A wheel for use on a conveyance with differential steering and a conveyance with differential steering

Abstract

Wheels are described including: a hub portion which is arranged to rotate about an axis; a ground contacting region which surrounds the hub portion; the ground contacting region is formed from a number of segments; each of the segments normally adopts a home position and is arranged to move to either side of its home position with respect to the hub for a limited distance away from the home position along a path of travel in a direction which is substantially transverse to the circumference of the hub portion; the wheel further includes means for returning each of the segments to their home positions; and wherein an inner region of each segment is arranged to support the hub away from the surface of the ground and moves by sliding against the outside of the hub portion.

Description

[0001] A WHEEL FOR USE ON A CONVEYANCE WITH DIFFERENTIAL STEERING

[0002] AND A CONVEYANCE WITH DIFFERENHAL STEERING

[0003] Technical Field

[0004] The present invention relates to wheels which are particularly suitable for use on conveyances or vehicles with differential steering arrangements. Embodiments of the invention find particular application in use on motorised wheelchairs and other conveyances that may be used in locations where there is also foot traffic such as in public spaces, on footpaths, and inside buildings.

[0005] Background to the Invention

[0006] Differential steering is the means of steering a land vehicle by applying more drive torque to one side of the vehicle than the other. The advantage of differential steering is its mechanical simplicity, which allows for vehicles that are highly robust. Differential steering is the primary means of steering tracked vehicles, such as tanks and bulldozers, and is also used in certain wheeled vehicles commonly known as skid-steer vehicles.

[0007] In a skid steer wheeled vehicle, the wheels are typically fixed in their orientation and are always aligned with the forwards direction of travel of the vehicle. When performing a turn, by applying more torque to some wheels than others, one or more of the wheels will “skid” across the surface over which the vehicle is travelling.

[0008] The skidding of the wheels (or tracks) makes these types of vehicles most suitable for use on loose ground, such as travelling on soil, sand or other loose ground. When used on hard surfaces then the wheels or tracks may be subjected to high wear rates. In addition, damage can be done by the wheels or tracks to the surface over which the vehicle or conveyance is travelling. Furthermore, skidding is an inefficient method of turning and results in energy loss. It has been tried to address the above problem of skidding by using so called “omni-directional” wheels, such as omniwheels or mecanum wheels. These wheels have transverse rollers provided about their peripheries. However, such arrangement can make a vehicle difficult to control on a sloped surface because the vehicle can slide uncontrollably in a transverse direction down the slope. In addition, the load bearing ability of these types of wheels is limited by the strength of the axles of the transverse rollers. So, in order to carry a high load, very large wheels must be used to accommodate rollers and axles of adequate strength, which in some applications necessitates the use of wheels of an impracticably large size.

[0009] There remains a need to provide improved arrangements for differential steering in vehicles and conveyances.

[0010] Summary of the Invention

[0011] In a first aspect the invention provides a wheel including: a hub portion which is arranged to rotate about an axis; a ground contacting region which surrounds the hub portion; the ground contacting region is formed from a number of segments; each of the segments normally adopts a home position and is arranged to move to either side of its home position with respect to the hub for a limited distance away from the home position along a path of travel in a direction which is substantially transverse to the circumference of the hub portion; the wheel further includes means for returning each of the segments to their home positions; and wherein an inner region of each segment is arranged to support the hub away from the surface of the ground and moves by sliding against the outside of the hub portion.

[0012] Each segment may be arranged to move by rotating about a region of the hub portion.

[0013] Each segment may be arranged to move laterally in relation to the hub portion.

[0014] The path of travel of each segment may be limited by regions of each segment abutting against the hub portion. The inside of each segment may conform with the outside of the hub portion.

[0015] The hub portion may include a series of projections which are interleaved with the segments; the projections guide the transverse movement of the segments and support the segments in a direction around the circumference of the hub portion during braking and acceleration.

[0016] The means for returning each of the segments to their home position may be in the form of a biasing means.

[0017] The biasing means may be magnetic.

[0018] Each segment may include at least one region of resilient material and the biasing means is effected by elastic deformation of the resilient material.

[0019] The segments may be snap fitted to the hub portion.

