HK1032218B - Steerable load-carrying assemblies - Google Patents

Description

Steerable load bearing assembly

no marking

The present invention relates to improvements in steerable load bearing assemblies and in particular, but not exclusively, to steerable, movable load bearing assemblies.

The present invention also includes a centralizing mechanism for use with such load bearing assemblies to assist in steering the entire assembly.

Throughout this specification reference will be made to a baby rocking cart, a stroller or push chair for babies, patients and the like. It is to be understood that such preferred embodiments are presented by way of example only and are not to be construed as limiting such utility. Indeed, the invention will be applicable to any assembly intended to be propelled by human power rather than power, including, for example, carts, hand trucks, shopping carts, two-wheeled carts, rovers, toy baby cradles, trailers, caravans, marine trailers, wheeled jacks for vehicles, wheelchairs, dining carts, hospital beds for medical lifts mounted on wheeled bases, work platforms, library carts, and the like having a plurality of wheels and/or casters.

Throughout this specification reference will be made to a wheel or wheels, including a castor or castors, or a wheel which acts as a castor.

Further, throughout this specification reference will be made to a chassis, including a framework.

According to the known prior art, children's bassinets usually have fixed wheels. This can cause undue and undesirable difficulties in use. For example, the steering circle of a wheel-mounted children's bassinet may be large, with significant limitations and impacts. There is also friction of the wheels during rotation, thus increasing wear.

According to the prior art, a movable assembly of the above type can be considered in one of three forms:

(i) the first is that all four wheels are fixed and cannot be steered in any way

(e.g., a conventional version of a children's bassinet).

(ii) The second type (e.g. children's rides and the like) having fixed rear wheels and front wheels

The rotation can be realized; or

(iii) Third, all four wheels can be independently rotated (e.g., supermarket shopping

A cart).

In fact, it has been found that each of these three forms exhibits a number of advantages that make it suitable for certain uses, but has the disadvantage of limiting its suitability for all uses.

When all four wheels are fixed (first version), one advantage is that the wheels can be very large in diameter, thus making the assembly easier to move over uneven terrain. Another advantage is that such an assembly is suitable for use along roads where the operator does not need to concentrate on handling the assembly during normal travel, but only when a change of direction is required. Thus, when larger diameter wheels are used on the fixed wheel assembly, the passenger's ride is smoother, and the result is more important when the passenger may be an infant. It has also been found that the fixed wheel assembly can walk over a sloping or undulating surface without excessive effort by the operator to maintain the assembly in the desired orientation, except when it is desired to change the orientation.

Such a fixed wheel assembly has the disadvantage of being difficult to change direction. Two commonly used methods are to press the handle down to lift the front wheel off the ground and turn the handle horizontally to orient the assembly in the new direction of travel; or lifting the handle to lift the rear wheel off the ground and turning the handle horizontally to achieve the desired new direction of travel. Both of these solutions may require the use of great strength and skill.

Additional disadvantages of such fixed wheel assemblies include excessive wear and tear on the frame members of the overall structure, which can cause the frame to bend or deform. Furthermore, the effort required by the operator may be excessive. As a result, fixed wheel type assemblies have been found to be unsuitable for use as items such as shopping carts where frequent changes in direction are required and often in a small area.

For the second form of the assembly, there is a fixed rear wheel and a rotatable front wheel. Such an assembly has the advantage of being easier to handle both in terms of space and force. However, this form has the disadvantage that small diameter wheels must be used to enable the castor-type rotational action to allow the front wheels to rotate through 360 degrees, as they are commonly mounted, or must rotate under the assembly. The use of such small diameter wheels makes it more difficult for such assemblies to travel over rough or uneven surfaces and also gives passengers a very uncomfortable ride when compared to assemblies with larger diameter fixed wheels. Furthermore, the rotatable front wheels are typically, or operate as, casters. Thus, they are not connected together and follow the terrain individually, which would cause the rotatable front wheel to face in different directions, making it extremely difficult for the operator to maintain control, particularly when the assembly is traveling over a sloped surface. With such assemblies, the operator must maintain attention and exert significant effort to keep the assembly oriented in the desired direction while traveling over an arcuate or sloped surface.

