CASTOR WHEEL ASSEMBLY

Abstract: A castor wheel assembly of the kind where a wheel (8) is biased into a straight-ahead position for normal use but which can swivel against the bias for steering a file of rigidly-engaged trolleys. The biasing is provided by the interengagement of a straight-edged cam plate (12) and a wire spring (14). The cam plate is fixed with respect to the trolley, while the spring swivels with the fork which supports the castor wheel. The spring (14) is held to the fork or clevis by having the free ends of the wire spring hooked under one side of the crotch of the fork while a bight provided at the mid-portion of the spring is clipped under the other side of the crotch.

Description: "CASTOR WHEEL ASSEMBLY" TECHNICAL FIELD This invention relates to castor wheel assemblies, that is to say assemblies comprising an un-driven ground wheel for the support of mobile articles, wherein the assembly may rotate about an upright castor axis relative to the article and wherein the area of contact between the wheel and the ground is horizontally spaced from the castor axis. Thus, when the article is being wheeled along, the said area of contact trails behind the castor axis in the direction of travel . BACKGROUND Usually, the assembly may rotate freely about the castor axis, so that the wheel exercises no control over the direction of travel. It is well known that supermarket trolleys, for example, are usually supported by four castor wheel assemblies, namely two front wheel assemblies that are respectively positioned under the front or leading corners of the trolley as it is pushed along in normal use, and two rear wheel assemblies similarly positioned under the rear or trailing corners of the trolley. It is also well known that shoppers find some difficulty in steering supermarket trolleys and in controlling the orientation of such trolleys in relation to their direction of travel. This springs from the castor wheels' lack of directional control upon the travel of the trolley. That difficulty would be overcome if each of the rear wheels of the trolley were non-castoring, with the wheel's axis of rotation set perpendicular to the front to rear centre line of the trolley. Alternatively control would be improved if castoring could be enabled only after a predetermined torque was experienced by the castor wheel assembly. Additionally shoppers, after taking trolley loads of goods from the supermarket to their cars, customarily leave the empty trolley in the car parking area for collection by the supermarket staff. To minimise collection costs the supermarket staff are required to retrieve a plurality of empty trolleys at one time as a substantially straight file of rigidly inter-engaged trolleys. Such a file of trolleys becomes unsteerable unless all of the trolley wheels are able to castor, so as to accommodate lateral movement of the front or rear of the file for steering purposes. Therefore it has been proposed to modify the rear wheel assemblies of super market trolleys so as to bias them into a straight ahead position for normal use as single trolleys, while allowing forced castoring against the bias for steering a file of two or more rigidly engaged trolleys. One prior known, biased castor wheel assembly has comprised a lobed cam resiliently clasped between multiple leaf springs enclosed within a housing. It is a relatively complex and expensive mechanism, and if retro-fitted to an existing free castoring trolley requires the complete replacement of that trolley's rear wheel assemblies. Another prior known device has included a cylindrical cam with a wave shaped track in its curved surface and a follower roller engaged in said track. The arrangement is such that as the wheel castors from a straight ahead position the trolley is raised by virtue of the roller following the track, and so a restoring torque is produced. This mechanism is also expensive and requires replacement of existing assemblies on retrofitting. Therefore, an object of the present invention is to provide for biased castoring by the insertion of several inexpensive components in an otherwise conventional free castoring assembly, which components may be quickly emplaced at little cost as and when routine maintenance is performed on the free castoring assembly. SUMMARY OF INVENTION The invention consists in a castor wheel assembly of the kind comprising a generally inverted U shaped clevis comprising a crotch portion and two downwardly inclined spaced apart legs, axle retainer formations at or near the lower ends of the respective clevis legs for the receipt of a wheel axle extending from one clevis leg to the other, a bearing defining an upright castor axis and comprising a stationary bearing part that is fixed to an article to be supported and a rotatable bearing