[0020] The segments may engage with a guide as the means to return them to their home position.

[0021] The guide may be provided on the inside of a cowl which partially surrounds the wheel.

[0022] In a second aspect the invention provides a conveyance including ground contacting wheels, wherein at least one of the wheels is in accordance with the first aspect of the invention.

[0023] Brief Description of the Drawings

[0024] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a wheel;

[0025] Figure 2 is a side view of the wheel of figure 1;

[0026] Figure 3 is a front view of the wheel of figure 1;

[0027] Figure 4 is a vertical cross sectional view through the view of figure 3;

[0028] Figure 5 is a side view of the hub portion of the wheel of figure 1;

[0029] Figure 6 is a front view of the hub portion of figure 5;

[0030] Figure 7 is a cross sectional view through the line A-A of figure 5;

[0031] Figure 8 is a cross sectional view through the line B-B of figure 5;

[0032] Figure 9 is an underside perspective view of a motorised wheelchair;

[0033] Figure 10 is a schematic view illustrating differential steering being used to effect a left hand turn in the wheelchair of figure 9;

[0034] Figure 11 is a cross sectional view similar to figure 4 during a left hand turn;

[0035] Figure 12 is a cross sectional view similar to figure 4 during a right hand turn;

[0036] Figure 13 is a cross sectional view of another embodiment of a wheel during a right hand turn;

[0037] Figure 14 is a cross sectional view of another embodiment of a wheel;

[0038] Figure 15 is cross sectional view of another embodiment of a wheel;

[0039] Figure 16 is a side view of another embodiment of a wheel; Figure 17 is a cross sectional view along the line A of figure 16;

[0040] Figure 18 is an underside perspective view of the cowl of the wheel of figure 16;

[0041] Figure 19 is a side cross sectional view through the cowl of figure 18;

[0042] Figure 20 is a perspective view of another embodiment of a wheel;

[0043] Figure 21 is a side view of the wheel of figure 20;

[0044] Figure 22 is a cross sectional view along the line A of figure 21;

[0045] Figure 23 is a perspective view of the hub of the wheel of figure 20;

[0046] Figure 24 is an upper perspective view of one of the segments from the wheel of figure 20;

[0047] Figure 25 is an alternative perspective view of the segment of figure 24; and

[0048] Figure 26 shows an alternative version of segment which can be used in the wheel of figure 20.

[0049] Detailed Description of the Preferred Embodiment

[0050] Referring to figures 1 to 4, a wheel 10 is shown including a hub portion which includes a stainless steel hub member 20. Hub member 20 is arranged to attach in use to an axle 100 (see fig 4) by way of keyed aperture 21 and to rotate on the axle about a central axis.

[0051] A ground contacting region formed from a number of segments 30 surrounds the hub member 20. The segments bear against the ground in use as indicated by the ground surface A in the figures.

[0052] As best seen in figure 4, each of the segments is formed from a nylon circlip body 32. A region of rubber tread 34 is bonded to the outside of the circlip 32 and a magnet 36 is embedded inside the circlip. The circlip 32 is snap fitted around the hub member 20.

[0053] The outer region 23 of the hub member 20 is generally in the shape of a torus. The inside surface of each segment 30 conforms with the outside surface of the hub member 22. Magnets 26 are fitted into the hub member 20 and covered by a protective sheath 28. The magnets 26 are oriented to attract the corresponding magnet 36 in each of the segments 30. That is, the North pole of one magnet pair faces towards the South pole of the other magnet in the pair.

[0054] Each of the segments 30 are free to move by rotating with respect to the hub member 20 for a limited distance in a direction which is substantially transverse to the circumference of the hub portion along a path of travel that curves around the hub portion. The attraction of the magnets 26 and 36 biases each segment to a centred home position as seen in figure 4. Each segment can rotate to either side of its home position during use if the biasing force of the magnets 26, 36 is overcome as will be later described.

[0055] Hub member 20 includes a number of projections in the form of paddles 40 which are interleaved with the segments 30 and which bear against and support the segments 30 in use during braking and acceleration.

