AU2021202859A1

AU2021202859A1 - Retractable wheel system

Info

Publication number: AU2021202859A1
Application number: AU2021202859A
Authority: AU
Inventors: Garry Richardson
Original assignee: Cahejo Pty Ltd
Current assignee: Cahejo Pty Ltd
Priority date: 2020-05-06
Filing date: 2021-05-05
Publication date: 2021-11-25

Abstract

A retractable wheel system for a towable apparatus comprises a wheel engageable with a ground surface and a yoke assembly that rotatably supports the wheel. The yoke assembly is pivotally attached to an articulated chassis frame of the towable apparatus to pivot under gravity between a retracted and a deployed configuration when the chassis frame moves between, respectively, a folded and an unfolded configuration. A coupling assembly is connected to the yoke assembly that forces the yoke assembly to pivot towards the deployed configuration such that the wheel engages the ground surface when a pulling force is exerted on a cable connected to the coupling assembly. The system also comprises an actuating mechanism comprising a lever pivotally attached to the chassis frame and an actuator for actuating the lever pivotally from a first position to a second position. The cable is connected to the lever such that the lever exerts the pulling force on the cable when the lever is actuated towards the second position. CNCNN 00C CDJ

Description

CNCNN

00C

CDJ RETRACTABLE WHEEL SYSTEM

Field

[0001]The present invention relates to agricultural equipment and, more particularly, to a retractable wheel system for towable agricultural equipment such as seeding bars and tillage machines.

Background

[0002] Various types of towable machinery and equipment are commonly used in agriculture to carry out work on farmland. For example, seeding bars are used to sow and plant seeds into soil across large paddocks. A seeding bar typically comprises a wide chassis frame that has a drawbar on its frontmost leading edge for connecting the seeding bar to a tractor or other towing vehicle. The chassis frame comprises a set of ground-engaging swivel caster wheels at its front leading edge and a set of fixed wheels at its rear trailing edge.

[0003] The chassis frame may be articulated and comprise a pair of wing frame assemblies that outwardly extend in opposed directions from the centre of the chassis frame. Each wing frame may comprise a set of frame sections hingedly joined together by pin joints. The joints enable the wing frames to be moved between folded and unfolded configurations by a set of hydraulic actuators mounted on the chassis. The wing frames are moved into their unfolded configurations when the seeding bar needs to be used on farmland. The wing frames are moved into their folded configurations when the seeding bar needs to be transported away from the farmland and/or stored in a hanger.

[0004] The wheels of a seeding bar are large and are connected to the wing frames of the chassis frame using structurally robust and heavy yoke assemblies that rotatably support the axles of the wheels. The yoke assemblies are typically pivotably attached to the wing frames such that the yoke assemblies, and therefore the wheels, pivot under gravity between retracted and deployed configurations when the wing frames move between their folded and unfolded configurations respectively. When the wing frames are unfolded and the wheels are deployed, the yoke assemblies must be held securely in place such the wheels hold the chassis frame above the ground surface. The wheels are subjected to powerful forces during use and if the yoke assemblies are not adequately secured, then they can pivot and cause the chassis frame, and any connected earth working tools, to sag towards the ground surface and become damaged. It is also advantageous if the yoke assemblies can be pivoted relative to the chassis frame by small amounts in a controlled manner when they are deployed. By doing this, the height that the chassis frame is suspended above the ground surface by the wheels can be adjusted along with any tines or similar earth working tools on the chassis frame.

[0005] Further, when the wing frames of known seeding bars are folded for storage, the wheels project outwardly away from the chassis frame which can cause the yokes to be subjected to substantial strain. The wheels also occupy a large amount of space which can present a hazard during transportation and make it difficult to store the seeding bar when space is limited.

[0006] It is to be understood that, if any prior art is referred to herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art, in Australia or any other country.

