GB2184200A - Improvements in or relating to yokes for universal joints - Google Patents

Abstract

In a universal joint, wherein an aperture (5) in each yoke arm 3A,3B houses a plastics bush (6) rotatably receiving a respective boss of the cross-member 9, each bush (6) is inserted into its aperture bore (5) in a self-locking manner and to this end is provided with at least one resilient tang (10) which bears against the innerface of the arm (3A, 3B) adjacent the aperture in which the bush is fitted. Accordingly, each bush is restrained from moving axially outwardly of its aperture after insertion therein. The bushes also bear against parts of the cross-member which thus limits inwards axial movement of the bushes. <IMAGE>

Description

SPECIFICATION Improvements in or relating to yokes for universal joints This invention relates to a universal joint and to a yokefora universal joint.

Conventional universal joints incorporated in, for example, steering columns of vehicles, can include two yokes interconnected by a hard cross-piece or member, the four bosses of the cross-piece being fitted in respective bores or apertures ofthetwo yokes by means of metal bushes containing needle bearings, each metal bush being pressed in one of the apertures ofthe yokes so that it fits over the end of a respective boss of the cross-piece. In orderthat the bushes can resist end loadingstransmittedvia the cross-piece, they are often staked in the apertures ofthe arms ofthe yokes and/orthe material of the yokes is peened over the ends of the bushes, which demands considerable force and special equipment.

According to one aspect ofthe present invention, there is provided a yoke having a pair of spaced arms with opposed apertures, a cross-member having opposed trunnions or bosses each capped by a bush bearing against a pair of the member, the bushes being fitted into said opposed apertures and each having at least one integral, resiliently deformable tang engaged with the innerface ofthe arm having the aperture into which the bush is fitted to prevent axial outwards movement of the bush.

According to a second aspect ofthe present invention, there is provided a universal joint including two yokes, each yoke being essentially as defined in the preceding paragraph and being interconnected via a said cross-member.

According to a third aspect of the present invention, there is provided a vehicle steering column incorporating a universal joint which is essentiallyasdefined in the preceding paragraph.

Fora better understanding ofthe invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which Figure lisa diagrammatic, partly-exploded, perspective view of a universal joint for a vehicle steering column, Figure 2 is a diagrammatic, partly-exploded, sectiona I view of part ofthe universal joint shown in Figure 1, Figure 3 is a diagrammatic underneath plan view of part ofthe universal joint shown in Figure2, Figure4 is a viewsimilarto Figure 3 showing a modification, and Figure5showsafurthermodified partofthe construction illustrated in Figure 2.

Referring firstly to Figures 1 to 3, the universal joint connects two shafts 1 and 2 and includes two identical yokes 3 and 4, each of which has two parallel arms 3A, 3B and 4A, 4B, respectively. Each arm 3A, 3B and 4A, 4B has respective opposed apertures 5, which each receive a plastics self-locking bush 6.

In the embodiment shown in Figures 1 to 3 and 5, each bush 6 is substantially cylindrical on its outside and has a closed cylindrical bore 7 to receive a respective trunnion or boss 8 of a metal cross-member 9. The cross-member 9, being of cruciform configuration, thus has four bosses 8, each boss 8 being able to be fitted as a sliding fit inside the closed bore 7 of a respective bush 6.

Each bush 6 is arranged to be a friction fit within its associated aperture 5 of the yoke 3 or4 and is provided intermediate its length with at least one integral resilientlydeformabletang l0which, in its relaxed position, protrudes outwardly beyond the basically cylindrical form ofthe bush 6 close to its inner end, i.e. the end adjacent the open end of its closed bore 7.In the embodiment illustrated, there arethreetangsi0toeach bush 6, equally-spaced around the outer circumference thereof and each tang 10 is arranged so that it can be pressed back under its resilient bias into an adjacent longitudinal groove 11 which is formed parallel to the axis ofthe bush 6 on its outer periphery. Thetip of each tang 10 is positioned approximately two-thirds of the way down the length ofthe bush from its outside end remote from its bore 7.

