The invention relates to a protective bellows for protecting the

open end of the casing of an articulated transmission joint

which incorporates individual rotary elements permitting angular

movement of the joint.

Such a bellows is known, for example, from US-A-3 623 340. This

bellows incorporates a radially inwardly directed wall which is

intended to stiffen the bellows against centrifugal force. A

problem which can occur, however, with known bellows is that the

rotary elements, such as balls, of the transmission joint can

become axially dislodged under extreme conditions of operation,

with potentially significant operational disadvantages. The

invention is concerned with overcoming this problem.

According to the invention, therefore, the known form of bellows,

as first set forth above, is characterised in that the bellows

has an integral zone extending around the inside of the bellows

adjacent the bellows end to be fitted to the open end of the

casing of the joint, the integral zone comprising material which

extends both radially inwards of the bellows and axially towards

the said bellows end, whereby to tend to block dislodgement of

the rotary element from the joint when the bellows is fitted to

the open end of the casing.

A protective bellows embodying the invention will now be

described, by way of example only, with reference to the

accompanying diagrammatic drawings in which:

Figure 1 is a longitudinal half-section through one of the

bellows embodying the invention, shown fitted to an articulated

transmission joint;

Figure 2 corresponds to Figure 1 but shows a modified form of the

bellows of Figure 1; and

Figure 3 is a cross-section on the line III-III of Figure 2.

Figure 1 shows in diagrammatic form an articulated joint 5 of the

transmission system of a motor vehicle. The joint 5 is in the

form of a bowl-shaped casing 6 which is connected to an input

shaft 8 so that the casing 6 rotates with the input shaft 8. The

joint 5 has an output shaft 10 connected (in this example) to one

of the driving wheels of the vehicle. The shaft 10 is rigid with

an inner element 12 supporting a plurality of balls 14 (of which

only one is shown in the drawing) each of which engages in a groove 16 in the element 12 and also in a groove 18 on the inside surface of the casing 6. The balls 14 are further supported in a cage 20. Therefore, as the casing 6 is rotated by the input

shaft 8, this rotational movement is transmitted to the output

shaft 10 via the grooves 18 and 16 and the balls 14. The balls

14 may be replaced by rollers.

In known manner, the provision of the balls 14 enables angular

movement between the axis of the output shaft 10 and the axis of

the input shaft 8 to take place, up to a maximum of about 50

degrees, thereby accommodating corresponding movement of the road wheel.

In order to protect the mechanism of the joint 5 from the effects

of moisture and dirt and other contamination, a protective bellows 24 is provided. This bellows is advantageously produced

by blow moulding from thermoplastics material. It comprises a

number of individual bellows turns 26,28 which integrally extend

between the two ends of the bellows. At one end of the bellows, a large diameter fixing collar 30 is provided which locates in a groove 32 on the outside of the casing 6 and is firmly secured in position by an annular clamp 34. At the opposite end of the

bellows, a small diameter fixing collar 36 is provided which is clamped around the outside of the shaft 10 by a fixing clamp 38.

In addition to the angular movement permitted by the joint 5, it

is normal in such joints to permit small limited movement of the

shaft 10 in an axial direction relative to the casing 6. During

such axial movement, the inner element 12 moves with the shaft

10, and the permitted amount of axial movement is indicated at L. This permitted movement may be of the order of 40 to 60

millimetres although in practice only 5 to 15 millimetres of movement may take place. Although this permitted axial extension is advantageous in accommodating corresponding axial movement of

the shaft 10, it is disadvantageous in that there is a risk that,

at the extreme limit of the extension, the balls 14 may become dislodged from their grooves 16,18. Clearly, this renders the joint 5 inoperative. If such dislodgement takes place during assembly of the joint onto the vehicle, it requires skilled

rectification by an expert. If it takes place during operation

of the vehicle, it will be damaging and dangerous.

In order to deal with this problem, the bellows 24 of Figure 1 is provided with a rigid zone 40 which extends integrally and

radially inward of the bellows adjacent its large diameter end

so as to comprise a portion directed towards the shaft 10 and a

portion directed towards the balls 14. This rigid zone provides an inclined barrier extending partway across the open mouth of the casing 6 and positively prevents dislodgement of the balls

14 out of this mouth.

The rigid zone 40 can be produced by injection moulding, with the remainder of the bellows being subsequently produced by blow

moulding. The shape and size of the zone 40 can be varied

according to the type and size of the joint 5 and the size of the

balls (or rollers) . In addition, the radially inward extension

of the rigid zone 40 can be adjusted to allow the amount of

angular movement permitted for the axis of the shaft 10.

Figures 2 and 3 show a modified arrangement in which the rigid

zone 40 is of reduced mass and thickness, comprising radially directed and circumferentially separated webs 42. The spacing

between the webs 42 is less than the diameter or cross-section and size of the balls 14. The webs 42 are strengthened by a radially and circumferentially extending wall 43, but this may be omitted if desired. The zone 40 of Figures 2 and 3 operates

in the same way as the zone 40 of Figure 1 but has the advantage of reduced weight and cost.

The arrangements illustrated provide a very economic and effective way of preventing dislodgement of the balls or rollers

of a universal joint when axial movement of the transmission shaft takes place. The rigid zones 40 can be produced at very

small additional cost when the bellows is moulded. The operation of fixing the bellows in position on the vehicle is unaffected

by the provision of the rigid zones 40. The arrangement is thus

very advantageous as compared with the provision of a rigid metal

cap which has hitherto been fitted over the open end of the

casing 6 of the joint 5 for preventing axial dislodgement of the balls or rollers. Such a cap has to be clipped over the open end of the casing 6 and secured in position by suitable means, necessitating a separate fixing operation after the joint has

been fitted in position and before the bellows is fitted.

Furthermore, this metal cap is relatively more expensive and heavier than the rigid zones 40. In addition, the use of the

separate metal caps is disadvantageous because it requires an additional part to be ordered and stored.