FIELD OF INVENTION

This invention relates to a wheel arrangement for moving on uneven terrain. Specifically, the wheel arrangement may be used for non-driven and load bearing applications such as, but not limited to, a trolleys or carts.

BACKGROUND OF THE INVENTION

The wheel and axle is one of the six simple machines. It has undergone several adaptations for use in varying conditions, including that of negotiating uneven terrain. One disadvantage of the wheel is travelling over uneven terrain, shocks or bumps may be introduced thus making the ride less smooth. Another disadvantage is that when maneuvering over an obstacle such as a step of similar size order, it will experience significant impact force.

To combat these difficulties, one solution is to employ a three-wheel assembly, where each wheel is placed at the end of an arm extending from a central axle. As one of the three wheels contacts an obstacle, such as a step, the three wheel assembly rotates about the axle of the first wheel so as to place the next wheel close to or on the step. Further movement of the trolley therefore allows rotation about the axle of the second wheel until the second and third wheel are positioned on a horizontal surface allowing the trolley to move as before.

The motion in climbing the step is, therefore, a“clunking” discontinuous process as the three wheel assembly transitions from the step contacting stage, to the rotation of the second wheel to the top of the step. This is repeated for each step.

Further, unlike the larger wheels of a conventional trolley, the three-wheel assembly is essentially operating on three small wheels, with all the inherent difficulties smaller wheels provide when traversing rough terrain. In order for the three wheel assembly to climb a step, the arm must be long enough to provide sufficient clearance between the wheels, and so there is a balance between avoiding extraordinarily long arms and wheels of sufficient diameter to be completely unusable during normal operation. Consequently, apart from any benefit in climbing the step, the three wheel assembly is difficult to maneuver for the vast majority of its operation.

Further still, the three wheel assembly has two contact points at each side of the trolley cart which constrain the trolley movement along a straight line path. Hence, the user needs to exert a larger force to turn the trolley if he wants to change the trolley heading. The effort also increases with the load which is carried by the trolley.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a wheel arrangement for comprising: an outer wheel having an outer rolling surface for rolling across a terrain; an inner structure engaged with the outer wheel and arranged to move along an inner circumferential track of the outer wheel, such that the inner structure moves relative to the outer wheel; wherein the inner structure includes a load point for receiving an external load, said load point offset from a centre of the outer wheel, said external load including a weight applied to the load point and a force to initiate movement of the wheel arrangement.

In a second aspect, the invention provides a method for a wheel arrangement according to claim 1, to move over an obstacle, the method including the steps of: the outer wheel contacting the obstacle; applying a load to the load point of the inner structure to initiate movement over the obstacle, the inner structure moving relative to the outer wheel to re distribute the applied external load, and so; the inner structure applying a force to the outer wheel in a direction initiating movement over the obstacle, and; the outer wheel rolling over the obstacle.

The inner structure, being free to rotate within the outer wheel, redirects its momentum in a circular path by sliding along the rail within the outer wheel instead of coming to an abrupt stop due to the impact as a normal wheel would have. This potentially dampens the impact and reduces any shock being transmitted to and felt by the user’s hand. The wheel arrangement may be able to utilize a larger outer wheel diameter to smooth out bumps on an uneven or rough surface (e.g. gravel, bumpy surfaces).

The wheel arrangement may have the potential to provide a smoother motion path up a staircase, reducing the jerkiness felt by the user and consequently reducing the effort required for stair climbing with a portable shopping trolley.

The three wheel assembly may also facilitate smooth transitioning during stair-climbing. However, due to the nature of the three wheel assembly‘s design, it may experience a higher resistance when one tries to make a turn. This is due to the fact that such mechanisms always have 4 wheels on the ground and they constrain the motion to move along one direction.

BRIEF DESCRIPTION OF THE DRAWINGS

It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

Figures 1 is a schematic view of a trolley having a wheel arrangement according to one embodiment of the present invention;

Figures 2A to 2C are sequential elevation views of a wheel arrangement according to a further embodiment of the present invention;

Figures 3A and 3B are various views of a wheel arrangement according to a still further embodiment of the present invention;

Figures 4A to 4F are various views of a wheel arrangement according to a still further embodiment of the present invention;

Figures 5A to 5D are various views of a wheel arrangement according to a still further embodiment of the present invention; Figures 6A to 6C are various views of a wheel arrangement according to a still further embodiment of the present invention, and;

Figures 7A to 7C are various views of a wheel arrangement according to a still further embodiment of the present invention.

DETAILED DESCRIPTION

The core invention includes an outer wheel, having a rolling surface for rolling across the terrain. An inner structure is located within the inner wheel, and arranged to move relative to the outer wheel, such as rolling along an inner circumferential track of the outer wheel.