To assemblethe universal joint, one oftheyokes, forexamplethe yoke 3, istaken and the cross-member9 is positioned so that two of its bosses 8 extend into the respective opposed apertures 5 ofthatyoke (this condition is illustrated in the upper portion of Figure 2). Two bushes 6 are then pressed from the outside faces of the arms of the yoke as a friction fit into the respective apertures 5 and, in so doing, the or each tang 10 is pressed inwardly of its bush 6 as it passes through the aperture 5.Once the bush 6 has been pressed sufficiently far into the aperture 5, part of the bush protrudes inwardly ofthe yoke out of the aperture 5 and the or each tang 10 of that bush will spring outwardly to its relaxed position to engage against the innerface of the arm ofthe yoke adjacent the aperture in which that bush is housed. This condition is illustrated in the construction shown in the lower portion of Figure 2. Once in that position, the bush 6 has locked itself against ejection from the aperture 5 and entraps and caps the boss 8 which had been positioned in the aperture 5. The process is repeated with the other yoke 4 to form the universaljoint.

Thus, each bush 6 is restrained by itstangs 10from moving axially outwardly of its aperture 5. In addition, each bush 6 bears against a part ofthe cross-member9,aswill be morefully described later, the cross-member 9 thus acting to restrain the bushes 6 from moving axially inwardly of their apertures.

The cross-member 9 is able to rotate relatively to the bushes 6 in which it is entrapped and it is importantthatthe bushes 6 themselves cannot rotate in their apertures 5 by radial loading on the bushes. To this end, it is possible that the friction fit ofthe bushes in the apertures 5 is sufficient to prevent rotation ofthe bushes but, to ensure this, a self-locking screw or pin (not shown) can be, for example, forced into one ofthe grooves 11 ofthe bush from outside the yoke to enhance the friction fit effect of the bush 6 in the aperture 5.

Another possibility is to provide non-circular apertures 5 in the arms ofthe yoke with bushes 6 having correspondingly non-circular, outer faces fitted in them. For example, as illustrated in Figure 4, the outer faces ofthe bushes 6 may be hexagonal with the tangs 10 and grooves 11 being provided centrally on the alternate outerfiatfaces ofthe bushes. These bushes would therefore be fitted in corresponding, preferably hexagonal, apertures 5 in the yoke. The interior bores 7 ofthe bushes would, of course, still be cylindrical.

To facilitate rotation of the bosses 8 in their bushes 6, the bushes 6 could be formed of self-lubricating material. Materials to serve this purpose forthe bushes 6 could be acetal, lubricated (anti-friction) nylon, a polyester, or PTFE and silicone. Preferably, the bushes 6 are formed from a thermoplastics material.

When the yokes are assembled with the bushes 6 in place capping the bosses 8 ofthe cross-member 9, the distance between the outer ends of opposed bushes 6 is greaterthan the distance between the corresponding opposed innerfaces ofthe yoke arms 3, 4 so thatthe bushes 6 are lying at least partly within the apertures 5.

It is importantthatthe bushes 6 are able to resist end loading orthruston them which is likely to occur when the universal joint is in use, particularly if it is intendedforincorporation in a steering column ofa vehicle. in the embodiment shown in Figure 2, the bush 6 and associated boss 8 as shown in the lower portion ofthat Figure areso dimensioned thatthe boss 8 has a shorter length than the length ofthe closed bore 7 of the bush 6 in which it is fitted.

Accordingly, the end loading orthrustistransmitted from a shoulder of a centre block 9A ofthe cross-member 9to the inner end face ofthe bush 6 adjacent the open end of its closed bore 7, with which inner end face the shoulder is in contact. The distance between the opposed shoulders ofthe block9A plusthe sum ofthe protruding lengths of the two opposed bushes 6 protruding inwardly ofthe innerfaces of the opposed arms ofthe yoke equals the distance between these innerfaces at their apertures 5.

In the alternative embodiment illustrated in Figure 5, the boss 8 has a length greater than that ofthe closed bore 7 of the bush 6 so that the end face ofthe boss 8 bears against the closed end ofthe bore 7 of the bush 6.

In this case, the distance between the opposed shoulders ofthe block9A, plusthe sum ofthe protruding lengths of the two opposed bushes 6 protruding inwa rdly of the in ner faces of the opposed arms ofthe yoke, plusthe sum ofthetotal axial spacing between the opposed shoulders ofthe block 9A and the respective facing end faces ofthe bushes 6, equals the distance between the inner faces of the arms at their apertures 5.