An assembly having four independently rotatable wheels-a third form-has the following advantages: is very easy to operate; can rotate in the length of the rotary drum; and can be used equally well and effectively when pushed and/or pulled in either direction. Such an assembly has thus been found to be particularly suitable for use as a shopping cart, a baby amusement ride and the like.

This assembly also exhibits several disadvantages. First, such assemblies are best suited for use on horizontal, flat surfaces, which are difficult to maintain control when moving such assemblies across a slope. Furthermore, since all wheels must be able to rotate 360 degrees, this form of assembly can only be made with smaller diameter wheels, even if the wheels are locked in a forward position, allowing only forward movement, which in turn results in a less comfortable ride for the passengers. Since all four spinning wheels are caster sets, they can be operated individually, especially when traveling over uneven surfaces. Since the wheels are not connected, they can all face different directions at any given time. Thus, such assemblies are difficult to control.

Known load bearing assemblies have a tendency to cause the direction of movement to easily flip. Various devices have been used in an attempt to improve steering ability, but none have been successful. The present invention seeks to overcome the problems and disadvantages of the prior art by providing a mechanism to maintain the steerable wheel of a steerable assembly in a position that allows for straight ahead movement and to act to return the steerable wheel to a position corresponding to straight movement of the assembly. Preferably this is independent of the range of steerable wheel displacement due to terrain variations etc.

On the other hand, the invention preferably acts to prevent any tendency that the assembly may show to move out of position corresponding to a straight forward movement, and to compensate for this tendency of the assembly to divert in any line other than a straight line.

Steering systems for the load bearing assemblies of the present invention have been little developed in the past. For example, PCT/GB96/00687 discloses a trolley, such as a supermarket trolley, having a castor at each corner. The casters are arranged as a driving (rear) caster and a driven (front) caster. A worm gear causes the master castor on one side to drive the slave castor on the other side so that when the master castor rotates in one direction the slave castor rotates in the opposite direction. However, the casters are not connected from side to side. Thus, the caster wheels of one side can be turned to the right (rear) and left (front), while the caster wheels of the other side can be turned to the left (rear) and right (front). This will disturb the overall operation. It is also only suitable for casters to be placed directly under the frame and is not suitable for any other type of wheel nor for any other type of product.

Furthermore, us 4348033 and 4405140 relate to steerable connecting skids whose four rollers are connected to enable them to be steered. However, the mechanism involved is a complex arrangement, requiring many parts and using cables and linkages. Furthermore, it is intended to be controlled from the inside rather than from the outside. This is a basic difference in that there is a passenger who can drive the appliance when controlled from inside and does not intend to drive it with external force. For a device such as a baby bassinet or trolley, it is driven from the outside and is therefore intended to be controlled by external forces. Furthermore, for devices such as baby strollers or carts, it is intended that no internal force is used for control, otherwise the direction of the cart or cart can be controlled by a small child or baby who is merely crawling, which is quite the opposite of what is required.

According to a first aspect of the present invention there is provided a mobile load bearing assembly comprising a chassis having a plurality of wheels arranged in a first set of wheels and a second set of wheels, each wheel being rotatable and swiveling relative to the chassis; the wheels of the first wheel set are connected by a first connecting rod, and the wheels of the second wheel set are connected by a second connecting rod; wherein one wheel of the second wheel set is connected to an opposite one of the wheels of the first wheel set with a link so that when one wheel of the first wheel set rotates in one direction relative to the chassis, all of the wheels of the first wheel set rotate in unison in that direction and all of the wheels of the second wheel set rotate in unison in the opposite direction.

Preferably, there are two wheels in the front wheel set. More preferably, there are two wheels in the rear wheel set. Advantageously, the chassis has a front cross member and a rear cross member. More advantageously, the front cross member is a front link. Further, the rear cross member may be a rear link.

Preferably, the link is a bar or rod rotatably connected to one of the front wheels and diagonally connected to an opposite rear wheel.

According to another aspect of the present invention there is provided a mobile load bearing assembly comprising means for providing three different modes of operation for the rear wheel set, these modes corresponding to straight travel (forward or backward), fully steerable travel (also forward or reverse), and a braking mode.