The inner structure including a load point arranged to receive an external load, such as an applied weight and a force to initiate movement of the wheel arrangement. For instance, in the case of a trolley, the weight to be carried by the trolley is directed to the load point. The trolley may also be pulled or pushed through this load point to initiate movement.

In one embodiment, the inner circumferential track of the outer wheel provides a smooth rolling path for the inner structure to travel. When the trolley is pulled on a normal flat terrain, the inner structure rolls within the outer wheel which, in turn, causes the outer wheel to roll on the terrain. When the outer wheel encounters an obstacle, for example, when it hits a small step, the inner structure continues to roll along the inner track of the outer wheel until the resulting position of the inner structure with respect to the outer wheel enables the outer wheel to rotate over the step. As such, the user will experience lower jerk when trying to pull the trolley on uneven terrain. Beside shopping cart or trolley, the concept can be applied to industrial domain for manual handling and transportation of heavy load in an environment with uneven terrain. It can also be applied to larger carriage which needs to be towed on uneven terrain by say a track vehicle.

Figures 1 and 2A to 2C, show the operation of the wheel arrangement, according to one embodiment. Figure 1 shows a trolley 100 having a load 106 fixed to a frame 108. The frame 108 is fixed to wheel arrangement 101 according to this embodiment, through a load point 112 of an inner structure, in this case an inner wheel 102, which is free to roll within an outer wheel 104.

As will be discussed below, a characteristic of the invention is demonstrated by the smooth travel path of the load point 113 as trolley 100 ascends the steps 110.

As shown in more detail in Figures 2A to 2C, the wheel arrangement 200 is shown at rest on a surface 206. As the inner wheel 204 is mounted to the load 224 in the trolley at the load point 208, whilst at rest, the load point of the inner wheel is directly below the centre 218 of the outer wheel 202.

As a force/load 220A is applied through the trolley frame 108, the wheel arrangement 200 commences motion 207. The inner wheel 204 is free to move relative to the outer wheel by rolling along the inner circumferential track within the outer wheel 202. As such, to balance the various forces, the outer wheel 202 moves to the right to due to a moment created. The moment is created due to the horizontal offset of the inner wheel load point 224 from the ground contact point of the outer wheel (need to add a label). It will be noted that the movement of the load point will follow a circular path 211 which is fixed with respect to the outer wheel 202.

On approaching a step 201, the outer wheel 202 first stops abruptly when it hits the step 201. The inner wheel 204 continues to travel within the outer wheel. The load point 208 of the inner wheel will continue to travel along the circular path 211 until it reaches a certain height where the outer wheel 202 will start to move upwards. When the whole wheel mechanism has risen to a particular height, it will start to rotate about the step comer 222 and eventually roll onto the step plane (label?).

Figures 3A and 3B show a further embodiment of the present invention. This embodiment is similar to that of Figures 1 and 2, in that the wheel arrangement 310 includes an inner structure, in this case an inner wheel 304, free to move/roll along an inner circumferential track 305. In this case, the inner circumferential track is not a flat annular surface, but includes inclined surfaces which are useful to facilitate self-alignment of the inner wheel within the outer wheel during operation. The inner wheel 304 includes a load point, in the form of an axle 308 which is mounted to the frame 310 of the trolley, and so arranged to support the load of the trolley. The inner wheel moves within a cavity 312 of the outer wheel 302. It will be noted that, in this embodiment, the fixed axle provides a lateral limit preventing radial movement of the inner wheel 304, so as to follow an annular path within the cavity 312.

Figures 4A to 4F show an alternative embodiment, whereby the inner structure is a sliding mechanism 440 arranged to move relative to the outer wheel 404 using a pair of rollers 446, 449. The inner circumferential track includes an annular cavity 406 having an annular opening 407. The rollers 446, 449 roll against first rolling surface 430 or second 432 rolling surfaces within the cavity 406 so as to position the sliding mechanism 440 as with the earlier embodiments. It will be appreciated that, whilst this embodiment engages the outer wheel using rollers, other low friction elements may be used for the inner structure to engage and slide with the outer wheel. Thus, the circumferential track may be a groove through which a sliding mechanism of the inner structure is engaged with.

The sliding mechanism comprises the pair of rollers 446, 449 mounted to a slide element 447 through axles 442, 443. The load point 444 to which the axle 450 of the trolley is attached, engages the slide element 447 so as to move along the annular opening 407.

The outer wheel 400, in which is located the circumferential track 406, can be reduced in size through the reduction in size of the sliding mechanism 440. In fact, the outer wheel 400 resembles a planar annular disc, with the track positioned between an inner 404 and outer 402 plate surface.

