GB2263397A

GB2263397A - Castors

Info

Publication number: GB2263397A
Application number: GB9226615A
Authority: GB
Inventors: Stafford Thomas Screen
Original assignee: Colson Castors Europe Ltd
Current assignee: Colson Castors Europe Ltd
Priority date: 1992-01-09
Filing date: 1992-12-21
Publication date: 1993-07-28
Anticipated expiration: 2012-12-21
Also published as: GB2263397B; ITRM930009A1; IT1261161B; GB9200378D0; DE4300204A1; ITRM930009A0; JPH05246204A; GB9226615D0

Description

2263397

CASTORS DESCRIPTION

The invention relates to castors and in particular to castors for supporting articles such as wheel chairs and supermarket and airport trolleys which are liable to experience considerable impact forces in use, or as a result of mis-use.

It may thus occur that such an article is dropped onto its castor wheels. or a wheel of the castor, or the castor body journalling the wheel or wheels, suffers an impact, as in a generally horizontal direction. In either event, the castor body will tend to rotate relative to the mounting head by which the castor is mounted to the article. The castor bearing cap be highly stressed as a result of such impact forces and may be damaged so as to impair swivelling, or even destroyed so that the castor falls apart. The invention is concerned with the provision of a castor incorporating means whereby such impact stresses can be accommodated or resisted.

The invention accordingly provides a castor comprising a mounting head for mounting the castor on an article which it is to support, a castor body journalling one or more wheels for rotation about a wheel axis, a bearing by which the body is journalled on the mounting head for rotation about an upright swivel axis spaced from the wheel axis, and means providing support for the bearing by limiting relative twisting or rotational movement of the castor body and the mounting head about axes transverse to the swivel axis. The support means can thus function as a stop or shock absorber acting between the body and the head at one or more positions axially spaced from the bearing along the pivot axis to limit relative pivoting.

The support means can be provided in a variety of ways, as by the provision of closely adjacent coaxial cylindrical surfaces of the castor body and the mounting head above and/or below the bearing. Alternatively, a sleeve or sleevelike member can be provided within the spacing between such surfaces. Any twisting action experienced by the bearing about a transverse axis is thus resisted by the cylindrical surfaces directly or by the sleeve member, which may be squeezed between them but which tends to maintain the surfaces in, or approximately in, coaxial relationship. Such a sleeve or washer can conveniently be located axially between an upper or a lower cap or cover for protecting the bearing against dust and dirt and the bearing itself, or can be an integral part of such a cap or cover.

There is described in GB-A-2 240 266, the contents of which are incorporated herein by reference, a variety of means for preventing or reducing shimmying of a castor by promoting friction between the mounting head and the castor body. The support means of the present invention can conveniently also provide such frictional resistance to swivelling. The support means can thus comprise an elongate washer or sleeve having a portion shaped to be in frictional engagement with the body and the mounting head. The frictional portion can comprise an annular disc portion at one end of the sleeve which engages at its outer edge a surface of the body transverse to the swivel axis, the sleeve being held against rotation relative to the mounting head frictionally or mechanically as by clamping.

The invention will be understood to provide a means for enhancing the resistance of a castor to impact forces which is extremely simple and consequently highly cost effective.

The invention is further described below, by way of example, with reference to the accompanying drawing, in which the single figure is a partial sectional side view of a castor embodying the invention.

The illustrated castor comprises a mounting head 1 for the castor by which it can be mounted on a wheelchair or other article to be supported. The head 1 comprises a shaft or stem provided with a screw-threaded upper end portion 2 which can be received within a tapped recess in the wheel chair. Beneath this upper end portion 2 there is provided a hexagonal portion 4 of greater diameter beneath which is located an upper circular cylindrical portion 5 and a lower circular cylindrical portion 6 of slightly smaller diameter so that an annular step 7 is formed between the two cylindrical portions. At its lower end, the head 1 has a screw-threaded portion 9.

The tubular inner ball race 10 of a high quality ball bearing is received on the lower cylindrical portion 6 and is held in place between the step 9 and a washer 11 received between the race and a hexagonal nut 12 received on the threaded lower end portion 9 of the head. Instead of the nut 12, a rivetted construction could be employed.

The castor also comprises a castor body 20 having a pair of side arms 21, of which only one is seen, extending downwardly from a yoke 22 and journalling a castor wheel 24 between them at their lower ends. The yoke 22 has a vertical bore and the outer race 25 of the ball bearing is secured within a groove 26 in the wall of the bore. The castor body 20 may be moulded in plastics material, and the outer ball race 25 can then be integrally moulded into the yoke 22. The axis of the ball bearing defines the upright swivel axis of the castor about which the body 20 can swivel relative to the mounting head 1.