According to another aspect of the present invention, there is provided a device for controlling the direction of travel of a steerable assembly, the device comprising:

(i) a first member operably associated with one or more steerable wheels of the assembly

The connecting rods are connected;

(ii) at least one further member associated with a fixed chassis member of the assembly, at least

One of the other members being movable relative to the fixed base between inoperative and operative end positions

A disk selectively and continuously rotatably movable; and

(iii) a resilient means associated with at least one of the other members,

the arrangement is such that, in use, when the combined steerable wheel direction changes, the first member and at least one further member come into contact, whereby the resilient means acts to return the at least one further member to its inoperative position, thereby to correct the steering of the assembly.

In order that the invention may be more clearly understood and put into practical effect, there shall now be described by way of non-limitative example only a preferred embodiment of a mobile load bearing assembly according to the present invention, the description being with reference to the accompanying illustrative drawings in which:

FIG. 1 is a top plan view of a first embodiment of a chassis of a moveable load bearing assembly;

fig. 2 is a view similar to fig. 1 showing the assembly configuration of fig. 1 most suitable for steering, wherein all of the wheels are steerable;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 1 and in the direction of arrows 3-3;

FIG. 4 is a view similar to FIG. 3 showing another embodiment of an assembly in accordance with the present invention;

FIG. 5 is a partial top view of the alternative embodiment shown in FIG. 4;

FIG. 6 is a top plan view of the embodiment of FIGS. 4 and 5 when in a straight-ahead mode;

FIG. 7 is a view similar to FIG. 6 but when turned to the left;

FIG. 8 is a side view of one of the rear wheels of the assembly of FIGS. 4-7, when in the locked position, in which all of the wheels are fixed against any rotation, the entire device acts in a conventional manner;

FIG. 9 is a view similar to FIG. 8 showing a second configuration of the rear wheel of the alternate embodiment of FIG. 4, wherein all of the wheels are steerable;

FIG. 10 is a third configuration of the rear wheel similar to FIGS. 8 and 9 but showing the rear wheel in a braking mode;

FIG. 11 is a view taken along line 11-11 and arrows 11-11 of FIG. 10;

FIG. 12 is a side view of the alternative embodiment of FIGS. 4-11 of an assembly according to the present invention;

FIG. 13 is a partial rear view of another embodiment of the present invention incorporating a concentrating mechanism; and

FIG. 14 is a view similar to FIG. 13 showing another form of a concentrator or mechanism according to the present invention.

Referring now to fig. 1 to 3, there is shown a chassis formed by the interconnection of separate front and rear cross members 2 and 3, and cooperating longitudinal members 4. The members 2, 3 and 4 form the chassis 1 and are interconnected in any known manner, such as for example by welding, bolts, latches, etc., to produce a substantially rigid chassis 1. As shown in figure 3, each member 4 is an elongate member having a longitudinal portion 4b and extending from its rear end an arcuate portion 4a, the arcuate portion 4a being adapted, in use, to receive and releasably retain a collapsible assembly which is also adapted to co-operate with a load carrying device.

A wheel assembly 5 is mounted at or near each end of each cross member 2, 3. The wheel assembly 5 is formed by a wheel 6, a steering shaft 7 on which the wheel 6 is mounted for rotation, a rotation shaft 8 fixedly connected to the cross members 2, 3, and a wheel hub 9 rotatably mounted relative to the rotation shaft 8, preferably using suitable types of pads or bearings. The hub 9 is rotatably and releasably mounted relative to the axis of rotation 8 by the use of a cotter pin or the like. The steering shaft 7 is coupled to the hub 9 in such a way that it is substantially at right angles to the axis of rotation 8. Each wheel 6 is rotatable about its steering axis 7 and also about a respective axis of rotation 8 relative to the chassis 1. In another solution (not shown in the figures), a castor wheel consisting of two juxtaposed wheels is mounted via a hub and pivot for rotation or swiveling with respect to the chassis 1, each of the two juxtaposed wheels being mounted for swiveling at the free end of the steering shaft.

