more particularly but not exclusively, to such a twist beam when part of a structure for supporting a wheel or wheels of a vehicle.

According to one aspect of the present invention, a twist beam for resisting bending and twisting loads, comprises fibre-reinforced pastics material of tubular form, the twist beam having a slit, or a plurality of slits, extending along the twist beam so as to increase the torsional flexibility of the twist beam to a required value.

Preferably, the slit or slits extend in a direction parallel to the longitudinal axis of the twist beam, and the slits might lie along a straight line.

Desirably, the fibre reinforcement comprises layers of fibres helically extending about the twist beam, and the fibres in a said layer might be at one helix angle and the fibres in other said layers might be at other helix angles.

The tubular form of the twist beam might be defined by a circular, elliptical, or rectangular shape, or modifications thereof.

In one form of the invention, the twist beam is integral at each end thereof with a respective tubular arm member comprising fibre-reinforced plastics material. Pivot means may be at one end of each arm member, and wheel mounting means at the other ends thereof.

In another aspect of the invention, there is provided a method of manufacturing a fibrereinforced plastics twist beam, the method comprising, helically winding fibres about a mandrel to form a tubular precursor, impregnating the fibres, curing the resin, and cutting a slit or a plurality of said slits along the precursor to produce a twist beam having a required torsional flexibility.

In yet a further aspect of the invention, there is provided a method of manufacturing a fibre-reinforced plastics twist beam, the method comprising, superimposing a plurality of layers of fibres one upon another, impregnating each layer of fibres with a resin, partially curing the resin, deforming the partially cured layers into the shape of a tubular precursor of the twist beam, producing a slit or a plurality of slits along the precursor, and curing the resin.

The slit or slits may be produced by cutting through the precursor or the cured precursor, or by shaping the layers such as to define the twist beam with the slit or slits therein when the partially cured layers are deformed. It will be understood that the fibres might be impregnated before, during, or after winding or superimposition thereof.

As used herein, 'helix angle' refers to the angle of the helix relative to the longitudinal axis thereof.

The invention will now be further described by way of example only with reference to the accompanying drawing, in which:~ Figure 1 shows a perspective view of part of an H-frame of a vehicle; Figure 2 shows to an enlarged scale a sectional view on the line Il-Il of Fig. 1; Figure 2a shows to an enlarged scale a sectional view on the line Ila-Ila of Fig. 1; Figure 2b shows to an enlarged scale a sectional view on the line llb-llb of Fig. 1; Figure 3 shows to an enlarged scale a sectional view on the line Ill-Ill of Fig. 1; Figure 3a shows a sectional view on the line Illa-lila of Fig. 3; Figure 4 shows to an enlarged scale a sectional view on the line IV-IV of Fig. 1, and Figure 5 shows a modification of the view of Fig. 2.

Referring now to Fig. 1, part of an H-frame 10 is shown for supporting the rear wheels (not shown) of a vehicle. The H-frame 10 comprises a fibre-reinforced plastics, rectangular tubular twist beam 12 which is secured perpendicularly at each end (only one is shown) to a respective fibre-reinforced plastics, trailing arm 14 of hollow cylindrical form and defining a bore 15. A steel mounting member 16 locates near one end of the trailing arm 14, and a rubber cushioned, pivot mounting 18 locates near the other end.

Fibre-reinforced plastics gusset members 19 bonded to the trailing arm 14, stiffen the junction between the twist beam 12 and the trailing arm 14.

In greater detail, the twist beam 12, as shown in Fig. 2, at each end (only one is shown) is bonded to and locates about a rectangular spigot 20 having a shoulder 21 and extending from a fibre-reinforced plastics insert 22 bonded to the trailing arm 14, the insert 22 extending through an aperture 19 in the trailing arm 14 and having flat faces 24, 26 that locate between and are bonded to corresponding flat faces of respective segment-shaped fibre-reinforced plastics filler pieces 32, 34- bonded to the trailing arm 14.

A rectangular cross-section cavity 31 extends in the insert 22 to reduce the weight of the insert 22.

Referring now to Fig. 2a, a slit 38 (e.g. ""2 mm wide) extends longitudinally along the twist beam 12 at a lower corner 39 to increase the torsional flexibility of the twist beam 12 to a required value. As shown in Fig. 2b, the gusset members 19 are integral with the insert 22 and protrude through respective slots 40 in the twist beam 12.

Referring again to Fig. 1, the mounting member 16 has a square-shaped portion 42 that extends through close-fitting squareshaped holes 44 (only one is shown) in the trailing arm 14 and, as shown in Figs. 3 and 3a, extends through a close-fitting squareshaped hole 46 in a fibre-reinforced plastics, cylindrical insert 48 that locates in the bore 15 and is bonded to the trailing arm 14. One end 50 of the mounting member 16 is shaped to locate a wheel assembly (not shown), and the other end is cranked at 52 and has a cylindrical stub po#rtion 53 to provide a location for a conventional spring and hydraulic shock absorber system 54 (shown only in part and in chain dotted outline).The insert 48 has a central cavity 56 in which two diametrically disposed sets of longitudinal extending lugs 58, 60 extend, each lug 58 having a location hole 62 for a steel selftapping screw 64 which extends through a close-fitting hole 65 in the square-shaped portion 42 and screws into the lug 60.

