GB2285575A - Castor assembly - Google Patents

Abstract

A low-height castor assembly comprises an inverted generally cup-shaped body part 10, an inverted generally cup-shaped carrier 11 mounted on a spigot 16 within the body part for rotation relatively thereto about a central vertical axis, and a wheel assembly 27 mounted on the carrier for rotation about a horizontal axis displaced laterally with respect to said vertical axis. The wheel assembly partly projects below the body part 10 and carrier 11 for engagement with the floor, in use. The upper surface of the upper wall 17 of the carrier 11 is formed with a part-conical plain hearing surface 21 which cooperates with a mating part-conical plain bearing surface 22 formed on the lower surface of the upper wall 15 of the body part. <IMAGE>

Description

"A Castor Assemblv" The invention relates to castor assemblies for use on furniture and the like, and sets out to provide a strong and effective castor assembly which is of low vertical height.

With some types of furniture there is a requirement that the castor assemblies used on it should be of small overall height and should project only a very short distance below the bottom of the article of furniture. For example, one article of furniture of this kind is a movable pedestal filing cabinet which requires to be of such an overall height that it may be fitted under an office desk top. The filing cabinet may be required to have two filing drawers one above the other, each drawer being sufficiently deep to receive hanging files of A4 size. In practice these dimensional restraints on the filing cabinet have the effect that there remains very little vertical space available within which to fit castor assemblies to the bottom of the pedestal.It is not therefore possible to fit conventional castor assemblies of the kind where the whole of the castor wheel is located below the bottom surface of the article of furniture, being mounted either on a plate which is screwed to the bottom surface or on a spigot which is received in a socket in the bottom surface.

In order to overcome this problem it has been proposed to provide a castor assembly comprising an inverted generally cup-shaped body part, an inverted generally cup-shaped carrier mounted within the body part for rotation relatively thereto about a central substantially vertical axis, and a wheel assembly mounted on the carrier for rotation about a substantially horizontal axis displaced laterally with respect to said vertical axis, the wheel assembly partly projecting below the body part and carrier for engagement with the floor, in use.

With such a castor assembly the cup-shaped body part may be received in a socket in the underside of the piece of furniture so that the clearance between the underside of the piece of furniture and the floor is determined solely by the extent to which the wheel assembly needs to project below the body part and carrier.

However, existing castor assemblies ofthis type suffer from severe disadvantages due, for example, to the carrier binding within the cup-shaped body part so that it does not rotate freely relative thereto. It will be appreciated that such free rotation is essential in order to achieve the required castor effect. In one existing design an array of ball bearings is located between the carrier and body part in an attempt to improve the free rotation of the carrier. However, most furniture fitted with castors remains stationary in one position for most of the time and the castors are required to function only occasionally.As a result of long standing, therefore, the ball bearings tend to form depressions in the bearing surfaces which they engage so that when the article of furniture eventually comes to be moved they do not provide the free rotation of the assembly which is required. The present invention sets out to provide a novel form of low height castor assembly which may overcome this and other disadvantages of existing castor assemblies of the general type referred to above.

(In this specification expressions such as "upper", "lower", "downwardly" etc., refer to the orientation of the castor assembly when in its normal position of use fitted to the underside of an article of furniture.) According to the invention, in a low height castor assembly of the kind referred to, the upper surface of the upper wall of the carrier is formed with a part-conical plain bearing surface which cooperates with a mating part-conical plain bearing surface formed on the lower surface of the upper wall of the body part.

Since the bearing surfaces are plain no deformation occurs with long standing of the article offurniture, and since the bearing surfaces are part-conical, there is automatic compensation for any wear in the surfaces. In addition, the interengaging bearing surfaces, being part-conical, tend to locate the carrier accurately within the body part so as to reduce the risk ofthe carrier binding on any part of the surrounding body part and thus preventing its free rotation.

Preferably the part-conical bearing surfaces are so located that, when the bearing surfaces are in engagement, the peripheral wall of the cup-shaped carrier is spaced inwardly from the peripheral wall of the cup-shaped body part.

Preferably the part-conical bearing surface on the carrier faces outwardly and the mating part-conical bearing surface on the body part faces inwardly.

The body part and carrier may be formed with an axially located rotatable spigot and socket assembly. For example, the upper wall of the body part may be formed with an axial spigot which extends downwardly into an axial socket in the upper wall of the carrier. Preferably the spigot and socket are provided with retaining means to retain the carrier on the body part. For example, the spigot may pass completely through the socket and may be formed at its lower extremity with an outward projection to prevent its upward withdrawal through the socket.

The aforesaid wheel assembly preferably comprises a plurality of separate but coaxial wheels mounted on the carrier for rotation independently of one another. For example, the separate wheels may be rotatably mounted side-by-side along a common fixed shaft which is mounted on the carrier.

The following is a more detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawings in which: Figure 1 is a vertical cross section through one form of castor assembly according to the invention; and Figure 2 is an underside view of the castor assembly.

Referring to the drawings, the castor assembly comprises an inverted cup-shaped body part 10 within which is located a cup-shaped carrier 11. The peripheral wall 12 of the carrier is of such a height that its lower peripheral edge is substantially level with the lower edge of the peripheral wall 13 of the body part 10. The lower edge of the peripheral wall 13 ofthe body part is formed with an outwardly projecting annular flange 14.

In use the castor assembly is received in a circular socket formed in the undersurface of the article of furniture to which the assembly is to be fitted, the flange 14 bearing against the undersurface of the article of furniture around the socket.