One of the front wheels 6 is connected to an opposite rear wheel 6 via a suitable link 11. The front wheels 6 are connected together in any suitable manner and the rear wheels 6 are also connected together. The end result of this arrangement is that all four wheels 6 are steerable, and the front and rear pairs of wheels can move in opposite directions respectively.

Referring now to fig. 1 and 2, an engagement member 20 is associated with each hub 9 and extends at an angle therefrom. The engagement member 20 is preferably somewhat boomerang shaped so that its front portion 20a contacts the longitudinal member 4 before contacting the wheel 6 when required, thereby acting as a limit to the rotational movement of the wheel 6 relative to the chassis 1. The engagement members 20 associated with the rear wheels 6 are interconnected via a rear link 21, and the engagement members 20 associated with the front wheels 6 are interconnected via a front link 22. One of the rear wheels 6, and the opposite (diagonal) one of the front wheels 6, has associated therewith a further member 23 fixedly connected to the hub 9 and extending at an angle relative to the hub 9 and the engaging member 20. The two other members 23 are interconnected via a link 11 so that when the rear wheel 6 is turned or rotated in a given direction about its axis of rotation 8, the front wheel 6 is turned or rotated in the opposite direction about its respective axis of rotation 8. In this way, a fully controllable steering of the entire chassis 1 and the associated wheel assembly 5 is achieved. The assembly causes the wheels 6 to undergo or operate in a caster-type action.

A body to be connected to the chassis 1 is preferably connected to the front link 22 at point a (fig. 1) and is preferably pivotally connected to the rear link at point b (fig. 3). In this way, the body can be used to control the direction of the front wheel 6, and thus the associated wheel 6, by acting directly on the link 22.

Referring now to fig. 4-12 of the drawings, there is illustrated another embodiment of a moveable load bearing assembly. The same numbering system is used as in the embodiment of fig. 1-3. The alternative embodiment comprises a chassis 1, the chassis 1 being formed by an interconnection of separate front and rear cross members 2 and 3 and a co-operating longitudinal member 4. The various members 2, 3 and 4 constituting the chassis 1 are joined together in any known manner, for example by welding, bolts, latches, etc., so as to obtain a substantially rigid structure.

There may be two front cross members 2, one mounted above the other; and two rear cross members 3, also mounted one above the other. Between which the longitudinal members 4 extend. The actual components used for the chassis 1 do not form an essential part of the invention.

Wheel assemblies 5 are mounted at or near each end of each cross member 2 and 3. The assembly 5 is formed of a single wheel 6, a steering shaft 7 on which the wheel 6 is mounted for rotation, a rotating shaft 8 fixedly connected to and extending between the pair of cross members 2 and 3, and a hub 9 rotatably mounted on the rotating shaft 8, preferably with suitable types of bushings or bearings. The hub 9 is rotatably and releasably mounted relative to the rotation shaft 8. The steering shaft 7 is coupled to the hub 9 so that it is substantially at right angles to the axis of rotation 8. As a result, the wheel assembly 5 functions as a caster that is rotatable with respect to the chassis 1.

One of the front wheels 6 is connected to an opposite rear wheel 6 via a suitable link 11. The front wheels 6 are connected together in any suitable manner; and the rear wheels 6 are also connected together. Preferably, the hub 9 for each front wheel assembly 5 is fixedly and rotatably connected to another link-in the form of a rod or the like extending transversely to the chassis 1. In a similar manner, the opposing rear wheel assemblies 5 are fixedly and rotatably connected by another cross member or link. The end result of this configuration is that all four wheels are steerable.

In a similar manner to the embodiment shown in fig. 1 to 3, the hub 9 of at least one of the respective front and rear wheel assemblies 5 is associated therewith and extends therefrom at an angle to the other member 23. The opposite other member 23 of the front and rear wheels 6 is interconnected by a link 11. The engagement members 20 of the hub 9 of the front wheel 6 are interconnected via a link 22 to enable the front wheel to turn (be rotatable) in unison relative to the chassis 1. In a similar manner, the opposite rear wheels 6 are interconnected via a link 21 so that the rear wheels 6 can also turn (rotate) in unison. The net result is that when the rear wheels 6 are turned or rotated in a given direction relative to the chassis about their respective axes of rotation 8, the front wheels 6 are turned or rotated in the opposite direction.

