AU1838301A - Suspension for a wheel assembly of a road vehicle - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: SUSPENSION FOR A WHEEL ASSEMBLY OF A ROAD VEHICLE Applicant: TRANSIT ENGINEERING PTY. LTD.

The following statement is a full description of this invention, including the best method of performing it known to me: 1 Document SUSPENSION FOR A WHEEL ASSEMBLY OF A ROAD VEHICLE This invention relates generally to a suspension for a wheel assembly of a road vehicle and, in particular, to a secondary suspension for mounting a secondary rear wheel assembly adjacent to a first or primary rear wheel assembly of a road vehicle in order to increase the load carrying capacity of that vehicle. The suspension is applicable to small to medium load carrying utility vehicles, and it will be convenient to hereinafter disclose the invention in relation to that exemplary application. It is to be appreciated, however, that the invention is not limited to that application.

Small to medium load carrying utility vehicles with a tray or van configuration typically have front and rear single axle wheel assemblies. Those wheel assemblies usually limit the load carrying capacity of the vehicle to about one tonne. However, that capacity can be restrictive for some business and commercial applications for which the vehicle would be otherwise suitable, for example ambulances.

One way of increasing the load carrying capacity is to provide a second, supplementary rear wheel assembly, so that the load is supported on dual or tandem rear wheel assemblies. That approach enables an increase in the load o carrying capacity without the need for construction of a different, higher capacity 20 vehicle for those applications when it is required.

However, the provision of the tandem wheel assemblies has usually involved removing and replacing the existing single wheel assembly and its associated suspension with an entirely new tandem wheel assembly and suspension. Thus, the existing wheel assembly and suspension has not been 25 utilised. It is not an economically attractive proposition to convert a vehicle having a single rear wheel assembly to one having a tandem wheel assembly.

As a consequence, the capabilities of such vehicles are often not able to be fully 00 exploited.

An object of the present invention is to provide a secondary suspension for mounting a vehicle wheel assembly to a road vehicle in order to increase the load carrying capacity of that vehicle.

Another object of the present invention is to provide a secondary suspension for mounting a secondary wheel assembly to a road vehicle to form a tandem rear wheel assembly.

W:kateSPECICAPoflRN60873.doc With those objects in mind, the present invention provides, in one aspect, a secondary suspension for a road vehicle having a primary suspension supporting a primary road engaging wheel assembly, the second suspension including: a pair of suspension assemblies for mounting to a vehicle chassis in spaced apart relation, each assembly having an elongate suspension member mountable to the vehicle chassis and connectable to the primary suspension, the suspension members in use of the secondary suspension supporting a secondary road engaging wheel assembly therebetween so that the second suspension operates in tandem with the primary suspension and the primary and secondary wheel assemblies cooperate with one another to support the vehicle.

In another aspect, the present invention provides, in combination, the above secondary suspension and a secondary wheel assembly supported thereby.

In a further aspect, the present invention provides a suspension system for a road vehicle having a tandem rear wheel assembly, the suspension system including: a primary suspension supporting a primary road engaging e wheel assembly; and, the above secondary suspension supporting a secondary road engaging wheel assembly in trailing relation to the primary wheel 20 assembly, relative to the direction of forward travel of the vehicle.

Preferably, each suspension member has opposed end portions, and a mounting portion intermediate the end portions. The suspension member is "preferably mountable to the vehicle chassis at the mounting portion so as to extend longitudinally of the vehicle.

25 Preferably, the suspension members are mountable at the mounting portions for limited movement relative to the vehicle chassis. That mounting preferably provides for limited pivotal movement about an axis extending parallel to an axle unit of the secondary wheel assembly. The suspension members are preferably also mountable for limited linear movement toward and away from the overlying vehicle chassis. A respective mounting unit preferably mounts each suspension member to the vehicle chassis for that limited movement. In one preferred arrangement, each mounting unit includes a mounting bracket mountable to a respective chassis rail so as to depend W: WeXSPECI\CAPoflRN608739.doc 4 therefrom, and a connection member connecting the respective suspension member to the mounting bracket.

