GB2274983A - Castor - Google Patents

Abstract

In a castor for use in particular on wheelchairs, the castor comprises a mounting portion 4 for mounting the castor, a body portion 22 journalling one or more castor wheels 24 for rotation about a wheel axis, and a ball bearing 27 connecting together the mounting and body portions for relative rotation about an upright swivel axis spaced from the wheel axis, means eg washers 12, 14 is provided to prevent separation of the mounting and body portions in the event of damage to the ball bearing such as to permit escape of the bearing balls. <IMAGE>

Description

CASTORS DESCRIPTION The invention relates to castors and in particular to castors for use in supporting articles such as wheelchairs, where it is important that the castor continue to provide support notwithstanding damage due for example to impact forces experienced in use or as a result of misuse.

It may thus occur that a castor suffers an impact sufficient to damage the bearing, by which the castor body, which carries the castor wheel or wheels, is journalled for swivelling on the mounting head, by which the castor is secured to the wheelchair or other article. The bearing is typically a precision ball bearing and the damage may be sufficient to cause the bearing cage to disintegrate. The balls of the ball bearing could escape from between the ball races, so that the castor body is no longer carried by the mounting head and can separate from it. Where the parts of a wheelchair castor separate in this way, the chair is no longer supported at one corner and will tilt, perhaps ejecting a handicapped occupant who may suffer injury as a consequence.

The invention is concerned with the provision of a castor incorporating means whereby destruction of the swivel bearing of the castor does not result in rapid separation of the castor wheel or wheels from the rest of the castor.

The invention accordingly provides a castor comprising a mounting portion for mounting the castor on an article which it is to support, a body portion journalling one or more wheels for rotation about a wheel axis, a bearing by which the body portion is journalled on the mounting portion for rotation about an upright swivel axis spaced from the wheel axis, and retention means preventing separation of the mounting and body portion of the castor in the event of separation of the bearing components. The retention means can thus function so that the castor continues to support the article to which it is secured even in the event of disintegration of the bearing.The swivelling facility provided by the bearing will be impaired or no longer available but this presents only inconvenience, not a risk of injury, to the occupant of a wheelchair, and serves to indicate that the castor has become faulty.

The retention means can be provided in a variety of ways. For example, washers in close axial adjacency to a ball bearing can be provided to prevent escape of the bearing balls from between the ball races. The parts of the castor adjacent the bearing can instead be shaped to perform the function of one or both washers.

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 according to the invention, showing a first embodiment on the lefthand side of the swivel axis, and a second embodiment on the righthand side.

The illustrated castor comprises a mounting portion or mounting head 1 of 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 wheelchair. Beneath this upper end portion 2 there is a hexagonal portion 4-and beneath this, upper and lower circular cylindrical portions 5 and 6. The portion 5 is within the transverse cross-section of the portion 4 and the lower 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.

Referring to the lefthand side of the Figure, the tubular inner ball race 10 of a high quality ball bearing is received on the lower cylindrical portion 6 between an upper washer 12 and a lower washer 14. A hexagonal nut 15 received on the threaded lower end portion 9 of the head clamps the ball race 10 and the upper and lower washers between it and the step 7. Instead of the nut 15, a rivetted construction could be employed.

The castor also comprises a body portion or castor body 20 having a pair of side arms 21, of which only one is seen, extending downwardly from a fork 22 and journalling a castor wheel 24 between them at their lower ends. The fork 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 fork 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 an inner sleeve portion which extends downwardly around the cylindrical portion 5 beneath the hexagonal portion. The lower end of the sleeve portion engages the washer 12 to provide location vertically for the cover. At its outer edge, the main cover portion 31 has a downwardly descending skirt surrounding the upper end of the fork 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 received within the lower part of the bore of the fork 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 received within the lower part of the bore of the fork 22.

