The invention relates to a protective bellows made of elastomeric material and comprising at least one fixing collar and a plurality of bellows turns extending from the fixing collar to an opposite longitudinal end of the bellows, the bellows turns

comprising peaks and troughs, the elastomeric material of the

bellows being integrally connected along its length but being of a plurality of different types arranged longitudinally of the bellows with respect to each other.

Such a bellows is known from EP-A-0 487 840. In this bellows, all the bellows turns are made from a thermoplastic elastomer of one type and the fixing collar is made from an elastomer of a different type. With such a bellows, the characteristics of the material of the bellows turn are substantially the same along the length of the body of the bellows and this may not be suitable

for certain applications. The invention aims to deal with this problem.

According to the invention, therefore, the known protective bellows is characterised in that at least one of the bellows

turns is of a first one of the types of elastomeric material and at least another of the bellows turns is of a second one of the

types of elastomeric material.

In this way, different longitudinally arranged portions of the bellows turns can be given different characteristics to suit their particular purposes.

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 section through one of the protective bellows, for protecting a universal joint in a vehicle transmission system; and

Figure 2 is a longitudinal half-section through another form of the bellows, for protecting the steering mechanism of a vehicle.

As shown in Figure 1, the bellows 4 comprises a plurality of bellows turns 5 having peaks 5A and troughs 5B and which extend between a large diameter fixing collar 6 and a small diameter fixing collar 8. In use, the large diameter fixing collar 6 is

clamped around the casing 10 of the transmission joint. The drive shaft 12 emerges from the casing 10 and the small diameter fixing collar 8 is mounted around it. Suitable clamping rings or other fixtures may be used to secure the fixing collars 6 and

8 in position.

The bellows 4 is advantageously produced from elastomeric

thermoplastic material such as by blow-moulding. In accordance

with a feature of the bellows being described, however, the material from which the bellows is moulded has non-homogenous physical characteristics, although the material of the complete bellows is integral throughout. In this way, therefore, different parts of the bellows can be arranged to have particular physical characteristics according to the respective functions which they have to perform.

Therefore, over a region A, the material of the bellows turns 5 is of a first type selected to have particular characteristics suited to their position close to the universal joint 10. Over the region B, though, the bellows turns 5 are made from a second type of thermoplastic elastomer, this material being suited to the characteristics required of the bellows turns over this portion of the bellows which are spaced from the universal joint

10 and are of reduced diameter and may need to be stiffer so as

not to come into contact with the shaft 12.

In addition, in the bellows 4 the fixing collars 6 and 8 can be produced from a third type of thermoplastic material which is selected to have characteristics suited to the functions of ease of assembly and good sealing. This material must be such that it can be relatively easily stretched, so that the collars 6,8 can be placed over the outside of the casing 10, or the outside of the shaft 12, as the case may be. However, it must also then resile so as to grip and seal around the casing 10 or the shaft

12. Furthermore, the material must be selected so that this good gripping and sealing function is maintained throughout the life of the bellows.

The material of the bellows turns must have good dimensional flexibility and must enable the bellows turns to flex easily through large angles of deflection when the axis of the shaft 12 becomes angularly offset as permitted by the universal joint. At the same time, though, the material of the bellows turns 5 must be such that it is not damaged by contact wear or by the heat generated by such flexing.

By constructing the bellows from different types of material in this way, each of the materials is selected for optimum

performance for the particular functions which the respective parts of the bellows have to carry out.

The bellows 14 in Figure 2 is for protecting the rack of a vehicle steering mechanism. It comprises bellows turns 16 having

peaks 16A and troughs 16B. The bellows turns 16 extend between

a relatively large diameter fixing collar 18 to a generally cylindrical skirt portion 20. From the latter, further bellows turns 22.

As shown in Figure 2, the fixing collar 18 attaches around the outside of the casing 28 of the steering mechanism. From the latter, the steering rod 30 extends to a casing 32. Casing 32 encloses a universal joint connected to a rod end 34, the joint permitting the rod end 34 to articulate angularly with respet to the axis of the rod 30. The rod end 34 extends through the small diameter fixing collar 24, the latter gripping around the rod end 34.

The large diameter fixing collar 18 may be provided with a shaped inwardly directed shoulder for engaging a groove in the outside

of the casing 24 so as to secure it to the casing. Other fixing means may be used instead. At the opposite end of the bellows, the small diameter fixing collar 24 may be secured around the rod end 34 by means of a fixing clamp (not shown) or it may simply grip the rod end resiliently.

During operation of the steering mechanism, the rod 30 moves axially and the rod end 34 moves angularly with respect to the rod 30, this angular movement being permitted by the universal joint in the casing 32. The bellows turns 16 accommodate the axial movement of the rod 30. During the angular movement of the rod end 34, the bellows turns 22 flex correspondingly. The skirt portion 20 ensures that the bellows turns 16 are unaffected by this angular movement .

Again, the bellows is advantageously produced from elastomeric thermoplastic material such as by blow-moulding extrusion. In accordance with a feature of the bellows being described, the bellows is integrally moulded from materials having different physical characteristics which are respectively suited to the different functions to be carried out by different parts of the bellows.

Thus, the bellows turns 16 are constructed from material of a first type which has to be capable of axial movement and to have sufficient strength and dimensional stability to maintain this capability throughout the life of the bellows and to maintain clearance around the rod 30. It also has to be capable of withstanding heat generated by the axial movement.

The material of the bellows turns 22 is of a second type selected

so as to be suitable for the angular movement which this part of the bellows is to undergo. Again, it needs to have good dimensional stability and to be able to withstand the heat generated by the angular movement.

Furthermore, the material of the fixing collar 18 may be material of a third type which is selected so as to be flexible and resilient. This enables it to be stretched relatively easily so as to enable it to be fixed around the outside of the casing 28, but it must also be capable of resiling so as to seal and grip against the outside of the casing and to maintain this characteristic throughout the life of the bellows. The material for the fixing collar 24 may also be of the third type or of a different type. The rod end 34 may have an enlarged shoulder 38. Therefore, the material of the collar 24 has to be capable of

being stretched over this shoulder 38 during assembly.

Finally, the skirt portion 20 is constructed from material of a further type which is arranged to be relatively rigid so as to locate itself securely on the casing 32.

In this way, each of the bellows 4 and 14 can be integrally moulded but can nevertheless be constructed from different materials each selected to be the most effective and economic for the particular functions to be performed by the different parts of the bellows.

In the embodiments described, the different types of elastomeric material produced by the blow-moulding or other process must be such that they are chemically compatible with each other so that the bellows is produced as an integral whole. Over each region where two different types of the material meet, the different

types of material will merge together at the join.