Preferably, each suspension member is connectable at one end portion thereof to the primary wheel assembly, and is mountable at the other end portion thereof to the secondary wheel assembly. The one end portions are preferably located forward of the other end portions, relative to the direction of forward travel of the vehicle, so that in use the secondary wheel assembly is positioned behind the primary wheel assembly.

Each suspension member is preferably pivotably connectable at the one end portion to an axle unit of the primary wheel assembly. To that end, each suspension assembly preferably includes at least one connection bracket rigidly mountable to the axle unit, and a pivot pin pivotably connecting the connection bracket to the one end portion of the respective suspension member.

In one preferred arrangement, each suspension member is rigidly mountable at the other end portion thereof to an axle unit of the secondary wheel assembly.

In an alternative preferred arrangement, each suspension member is mountable at the other end portion thereof to an axle unit of the secondary wheel assembly to allow relative movement between the suspension member and secondary 20 wheel assembly. That mounting provides for pivotal movement about axes extending perpendicular to a longitudinal axis of the second wheel assembly. In this way the primary and secondary wheel assemblies can twist relative to one another about a central longitudinal axis of the vehicle. Preferably, a mounting bracket is pivotably connected to the other end region of each respective 25 suspension member and rigidly connectable to the axle unit to achieve the pivotal mounting.

Preferably, each suspension member is connectable at the one end Iportion thereof to the primary wheel assembly at or adjacent a mounting of an axle unit of the primary wheel assembly to a leaf spring. Each suspension member preferably extends in the same vertical plane as its associated leaf spring upon installation of the secondary suspension. With this arrangement, the suspension members are shaped to clear the springs for unimpeded movement of the suspension members. That is preferably achieved by providing the suspension members with access openings through which the W: kate\SPEC\CAPoflRN608739.dOC respective springs pass with clearance upon installation of the secondary suspension.

Preferably, damper means are provided for damping movement of the suspension members relative to the chassis. That damper means preferably includes at least one damper member associated with each suspension member for acting between the suspension member and vehicle chassis.

In one preferred arrangement, the damper members include at least one hydraulic or pneumatic piston and cylinder damper for extending between each suspension member at or adjacent the other end portion thereof and the vehicle chassis.

In addition or alternatively, the damper members can include hydraulic or pneumatic bag dampers for extending between the suspension members, one on either side of the mounting portion, and the vehicle chassis. Control means is preferably provided to vary the pressure of the bag dampers and thereby control the degree of damping provided to the secondary suspension.

The damper members can further include one or more spring members for location between the mounting portions and vehicle chassis to damp upward linear movement of the suspension members. The or each spring damper can be a rubber spring.

20 Preferably, the suspension members are rigid suspension beams. The mounting portion of each beam is preferably located closer to the one end portion, providing each suspension beam with unequal beam sections extending from the mounting portion to a respective end portion. Those beam sections are preferably angled relative to one another. In one arrangement, the 25 beam sections extend downwardly from the mounting portion in a common vertical plane so that each beam has a generally inverted V-shape.

The following description refers to preferred embodiments of the •suspension of the present invention. To facilitate an understanding of the invention, reference is made in the description to the accompanying drawings where the suspension is illustrated in those preferred embodiments. It is to be understood that the suspension is not limited to the preferred embodiments as hereinafter described and as illustrated in the drawings.

In the drawings: W:AkateSPECICAPoflRNM08739.doc 6 Fig. 1 is a side view of a utility vehicle incorporating a secondary suspension according to a preferred embodiment of the present invention; Fig. 2 is a schematic perspective view of the primary and secondary suspensions from the vehicle of Fig. 1 mounted to axle unis of the respective wheel assemblies; Fig. 3 is a perspective view of the secondary suspension of Fig. 2 mounted to the axle unit of the secondary wheel assembly; Fig. 4 is an end view of the secondary suspension of Fig. 3, mounted to a vehicle chassis, but with some of the dampers removed for clarity; Fig. 5 is a side view of the secondary suspension of Fig. 4; Fig. 6 is a top plan view of the secondary suspension of Fig. 3; Fig. 7 is a side view of the other end portion of one suspension beam of the secondary suspension showing an alternative mounting of the suspension beam to the secondary wheel assembly; Fig. 8 is a top plan view of the suspension beam other end portion of Fig.