part that is fixed to the clevis crotch portion, and a bolt coaxial with the castor axis extending through the stationary bearing part to affix it to the article, characterised by biasing means comprising spacer means pierced by the bolt and contacting the stationary bearing part, a cam plate pierced by the bolt and spaced by the spacer means above the clevis crotch portion for clamped affixture to the article, which cam plate has mutually perpendicular major and minor axes of symmetry intersecting the castor axis, and a wire loading spring comprising two spaced apart, generally inverted U or V shaped side portions and a connector portion extending between the ends of first corresponding limbs of the respective spring side portions; the spring connector portion and the ends of second corresponding limbs of the respective spring side portions being adapted to snap engage the clevis crotch portion whereby the respective spring side portions bear resiliently against opposed edges of the cam plate . In a further broad form of the invention there is provided biasing means for a castor wheel assembly of the kind comprising a generally inverted U shaped clevis comprising a crotch portion and two downwardly inclined spaced apart legs, axle retainer formations at or near the lower ends of the respective clevis legs for the receipt of a wheel axle extending from one clevis leg to the other, a bearing defining an upright castor axis and comprising a stationary bearing part that is fixed to an article to be supported and a rotatable bearing part that is fixed to the clevis crotch portion, and a bolt coaxial with the castor axis extending through the stationary bearing part to affix it to the article ; said biasing means comprising spacer means adapted to be pierced by the bolt and contacting the stationary bearing part, a cam plate adapted to be pierced by the bolt and spaced by the spacer means above the clevis crotch portion for clamped affixture to the article, which cam plate has mutually perpendicular major and minor axes of symmetry intersecting the castor axis, and a wire loading spring comprising two spaced apart, generally inverted U or V shaped side portions and a connector portion extending between the ends of first corresponding limbs of the respective spring side portions; the spring connector portion and the ends of second corresponding limbs of the respective spring side portions being adapted to snap engage the clevis crotch portion whereby the respective spring side portions bear resiliently against opposed edges of the cam plate . In yet a further broad form of the invention this is provided, in combination, a spring and cam plate assembly adapted for fitting to a castor wheel assembly; said castor wheel assembly including a wheel rotatably supported within an inverted U shaped clevis; said clevis including a crotch portion adapted for rotatable support above a substantially upright castor axis of a mobile article; said cam plate adapted for fixed connection above said clevis so as to be fixed relative to said mobile article; said spring adapted for external mounting to said clevis; said spring engageable with said cam plate so as to provide a predetermined resistance to rotation of said clevis from a straight ahead position relative to said mobile article. Preferably said cam plate includes a major axis and a minor axis. Preferably said cam plate includes flats parallel to and spaced from said major axis. The cam plate may include opposed arcuate portions spaced symmetrically from said minor axis. In a preferred form the spring is adapted for external snap fit to said clevis. Preferably said spring is adapted for external snap fit to said clutch portion of said clevis. Preferably said spring includes opposed side portions connected at at least one end by a connection portion. Preferably said bridge portion includes an inwardly and upwardly directed bight for engagement with an edge portion of said clutch portion of said clevis. Preferably said spring includes a formation opposed to said bight for engagement with an opposed edge of said clutch portion. Preferably said side portions resiliently engage said cam plate. In a particular preferred form apex portions of said side portions engage said cam plate. In yet a further broad form of the invention there is provided a spring adapted for fitting to a castor wheel assembly; said castor wheel assembly including a wheel rotatably supported within an inverted U shaped clevis; said clevis including a crotch portion adapted for rotatable support about a substantially upright castor axis of a mobile article; a cam plate adapted for fixed connection above said clevis so as to be fixed relative to said mobile article; said spring adapted for external, snap fit mounting to said clevis; said