In accordance with the invention, the washers 12 & 14 have outer diameters such that the balls 27 of the ball bearing are retained between them, even though the inner and outer races 10 & 25 become damaged so as to be no longer able to retain the balls in their working positions. The castor body 20 cannot then drop away out of the mounting head because the balls become jammed within the annular volume defined by the washers 12 and 14 and by the races 10 and 25.

There is consequently no danger that the effective groundengaging surface of the castor will become the lower end of the threaded stem portion 9, or the cover 40, instead of the wheel 24. Swivelling may be prevented, or at least extremely difficult, but this alerts the user to the damaged condition of the castor.

In the alternative embodiment shown at the righthand side of the Figure, the inner ball race 10 is clamped directly between the step 7 and the nut 15 and the ends of the outer ball race 25 are abutted by an upper washer 32 and a lower washer 34. The outer edges of the washers register with the outer surface of the ball race 25 and the outer edge portions of the washers are received together with the ball race in the groove 26. The inner edges of the washers 32 and 34 are located, relative to the lower portions of the mounting head 1, so that the washers function in the same way as the washers 12 & 14.

The invention can of course be embodied in a variety of ways other than as specifically described and illustrated.

For example, the washer 12 could be used together with the washer 34 instead of the washer 14. The washer 14, could be used with the washer 32 instead of the washer 12. The function of the washers could be performed by other portions of the castor, appropriately shaped.

Claims (13)

1. A castor comprising a mounting portion for mounting the castor on an article which it is to support, a body portion mounting at least one wheel for rotation about a wheel axis, a bearing connecting together the mounting and body portions for relative rotation about an upright swivel axis spaced from the wheel axis, and means preventing separation of the mounting and body portions in the event of damage to the bearing.

2. A castor as claimed in claim 1 wherein the bearing comprises rolling elements received in spacing between inner and outer races, and the separation preventing means comprises means preventing escape of the rolling elements from between the races.

3. A castor as claimed in claim 2 wherein the separation preventing means comprises at least one washer restricting the spacing between the races at at least one end of the bearing.

4. A castor as claimed in claim 2 or 3 wherein the separation preventing means comprises a part of the body portion and/or of the mounting portion restricting the spacing between the races at one or both ends of the bearing.

5. A castor comprising a mounting portion for mounting the castor on an article which it is to support, a body portion mounting at least one wheel for rotation about a wheel axis, the body portion having an aperture receiving the mounting portion therein, a bearing having inner and outer portions on the mounting and body portions respectively, the bearing permitting the body portion to swivel relative to the mounting portion about an upright swivel axis spaced from the wheel axis, and means limiting relative movement along the swivel axis of the bearing inner and outer portions, such movement being otherwise permitted by damage to the bearing, to thereby prevent separation of the mounting and body portions.

6. A castor as claimed in claim 5 wherein the bearing is a ball bearing having bearing balls received between the inner and outer bearing portions, and the limiting means comprises means preventing escape of the bearing balls from between the inner and outer bearing portions.

7. A castor as claimed in claim 6 wherein the limiting means projects outwardly from the mounting portion.

8. A castor as claimed in claim 6 wherein the limiting means projects inwardly from the body portion.

9. A castor as claimed in claim 6 wherein the limiting means comprises at least one of a flange extending inwardly from the body portion and a flange extending outwardly from the mounting portion.

10. A castor as claimed in claim 6 wherein the outer bearing portion is received in an annular recess in the body portion and the limiting means comprises a washer at one or each end of the bearing, the or each washer extending outwardly from the recess.

11. A castor as claimed in claim 6 wherein the inner bearing portion is retained between annular surfaces of the mounting head and wherein the limiting means comprises a washer at at least one end of the bearing between the inner bearing portion and the adjacent annular surface.

12. A castor as claimed in claim 11 wherein the lower annular surface is provided by a retaining nut by which the inner bearing portion is clamped to the mounting head.

13. A castor substantially as herein described with reference to the lefthand or the righthand side of the figure of the accompanying drawings.