Summary

[0007] According to the present invention, there is provided retractable wheel system for a towable apparatus, comprising: a wheel engageable with a ground surface below the towable apparatus; a yoke assembly that rotatably supports the wheel, wherein the yoke assembly is pivotally attached to an articulated chassis frame of the towable apparatus and is configured to pivot under gravity between a retracted configuration and a deployed configuration when the chassis frame moves between, respectively, a folded and an unfolded configuration; a coupling assembly connected to the yoke assembly, wherein the coupling assembly is configured to force the yoke assembly to pivot towards the deployed configuration such that the wheel engages the ground surface to support the chassis frame above the ground surface when a pulling force is exerted on a cable connected to the coupling assembly; and an actuating mechanism provided on the chassis frame, wherein the actuating mechanism comprises a lever pivotally attached to the chassis frame and an actuator configured to actuate the lever pivotally from a first position to a second position, and wherein the cable is connected to the lever such that the lever exerts the pulling force on the cable when the lever is actuated towards the second position.

[0008] The actuator may comprise a hydraulic actuator.

[0009] The hydraulic actuator may be arranged such that the hydraulic actuator expands to actuate the lever into the second position.

[0010] The hydraulic actuator may be substantially vertically oriented relative to the chassis frame.

[0011] The cable may be connected indirectly to the lever via a bracket and crank arm arrangement disposed towards a base of the hydraulic cylinder.

[0012] The retractable wheel system may further comprise a damper configured to dampen movement of the yoke assembly when the yoke assembly pivots under gravity between the retracted and the deployed configuration.

[0013] The damper may comprise a hydraulic cylinderwith a piston rod connected between the yoke assembly and the chassis frame.

[0014] The yoke assembly may further comprise a tether that limits movement of the yoke assembly when the yoke assembly has pivoted under gravity fully into the deployed configuration.

[0015] The cable may extend along an axis of the chassis frame and the chassis frame may comprise one or more retainers for holding the cable in position.

[0016] The chassis frame may comprise a plurality of frame sections joined together in an articulated arrangement by a plurality of hinge joints, and the cable may be held by the retainers in an elevated position above the hinge joints.

[0017] Each of the retainers may comprise a laterally extending support member that limits movement of the cable away from the hinge joints.

[0018] The support member may be spaced apart from the chassis frame to accommodate movement of the cable relative to the support member when the cable is slack.

[0019] The support member may be spaced apart from the chassis frame by a distance that causes the cable to be held taught by the support member when the chassis frame moves into the folded configuration and the yoke assembly pivots into the retracted configuration.

[0020] The support member may comprise a cylinder having a longitudinal axis extending laterally across the cable.

[0021] The cylinder may comprise a roller that is rotatable about the longitudinal axis.

[0022] The roller may be rotatably supported by a pair of bracket arms, and the cable may extend through a space enclosed by the bracket arms and the roller.

[0023] The chassis frame may be elongated and the actuating mechanism may be mounted centrally along a longitudinal axis of the chassis frame.

[0024] The retainers may be arranged such that they hold the cable along the longitudinal axis of the chassis frame.

[0025] The present invention also provides a towable agricultural apparatus, comprising: an articulated chassis frame moveable between a folded configuration and an unfolded configuration; a plurality of wheels that are engageable with a ground surface below the towable agricultural apparatus; a plurality of yoke assemblies that rotatably support the wheels, wherein the yoke assemblies are pivotally attached to the chassis frame and are configured to pivot under gravity between retracted configurations and deployed configurations when the chassis frame moves between, respectively, the folded and the unfolded configuration; coupling assemblies connected to the yoke assemblies, wherein the coupling assemblies are configured to force the yoke assemblies to pivot towards the deployed configuration such that the wheels engage the ground surface to support the chassis frame above the ground surface when a pulling force is exerted on a cable connected to the coupling assemblies; and an actuating mechanism provided on the chassis frame, wherein the actuating mechanism comprises a lever pivotally attached to the chassis frame and an actuator configured to actuate the lever pivotally from a first position to a second position, and wherein the cable is connected to the lever such that the lever exerts the pulling force on the cable when the lever is actuated towards the second position.

[0026] The chassis frame may comprise a pair of wing frame assemblies outwardly extending from a centre of the chassis frame. The wheels, yoke assemblies and coupling assemblies may be arranged along the wing frame assemblies. The actuating mechanism may be disposed at the centre of the chassis frame and the towable apparatus may comprise a pair of cables that connect the actuating mechanism to the coupling assemblies.

[0027] Each of the wing frame assemblies may comprise a plurality of frame sections joined together in an articulated arrangement by a plurality of hinge joints. Each of the frame sections may comprise at least one of the wheels, yoke assemblies and coupling assemblies.