If desired, for this embodiment, the cross members 2, 3 may be joined into a central cross member, giving the chassis 1 a generally H-shape. In addition, the cross members 2, 3 may be omitted and replaced by wire or similar baskets which will be securely and/or releasably mounted between the longitudinal members 4, in which case the baskets 29 add structural strength to the chassis 1 and are considered part of the chassis 1.

In the embodiment shown in fig. 4 to 10, the chassis 1 and associated wheels 6 can be set to one of three operating modes, including:

(i) a first mode in which all wheels 6 are locked in direction and also rotatable, from

To facilitate forward or backward straight line motion;

(ii) a second mode in which the wheels 6 are steerable, about their respective steering axes 7 and about

Rotatable about their respective axes of rotation 8; and

(iii) a third mode in which the rear wheel 6 is locked against rotation.

Referring particularly to fig. 8-11, three modes of operation are shown. A longitudinally and outwardly extending positioning member 30 is fixedly mounted on at least one of the rear rotary shafts 8. Associated with the engagement member 20, now part of the hub 9, for each rear wheel 6, and rotatably mounted relative thereto, is a respective lever member 31, each lever member 31 being in turn connected to the adjacent end of a link member 21 extending transversely of the chassis 1. The lever member 31 is rotatably connected to the engagement member 20 by any suitable means, such as a pin 33. The lever member 31 has a bolt 34 extending therefrom at substantially right angles thereto which cooperates with a shaped rear end portion of the engagement member 20 in a cam follower type arrangement.

The lever member 31 is selectively movable between three positions, shown in fig. 8, 9 and 10, respectively, each corresponding to three operating modes. The force applied to the link member 21, for example with the operator's foot, can transfer motion to the components of the link member 21 and associated lever member 31 to move the components to a desired position to achieve a desired mode of operation.

When in the position shown in figure 8, the lever member 31 engages the locating member 30, preventing rotational movement of the rear wheel 6-and in turn preventing rotational movement of the connected front wheel 6-but still allowing rotation of the wheel itself. In this mode, all wheels 6 are in a position allowing straight forward movement.

When moved to the position shown in fig. 9, all wheels 6 are rotatable and also rotatable, the whole assembly thus being steerable as described above.

When the lever member 31 is moved to the position shown in fig. 10, the bolt 34 contacts between inwardly directed projections 35 located around a hub 36 of the rear wheel 6 to prevent the rear wheel 6 from rotating.

Referring now to fig. 12, there is illustrated a frame adapted to receive and releasably clamp thereto, a suitable device for receiving a load, such as a tray or the like, a child's cradle, or the like. The illustrated arrangement is adapted to be releasably or fixedly connected to a steerable wheel assembly of the type mentioned above in any known manner, such as by a latch.

If desired, the positioning member 30 may be included in the arcuate portion 4a of the longitudinal member 4 so that the bolt 34 can engage in a suitable groove or indentation (not shown) in the arcuate portion 4 a.

The assembly of the present invention was found to show important advantages when compared to known assemblies. Since all wheels are mechanically linked and can be used in either fixed wheel or fully steerable modes, all of the advantages associated with fixed wheel assemblies can be realized without any of the inherent disadvantages associated therewith-as previously mentioned in the specification. Furthermore, the advantages associated with four-wheel steerable assemblies are significant and also free of disadvantages. The same result can be obtained by comparing the assembly of the invention with known assemblies using four separate sets of rotating wheels.

At the same time, when the wheels 6 are outside the periphery of the chassis 1, there are no upper and lower limits on the diameter of the wheels 6, and therefore it is possible to use wheels 6 of larger diameter (to give a smoother ride) which are also able to turn in the same way and to substantially the same extent as small diameter wheels.

With reference to the embodiment of fig. 13, it will be appreciated that it is adapted to be disposed between a first fixed rod or like member 201 and a movable rod or link 202, the member 201 forming a horizontal frame member of the chassis of the stroller, trolley or the like, the member 202 extending horizontally between the steerable wheels of the stroller, trolley or the like.