Projecting outwardly of the flange 14 are three equally circumferentially spaced mounting lobes 29 formed with holes 30 whereby the lobes 29 may be screwed to the underside of the article of flirniture. The circular socket in which the assembly is received may then be slightly larger tan the assembly, so that the position of the assembly may be adjusted slightly before it is secured by screwing the mounting lobes 29 in position. This allows for possible tolerances in the positioning of the circular socket.

Although this is the preferred method of fitting the assembly, the peripheral wall 13 of the body part may instead be a tight interference fit in the socket, and may be formed with axially extending ribs to improve the fit. In this case the lobes 29 may be omitted.

The upper wall 15 of the body part 10 is formed with a central hollow downwardly extending spigot 16 which passes through a central circular aperture in the upper wall 17 of the carrier 11. The carrier 11 is freely rotatable around the spigot 16 and is retained on the spigot by an outer peripheral enlargement 18 integrally formed on the lower extremity of the spigot. The carrier and body part are moulded from plastics material and the arrangement is such that the enlargement 18 on the spigot may be snapped through the central aperture in the carrier 11. In order to facilitate this "snap through" action, the enlargement 18 may comprise a series of thin annular flanges (not shown) spaced one above another on the extremity ofthe spigot.An upstanding circular wall 19 is formed on the upper wall 17 of the carrier and is spaced around and slightly outwardly of the central aperture, for added strength.

Integrally moulded with the upper wall 17 of the carrier 11 is an upstanding annular wall 20 having an outwardly facing part-conical bearing surface 21. This plain bearing surface mates with a corresponding inwardly facing part-conical bearing surface 22 integrally formed on the upper wall 15 of the body part.

The dimensions of the carrier are such that when the part-conical bearing surfaces are in mating engagement the outer surface of the peripheral wall 12 of the carrier is spaced slightly inwardly from the peripheral wall 13 of the body part, as indicated at 23.

In use the space between the upper wall 17 of the carrier and the upper wall 15 ofthe body part is filled with grease, so as to provide lubrication for the bearing surfaces 21, 22 and the spigot 16.

As best seen in Figure 2, the interior of the carrier 11 is integrally formed with two spaced parallel walls 24 which extend part-way across the carrier 11 and are then connected to the peripheral wall 12 by further walls 28, also integral with the carrier, extending at right angles to the walls 24 respectively. A metal shaft 25 extends horizontally between the walls 24. The ends of the shaft 25 are snapped into, and retained by, undercut recesses formed in the walls 24. As may be seen from Figure 1 the shaft 25 is spaced laterally from the central axis 26 of the castor assembly.

Three separately formed wheels 27, which may also be formed from plastics, are freely rotatable on the fixed shaft 25. Although three independently rotatable wheels are shown in the drawings, a different number of wheels, e.g. one or two, may be provided on the shaft 25 if required. The provision of multiple independently rotatable wheels allows rotation of the carrier 11, and the castoring action, to take place without undue scuffing of the wheels 27 on the floor, which would be the case if only a single wheel of equivalent axial width were provided.

Although the body part 10, carrier 11 and wheels 27 are preferably moulded from plastics, they may also be manufactured from any other suitable material.

The described arrangement provides a strong and effective castor assembly of low height. At the same time, the provision of the central spigot 16 provides for strong and rigid connection between the carrier and body part, while the part-conical plain bearings ensure smooth and free rotation of the carrier without binding.

Claims (11)

1. A castor assembly comprising an inverted generally cup-shaped body part, an inverted generally cup-shaped carrier mounted within the body part for rotation relatively thereto about a central substantially vertical axis, and a wheel assembly mounted on the carrier for rotation about a substantially horizontal axis displaced laterally with respect to said vertical axis, the wheel assembly partly projecting below the body part and carrier for engagement with the floor, in use, the upper surface of the upper wall of the carrier being formed with a part-conical plain bearing surface which cooperates with a mating part-conical plain bearing surface formed on the lower surface of the upper wall of the body part.

2. A castor assembly according to Claim 1, wherein the part-conical bearing surfaces are so located that, when the bearing surfaces are in engagement, the peripheral wall of the cup-shaped carrier is spaced inwardly from the peripheral wall of the cupshaped body part.

3. A castor assembly according to Claim 1 or Claim 2, wherein the part-conical bearing surface on the carrier faces outwardly and the mating part-conical bearing surface on the body part faces inwardly.

4. A castor assembly according to any of Claims 1 to 3, wherein the body part and carrier are formed with an axially located rotatable spigot and socket assembly.

5. A castor assembly according to Claim 4, wherein the upper wall of the body part is formed with an axial spigot which extends downwardly into an axial socket in the upper wall of the carrier.

6. A castor assembly according to Claim 4 or Claim 5, wherein the spigot and socket are provided with retaining means to retain the carrier on the body part.

7. A castor assembly according to Claim 6, wherein the spigot passes completely through the socket and is formed at its lower extremity with an outward projection to prevent its upward withdrawal through the socket.

8. A castor assembly according to any of the preceding claims wherein the wheel assembly comprises a plurality of separate but coaxial wheels mounted on the carrier for rotation independently of one another.

9. A castor assembly according to Claim 8, wherein the separate wheels are rotatably mounted side-by-side along a common fixed shaft which is mounted on the carner.

10. A castor assembly according to any ofthe preceding claims, wherein outwardlyprojecting mounting lugs are provided spaced apart around the lower periphery of the inverted generally cup-shaped body part.

11. A castor assembly substantially as hereinbefore described with reference to the accompanying drawings.