[0028] The present invention also provides a seeding bar, comprising: an articulated chassis frame moveable between a folded configuration and an unfolded configuration; a plurality of wheels that are engageable with a ground surface below the towable agricultural apparatus; a plurality of yoke assemblies that rotatably support the wheels, wherein the yoke assemblies are pivotally attached to the chassis frame and are configured to pivot under gravity between retracted configurations and deployed configurations when the chassis frame moves between, respectively, the folded and the unfolded configuration; coupling assemblies connected to the yoke assemblies, wherein the coupling assemblies are configured to force the yoke assemblies to pivot towards the deployed configuration such that the wheels engage the ground surface to support the chassis frame above the ground surface when a pulling force is exerted on a cable connected to the coupling assemblies; and an actuating mechanism provided on the chassis frame, wherein the actuating mechanism comprises a lever pivotally attached to the chassis frame and an actuator configured to actuate the lever pivotally from a first position to a second position, and wherein the cable is connected to the lever such that the lever exerts the pulling force on the cable when the lever is actuated towards the second position.

Brief Description of Drawings

[0029] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is an isometric front view of a seeding bar, wherein the seeding bar comprises a retractable wheel system according to an example embodiment of the invention; Figure 2 is an isometric elevated view of the seeding bar; Figure 3 is an isometric rear view of the seeding bar; Figure 4 is an isometric view of an outermost wing frame section of the chassis frame of the seeding bar; Figure 5 an isometric view of the wing frame section shown from the rear of the seeding bar; Figure 6 is an isometric view of an outermost retractable wheel of the wing frame section; Figure 7 is an isometric view of a set of cables and coupling assemblies that are connectable to retractable wheels of the system; Figure 8 is an enlarged isometric view of one of the cables; Figure 9 is a first enlarged isometric view of a hydraulic actuator of the system; Figure 10 is a further enlarged isometric view of the hydraulic actuator; and Figure 11 shows the seeding bar when the chassis frame is in a folded configuration.

Description of Embodiments

[0030] Referring to the Figures, an example embodiment of the present invention provides a retractable wheel system 10 for a towable apparatus 12. The system comprises a wheel 14 engageable with a ground surface below the towable apparatus 12. The system 10 also comprises a yoke assembly 16 that rotatably supports the wheel 14. The yoke assembly 16 is pivotally attached to an articulated chassis frame 18 of the towable apparatus 12 and is configured to pivot under gravity between a retracted configuration and a deployed configuration when the chassis frame 18 moves between, respectively, a folded configuration (see Figure 11) and an unfolded configuration (see Figure 1). The system 10 also comprises a coupling assembly 20 connected to the yoke assembly 16, wherein the coupling assembly 20 is configured to force the yoke assembly 16 to pivot towards the deployed configuration such that the wheel 14 engages the ground surface to support the chassis frame 18 above the ground surface when a pulling force is exerted on a cable 22 connected to the coupling assembly 20. The system also comprises an actuating mechanism provided on the chassis frame 18, wherein the actuating mechanism comprises a lever 56 pivotally attached to the chassis frame 18 and an actuator 24 configured to actuate the lever 56 pivotally from a first position to a second position. The cable 22 is connected to the lever 56 such that the lever 56 exerts the pulling force on the cable 22 when the lever 56 is actuated towards the second position.

[0031] More particularly, in the example depicted the towable apparatus 12 comprises a seeding bar of the type that is commonly towed by a tractor and used to plant seeds in farmland. The seeding bar 12 may comprise a plurality of the wheels 14 that are attached pivotally to leading and trailing edges of the chassis frame 18 by a plurality of the yoke assemblies 16. The wheels 14 on the leading edge may comprise swivel casters 26 and the wheels 14 on the trailing edge may comprise ordinary wheels 28 having axles that are held in a fixed orientation relative to the chassis frame 18. A drawbar 30 may be attached to the leading edge of the chassis frame 18 that is used to connect the seeding bar 12 to a tractor or other towing vehicle. The seeding bar 12 may also comprise a plurality of tines attached to the chassis frame 18 that press into the ground surface when the chassis frame 18 is positioned sufficiently close to the ground surface.