spring engageable with edge portions of said cam plate so as to provide a predetermined resistance to rotation of said clevis from a straight ahead position relative to said mobile article Preferably the spring is adapted for external snap fit to said clevis. More preferably said spring is adapted for external snap fit to said clutch portion of said clevis. In a particular form said spring includes opposed side portions connected at at least one end by a connection portion. Preferably said connection portion includes an inwardly and upwardly directed bight for engagement with an edge portion of said clutch portion of said clevis. Preferably said spring includes a formation opposed to said bight for engagement with an opposed edge of said clutch portion. Preferably said side portions resiliently engaged said cam plate. In a particular form of the spring, apex portions of said side portions engage said cam plate. BRIEF DESCRIPTION OF THE DRAWINGS By way of example, an embodiment of the above described invention is described in more detail hereinafter with reference to the accompanying drawings . Figure 1 is an exploded perspective view of a supermarket trolley wheel assembly according to the invention. Figure 2 is a perspective view of a wire spring, being a component of the assembly of figure 1. Figure 3 is a side elevation of the assembly of figure 1. Figure 4 is a sectional view taken on the castor axis of portion of the assembly of figure 1, drawn to a larger scale . Figure 5 is a plan view of the assembly of figure 1 with the wheel in its straight ahead position. Figure 6 is a view similar to figure 5 with the wheel castored to a small degree from the straight ahead position. MODE OF CARRYING OUT INVENTION The illustrated assembly comprises a conventional free castoring assembly fitted with the components which convert it into a biassed castor assembly according to the invention. The conventional components comprise a generally inverted U shaped clevis 4. That clevis is a sheet metal pressing comprising a crotch portion 5 forming a bearing housing 25 therewithin and two downwardly inclined, arcuate plate like legs 6. The legs 6 have clearance holes near their lower ends to receive a wheel axle 7 extending from leg to leg, on which a ground wheel 8 may rotate. Due to the shape of the legs 6 the wheel axle 7 is displaced horizontally a distance D from an upright castor axis ZZ extending coaxially through the housing 25. It follows, of course, that the area of contact between the rim or tyre of the wheel 8 and the ground is likewise displaced horizontally from the castor axis. The housing 25 holds a single row, deep groove, ball bearing comprising an inner race 9 tight upon a bolt 10 and an outer race 11 fixed within the housing 25. Thus the bearing defines a castor axis ZZ, coaxial with the bolt 10, about which the axle 7, and thus the wheel 8, may orbit. In use, the bolt 10 extends through a frame member (not shown) of a supermarket trolley for securement of the wheel assembly thereto. In accordance with the present invention the above described conventional arrangements are furnished with biassing means comprising a tough, self-lubricating plastics cam plate 12, a spacer washer 13 and a one piece wire spring 14. The spacer washer 13 rests upon the stationary inner race 9. It has serrated faces or is otherwise conditioned to promote a high coefficient of friction between itself and the inner race and between itself and the cam plate 12. A second such washer 15 may be provided between the cam plate 12 and a clamping nut 16. It will be appreciated that tightening the nut 16 effectively fixes the cam plate 12 relative to the bolt 10, and thus, in use, relative to the trolley The cam plate 12 is a circular disk but for the absence of two diametrically opposed segments, thus it has a major axis of symmetry XX (equal to the diameter of the circular disk) and a minor axis of symmetry YY (equal to the distance between the flats on the disk perimeter) . In use the cam plate 12 is oriented so that its major axis is aligned with the direction of straight ahead forward travel of the trolley, or, may be, slightly inwardly of that direction to provide a degree of "toe-in" for the rear wheels. The wire spring 14 is shaped to provide two, spaced apart, generally inverted U shaped side portions 17, each comprising a first limb 18 and a second limb 19, joined at an apex portion 27. A connector portion 20 extends between the lower ends of the limbs 18 so as to resiliently join them together. The connector portion 20 has a central, inwardly and upwardly directed bight 21 formed in it, adapted to engage under a front edge of the clevis crotch portion 5. Each free end of the limbs 19 is furnished with a hook formation 22 adapted to engage about a rear edge of the