7; and, Fig. 9 is a perspective view of the suspension beam other end portion of Fig. 7.

Referring initially to Fig. 1, there is generally shown a utility vehicle V 20 having a cabin B and a load bearing tray T mounted on a rigid chassis C. The chassis C includes a pair of spaced apart rails R (only one of which is shown) extending longitudinally of the vehicle V. The vehicle V is supported on ground o:ooo G by a single front wheel assembly WF, and a pair of rear wheel assemblies Wp, Ws acting in tandem. The front wheel assembly WF is mounted to the chassis C through a conventional suspension (not shown), whilst the rear wheel assemblies Wp, Ws are mounted to the chassis C through a suspension system 1 including primary and secondary suspensions 2,3, respectively.

"0 "The suspension system 1 is shown in more detail in Fig. 2, where primary suspension 2 is mounted on an axle unit Ap, and a first embodiment of the secondary suspension 3 is mounted on an axle unit As, of their respective wheel assemblies Wp, Ws.

The primary suspension 2 is of convention construction for a utility vehicle V having a load carrying capacity of about one tonne, and for which the present invention is particularly applicable. That suspension 2 has a pair of W:\ateSPECICAPoflRN608739.doc 7 springs, such as leaf springs 4, positioned beneath a respective chassis rail R.

Each spring 4 extends along a respective rail R, and has a pair of end portions 5,6, at which the springs 4 are mounted to their rails R. Each leaf spring 4 will typically have multiple leaves 7 and will extend in a downward semi-elliptic arc in a plane of the respective rail R between the end portions 5,6.

Mounting of the leaf springs 4 to the rails R is such as to permit flexing movement toward and away from the respective chassis rails R during operation of the suspension 2, as will be well appreciated by those skilled in the art. Each end portion 5,6 is mounted so as to permit pivotal movement between the springs 4 and rails R, with at least one end portion 5 of each spring 4 being mounted through a shackle or link 8 to accommodate flexing of the springs 4.

The primary rear wheel assembly Wp, supported by the primary suspension 2, includes axle unit Ap extending between and rigidly mounted on the leaf springs 4 intermediate their end portions 5,6. That mounting is by way of mounting units 9, each of which includes a mounting plate 10 positioned adjacent a lower leaf 7 of the respective leaf spring 4, and a pair of U bolts 11 fitting over a housing H of the axle unit Ap, passing the leaf spring 4 one each thereof, and through holes in the mounting plate 10. Tightening of nuts on the bolts 11 rigidly clamps the leaf springs 4 and axle unit Ap together.

S 20 The primary suspension 2 also includes dampers 12 for damping movement, particularly shock movement, of the springs 4 during suspension ,operation. Those dampers 12 can be in the form of elongate piston-cylinder double acting shock absorbers 13, one each associated with a respective leaf spring 4 and extending between the spring 4 and its associated chassis rail R.

25 The shock absorber 13 can be mounted at one end to the mounting unit 9, and at the other end to the associated chassis rail R.

The secondary suspension 3 is shown in greater detail in Figs. 3 to 6, and includes a pair of suspension assemblies 14 mounted in parallel, spaced apart relation along respective chassis rails R. Each suspension assembly 14 is of the same construction and has an elongate suspension beam 15 mounted to a respective chassis rail R so as to extend along, beneath that rail. That mounting is at a mounting portion 16 of each beam Each suspension beam 15 has opposed end portions 17,18, and the mounting portion 16 is located intermediate those end portions 17,18. In this W:*ate\SPECI\CAPoflRN608739.doc 8 embodiment, the mounting portion 16 is near a midway position between the end portions 17,18, although closer to end portion 17. With this arrangement, each beam 15 has one section 19 extending from the mounting portion 16 and incorporating the end portion 17 which is shorter than another section 20 which extends from the mounting portion 16 to the end portion 18. As will become more apparent hereinafter, those unequal beam sections 19,20 have the effect during suspension operation that loading on the primary wheel assembly Wp is always greater than on the secondary wheel assembly Ws. In the exemplary application, the primary wheel assembly Wp will provide vehicle drive to the ground G, whilst the secondary wheel assembly Ws will be non-driven. As a result, the suspension beam geometry ensures better traction is achieved through the primary wheel assembly Wp. It will be appreciated that, in an alternative embodiment, the secondary wheel assembly Ws may be driven, in which case the geometry of the suspension beams 15 will be altered accordingly.

