Protective bellows

A protective bellows (24) covers over the end of, and protects the mechanism within, the casing (6) of a universal or articulated joint (5). The universal joint (5) is of normal construction, its casing (6) being drivingly connected to an output shaft (10) by ball or rollers (14) mounted in grooves (16) on an inner element (12) fixed to the output shaft (10) and in grooves (18) on the inner face of the casing (6). The balls or rollers (14) permit the desired angular movement of the axis of the output shaft (10) relative to the axis of the casing (6). In addition, a certain amount of axial movement (L) is permitted. In order to resist any tendency of this axial movement to dislodge the balls or rollers (14) from the casing (6), a rigid zone (40) is integrally molded onto the inside of the bellows (24) adjacent its large diameter end. This rigid zone (40) extends in a radial direction part way across the open end of the casing (6) to resist dislodgement of the balls or rollers (14).

The invention relates to a protective bellows having an end fitted to and 
protecting the open end of the casing of an articulated transmission joint 
which incorporates individual rotary elements permitting angular movement 
of the joint, the bellows having an integral zone extending around the 
inside of the bellows adjacent the bellows end and adjacent to the open 
end of the casing of the joint to which that bellows end is fitted, the 
integral zone comprising material which extends both radially inwards of 
the bellows and axially towards the said bellows end so as to be contacted 
by a rotary element dislodged from the joint. 
Such a bellows is known, for example, from DE-A-2 927 648. In this bellows, 
the integral zone is reinforced by a metal cap which is clipped to the 
open end of the casing of the transmission joint and has a portion 
extending in a radially inward direction partway across the open end of 
the casing so as to reinforce the integral zone of the bellows. A 
dislodged rotary element of the joint is therefore blocked against further 
dislodgement by the reinforcing effect of this radially directed portion 
of the metal end cap. Such a metal cap adds weight, complexity and cost 
and may locally adversely affect the flexibility of the bellows. The 
invention aims to overcome these problems. 
According to the invention, therefore, the known form of bellows as first 
set forth above is characterised in that the integral zone is devoid of 
separate reinforcement whereby it alone prevents further dislodgement of 
the rotary element.

FIG. 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 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 FIG. 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. 
FIGS. 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 FIGS. 2 and 3 operates 
in the same way as the zone 40 of FIG. 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.