[0001] The present invention relates to a tandem wheel assembly for a trailer and more particularly to a suspension system thereof.

[0002] Trailers having two wheels on each side of the trailer are known as tandem wheel trailers. These trailers are more maneuverable on sealed roads and can handle more weight than trailers with only one wheel on each side. However, the applicant has noted that the wheels of tandem wheel trailers can become unbalanced when used over undulating terrain and consequently are less stable and further are more prone to wear and damage.

[0003] According to a first aspect of the present invention there is provided a tandem wheel assembly for mounting to a trailer, comprising a support for mounting to structure of the trailer, the support carrying a pair of tandem wheels via swing arm assemblies which permit each wheel to pivot relative to the support in a vertical plane, a suspension arm associated with the pair of tandem wheels, the suspension arm being pivotally attached to the support for pivotal movement in a vertical plane extending transversely to the axes of the wheels, opposite end portions of the arm being linked to a respective one of the swing arm assemblies of the pair of wheels, the linkage of at least one of the end portions to its associated swing arm assembly including at least one suspension element.

[0004] According to a second aspect of the present invention, there is provided a tandem wheel assembly for mounting to a trailer, comprising a main beam for mounting to structure of the trailer to extend transversely to the longitudinal axis of the trailer, the beam carrying opposite pairs of tandem wheels via swing arm assemblies which permit each wheel to pivot relative to the beam in a vertical plane, a suspension arm associated with each pair of tandem wheels, the suspension arm being pivotally attached to the main beam transversely to the axis of the beam for pivotal movement in a vertical plane, opposite end portions of the arm being linked to a respective one of the swing arm assemblies of the associated pair of wheels, the linkage of at least one of the end portions to its associated swing arm assembly including at least one suspension element.

[0005] Preferably, the at least one suspension element is a coil spring.

[0006] Preferably, the at least one suspension element is an air spring.

[0007] According to an embodiment, a linkage of the other end portion of the suspension arm and associated swing arm assembly is configured to provide a levering action.

[0008] According to an embodiment, the other end portion of the suspension arm and associated swing arm assembly is constrained to limit separation thereof.

[0009] According to an embodiment, the constraint to limit separation is provided by a loop extending from the swing arm assembly, the loop being adapted to receive the associated end portion of the suspension arm.

[0010] According to an embodiment, the retaining element has a dampening element at a connection point between the other end portion of the suspension arm and associated swing arm assembly.

[0011] According to an embodiment, the linkage at the other end portion of the suspension arm includes at least one suspension element. Preferably, that suspension element is a coil spring.

[0012] Preferably, the coil spring(s) progressively changes in overall external diameter from an end adjacent the respective end of the suspension arm and an end adjacent the associated swing arm assembly.

[0013] According to an embodiment, the swing arm assemblies are mounted below the suspension arm. [0014] According to an embodiment, the end portions of each swing arm assemblies adjacent to the support/main beam are constrained to limit downward movement of each swing arm assemblies.

[0015] Preferably, the constraint to limit downward movement of each swing arm assemblies is provided by a stop arm pivotally attached to the support/main beam and extending transverse thereto, opposite end portions of the stop arm being arranged under each respective swing arm assembly of the associated pair of tandem wheels.

[0016] According to an embodiment, the swing arm assemblies are mounted above the suspension arm.

[0017] The present invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0018] Figure 1 is a perspective view of a tandem wheel assembly mounted to a trailer according to an embodiment of the present invention;

[0019] Figures 2 to 4 are front, perspective and side views of the tandem wheel assembly of Figure 1;

[0020] Figure 5 is a schematic representation of a vertical cross-section of the assembly of Figures 1 to 4;

[0021] Figure 6 is a perspective view of a tandem wheel assembly according to a further embodiment of the invention;

[0022] Figure 7 is a top view of a pair of tandem wheel assemblies of Figure 6, carried on end portions of a beam;

[0023] Figure 8 is a schematic view of the tandem wheel assembly of Figures 6 and 7; [0024] Figure 9 is a schematic view of a tandem wheel assembly according to another embodiment of the invention; and

[0025] Figure 10 is a schematic view of a tandem wheel assembly according to a yet another embodiment of the invention.