The castor includes also an annular upper cap or cover 30 which serves to protect the ball bearing from the entry of dust or dirt. The cover 30 can be moulded in plastics material and has an annular main portion 31 with a hexagonal inner periphery. which engages around the hexagonal portion 4 of the head 1, and a downwardly and inwardly stepped portion 32, which extends around the cylindrical portion 5 and beneath the hexagonal portion. At its outer edge, the main cover portion 31 has a downwardly descending skirt surrounding the upper end of the yoke 22.

To enclose the bearing from below, a generally bowlshaped lower cap or cover 40 is provided. The cover 40 has a lower end wall 41 from which a skirt portion 42 extends upwardly, to be partially received within the lower part of the bore of the yoke 22. The bore and the skirt portion 42 are shaped to make a snap-fit connection, as by means of an outer bead 44 at the upper end of the skirt portion and received in a groove in the bore. A flange 45 protruding outwardly of the skirt portion abuts the lower surface of the yoke.

In accordance with the invention, the radial thickness of the skirt portion 42 is sufficient for its inner surface to be closely spaced from the nut 12. If a rivetted construction is employed in place of the nut 12, the inner surface is again shaped to provide appropriate close spacing. Also in accordance with the invention a sleeve or washer 50 is received around the cylindrical portion 5 with narrow spacing from the surrounding cylindrical surface of the bore of the yoke 22. The washer 50 may be moulded of plastics material and is trapped axially between the upper cover 30 and the upper edge of the inner race 20 which extends outwardly into the bore of the yoke 22 from beyond the step 7.

If the illustrated castor should be dropped generally vertically, the mounting head will tend to rotate relative to the castor body 20 as indicated by the arrow A because the wheel axis and thus the lowest point of the wheel is offset laterally from the swivel axis.

The upper end of the washer 50 will be engaged between the yoke 22 and the portion 5 so any such rotation transverse to the swivel axis will be severely restricted so as to limit the resultant stresses on the bearing, which might be sufficient to cause the ball bearings to break out of the outer race. In a similar way, the skirt portion 42 of the cover 40 will be engaged between the nut 12 and the bore of yoke 22, to resist the rotational forces. The skirt portion 42 and the washer 50 of course serve to protect the bearing also against any other forces which tend to produce the relative rotation.

To oppose shimmying of the castor, the washer 50 is provided at its upper end with an outwardly extending resilient annular disc portion 51 which overlies the upper end of the yoke 22 and engages it by way of a downwardly extending ridge 52. The washer 50 is frictionally engaged with the cylindrical portion 5 or is clamped to the mounting head 1 against relative rotation, so swivelling of the castor body on the mounting head is frictionally resisted by the engagement of the rim 52 on the upper end of the yoke 22.

The invention can of course be embodied in a variety of ways other than as specifically described and illustrated. For example, the washer 50 could be an integral part of the upper cover 30, and frictional resistance to swivelling could be provided by the cover 40.

Claims

1. A castor comprising a mounting head (1) for mounting the castor on an article which it is to support, a castor body (20) journalling one or more wheels (24) for rotation about a wheel axis, and a bearing (10,25) by which the body is journalled on the mounting head f or rotation about an upright swivel axis spaced from the wheel axis, the castor being arranged to limit or prevent relative twisting or rotational movement of the castor body (20) and the mounting head (1) about axes transverse to the swivel axis.

2. A castor as claimed in claim 1 wherein the twisting or rotational movement is limited or prevented by support means (42;50) received between the castor body (20) and the mounting head (1) at at least one position axially spaced from the bearing (10,25) along the pivot axis to limit the relative twisting.

3. A castor as claimed in claim 2 wherein the support means comprises at least one sleeve-like member (42;50) between adjacent coaxial surfaces of the castor body (20) and the mounting head (1).

A. A castor as claimed in claim 3 wherein the adjacent coaxial surfaces are constitued by a cylindrical portion of the mounting head (1) and a bore in the castor body receiving the stem portion and the bearing (10, 25).

5. A castor as claimed in claim 3 or 4 having a sleevelike member in the form of a skirt portion (42) of a cover (40) for protecting the bearing against dust and dirt.

6. A castor as claimed in claim 3, 4 or 5 having a sleeve-like member in the form of a washer (50) located axially between the bearing and a cap or cover (30) for protecting the bearing (10,25) against dust and dirt.

7. A castor as claimed in any preceding claim wherein the support means (50) provides frictional resistance to swivelling of the castor body (20) on the mounting head (1).

8. A castor as claimed in claim 7 wherein the support means (50) is shaped to be in frictional engagement with both the castor body (20) and the mounting head (1).

9. A castor as claimed in claim 2, 3 or 4 wherein the support means comprises a sleeve (50) around a cylindrical portion (5) of the mounting head (1) and having an annular disc portion (51,52) at one end of the sleeve which frictionally engages at its outer edge a surface of the castor body (1) transverse to the swivel axis, the sleeve being frictionally or mechanically held against rotation relative to the mounting head.

10. A castor substantially as herein described with reference to the accompanying drawing.