Referring now to Fig. 4, the pivot mounting 18 is supported by a fibre-reinforced plastics insert 68 that locates in the bore 15 and is bonded to the trailing arm 14. The pivot mounting 18 fits in a cylindrical hole 70 in the insert 68, and protrudes through cylindrical holes 72 in the trailing arm 14. The pivot mounting 18 is of conventional construction, and essentially comprises, a steel cylindrical casing 74 in which an annular rubber member 76 has been compressed with a steel liner 78 inside the rubber member 76 to provide a location for a pivot pin (not shown).

The H-frame 10 performs in use in a conventional manner, but with a considerable reduction in weight in comparison with a metal-based H-frame. The torsional flexibility of the twist beam 12 is greater than that of a corresponding twist beam 12 without the slit 38, because of the effect of the slit 38.

Selection of the length of the slit 38 allows a desired increase in torsional flexibility of the twist beam 12 to be achieved. A similar effect can be achieved by the use of a number of shorter !its extending along the twist beam 12, and in this case the effect of the torsional flexibilty depends not only on the total length of slit, but also on the number of slits into which the total length is divided. It will be appreciated that the presence of the slit 38 whilst increasing the torsional flexibility has little effect on the stiffness of the twist beam 12 in bending. Although the slit 38 has been shown at the lower corner 39 of the twist beam 12 to assist drainage therefrom, it may be positioned elsewhere along the twist beam 12 and need not extend longitudinally. The width of the slit 38 is not critical, and may be greater than or less than the aforesaid 2 mm.

The fibres in the twist beam 12 and the trailing arm 14 are selected and aligned to meet particular stress conditions and directions. Thus about 50% of the fibres in the twist beam 12 may extend at extremely small helix angles (-0") to the longitudinal axis of the twist beam 12, and the remaining fibres extend at helix angles of about + 45 along the twist beam 12. whilst the fibres in the trailing arm 14 may extend at helix angles of about i 30 along the trailing arm 14, although it will be appreciated that other helix angles may be used.The fibres in the twist beam 12 and the trailing arm 14 may be applied by a conventional filament winding technique, in which a continuous filament of the fibres is wound about a mandrel of the desired internal shape of the twist beam 12 or trailing arm 14 to form a precursor. Resin may be applied to the filaments before winding, during winding or after winding. After the winding operation, the resin in the precursor is partially cured and the slot 40 cut from the twist beam 12 precursor, and the aperture 19. the square-shaped holes 44, and the cylindrical holes 72 cut from the trailing arm 14 precursor. Curing of the resin is then completed.The inserts 22, 48 and 68, and the filler pieces 32, 34 may be positioned and joined to the twist beam 12 or trailing arm 14 using a suitable bonding agent such as Permabond ESP1 05. Alternatively, the inserts 22, 48 and 68, and the filler pieces 32, 34 may be installed in the partially-cured state in the partially-cured precursors of the twist beam 12 or the trailing arm 14, and cured with the twist beam 12 or trailing arm 14 precursors and thus become bonded thereto.

The slit 38 or slits may be cut in the twist beam 12 after curing or before curing. In order to assist winding of the fibres about the twist beam 12, the flat sides of the twist beam 12 precursor may be slightly domed by the mandrel by about 1-2 mm and the corners rounded. The mandrel may be removed at a convenient stage in the production of the twist beam 12 and the trailing arm 14, for example after the partial curing of the resin.

Alternatively, a plastics foam-based mandrel may be used, such as that described in British patent application No. 2 125 001 A, and only those parts of the mandrel removed where space is required for the inserts 22, 48 and 68.

As an alternative to the use of a filament winding technique the fibres might be in the form of pre-pregs (fabrics) of fibres, which after resin-impregnation are press-moulded and partially cured, and then deformed into the desired shape of the twist beam 12 or trailing arm 14 and finally cured.

The fibres might comprise:~ (a) Glass fibres in the form of continuous rovings made from types E or R glass by a number of manufacturers with a variety of filament diameters, Tex values (weight of roving in gms per 1000my and surface finishes.

An example is Type 051 L, 1200 Tex produced by Silenka Limited of Holland.

(b) Carbon fibres in the form of continuous rovings or tows. Fibres are available from a number of manufacturers in tows containing 1000, 3000, 6000 and 12,000 filaments per tow, and in various grades relating to the level of fibre strength and modulus. An example is Type XAS fibre available from Courtaulds Lim ited of Coventry, England.

The resinss used are typically of the epoxide type, but may also be of the polyester, phe nolic, vinyl ester, or polyimide varieties provided that they have a sufficiently low viscosity and an adequate 'pot life', to enable winding or laying to be completed before gelation occurs. A typical epoxide system is Ciba-Geigy's MY750 resin mixed with HY906 hardener and DY062 accelerator in proportions 100/90/1 (by weight) respectively. A typical cure schedule for such a resin is 2 hours at 120 C followed by 5 hours at 165 C.