[0026] Figures 2 to 10 are various views of a tandem wheel assembly 2, 18, 40 according to preferred embodiments of the present invention which is intended for mounting to a trailer 4. The trailer can be a caravan or any other kind of load-carrying trailer such as a camper, car or a boat trailer as exemplified in Figure 1.

[0027] The tandem wheel assembly 2, 18, 40 has a support 6, 20, 42 which is to be attached to the chassis or structure, such as opposite sides of a frame of the trailer 4. The assembly 2, 18, 40 includes pairs of tandem wheels 8, 22, 44 carried by the support 6, 20, 42 via swing arm assemblies 10, 24, 46 which permit each wheel 8, 22, 44 to pivot relative to the support 6, 20, 42 in a vertical plane. Figures 2 to 4, 6 and 7 are views of the tandem wheel assembly 2, 18 wherein the support 6, 20 is configured as a main beam 6, 20, which extends transversely to the longitudinal axis of the trailer 4 and where each opposing end portion of the beam 6, 20 carries a pair of tandem wheels 8, 22 via the associated swing arm assemblies 10, 24.

[0028] The assembly 2, 18, 40 also has a suspension arm 12, 26, 48 associated with each pair of tandem wheels 8, 22, 44. The suspension arm 12, 26, 48 is pivotally attached to the support 6, 20, 42 allowing pivotal movement of the arm 12, 26, 48 relative to the support 6, 20, 42 in a vertical plane extending transversely to the axes of the wheels 8, 22, 44. If the support 6, 20, 42 is configured as a main beam 6, 20, 42, as shown in the Figures, then the pivotal movement can be in a vertical plane extending transversely to the axis of the main beam 6, 20, 42.

[0029] As exemplified in Figures 2 to 5, each end portion of the arm 12 is linked to a swing arm assembly 10 of the pair of wheels 8 by a suspension element 14, illustrated in Figures 2 to 5 as a coil spring, which acts to absorb the shock experienced by its associated wheel 8. The assembly 2 also has a pair of shock absorbers 15 which act to absorb the impact and rebound of the coil springs 14, each shock absorber 15 being located within each coil spring 14, as illustrated in Figures 2 to 5, and acting between the suspension arm 12 and associated swing arm assembly 10.

[0030] The coil spring 14 has a uniform pitch or coil spacing and is formed of a coiled wire with a constant diameter. The coil spring 14 has an external coil diameter which is constant over its length. Alternatively, the coil spring 14 can have an external coil diameter which progressively reduces from one end to the other such that the coil spring 14 has an overall conical shape. Such a coil spring 14 provides a progressive deflection rate such that the coil spring 14 deflects readily under a light load but has an increased resistance for heavier loads. It can be appreciated that any other coil spring described in further embodiments of the invention may also have an external coil diameter which progressively reduces from one end to the other such that the coil spring has an overall conical shape.

[0031] In alternative embodiments of tandem wheel assemblies 18, the combination of an end portion of the suspension arm 26 and its associated swing arm assembly 24 is configured as will be described below to engage so as to provide a levering action 30 as exemplified in Figures 6 to 9, which allows pivotal movement in the vertical plane. The other end portion of the suspension arm 26 has a linkage including a suspension element 28, 36, exemplified in Figure 8 as an air spring 28 and in Figure 9 as a spring coil 36. It can be appreciated that this suspension element 28, 36 provides the primary suspension effect in these tandem wheel assemblies 18. In these assemblies 18, there is also provided shock absorbers 29, 37 which absorb the impact and rebound of each suspension element 28, 36, each shock absorber 29, 37 acting between the suspension arm 26 and associated swing arm assembly 24.

[0032] With reference to Figures 6 to 9, the tandem wheel assembly 18 also includes, at the end portion of the suspension arm 26 remote from the suspension element 28, 36, a retaining element 32 for limiting the separation between the end portion of the suspension arm 26 and associated swing arm assembly 24. The retaining element 32 is in the form of a loop which extends generally transverse from the swing arm assembly 24, the end portion of the suspension arm 26 being received in the loop. The assembly 18 also has a dampening member 34 at the retaining element 32, illustrated in Figure 8 and 9 in the form of a portion of elastic material for example rubber, which acts to dampen shock associated with contacts between the end portion of the suspension arm 26 and associated swing arm assembly 24 at the connection point thereof.