[0032] The chassis frame 18 may be elongated and comprise a centrally disposed frame section 32 that has a pair of outwardly extending wing frame assemblies 34, 36 connected thereto. The wing frame assemblies 34, 36 may each comprise a plurality of frame sections that are joined together in an articulated arrangement. As shown in Figure 4, the frame sections may be joined together by a plurality of hinge joints 38. The hinge joints 38 enable the frame sections to fold relative to one another about rotational axes 39 such that the chassis frame 18 can move between its folded and unfolded configuration. In Figures 1 to 3, the chassis frame 18 is shown in its unfolded configuration and the wing frame assemblies 34, 36 extend horizontally across the ground surface. In Figure 11, the chassis frame 18 is shown in its folded configuration and the wing frame assemblies 34, 36 are fully retracted.

[0033] Referring to Figure 6, the yoke assembly 16 of each retractable wheel 14 may comprise an uppermost and a lowermost support 40, 42 that are each hingedly connected by pin joints to an innermost subframe 44 connected to the chassis frame 18. The outermost ends of the supports 40, 42 may each be hingedly connected by pin joints to an outermost subframe 46. The outermost subframe 46 may extend vertically between the two supports 40, 42 substantially in parallel alignment with the innermost subframe 44. The axle of the wheel 14 may be rotatably attached to the outermost subframe 46 by a fork or similar bracket assembly attached to an underside of the outermost subframe 46.

[0034] The two subframes 44, 46 and supports 40, 42 together form a box-like structure that is quadrilateral-shaped in cross section. The relative configuration of the various pin joints allows the outermost subframe 46 to move up and down relative to the chassis frame 18 freely under gravity when the wing frame assembly 34 moves between its folded and unfolded configuration. By extension, it will be appreciated that the pin joints allow the wheel 14 to move under gravity between its retracted and deployed configuration.

[0035] The yoke assembly 16 may further comprise a short tether 48 that limits rotational movement of the two supports 40, 42 when the yoke assembly 16 has pivoted fully into its deployed configuration. The tether 48 may comprise a steel cable or chain connected between the supports 40, 42. When the supports 40, 42 have pivoted away from the chassis frame 18 by their maximum extent, the tether

48 is pulled into tension by the supports 40, 42 which limits their further rotational movement.

[0036] As most clearly shown in Figure 4, the yoke assembly 16 may further comprise a damper 50 configured to dampen movement of the yoke assembly 16 when it pivots between the retracted and deployed configuration. The damper 50 may comprise a hydraulic cylinder with a piston rod connected between the yoke assembly 16 and the chassis frame 18. The damper 50 may be configured such that when the yoke assembly 16 pivots under its own weight into the deployed configuration, the piston rod is pulled out from the hydraulic cylinder by the yoke assembly 16. Conversely, when the yoke assembly 16 pivots into the retracted configuration, the piston rod is pushed back into the hydraulic cylinder by the yoke assembly 16. The hydraulic fluid in the cylinder dampens and governs the movement of the yoke assembly 16.

[0037] The chassis frame 18 may comprise a pair of the cables 22 that extend from the actuating mechanism 24 outwardly along the two wing frame assemblies 34, 36. Referring to Figure 7, the cables 22 may comprise metal chains and the chassis frame 18 may comprise a set of retainers 52 that hold the chains 22 in position along the longitudinal axis of the chassis frame 18. The retainers 52 may be configured such that the chains 22 are held in an elevated position above the hinge joints 38 of the wing frame sections. More particularly, referring to Figure 8 the retainers 52 may comprise elongate support members 54 laterally extending across the chains 22 that limit movement of the chains 22 away from the hinge joints 38. Each support member 54 may comprise a cylindrical roller that is rotatable about an axle held by a pair of bracket arms. The chains 22 may extend through the retainers 52 via the space that is enclosed by the bracket arms and roller 54.

[0038] The rollers 54 may be spaced apart from the chassis frame 18 such that they accommodate movement of the chains 22 relative to the rollers 54 when the chains 22 go slack during use. Preferably, the rollers 54 are spaced apart from the chassis frame 18 by a distance that causes the chains 22 to be held taught by the rollers 54 when the chassis frame 18 moves into the folded configuration and the yoke assemblies 16 pivot into their retracted configurations.