The inserts 22, 48, 68 and the filler pieces 32, 34 may be made by press-moulding with sheet moulding compounds (SMC's), or dough moulding compounds (DMC's). These compounds are specially formulated to flow readily when heated in a mould so as to fill all the mold cavities, and then to undergo gelation and cure. Sheet moulding compounds can take a variety of forms, for example:~ (i) approximately equal portions of chopped glass fibres up to 50mm long, polyester resin, and inert, inorganic filler (calcium carbonate, talc) plus thickening agents. The fibres tend to be randomly oriented within the plane of the compound which is usually formulated as a paste 5-10mm thick supported on a polymer film; (ii) similar to (i) above but with up to 55% glass fibre at the expense of the filler content; (iii) higher strength compounds with a combination of continuous and chopped fibres.

The continuous fibres are usually oriented in one particular direction or in tow directions at a fixed angle to each other.

Dough moulding compounds may be similar to SMC's (i) above but with much shorter glass fibres, usually up to 15 mm.

The proportion of resin and filler in SMC's and DMC's may be varied to provide a required strength and stiffness of the moulded compound.

When high production rates and high strength are required, injection moulding techniques may be used, the moulding compounds usually incorporating short carbon fibres.

The twist beam 12 and the trailing arm 14 may each be of any convenient cross-sectional shape, such as rectangular, circular, elliptical, or modifications thereof, depending on the loads to be withstood and the space available, for example as shown in Fig. 5 in which part of a fibre-reinforced plastics, square tubular trailing arm 86 is shown. A fibre-reinforced plastics insert 88 similar in many respects to the insert 22 of Fig. 2 is bonded to and locates between the flat sides of the trailing arm 86, the use of filler pieces not being necessary. The twist beam 12 locates about and is bonded to a rectangular spigot 90 of the insert 88. Should it be necessary to join a circular or some other shaped twist beam to a trailing arm 14, 86, an appropriately shaped spigot of an insert 22, 88 in the trailing arm 14, 86 can be used.

If the twist beam 12 is used in conjunction with a location rod to limit lateral motion of the twist beam 12 (i.e. a Panhard rod), the bending load on the twist beam 12 in the plane of the H-frame 10 is reduced, and hence the gussets 19 can be made smaller.

In order to provide additional support at the junction of the twist beam 12 and the trailing arm 1 4, upright fibre-reinforced plastics gussets (not shown) may be fitted.

To a certain extent the plastics material used in the H-frame 10 is resistant to corrosion, but an outer coating of a material such as rubber, or an overwinding or Kvlar 49 aramid fibre, might be applied to provide additional environmental protection.

Although the twist beam of the invention has been described in relation to an H-frame, the twist beam may be used in other applications where it may be subjected to bending and twisting loads.

Claims

1. A twist beam for resisting bending and twisting loads, comprising fibre-reinforced plastics material of tubular form, the twist beam having a slit, or a plurality of slits, extending along the twist beam so as to increase the torsional flexibility of the twist beam to a required value.

2. A twist beam as claimed in Claim 1 wherein the slit or slits extend in a direction parallel to the longitudinal axis of the twist beam.

3. A twist beam as claimed in Claim 2 wherein the slit or slits lie on a straight line.

4. A twist beam as claimed in any one of Claims 1 to 3 wherein the fibre reinforcement comprises layers of fibres helically extending about the twist beam, the fibres in a said layer being at one helix angle and the fibres in other said layers being at other helix angles.

5. A twist beam as claimed in any one of Claims 1 to 4 wherein the twist beam is integral at each end thereof with a respective tubular arm member comprising fibre-reinforced plastics material, each said arm member extending substantially perpendicularly to the longitudinal axis of the twist beam.

6. A twist beam substantially as hereinbefore described with reference to and as shown in Figs. 1, 2, 2a, 2b, 3, 3a and 4 of the accompanying drawings, or modified substantially as described with reference to and as shown in Fig. 5 of the accompanying draw ings.

7. A method of manufacturing a fibrereinforced plastics twist beam, the method comprising helically winding fibres about a mandrel to form a tubular precursor, impregnating the fibres, curing the resin, and cutting a slit or a plurality of said slits along the precursor to produce a twist beam having a required torsional flexibility.

8. A method of manufacturing a fibrereinforced plastics twist beam, the method comprising, superimposing a plurality of layers of fibres one upon another, impregnating each layer of fibres with a resin, partially curing the resin, deforming the partially cured layers into the shape of a tubular precursor of the twist beam, producint a slit or a plurality of slits along the precursor, and curing the resin.

9. A method as claimed in Claim 8 wherein the slit or slits are produced by cutting through the precursor or the cured precursor.

10. A method as claimed in Claim 8 wherein the slit or slits are produced by shaping the layers such as to define the twist beam with the slit or slits therein when the partially cured layers are deformed.

11. A method of manufacturing a fibrereinforced plastics twist beam, substantially as hereinbefore described.