In a further embodiment, Figures 5A to 5C show a wheel arrangement 500 having an inner structure 508 positioned to fit within an outer wheel 502. The outer wheel includes a rolling surface 516 for rolling across the terrain. The inner structure includes three arms 504, 505, 520 projecting from a central core 509. A first arm 520 is directed upwards in the normal orientation, which aligns with the vertical axis of the load point array 510. The other two arms 504, 505 are inclined downwards on either side of the load point array 510. At the extreme end of each of the three arms is located a roller 518 which is arranged to roll along an inner circumferential track 501. In a further embodiment, to ensure the rollers remain in contact with the wheel, the inner circumferential track 501 may be profiled to include a circumferential projection to correspond with grooves in the rollers, such as that shown in Figure 7C. It will be appreciated that the reverse is also possible, whereby the rollers may have a circumferential projection arranged to engage with a circumferential groove in the track.

In a further embodiment, the arms 504, 505, 520 of the inner structure 508 may be retractable having a locking pin/hole 514. This allows the inner structure to be readily removed from the outer wheel for easy assembly or maintenance. It may also allow adjustment of the inner structure to fit with a larger or smaller diameter of outer wheel, and so make a single inner structure usable for a range of applications where the outer wheel diameter may vary.

Unlike the embodiments having an inner wheel, the inner structure 508 does not, itself, roll within the outer wheel 502. Instead, the inner structure 508 shifts its orientation through the relative movement between the inner structure and the outer wheel achieved through the rollers 518 rolling within the circumferential track. The shift in orientation will occur as the load is re-distributed through movement of the load point along the circular path 517, but once the applied loads reach an equilibrium state, the inner structure will maintain its relative position as the outer wheel rotates about it.

A further feature of this embodiment is the placement of the loading point. For the inner wheel embodiment, the offset of the load point from the centre of the outer wheel was achieved by selecting a diameter of the inner wheel, as the load point was inevitably the centre of the inner wheel. With the offset fixed for a fixed diameter, a wheel arrangement is formed for particular application without the ability for adjustment. For the current embodiment, because it is a structure that maintains a relatively constant relative position, the load point does not need to be at a centre of rotation of the inner structure. Taking advantage of this benefit, the current embodiment includes a load point array 510 having several load connection points for receiving the load 503 applied by the trolley: i) An inner position 511 closest to the outer wheel centre;

ii) An outer position 512, close to the rim of the outer wheel, and;

iii) An intermediate position 515.

The user/designed may therefore pre-determine a load connection to use as the load point, depending upon the application, with the inner position 511 more efficient for overall wheel movement on flat ground as it is closer to the conventional wheel, and the outer position 512 more useful in producing a smoother path over obstacles.

Figures 6A to 6C show a further embodiment of the wheel arrangement 600, which is similar in concept to that shown in Figure 5. Here the inner structure 641 includes five arms 642, 643, 645, 647, 649 extending from a central core 642. The arms 642, 643, 645, 647, 649 are also retractable so as to remove the inner structure from the outer wheel 648.

Having more arms/spokes provides better support for the inner structure 641 so that it is more difficult to dislodge from the outer wheel 648 in the event of impact. Thicker profiles may also be used for the parts to accommodate higher loads or impacts. In this 5-spoke embodiment, the inner structure 641 has a load point array 650 with seven load connections points for receiving a trolley shaft. Thus, this embodiment enables seven different offsets of the trolley shaft from the centre of the outer wheel. One of the load connection points 646 is positioned at the centre of the outer wheel 648. In this setting, the prototype wheel behaves like a normal wheel. As the axle mounting distance from the centre hole increases, the smoothening effect of the wheel mechanism is more pronounced especially when the cart is pull over uneven terrain. The load connection point 644, when used as a load point, therefore is arranged to provide the smoothest result on uneven terrain.

Figures 7A to 7C show a further embodiment of the present invention. Whilst the components are somewhat different from those of the previous embodiments, the fundamental function is the same.

The outer wheel is much the same as previous embodiments, particularly in providing a profiled inner circumferential track wheel 706 into which the rollers 712 fit through circumferential grooves 720.

One marked difference is the arrangement of the inner structure 704. In this embodiment, an annular ring is provided, with the rollers 712, 713, 715, 717, 719 mounted on axles 714 and placed uniformly about the peripheral edge. The rollers rolling along the circumferential trach 706 allow the inner structure 704 to move relative to the outer wheel, as with the previous embodiments. The inner structure further includes a load point 708 for receiving an applied load, such as from a trolley. In a further embodiment, it will be appreciated that several load points may also be included, and so a load point array, whilst not shown, may be equally applied for this embodiment.

The inner space 730 of the inner structure 704 allows for additional features to be added to the design (e.g. a number of trolley shaft holes, suspension system, etc).

In terms of manufacturing, it will be appreciated various embodiments of the present invention may involve the manufacture of separate components which are subsequently assembled. Alternatively, the outer wheel and inner structure may be manufactured as an entire unit using one or more additive manufacturing processes.