[0056] Referring now to figures 5 to 8, hub member 20 is shown in isolation. Hub member 20 is formed in one piece by casting from austenitic stainless steel. Apertures 29 are provided in the hub member for receiving the magnets 26 and sheaths 28. Paddles 40 are integrally formed with the hub member. Transverse channels 41 are formed between the paddles which support and guide the movement of the segments.

[0057] Operation of wheel 10 will now be described with reference to an example of a motorised wheelchair using the wheels 10. This example refers to the motorised wheelchair described and illustrated in applicant’s earlier international patent application PCT / AU2018 / 051065, the entire contents of which are incorporated herein by reference.

[0058] Referring to figure 9, a motorised wheelchair 50 is shown in which the wheels A, B, C, D are of the type of wheel 10 described above. Wheels A, B, C, D are attached to the wheelchair 50 so that they are aligned facing the normal forwards direction of travel.

[0059] Referring to figure 10, the wheelchair 50 is steered using a differential steering arrangement. In the diagram, the wheelchair is shown executing a turn to the left. To effect a turn to the left, the wheels A and C are driven at a higher torque than the wheels B and D. The torque applied to each wheel is represented by the length of the arrow associated with each wheel. The application of greater torque to wheels A and C causes the wheelchair to travel in the direction indicated by the dotted arrow, to effect a left hand turn.

[0060] Referring to figure 11, during the turn, sideways forces between the road and the wheel overcome the biasing force of the magnets 26, 36 and the segments of the wheel 30 slide sideways during their period of contact with the ground by rotating away from the home position. In figure 11, the segment 30 currently in contact with the ground has rotated to the limit of its arc of travel, where the end 39 of the segment 30 abuts the hub member 20.

[0061] As the wheel continues to rotate, the next segment will contact the ground. It can then also slide sideways to accommodate the turning of the vehicle to avoid any scrubbing or skidding of the wheel across the ground. When a segment that was in touch with the ground comes out of contact with the ground due to continued rotation of the wheel then the magnetic biasing arrangement pulls the segment back to its home position (as shown by segment 30a) ready for the continued revolution of the wheel for when they next touch the ground. As the wheel rotates each segment oscillates in sequence like a wave. Figure 12 illustrates the wheel 10 during a corresponding right hand turn. The segments rotate in the opposite direction.

[0062] During some turns, the segments will not rotate through the entire arc of their freedom or movement. The extent of rotation of the segments depends upon how tight the turn is which is being made, as well as the current speed and acceleration / deceleration of the of the vehicle, and the direction and extent of any incline in the ground over which the vehicle is travelling.

[0063] The arrangement provides stabilisation of the segments by means of a “sandwiching” effect that prevents the segments from inadvertently popping out from between the paddles. The segments, which partly interleave with the hub’s paddles and partly jut out to separate the hub from the ground, become sandwiched between the hub and the ground at the moment the paddles push on the segments to generate propulsion.

[0064] The arrangement does not involve the use of axles and rollers around the periphery, as seen in omni -wheels. The arrangement allows the segments to transmit weight to the ground directly, thereby avoiding types of axle and roller failure that may occur in omni -wheels.

[0065] The arrangement described above enables the wheel to better maintain its “contact patch” with the ground during turns, as the vehicle turns. It also results in less scrubbing of the wheels against the ground as compared with traditional wheels and this in turn reduces the risk of damage to the ground over which the vehicle is travelling. Furthermore, when oriented sideways to an inclined slope, the vehicle cannot roll sideways for an uncontrolled distance.

[0066] Referring to figure 13, a modified version of wheel 10’ is shown performing a right hand turn. This wheel differs from wheel 10 in that pairs of magnets 26a, 26b, 36a, 36b are provided in the hub and segments respectively. The pairs of magnets are again oriented so that they attract one another (North pole facing South pole) however in this embodiment the magnet 36b is provided in an opposite polarity to magnet 36a. So, for example, if magnet 36a had its North pole facing inwardly towards the hub and magnet 26a then magnet 36b would be oriented so that its South pole was facing inwardly. The attractive force between the pairs of magnets is thus augmented by a repelling force when the segment is moved away from its home position. In the lower portion of the wheel of figure 13, magnet 36a is attracted towards magnet 26a and magnet 36b is attracted towards magnet 26b. As well, magnet 36b is repelled by magnet 26a, which adds to the magnetic force biasing the segment to its home position.

