FIELD OF THE INVENTION

5 This invention relates to a roller bearing.

BACKGROUND TO THE INVENTION

Roller bearings conventionally have a set of rolling 10 members, which may be balls or rollers, supported in a cage between two members which have to be capable of relative movement. When this relative movement takes place, the rolling members roll between the two surfaces to allow this relative movement. The roller members are supported in the 15 cage so that they remain in the correct positions relative to one another, and so that the rolling members can be installed in the bearing as a single unit.

SUMMARY OF THE INVENTION

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According to the present invention, there is provided a roller bearing comprising a plurality of rolling members and a cage for the rolling members, wherein the rolling members and the cage are formed in a single moulding, and the 25 rolling members are initially . connected to the cage by readily rupturable necks.

With a bearing of this type, the formation of the cage and the rolling members in one piece makes for a very simple

30 manufacturing operation, without requiring any assembly step to locate the roller members in the cage. The bearing can

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« be assembled between the two surfaces which have to be capable of relative movement as a single, one-piece component. However as soon as there is relative movement

35 between the two surfaces, the readily rupturable necks which

connect the rolling members to the cage will be stressed and will rupture. As soon as this has happened, the rolling members can rotate freely of the cage, but still retained within the restraining walls provided by the cage.

The rolling members can be spherical or cylindrical, but the invention is particularly applicable to cylindrical rolling members with the readily rupturable necks being located at the opposite ends of the cylinder access so that the part of the broken necks remaining on the cylindrical rolling members do not come into contact with either of the two relatively moveable surfaces. In the rest of this specification, cylindrical rolling members will be referred to as "rollers", and spherical rolling members will be referred to as "balls".

A bearing of this type is useful in applications where, under normal circumstances, there is no movement between the relatively moveable surfaces, but where relative movement is required in an emergency, at which time a relatively large force will be applied between the two members to produce relative movement. This force can then be used to rupture the necks holding the rolling members to the cage. A roller bearing of this type can be very substantially cheaper to manufacture than a conventional roller bearing, and will also be substantially cheaper to install. It may also be convenient in some applications to install the bearing as a single component, and once the bearing is in place, to apply a force between the two surfaces to rupture the necks as a final step in assembly of a product.

The roller bearing is preferably manufactured as a plastics moulding from a suitable plastics material. Where the rolling members are rollers, the cage is preferably generally rectangular in form with rectangular apertures

therethrough in which the rollers are located, the thickness of the cage being less than the diameter of the rollers, and the width of each aperture in the cage being greater than the diameter of each roller.

Where the rolling members are balls, the cage may be of any suitable shape, with circular apertures in which the balls are located. The thickness of the cage will be less than the diameter of the rollers and the diameter of each aperture will be greater than the diameter of the balls.

The invention also extends to a steering column assembly for a motor vehicle, the steering column having two components capable of telescoping movements relative to one another in an accident, and a roller bearing as set forth above located between the members.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a roller bearing in accordance with the invention;

Figure 2 is a cross section through the bearing of Figure 1 on the lines AA;

Figure 3 is ε αetail of the part of the bearing within the circle B from Figure 1;

Figure 4 is an exploded view of a steering column in accordance with the invention; and

Figure 5 is a cross sectional view through the column of Figure 4 on the line V-V.

DESCRIPTION OF PREFERRED EMBODIMENTS

The bearing shown in Figure 1 is a linear bearing intended to be positioned between two surfaces 9, 10 (Figure 2) to provide a bearing which operates when relative movement between the surfaces 9, 10 takes place parallel to the planes of the surfaces.

The bearing has a cage 1 and rollers 5 located in apertures

4 in the cage. Each roller has a cylindrical surface 6 and two conical end portions 7 which are joined by means of a narrow neck 8 to a longitudinal part 2 of ^' the cage. As can be seen in Figure 2, the diameter of the cylindrical part of the rollers is greater than the thickness of the cage 1, and the width of the apertures 4 is greater than the diameter of the rollers.

The roller bearing consisting of the cage 1 and the rollers

5 can be moulded in a single moulding operation so that when the product is removed from the mould, the rollers are integral with the cage. At this stage the bearing can be handled as a single component.

However when the bearing is in use between two surfaces 9, 10 as shown in Figure 2 and when relative movement takes place between these surfaces then the rollers 5 will try to roll whereas the cage will only be able to move linearly. The force tending to move the surfaces 9, 10 relative to one another will stress the necks 8, which will then rupture, thus freeing the rollers 5 so that thereafter the rollers can operate in a conventional manner with the rollers running freely in the apertures 4 in the cage.

A bearing as described will have considerable resistance to relative movement initially until the necks 8 are broken, but as soon as these necks are broken then the bearing will function in the same way as a conventional linear bearing. The bearing is therefore suitable for use in cases where an initial movement between two surfaces will be a sudden, sharp movement. This is the case, for example, in a collapsible steering column which is intended to shorten in the event of an accident to prevent injury to the driver. It is desirable that a bearing be incorporated in such a column to allow the sliding movement to take place smoothly.

Figures 4 and 5 show part of a steering column, further details of which are shown in our European patent application number 89304558.3. The column has a support beam 18 which is securely mounted to a bracket 16 which forms part of the vehicle bodywork. The beam 18 has a channel-section track. The steering column itself has a steering shaft 30 to which a steering wheel 32 is attached.

The shaft 30 passes through a shroud 34, and a collapsible convoluted energy absorbing member 38 is located at the bottom of the shroud 34 between the shroud and the shaft 30.

The bottom end of the shaft is connected to a steering gear through a link 40 and a universal joint 42.

The shroud 34 incorporates a shoe 46 which slides in the channel section track, and a linear bearing 52 is placed between a wall of the shoe 46 and a wall 54 of the track.

Under normal conditions, there is no movement at all between the shroud 34 and the beam 18. However if there should be an accident in which the driver of the vehicle is thrown forward against the steering wheel 32, then the shroud can slide along the track, with the bearing 52 providing a

bearing for this movement.

The steering column 30 is secured to the support beam 18 by means of two fastenings. A fixed U-shaped clip secures a lower end of the column to the lower end 20 of the beam 18. A driver-adjustable fixing 48, 50, 24, 26 is provided at the top end of the guide 18. By loosening a nut on a threaded shank 26, the shaped head 50 of the shank can be loosened in a correspondingly shaped track 48, and the column can be pulled towards or away from the driver to adjust the height of the steering wheel. Once the desired height has been reached, then the nut on the shank 26 is re-tightened. This nut may be mounted on the end of a lever so that it can ^' be readily adjusted without the use of tools.

The necks 8 between the rollers 5 and the cage 1 may be snapped during this adjusting movement, or alternatively there may be sufficient slack when adjusting movement takes place to avoid this happening.

It is within the scope of the invention for a manufacturer installing a roller bearing as described to install the bearing in the desired position and then to apply the necessary sharp movement between the two surfaces to separate the rollers from the cage, so that by the time the product is sold the rollers are able to run freely.

The invention thus provides a very cheap way of installing a caged roller bearing.