The suspension beams 15 are movably mounted to the chassis rails R.

In particular, those beams 15 are mounted for limited pivotal or rocking movement about an axis X extending parallel with the axis of the axle unit As.

The suspension beams 15 are also mounted for limited linear movement toward and away from the overlying chassis rails R. That movement is generally along a vertical line Y. As a result of this mounting, the suspension beams 15 will move to accommodate movement of the secondary wheel assembly Ws up and down toward and away from the overlying chassis C during normal operation of the secondary suspension 3.

25 Each suspension assembly 14 includes a mounting unit 21 for mounting the respective suspension beam 15 to a chassis rail R to enable the limited pivotal and linear movement.

Each mounting unit 21 includes a mounting bracket 22 mounted to the respective chassis rail R, such as by welding or bolting thereto, so as to depend therefrom. Each bracket 22 includes a pair of bracket plates 23 arranged to depend from the respective chassis rail R in spaced apart relation so as to accommodate the mounting portion 16 of the respective suspension beam therebetween.

W:Akate\SPECfhCAPofRN608739.doc 9 Each mounting unit 21 also includes a connection member 24 connecting the respective suspension beam 15 to the mounting bracket 22 for pivotal and linear movement therebetween. Each connection member 24 includes a connection pin 25 supported in the mounting bracket 22 along the pivot axis X.

Each suspension beam 15, in turn, is carried on a respective pin Each connection pin 25 extends and is mounted in holes 26 in the respective spaced apart mounting plates 23. In addition, the mounting portion 16 of each suspension beam 15 has a connection hold 27 therethrough into which the respective connection pin 25 is journalled to allow pivotal movement of the beam 15 about the pivot axis X. The holes 26 in the mounting plates 23 are elongate to enable vertical sliding movement of the connection pins therealong, and thus vertical linear movement of the suspension beams relative to the mounting plates.

Each suspension beam 15 is connected at the end portion 17 to the primary wheel assembly Wp, and is mounted at the end portion 18 to the axle unit As of the secondary wheel assembly Ws. The suspension beams 15 will be mounted to the chassis rails R so that the end potions 17 will be forward of the o end portions 18, relative to the direction of forward travel of the vehicle V. In addition, the end portions 18 will be rearwardly of the mounting of the primary 20 wheel assembly Wp on the primary suspension 2, having regard to that vehicle travel direction. With this arrangement, the secondary wheel assembly Ws will be positioned behind or trailing the primary wheel assembly Wp.

The connection of the suspension beams 15 to the mounting units 9 is a pivotal connection to accommodate pivotal movement of the beams 15 about an 25 axis x parallel to the pivot axis X at the mounting portion 16. That connection is achieved through a pivot connection 28 incorporated into each mounting unit 9.

Those pivot connections 28 are located on top of the axle unit Ap.

Each pivot connection 28 includes a pair of spaced apart connection brackets 29, rigidly mounted to the axle unit Ap by the U bolts 11, and a pivot pin 30 extending between and secured to the connection brackets 29. That pivot pin 30 is journalled in a bushed hole (not shown) passing through the end portion 17 of the respective suspension beam In this first preferred embodiment, each suspension beam 15 is rigidly mounted at the end portion 18 to the axle unit As of the secondary wheel W:kateSPECIRCAPoflRN608739.doc assembly Ws. That mounting is achieved, in this embodiment, through mounting units 31, the same or similar as those used to mount the axle unit Ap of the primary wheel assembly Wp. Each mounting unit 31 includes a pair of U bolts 32 extending over a housing H of the axle unit As thereto. The end portions 18 are shaped to cradle or nest the axle unit housing H therein and so facilitate that rigid mounting.