[0039] Each coupling assembly 20 may comprise a pair of crank arms pivotally attached to the chassis frame 18. The crank arms 20 convert the pulling forces exerted on the chains 22 that act along the longitudinal axis of the chassis frame 18 into corresponding pulling forces acting laterally across the chassis frame 18 that pull the yoke assemblies 16 inwardly into the chassis frame 18. One of the two crank arms 20 may be connected directly to the relevant yoke assembly 16 that is positioned on the leading edge of the seeding bar 12. The other crank arm may be connected to a yoke assembly 16 positioned on the trailing edge of the seeding bar 12 via an elongate control rod 56. In this arrangement, the yoke assemblies 16 that are located on the leading edge of the seeding bar 12 pivot in an opposite direction to the yoke assemblies 16 located on the trailing edge of the seeding bar 12 when the chains 22 are pulled towards the centre 32 of the chassis frame 18 by the actuating mechanism 24. This advantageously allows the wheels 14 to be moved and controlled effectively by the actuating mechanism 24 and allows the wheels 14 to be stowed in a space efficient manner when the wing frame assemblies 34, 36 are folded.

[0040] Referring to Figures 9 and 10, the actuating mechanism 24 may be mounted centrally along a longitudinal axis of the chassis frame 18. The actuating mechanism 24 may be a hydraulic actuator comprising a vertically oriented hydraulic cylinder and piston rod. The hydraulic actuator 24 may be controlled using a user input device that is deployable in the driver's cab of a vehicle towing the seeding bar 12. The input device may be operatively connected to the hydraulic actuator 24 by a suitable wired or wireless communication means. The two end portions of the chains 22 may be attached to the piston rod of the hydraulic actuator 24 by a coupling mechanism 56 that causes the chains 22 to be pulled into tension when the piston rod is forced out of the hydraulic cylinder towards its second (raised) position, thus causing the actuator 24 to extend in length and go into compression. The coupling mechanism 56 may comprise a lever that has a first end 57 pivotally attached to a frame member section 58 positioned above the chassis frame 18. A second end 59 of the lever 56 may be pivotally attached to an end of the piston rod.

[0041] The chains 22 may be indirectly connected to the lever 56 via a bracket 60 arranged at a base of the hydraulic cylinder 24. The bracket 60 may comprise a pair of pivotally attached crank arms 62 (see Figure 8). The chains 22 may be connected to outermost ends of the crank arms 62. A pair of sub-chains 63 extending upwardly from uppermost ends of the crank arms 62 may be attached to a middle section of the lever 56. In this configuration, the chains 22 are pulled into tension by the crank arms 62 when the lever 56 is tilted upwardly by the piston rod moving into its raised position. Conversely, the tension in the chains 22 is released by the crank arms 62 when the lever 56 is tilted downwardly by the piston rod moving into its first (lowered) position.

[0042] The lever arrangement 56 of the actuating mechanism 24 provides a powerful means for tensioning the chains 22. Because the hydraulic cylinder and piston rod are vertically oriented, the actuating mechanism 24 is advantageously compact in size and occupies minimal space across the chassis frame 18. This efficient use of space allows other components and equipment to be attached to the chassis frame 18 with minimal interference and obstruction from the actuating mechanism 24. Further, it will be appreciated that a hydraulic actuator is generally more powerful when exerting a pushing force on its piston rod, than a pulling force. Because the hydraulic cylinder is arranged such that the piston rod provides a pushing force on the lever 56 to tension the chains 22, the actuating mechanism 24 is advantageously powerful and operationally efficient.

[0043] In use, the seeding bar 12 is connected to a tractor, or similar towing vehicle, using the drawbar 30. The articulated wing frame assemblies 34, 36 may then be extended from their deployed configurations into their unfolded configurations. This is performed by a set of laterally aligned hydraulic actuators 64 that are attached to each of the wing frame sections and the chassis frame 18. When the wing frame assemblies 34, 36 are unfolding, the weight of the yoke assemblies 16 and wheels 14 causes the yoke assemblies 16 to pivot towards the ground and into their deployed configurations under gravity. The dampers 50 operate to govern and dampen the pivotal movement of the yoke assemblies 16. The tethers 48 operate to stop further rotational movement of the supports 40, 42 of the yoke assemblies 16 when the yoke assemblies 16 have pivoted fully into their deployed configurations.