crotch portion 5. Thus it will be clear that the wire spring may be manually sprung apart to enable it to be securely positioned on the clevis 4, as shown in the drawings with the apex portions 27 of the side members 17 bearing resiliently against opposed edges of the cam plate 12. The arrangement is such that the apex portions 27 of the spring 14 bear against the cam plate 12 as aforesaid at or near the ends of the flats 23 in its periphery when the wheel is aligned in the straight ahead position (as is best seen in figure 5) . Any minor castoring movement of the wheel from that position requires the spring side portions 17 to be sprung apart as they slide against the edges of the cam plate, as shown in figure 6. This increases the stored energy in the spring and generates a restoring force urging the wheel to the stable equilibrium of the straight ahead position. If, nevertheless, the wheel is castored sufficiently from the straight ahead position to bring the spring side portions into contact with the arcuate edge portions of cam plate 12, further castoring movement causes no further straining of the spring. This provides for free castoring movement of the wheel in respect of lateral movement of the trolley, as needed for the steering of a file of trolleys. It will be appreciated that alternative embodiments of the invention may differ in detail from the above described embodiment, which is not to be seen as limiting the scope of the invention. In particular the shape of the wire spring may vary considerably from the illustrated shape. For example, the apices of the spring side portions 17 may be more peaked than shown, the limbs of those side portions may be straight, arcuate or otherwise differently shaped, and the shape of the connector portion and limb ends may be shaped in other ways providing for the functional engagement with the clevis. Indeed those parts of the spring may be very different to suit retrofitting to other castor wheel assemblies including clevises or their equivalents of designs differing from the conventional type described herein, provided the spring fulfills the functional requirements described above. Also the cam plate may be shaped differently providing it displays disparate major and minor axes, for example it may be elliptical, or it may be otherwise shaped to cause straining of the spring during and only during small departures of the wheel from the forward and reverse straight ahead positions. INDUSTRIAL APPLICABILITY Embodiments of the invention can be applied with advantage to supermarket trolleys having castor wheel assemblies in order to provide improved control .

Claims: CLAIMS 1. A castor wheel assembly of the kind comprising a generally inverted U shaped clevis comprising a crotch portion and two downwardly inclined spaced apart legs, axle retainer formations at or near the lower ends of the respective clevis legs for the receipt of a wheel axle extending from one clevis leg to the other, a bearing defining an upright castor axis and comprising a stationary bearing part that is fixed to an article to be supported and a rotatable bearing part that is fixed to the clevis crotch portion, and a bolt coaxial with the castor axis extending through the stationary bearing part to affix it to the article, characterised by biasing means comprising spacer means pierced by the bolt and contacting the stationary bearing part, a cam plate pierced by the bolt and spaced by the spacer means above the clevis crotch portion for clamped affixture to the article, which cam plate has mutually perpendicular major and minor axes of symmetry intersecting the castor axis, and a wire loading spring comprising two spaced apart, generally inverted U or V shaped side portions and a connector portion extending between the ends of first corresponding limbs of the respective spring side portions; the spring connector portion and the ends of second corresponding limbs of the respective spring side portions being adapted to snap engage the clevis crotch portion whereby the respective spring side portions bear resiliently against opposed edges of the cam plate . 