[0033] Figure 10 shows an alternative tandem wheel assembly 40 where the suspension arm 48 is located below the support 42 rather than above it, and the pair of tandem wheels 44 are carried by the support 42 via swing arm assemblies 46, permitting each wheel 44 to pivot relative to the support 42 in a vertical plane above the suspension arm 48, rather than below as illustrated in the exemplary embodiments of Figures 1 to 9. The linkages shown at either end portion of the suspension arm 48 and its associated swing arm assemblies 46 are coil springs however it can be appreciated that the tandem wheel assemblies can have combinations of suspension elements and/or levers, for example, a coil spring and a lever, or an air spring with a lever, or two air springs.

[0034] In this example shown in Figure 10, the linkages include suspension elements 50 exemplified as coil springs, which are mounted on the end portions of supports 52 which extend vertically and generally transverse to the suspension arm 48 at opposing end portions thereof. The lower end of each suspension element 50 is connected to an associated swing arm assembly 46 which is slidable along the support 52 thereby compressing and extending the suspension element 50 as the vertical separation between the wheels 44 of each pair changes.

[0035] During operation of the assembly 2, 18, 40 the vertical separation between the wheels 8, 22, 44 in each pair change in response to any undulating terrain such that the swing arm assemblies 10, 24, 46 will pivot independently about the support 6, 20, 42. Therefore, the shock absorption action of each wheel 8, 22, 44 is isolated from each other in each pair of tandem wheels 8, 22, 44. The linkages at the opposite ends of the suspension arm 12, 26, 48 whether configured as a suspension element 14, 28, 36, 50 such as a coil spring or air spring, or whether the combination of the suspension arm 26 and associated swing arm assembly 2 is configured to engage so as to provide a levering action 30, transmit the corresponding forces to the end portions of the suspension arm 12, 26, 48 which advantageously, by the pivoting action of the arm 12, 26, 48 balances the resultant load via the two linkages over each pair of wheels 8, 22, 44. Therefore, the tandem wheel assembly 2, 18, 40 allows a load of the trailer 4 to be spread more evenly over each pair of wheels 8, 22, 44 associated with a suspension arm 12, 26, 48 when the trailer 4 moves over undulating terrain. Advantageously, this provides for the tandem wheel assembly 2, 18, 40 to be more stable over undulating terrain and prevents wear and damage to the assembly 2, 18, 40.

[0036] The support 6, 20 has a stop arm 16, 38 for limiting downward movement of the swing arm assemblies 10, 24. The stop arm 16, 38 is pivotally attached transverse to the main beam 6, 20 and opposite end portions of the stop arm 16, 38 are arranged under each respective swing arm assembly 10, 24 of the associated pair of tandem wheels 8, 22. While the trailer 4 is in use on a sealed surface, the stop arm 16, 38 does not affect the operation of the swing arm assemblies 10, 24. However in the event the trailer 4 is travelling over undulating terrain and one of the wheels 8, 22 of each pair becomes airborne, the stop arm 16, 38 limits the downward movement of the swing arm assembly 10, 24 preventing over-extension of the suspension element 14, 28, 36 or lever 30. The pivoting action of the stop arm 16, 38 also acts in conjunction with the pivoting action of the associated suspension arm 12, 26 via the swing arm assemblies 10, 24 and associated linkages to balance the load between the airborne wheel 8, 22 and the opposite wheel 8, 22 thereby forcing the airborne wheel 8, 22 downwards towards the ground, advantageously improving the stability of the tandem wheel assembly 2.

[0037] As an alternative, the embodiments of the present invention as shown in the Figures can be modified such that there are two separate tandem wheel assemblies for mounting to a trailer, each tandem wheel assembly carrying a pair of tandem wheels and each assembly having a support which is mountable to structure of the trailer, on opposite sides thereof.

[0038] While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described exemplary embodiments.

[0039] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0040] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.