This invention relates to shaft assemblies. The invention has been developed in relation to shaft assemblies intended to be used in motor vehicles, and particularly to shaft assemblies as used in transmitting drive from a front mounted engine to the rear axle of a rear wheel drive vehicle. This is usually termed the propeller shaft.

Modern regulations place increasing constraints on noise levels which can be emitted by motor vehicles. One source of noise, which can be very noticeable to a bystander when the vehicle drives past, is the propeller shaft, which can "ring" under drive line vibrations. it will be appreciated that the basic element of the propeller shaft assembly is usually a metal tube, which inherently is liable to such noise emission. Measures such as enclosing the propeller shaft so that such noise is not audible outside the vehicle are not economically feasible, -and can cause further problems.

It is the object of the present invention to provide a shaft assembly which overcomes or reduces this problem in an economic manner.

According to the invention, we provide a shaft assembly comprising a tubular shaft member and a tubular element surrounding said shaft member with a space ^' defined therebetween, wherein said tubular element is supported at each end relative to said shaft member by a member, preferably of a resilient material, which is a press fit in said space.

In an assembly according to the invention, the tubular element surrounding the shaft member acts as a barrier to escape of noise generated by vibration in the shaft member. The assembly is virtually equivalent to an enclosure for the shaft member, but at much less cost than if a propeller shaft were to be enclosed in the structure of a vehicle. Further, the shaft assembly remains accessible for maintenance purposes, and access is not hindered to other parts of the vehicle. The tubular element does not itself generate noise as it is not subject to direct driveline vibrations. It is important that the tubular element as a whole does not move relative to the shaft member, because that may affect the rotary balance of the assembly, and the tightness of the press fit of the reslient members at the ends of the tubular element must be selected so as to be adequate for this purpose. It will be appreciated, however, that because the shaft member is transmitting torque whereas the tubular element is not, small angular displacements may occur between one or both ends of the tubular element and the shaft member in service. Such movements, which are resisted by friction at the surfaces of the press-fitted members, assist in damping torsional vibrations in the shaft assembly.

Each reslient member may comprise a split annulus of a suitable material, e.g. a plastics material. The use of a split annulus facilitates fitting over parts of the shaft assembly which may be of larger diameter than the tubular shaft member itself.

The resilient member may include formations which resist withdrawal thereof from said space. Such formations may comprise appropriately angled teeth.

A sealing ring .may be provided at or adjacent each end of said annular ^" element. This prevents dirt or water reaching the space between the tubular element and shaft member, which could otherwise cause balance or corrosion problems.

At least one balance weight may be secured to the shaft member, arranged to abut one of said members of resilient material to assist in holding the latter in place. This, of course, requires that a portion of the surface of the shaft member is not covered by the tubular element. If no portion of the surface of the shaft member is accessible, balance weights may be secured to the accessible surface of the tubular element. If the tubular element is of steel, steel balance weights may easily be spot welded in position and the requirement for such balance weights can be determined by setting the shaft assembly including the tubular element up in a balancing machine in the same way as conventional shafts have been balanced hitherto.

The invention will now be described by way of example with reference to the accompanying drawing, which is an elevation, partly in section, of a shaft assembly according to the invention.

The illustrated shaft assembly comprises a shaft member 10 which is of steel tube. At one end, it has secured to it, by a circumferential weld 11 , a yoke 12 of a Hookes universal joint indicated generally at 13. Part of another torque transmitting element, such as another joint yoke or an element of a sliding spline connection, is indicated at 14 at the other end of the tubular shaft member 10.

A tubular element 15 surrounds most of the length of the shaft member 10. The inside diameter of the tubular element 15 is such that a relatively small annular space is defined between it and the shaft member 10. The tubular element is secured at each end by a split annular member 16 of a resilient material such as a suitable plastics material. Each member 16 includes a flange 17 which abuts the end of tubular element 15, and a portion 18 which is a tight push fit into the annular space between the shaft member and the tubular element. The portion 18 is provided with deformable teeth on its outwardly facing surface, so as to resist being displaced from the space inside the tubular element. Resilient sealing rings 19 are provided one at each end of the tubular element 15, to seal the.space between the shaft member and tubular element, to prevent dirt or water entering the space.

To fit the tubular element to the shaft member, one of the members 16 and its associated sealing ring 19 would be placed onto the shaft member. Such positioning is assisted by the member 16 being in the form of a split annulus, so that it can be fitted over weld 11 or other large diameter portion of the shaft assembly. Thereafter ■the tubular element 15 can be fitted axially, after which the other sealing ring 19 and member 16 would be positioned on the shaft member 10 and pressed into place.

In the shaft assembly illustrated, balance weights 20 are secured by spot welding to the shaft member 10. The positioning of such balance weights 20 is such that they abut the one member 16, to assist In retaining the latter in position. Balancing of the shaft assembly must, of course, be carried out with the tubular element 15 fitted to the shaft member. If the tubular element 15

is of a material to which balance weights can readily be secured, such weights may of course be secured thereto instead of to the shaft member 10.

Some form of mechanical interfitting may be provided, operative between the tubular element 15 and a part of the shaft member 10 or one of its associated components such as universal yoke joint 12, positively to prevent the tubular element 15 from rotating relative to the shaft member. For example the tubular member may have a projection or recess at one part of its circumference, engaging a corresponding recess or projection provided on the shaft member or associated component.