In both cases, it will be seen that each bush 6 is able to take up anythrust from the cross-member 9, thetangs 10 resisting outward axial movementofthe bush 6 in the aperture 5. Inwards movement of the bushes is limited by the bosses 8 in bbth cases.

It will be appreciated that the present construction obviates the need to provide needle bearings in metal bushes as with conventional universal joints forvehiclesteering columns. Furthermore, the method of locking the plastics bush 6 into the aperture 5 does not require special equipment (as is needed forpeening the yoke material over the ends of the conventional bushes) and only requires minimal assembly force. Thus, overall costs are reduced.

Claims (20)

1. Ayokefora universal joint, the yoke having a pair of spaced arms with opposed apertures, a cross-member having opposed trunnions or bosses each capped bya bush bearing againsta partofthe member, the bushes being fitted into said opposed apertures and each having at least one integral, resilientlydeformabletang engaged with the inner faceofthearm having the aperture intowhichthe bush is fitted to prevent axial outwards movement of the bush.

2. Ayoke according to claim 1,whereinsaid cross-memberis made of metal.

3. Ayoke according to claim 1 or2,whereinsaid bosses and bushes are arranged so that the bosses are a sliding fit in the bushes.

4. Ayoke according to claim 1,2 or3,wherein each bush has a closed bore receiving a respective boss, the cross-member having a shoulder adjacent each boss each of which constitutes a said part of said cross-member and each bush having an end face surrounding its closed bore, and each boss having a shorter length than the length of the closed bore of the bush in which it is fitted so thatthrust can be transmitted from a said shoulder to said end face ofthe bush, the end faces bearing against the shoulders and the cross-memberthereby limiting axial inwards movementofthe bushes.

5. Ayoke according to claim 1, 2 or 3, wherein each bush has a closed bore receiving a respective boss, each boss having a greater length than the length ofthe closed bore of the bush in which it is fitted so that the closed end ofthe bore ofthe bush bears againstthe end face of the boss so that thrust can be transmitted via the end face of the boss to the bush, the cross-memberthereby limiting axial inwards movementofthe bushes.

6. Ayoke according to anyone ofthe preceding claims, wherein each bush has three said tangs.

7. A yolce according to any one ofthe preceding claims, wherein each bush is a friction fit in its aperture in the yoke.

8. Ayoke according to any one ofthe preceding claims, wherein each bush has a groove in its outer periphery associated with each tang, respectively, the groove enabling its associated tang to be depressed upon insertion of the bush into a said aperture oftheyoke.

9. A yoke according to claim 8, wherein a self-locking screw or pin is forced into a said groove from outside the yoke to provide a or the friction fit of the bush in its aperture.

10. Ayoke according to any one of claims 1 to 8, wherein each said aperture is non-circular and wherein the bush fitted in that aperture has non-circular outerfaces, the arrangement thereby preventing relative rotation of the bush in its aperture.

11. Ayoke according to claim 10, wherein each said aperture is hexagonal and the outer periphery of each said bush is correspondingly shaped, a said tang being provided in alternate peripheral faces of the bush.

12. Ayoke according to any one ofthe preceding claims, wherein the distance between outer ends of opposed bushes is greaterthan the distance between the corresponding innerfacesoftheyoke arms.

13. Ayoke according to any one ofthe preceding claims, wherein thetangs are positioned intermediate the lengths oftheir bushes.

14. Ayoke according to any one ofthe preceding claims, wherein each bush is made of a plastics material.

15. Ayoke according to claim 14, wherein each bush is made of a self-lubricating material.

16. A yoke according to any one of the preceding claims, wherein its arms are substantially parallel in the region of said apertures.

17. Ayoke,substantiallyashereinbefore described with reference to Figures 1 to 3, with or withoutthe modification ofFigure4andorthe modification of Figure 5 ofthe accompanying drawings.

18. Auniversal joint including twoyokes, each yoke being in accordance with any one ofthe preceding claims and being interconnected via a said cross-member.

19. A universal joint according to claim 18, substantially as herein before described with reference to Figures 1 to 3, with orwithoutthe modification of Figure 4 and/orthe modification of Figure 5 ofthe accompanying drawings.

20. Asteering column fora vehicle incorporating a universal joint according to claim 18 or 19.