The movable linkage 202 will be movable in the direction of the arrow (see fig. 13) as the wheel of the assembly rotates, which may occur for various reasons or due to several factors.

A member 203 is secured to the link 202 in any known manner, such as by welding, and is adapted to extend substantially perpendicularly therefrom. The member 203 may take the form of a rod-like member having a rotatable means, such as a roller 204, suitably disposed at its free end.

Two spaced apart substantially straight members 205 and 206 extend perpendicularly from the fixed chassis member 201 in the direction of the link 202, each member being rotatably movable relative to the fixed chassis member 201 in the direction of the arrow. The rotatable movement may be achieved in any known manner, for example by having members 205 and 206 catch on the stationary member 201 at 207. Also extending substantially perpendicularly from the stationary member and disposed between the spaced apart members 205 and 206 is a spacer 208 which is intended to maintain the space therebetween and is in the form of a projection which is attached to the stationary member 201 in any known manner, such as also by welding. The members 205 and 206 are interconnected at or near their uppermost free ends by a resilient member 209 of any known type, such as a spring.

The principle of operation of the centralized control mechanism according to the embodiment of fig. 13 is that the roller device 204 engages one of the members 205 or 206 when the linkage 202 moves left or right as the direction of the wheels of the assembly changes. As a result, the member 205 or 206 will move downwards in the direction of the arrow towards the fixed chassis member 201, overcoming the spring pressure generated by the resilient means 209. The resilient means 209 serves to attempt to return the member 203 and associated roller means 204 to the position shown in figure 13 where it is disposed between, but not in contact with, the upper free ends of the opposed members 205 and 206. Thus, the link 202 is forced to move in the opposite direction, which will straighten the wheels of the assembly to a straight forward position. It will thus be seen that the mechanism acts to compensate for any tendency for the assembly to turn in a direction other than straight, and to return to a straight forward position after it has turned.

Each member 205, 206 has a generally V-shaped cut-out portion 210 therein which applies an uneven pressure to the roller means 204 as it moves out of the central position as shown.

When only a single elastic means 209 is used to perform the concentrating action, this arrangement functions in an extremely simple but effective manner, regardless of the direction of movement of the link 202. For example, if a single spring means is associated with each member 205, 206, i.e. it is desired to select a leveling spring, there is no need to select a leveling spring since with the structure of the present invention the same force will be applied to both steering directions.

Referring to the embodiment shown in fig. 13, as soon as link 202 moves away from the position corresponding to the straight forward movement of this assembly, spring 209 acts to attempt to return link 202 to that position, thereby regaining the straight forward movement. The greater the deviation of the member 203 from the position due to terrain variations, or tight turns, the greater the spring tension acting to return the member to the position shown.

The embodiment of fig. 14 shows in solid lines the structure that turns the assembly into a straight line. The dashed lines in the figure represent what happens when this component is affected in any way so as to travel in a direction other than straight ahead.

In a similar manner to the embodiment of fig. 13, the alternative concentrating mechanism of fig. 14 is adapted to be located between a fixed rod or like member 301 and a movable rod or link 302, the fixed rod 301 forming a horizontal frame member of the chassis of the bassinet, stroller, trolley or like equipment, the link 302 extending horizontally between the steerable wheels of the bassinet, stroller, trolley or like equipment.

A member 303 is secured to the connecting rod 302 by any known means, such as by welding, and is adapted to extend substantially perpendicularly therefrom. The member 303 preferably takes the form of a rod-like member having a rotatable means in the form of a roller generally indicated by the reference numeral 304 suitably disposed at its free end in any known manner.

Two arm members 305 and 306 are fixed to the fixed member 301 and adapted to be rotatably movable relative to the member, the arm members 305 and 306 being rotatably movable relative to the fixed member 301 in the direction of the arrow depending on whether the assembly is traveling to the left or right. This rotatable movement may be achieved in any known manner, for example, by pinning the arm member to member 301 at 307. A suitable resilient means, such as a spring 310, may extend between the respective free ends of the arm members 305 and 306, the spring means 310 providing a bias to return the arm members 305, 306 to the position shown in solid lines in figure 14. There are means for limiting the range of rotatable movement of the arm members 305 and 306 relative to the fixed member 301. Preferably, such means would take the form of pins 308 and 309 on the stationary member 301 and are intended to contact the surfaces of the arm members 305 and 306.