2. Biasing means for a castor wheel assembly of the kind comprising a generally inverted U shaped clevis comprising a crotch portion and two downwardly inclined spaced apart legs, axle retainer formations at or near the lower ends of the respective clevis legs for the receipt of a wheel axle extending from one clevis leg to the other, a bearing defining an upright castor axis and comprising a stationary bearing part that is fixed to an article to be supported and a rotatable bearing part that is fixed to the clevis crotch portion, and a bolt coaxial with the castor axis extending through the stationary bearing part to affix it to the article ; said biasing means comprising spacer means adapted to be pierced by the bolt and contacting the stationary bearing part, a cam plate adapted to be pierced by the bolt and spaced by the spacer means above the clevis crotch portion for clamped affixture to the article, which cam plate has mutually perpendicular major and minor axes of symmetry intersecting the castor axis, and a wire loading spring comprising two spaced apart, generally inverted U or V shaped side portions and a connector portion extending between the ends of first corresponding limbs of the respective spring side portions; the spring connector portion and the ends of second corresponding limbs of the respective spring side portions being adapted to snap engage the clevis crotch portion whereby the respective spring side portions bear resiliently against opposed edges of the cam plate. 3. In combination, a spring and cam plate assembly adapted for fitting to a castor wheel assembly; said castor wheel assembly including a wheel rotatably supported within an inverted U shaped clevis; said clevis including a crotch portion adapted for rotatable support above a substantially upright castor axis of a mobile article; said cam plate adapted for fixed connection above said clevis so as to be fixed relative to said mobile article; said spring adapted for external mounting to said clevis; said spring engageable with edge portions of said cam plate so as to provide a predetermined resistance to rotation of said clevis from a straight ahead position relative to said mobile article. 4. The combination of claim 3 wherein said cam plate includes a major axis and a minor axis. 5. The combination of claim 5 wherein said cam plate includes flats parallel to and spaced from said major axis. 6. The combination of claim 4 or claim 5 wherein said cam plate includes opposed arcuate portions spaced symmetrically from said minor axis. 7. The combination of anyone of claims 3 to 6 wherein said spring is adapted for external snap fit to said clevis. 8. The combination of claim 7 wherein said spring is adapted for external snap fit to said clutch portion of said clevis . 9. The combination of claim 7 or claim 8 wherein said spring includes opposed side portions connected at at least one end by a connection portion. 10. The combination of claim 9 wherein said bridge portion includes an inwardly and upwardly directed bight for engagement with an edge portion of said clutch portion of said clevis. 11. The combination of anyone of claims 7 to 10 wherein said spring includes a formation opposed to said bight for engagement with an opposed edge of said clutch portion. 12. The combination of anyone of claims 7 to 11 wherein said side portions resiliently engaged said cam plate. 13. The combination of claim 12 wherein apex portions of said side portions engaged said cam plate. 14. A spring for use with the combination of anyone of claims 3 to 13. 15. A spring adapted for fitting to a castor wheel assembly; said castor wheel assembly including a wheel rotatably supported within an inverted U shaped clevis; said clevis including a crotch portion adapted for rotatable support about a substantially upright castor axis of a mobile article; a cam plate adapted for fixed connection above said clevis so as to be fixed relative to said mobile article; said spring adapted for external mounting to said clevis; said spring engageable with edge portions of said cam plate so as to provide a predetermined resistance to rotation of said clevis from a straight ahead position relative to said mobile article. 16. The spring of claim 15 wherein said spring is adapted for external snap fit to said clevis. 17. The spring of claim 16 wherein said spring is adapted for external snap fit to said clutch portion of said clevis. 18. The spring of claim 16 or claim 17 wherein said spring includes opposed side portions connected at at least one end by a connection portion. 19. The spring of claim 9 wherein said connection portion includes an inwardly and upwardly directed bight for engagement with an edge portion of said clutch portion of said clevis. 20. The spring of any one of claims 16 to 19 wherein said spring includes a formation opposed to said bight for engagement with an opposed edge of said clutch portion. 21. The spring of any one of claims 16 to 19 wherein said side portions resiliently engage said cam plate. 22. The spring of claim 21 wherein apex portions of said side portions engage said cam plate.

Inventors: HART-DAVIES THOMAS FIRTH, HORSNELL ROBERT LIONEL, HART-DAVIES, THOMAS, FIRTH, HORSNELL, ROBERT, LIONEL
Applicants: HART DAVIES THOMAS FIRTH, HORSNELL ROBERT LIONEL, WIN WIN INTERNATIONAL PTY LTD, HART-DAVIES, THOMAS, FIRTH, HORSNELL, ROBERT, LIONEL, WIN WIN INTERNATIONAL PTY. LTD.
Application year: 1998
Main classification: B60B33
IPC codes: B60B33