[0044] Initially, when the wing frame assemblies 34, 36 are unfolded, the chains 22 are held by the hydraulic actuator 24 in tension which causes the yoke assemblies 16 and wheels 14 to hold the chassis frame 18 suspended in an elevated position above the ground. This enables the seeding bar 12 to be pulled by the tractor into its starting position on the farmland without the tines of the seeding bar 12 engaging into the ground. When the seeding bar 12 is in the right position and orientation (for example, at the start of an A-B line on the farmland), the hydraulic actuator 24 releases the tension in the chains 22 by a small amount. This causes the chassis 18 to be lowered towards the ground and the tines to press into the soil. The seeding bar 12 may then be towed across the farmland by the tractor. The hydraulic actuator 24 maintains the tension in the chains 22 such that the wheels 14 are held securely in position and keep the chassis 18 supported above the ground surface at the desired height.

[0045] When the wing frame assemblies 34, 36 subsequently need to be retracted, the vertically oriented hydraulic actuator 24 releases the tension in the chains 22 causing them to go slack. The laterally aligned hydraulic actuators 64 are then activated such that they cause the wing frame sections to pivot relative to one another and move upwards. As the frame sections move, the weight of the wheels 14 and yoke assemblies 16 causes the yoke assemblies 16 to pivot towards the centre of the chassis frame 18, as shown in Figure 11. Eventually, the chains 22 are pulled taut by the yoke assemblies 16 which stops them from pivoting any further. The retainers 52 on the chassis frame 18 are positioned and dimensioned such that they cause the chains 22 to go taut when the yoke assemblies 16 are fully retracted.

[0046] The system 10 depicted in the Figures is shown being used on a seeding bar 12 but it will be appreciated that the system 10 may be used on other towable agricultural equipment. For example, the system 10 may be used to control pivotably wheels of tillage machines such as deep rippers.

[0047] For the purpose of this specification, the word "comprising" means "including but not limited to", and the word "comprises" has a corresponding meaning.

[0048] The above embodiments have been described by way of example only and modifications are possible within the scope of the claims that follow.

Claims

1. A retractable wheel system for a towable apparatus, comprising: a wheel engageable with a ground surface below the towable apparatus; a yoke assembly that rotatably supports the wheel, wherein the yoke assembly is pivotally attached to an articulated chassis frame of the towable apparatus and is configured to pivot under gravity between a retracted configuration and a deployed configuration when the chassis frame moves between, respectively, a folded and an unfolded configuration; a coupling assembly connected to the yoke assembly, wherein the coupling assembly is configured to force the yoke assembly to pivot towards the deployed configuration such that the wheel engages the ground surface to support the chassis frame above the ground surface when a pulling force is exerted on a cable connected to the coupling assembly; and an actuating mechanism provided on the chassis frame, wherein the actuating mechanism comprises a lever pivotally attached to the chassis frame and an actuator configured to actuate the lever pivotally from a first position to a second position, and wherein the cable is connected to the lever such that the lever exerts the pulling force on the cable when the lever is actuated towards the second position.

2. The retractable wheel system according to claim 1, wherein the actuator comprises a hydraulic actuator.

3. The retractable wheel system according to claim 2, wherein the hydraulic actuator is arranged such that the hydraulic actuator expands to actuate the lever into the second position.

4. The retractable wheel system according to claim 3, wherein the hydraulic actuator is substantially vertically oriented relative to the chassis frame.

5. The retractable wheel system according to any one of the preceding claims, wherein the cable is connected indirectly to the lever via a bracket and crank arm arrangement disposed towards a base of the hydraulic cylinder.

6. The retractable wheel system according to any one of the preceding claims, wherein the retractable wheel system further comprises a damper configured to dampen movement of the yoke assembly when the yoke assembly pivots under gravity between the retracted and the deployed configuration.

7. The retractable wheel system according to claim 6, wherein the damper comprises a hydraulic cylinder with a piston rod connected between the yoke assembly and the chassis frame.

8. The retractable wheel system according to any one of the preceding claims, wherein the yoke assembly further comprises a tether that limits movement of the yoke assembly when the yoke assembly has pivoted under gravity fully into the deployed configuration.

9. The retractable wheel system according to any one of the preceding claims, wherein the cable extends along an axis of the chassis frame and the chassis frame comprises one or more retainers for holding the cable in position.