[0067] Referring to figure 14, another embodiment of a wheel 110 is shown. This embodiment differs from the embodiment described above in that the segments include at least one region of resilient material and the biasing means is effected by elastic deformation of the resilient material.

[0068] Wheel 110 includes a hub member 120. This hub member differs from the one described above in that the recesses provided around the hub member do not house magnets. The stiff nylon segments are replaced by segments 130 which are formed entirely from a resilient rubber material. Each segment 130 is attached to the hub 120 by an internally located clamp member 129 which is secured in place by a hex head screw 128 which serves to clamp the ends of the associated segment 130 to secure it in place.

[0069] The hub 120 has a smooth outer surface and may for example be formed from polished stainless steel. A slippery coating such as grease or Teflon is applied to the inside surface of each segment 130.

[0070] Referring to the lower part of the wheel 130, lateral forces between the ground surface and the segment 130 which are experienced during a turn cause elastic deformation of the segment which causes it to slide around the hub 120 during the period that the segment is in contact with the ground. The region to the side of the wheel in the area of arrow E is stretched and the region in the area of arrow F is compressed. The deformation of the segment accommodates relative movement between the wheel and the ground which would otherwise result in the skidding of the wheel. As the wheel rotates further, and the segment comes away from contacting the ground, the compressed and stretched regions returns to their original forms in which forces in the segment on either side of the wheel are balanced. In this way, the segments are biased to a central resting position, and are able to move away from that position to either side of the wheel.

[0071] Wheel 110 is otherwise identical in operation to wheel 10 and also uses the supporting paddles in the same manner as wheel 10, although these are not visible in figure 14.

[0072] Referring to figure 15, another embodiment of wheel 210 is shown. Wheel 210 differs from wheel 110 in that the segments 130 are attached to the hub of the wheel by way of snap fit inserts 229. The inserts 229 are arranged to snip fit about tapered regions 221 of hub member 220. The segments 130 slide about the outer surface of the inserts 229. In figure 15, paddles 240 can be seen in dotted outline which guide the transverse movement of the segments and support the segments in use during braking and acceleration.

[0073] Referring to figures 16 to 19, another embodiment of a wheel 310 is shown. This embodiment differs from the wheel 10 in that the magnetic means for returning the segments to their home positions is replaced by an arrangement of guide formations which are provided inside a cowl 320 which engage with projections 322 provided on the segments 330 to return the segments to their home positions.

[0074] As best seen in figures 18 and 19, cowl 320 includes an inner guide formation 326 and an outer guide formation 324 which take the form of raised surface regions inside the cowl. Together, the guide formations 326, 324 define a depressed region 328 which is located between the guide formations.

[0075] As wheel rotates, when each segment 330 makes contact with the ground it may become displaced to either side of its home position, depending upon whether the vehicle is currently executing a left or right hand turn, to accommodate lateral movement between the wheel and the ground surface. However, as the wheel continues to rotate, when the segment leaves the ground it does not immediately spring back to its home position. Instead, the segment is guided by the guide formations 324, 326 as it revolves inside the cowl wherein the guide formations 324, 326 engage with the projections 322 on the segment to move the segment back to its home location. When a segment has rotated by 180 degrees its projections will be located at the region A indicated in figure 19 at which point the segment will have been returned to its home position.

[0076] Referring to figures 20 to 25, another embodiment of a wheel 410 is shown which includes a series of segments 430 which are snap fitted to a hub 420. In this embodiment, the biasing of the segments to their home position is effected by the segments themselves being formed from a resilient material which causes the segments to spring back to their home positions after they come away from contact with the ground.

[0077] Referring to figure 22, the segments 430 includes a moulded body 431 which is formed from a resilient, springy material such as Nylon or low friction TPU formulations. Each segment 430 further includes a ground contacting region 436 which is overmoulded onto the body 431 and which is formed from a relatively soft material such as Polyurethane to provide high friction and grip with the ground surface.