When in the position corresponding to the straight-ahead position shown by the solid line in fig. 14, the roller 304 has no force applied thereto because the stopper pins 308 and 309 function to prevent the arm members 305 and 306 from contacting the roller 304.

As the link 302 moves left or right, the roller 304 contacts the arm members 305 and 306 to urge the associated arm member in a downward direction, as indicated by the arrow, to overcome the pressure exerted by the spring 310 until the edge of the arm member that bears against the roller 304 is substantially parallel to the fixed member 301. When in that position, no further pressure is exerted on the roller 304. The operator will thus feel a resistance on either side of the centre until the relevant arm member 305 or 306 has moved downwards towards the fixed member to its maximum possible extent, at which point there is no more steering resistance.

This will tend to keep the steering in the central position, but will have little, if any, effect in any other steerable position. The shape of the free ends of the arm members 305 and 306 may be varied to change the "feel" imparted to the steering assembly. In an embodiment not shown, the free end of each arm member 305, 306 or each arm member 305, 306 may curve in an upward direction, creating increased tension that moves the cart's steering handle out of the straight-ahead position. However, in the illustrated embodiment, the free end of each arm member 305, 306 may be shaped such that spring tension is not effective when the entire assembly is turned in a direction other than straight ahead.

The embodiment of fig. 14 acts to counter any tendency for the steerable wheel of the assembly to "flow" out of the position corresponding to straight ahead motion. In contrast to the embodiment of fig. 13, the embodiment of fig. 14 only functions within a predetermined range of displacement of the linkage 302 and the associated member 303.

It is to be understood that the invention disclosed and described herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternatives to the present invention.

It will also be understood that the term "comprises" or its grammatical variants as used herein is equivalent to the term "includes" and should not be taken as excluding the presence of other elements or features.

Claims (10)

1. A manual load bearing assembly comprising a chassis having a plurality of wheels arranged in a first wheel set and a second wheel set, each wheel being rotatable and rotatable relative to the chassis, the wheels of the first wheel set being connected by a first link, the wheels of the second wheel set being connected by a second link, one of the wheels of the second wheel set being connected by a link to an opposite one of the wheels of the first wheel set, whereby when one wheel of the first wheel set rotates in one direction relative to the chassis, all of the wheels of the first wheel set rotate in unison in that direction and all of the wheels of the second wheel set rotate in unison in the opposite direction; wherein each wheel has a substantially vertical steering axis about which it can rotate relative to the chassis; a hub is mounted on each rotatable shaft, each wheel being rotatably mounted on a steering shaft mounted on its respective hub remote from the rotatable shaft such that each wheel acts in the manner of a castor wheel.

2. The assembly of claim 1, wherein: two wheels in the first wheel set are located on both sides of the chassis and two wheels in the second wheel set are located on both sides of the chassis.

3. The assembly of claim 1 or 2, wherein: the axle is connected to a chassis having two generally parallel and spaced apart longitudinal members extending between the first and second wheel sets.

4. An assembly according to claim 1 or 2, wherein a coupling member is connected to each hub, the first link connecting the coupling members of the first wheel set at its end remote from the axis of rotation.

5. An assembly according to claim 4, wherein the second link connects the engagement member of the second wheel set at its end remote from the axis of rotation.

6. The assembly of claim 4, wherein: the hub of one of the wheels of the second wheel set having a further member extending therefrom; the hub of the opposite one of the wheels of the first wheel set has a further member extending therefrom, the two further members being joined by a link.

7. The assembly of claim 3, wherein: at least one cross member is provided that extends between and is secured to the longitudinal members.

8. The assembly of claim 7, wherein: there are two cross members, one associated with the first wheel set and one associated with the second wheel set.

9. The assembly of claim 7, wherein: at least one of the cross members is a basket.

10. The assembly of claim 8, wherein: a body is provided that is attachable to the chassis and coupled to the first link at a first end of the chassis.