10. The retractable wheel system according to claim 9, wherein the chassis frame comprises a plurality of frame sections joined together in an articulated arrangement by a plurality of hinge joints, and wherein the cable is held by the retainers in an elevated position above the hinge joints.

11. The retractable wheel system according to claim 10, wherein each of the retainers comprises a laterally extending support member that limits movement of the cable away from the hinge joints.

12. The retractable wheel system according to claim 11, wherein the support member is spaced apart from the chassis frame to accommodate movement of the cable relative to the support member when the cable is slack.

13. The retractable wheel system according to claim 12, wherein the support member is spaced apart from the chassis frame by a distance that causes the cable to be held taught by the support member when the chassis frame moves into the folded configuration and the yoke assembly pivots into the retracted configuration.

14. The retractable wheel system according to any one of claims 11 to 13, wherein the support member comprises a cylinder having a longitudinal axis extending laterally across the cable.

15. The retractable wheel system according to claim 14, wherein the cylinder comprises a roller that is rotatable about the longitudinal axis.

16. The retractable wheel system according to claim 15, wherein the roller is rotatably supported by a pair of bracket arms, and wherein the cable extends through a space enclosed by the bracket arms and the roller.

17. The retractable wheel system according to any one of claims 9 to 16, wherein the chassis frame is elongated and the actuating mechanism is mounted centrally along a longitudinal axis of the chassis frame.

18. The retractable wheel system according to claim 17, wherein the retainers are arranged such that they hold the cable along the longitudinal axis of the chassis frame.

19. A towable agricultural apparatus, comprising: an articulated chassis frame moveable between a folded configuration and an unfolded configuration; a plurality of wheels that are engageable with a ground surface below the towable agricultural apparatus; a plurality of yoke assemblies that rotatably support the wheels, wherein the yoke assemblies are pivotally attached to the chassis frame and are configured to pivot under gravity between retracted configurations and deployed configurations when the chassis frame moves between, respectively, the folded and the unfolded configuration; coupling assemblies connected to the yoke assemblies, wherein the coupling assemblies are configured to force the yoke assemblies to pivot towards the deployed configuration such that the wheels engage the ground surface to support the chassis frame above the ground surface when a pulling force is exerted on a cable connected to the coupling assemblies; and an actuating mechanism provided on the chassis frame, wherein the actuating mechanism comprises a lever pivotally attached to the chassis frame and an actuator configured to actuate the lever pivotally from a first position to a second position, and wherein the cable is connected to the lever such that the lever exerts the pulling force on the cable when the lever is actuated towards the second position.

20. The towable agricultural apparatus according to claim 19, wherein: the chassis frame comprises a pair of wing frame assemblies outwardly extending from a centre of the chassis frame; the wheels, yoke assemblies and coupling assemblies are arranged along the wing frame assemblies; and the actuating mechanism is disposed at the centre of the chassis frame and the towable apparatus comprises a pair of cables that connect the actuating mechanism to the coupling assemblies.

21. The towable agricultural apparatus according to claim 20, wherein each of the wing frame assemblies comprise a plurality of frame sections joined together in an articulated arrangement by a plurality of hinge joints, and wherein each of the frame sections comprises at least one of the wheels, yoke assemblies and coupling assemblies.

22. A seeding bar, comprising: an articulated chassis frame moveable between a folded configuration and an unfolded configuration; a plurality of wheels that are engageable with a ground surface below the towable agricultural apparatus; a plurality of yoke assemblies that rotatably support the wheels, wherein the yoke assemblies are pivotally attached to the chassis frame and are configured to pivot under gravity between retracted configurations and deployed configurations when the chassis frame moves between, respectively, the folded and the unfolded configuration; coupling assemblies connected to the yoke assemblies, wherein the coupling assemblies are configured to force the yoke assemblies to pivot towards the deployed configuration such that the wheels engage the ground surface to support the chassis frame above the ground surface when a pulling force is exerted on a cable connected to the coupling assemblies; and an actuating mechanism provided on the chassis frame, wherein the actuating mechanism comprises a lever pivotally attached to the chassis frame and an actuator configured to actuate the lever pivotally from a first position to a second position, and wherein the cable is connected to the lever such that the lever exerts the pulling force on the cable when the lever is actuated towards the second position.

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