[0078] The body 431 includes two deformable arms 438 which have bulbous end regions 432 which a snap fit into grooves 422 provided on either side of hub 420 to retain the segments 430 on the hub 420. The body 431 of each of the segments 430 includes a moulded rib 434 which serves the dual purpose of adding rigidity to the ground contacting region of the segment and also locates, and is able to slide from side to side in, an associated transverse channel 441 which is formed between the paddle regions 440 of the hub (see figure 23). The hub 420 is formed from a material such as Nylon or Acetal to provide a low friction sliding interface between the outside of the hub 420 and the inside of the segment 430. Such an arrangement does not require any lubrication. As shown in the lower part of figure 22, as wheel 410 rotates the outer region of the hub 420 rests on the inside face of the ground contacting region of each segments to support the hub 420 away from the surface of the ground. The segments 430 are able to slide from side to side with respect to the hub 420 when in contact with the ground to accommodate lateral movement between the hub 420 and the ground during a turning operation to the left or the right. During the movement of the segment the arms 438 become elastically deformed. As wheel 410 continues to rotate and a segment 430 comes away from contact with the ground then the segment springs back to its original shape and therefore resumes its original centrally disposed home position.

[0079] Referring to figure 26, a modified version of a segment 430a is shown which can be used in the wheel 410. In this version, the body 43 la has been modified to provide stop regions 435 at either end of rib 434a. The stop regions abut against the hub to limit the extent of lateral movement of the segment to prevent damage to the arms 438.

[0080] Although the embodiments described above were described in relation to a motorised wheelchair, wheels according to the invention could be used on other types of vehicles or conveyances such as mobility scooters, motorised trolleys and various types of mobile robots, such as surveillance robots, delivery robots, toy robots, cleaning robots, home assistant robots and the like.

[0081] Embodiments of the invention are suitable for use in vehicles which employ rocker-bogies which usually employ skid-steering and hence can be difficult to steer.

[0082] Although the embodiment above described a wheel which attaches to a driven axle, the invention could also be applied to a so-called hub motor, wherein a drive motor is integrated into the wheel.

[0083] In conjunction with application of the invention, the hub itself may be engineered with characteristics to damp vibration and absorb shock.

[0084] Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated.

[0085] Finally, it is to be appreciated that various alterations or additions may be made to the parts previously described without departing from the spirit or ambit of the present invention.

Claims

CLAIMS:

1. A wheel including : a hub portion which is arranged to rotate about an axis; a ground contacting region which surrounds the hub portion; the ground contacting region is formed from a number of segments; each of the segments normally adopts a home position and is arranged to move to either side of its home position with respect to the hub for a limited distance away from the home position along a path of travel in a direction which is substantially transverse to the circumference of the hub portion; the wheel further includes means for returning each of the segments to their home positions; and wherein an inner region of each segment is arranged to support the hub away from the surface of the ground and moves by sliding against the outside of the hub portion.

2. A wheel according to claim 1 wherein each segment is arranged to move by rotating about a region of the hub portion.

3. A wheel according to any preceding claim wherein each segment is arranged to move laterally in relation to the hub portion.

4. A wheel according to any preceding claim wherein the path of travel of each segment is limited by regions of each segment abutting against the hub portion.

5. A wheel according to any preceding claim wherein the inside of each segment conforms with the outside of the hub portion.

6. A wheel according to any preceding claim wherein the hub portion includes a series of projections which are interleaved with the segments; the projections guide the transverse movement of the segments and support the segments in a direction around the circumference of the hub portion during braking and acceleration.

7. A wheel according to any preceding claim wherein the means for returning each of the segments to their home position is in the form of a biasing means.

8. A wheel according to claim 7 wherein the biasing means is magnetic.

9. A wheel according to claim 7 wherein each segment includes at least one region of resilient material and the biasing means is effected by elasticdeformation of the resilient material.

10. A wheel according to any preceding claim wherein the segments are snap fitted to the hub portion.

11. A wheel according to any preceding claim wherein the segments engage with a guide as the means to return them to their home position.

12. A wheel according to claim 11 wherein the guide is provided on the inside of a cowl which partially surrounds the wheel.

13. A conveyance including ground contacting wheels, wherein at least one of the wheels is in accordance with any one of claims 1 to 12.

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