In an alternative preferred embodiment, each suspension beam 15 is mounted to the secondary wheel assembly Ws to allow relative movement therebetween. That embodiment is shown in Figs. 7 to 9 and permits pivotal movement between the suspension beams 15 and the secondary wheel assembly Ws about axes Z extending perpendicular to the longitudinal axis O of the secondary wheel assembly As. This relative movement accommodates increased movement between the primary and secondary wheel assemblies Wp, Ws, allowing those assemblies to twist relative to one another about a central longitudinal axis of the vehicle V when travelling over uneven ground G.

In this alternative embodiment, each suspension beam 15 is mounted at the end portion 18 to the secondary wheel assembly through a respective mounting unit 33. Each mounting unit 33 rigidly connects to the axle unit As, and pivotably connects to a respective suspension beam 15. Each pivot 20 connection provides for movement between the mounting unit 33 and 'i respective suspension beam 5 about axis Z which extends longitudinally of the beam 15 at the end portion 18.

Each mounting unit 33 includes a mounting member 34 fitted between a respective end portion 18 and the axle unit As, and a pivot bolt 35 for pivotably 25 connecting the member 34 to the end portion 18. In this embodiment, that pivot bolt 35 also functions to rigidly fix the axle unit As to the mounting member 34, although in an alternative embodiment (not shown) separate fixing bolts can be provided for that purpose.

Each mounting member 34 includes a swivel plate 36 for seating on a bearing plate 37, and the end portion 18, for face-to-face pivotal movement therebetween. The bearing plate 37 provides an end bearing face 38 lying in a plane perpendicular to the axis Z.

Each mounting member 34 also includes a mounting bracket 39 to which the axle unit As is rigidly fixed. The mounting brackets 39 may be formed W:VteSPECICAPoflRN608739.doc 11 integral with or rigidly connected to the swivel plates 36. The mounting brackets 39 are conveniently shaped to cradle or nest the axle unit housing H therein and so facilitate rigid fixing. The brackets 39 may be C-shaped in transverse crosssection for receiving a cylindrical axle unit As.

Each pivot bolt 35 extends through aligned holes in the bearing plate 37, swivel plate 36, mounting bracket 39 and axle unit As in order to mount the secondary wheel assembly Ws to each mounting member 34 and suspension beam 15. As indicated above, fixing bolts, such as U-bolts can be provided for separately fixing the axle unit As to the mounting brackets 39. In that case, the pivot bolts 35 simply pivotably connect the respective mounting brackets 39 and swivel plates 36 to the bearing plates 37.

The suspension beams 15 are configured so that the secondary suspension 3 will fit or mate with the existing primary suspension 2. In particular, the suspension beams 15 will ensure that the secondary wheel assembly Ws are arranged in an appropriate aligned tandem relationship with the primary wheel assembly Wp.

To that end, each suspension beam 15 is longitudinally shaped to enable S* connection at the end portion 17 with the mounting unit 9 and to the mounting unit 21 at the mounting portion 16, whilst the secondary wheel assembly Ws 20 remains aligned with the primary wheel assembly Wp. That shaping, includes .o angling each beam 15 between the end portions 17, 18, so that the beam sections 19,20, of each beam 15 are angled relative to one another. In particular, each beam section 19,20 is angled downwardly from the mounting portion 16 in a common vertical plane so that the beam 15 has a generally 25 inverted shallow V-shape.

The suspension beams 15 extend in the same vertical planes as heir associated leaf springs 4. In order to ensure that the beams 15 and springs 4 •do not contact or impede movement of one another, the suspension beams are shaped to clear the springs 4. That is achieved, in these embodiments, by providing each suspension beam 15 with an access or opening 40 through which the respective spring 4 passes with clearance. That recess or opening is elongate and extends along each beam section 20 a substantial distance between the mounting portion 16 and end portion 17.

W:cateSPECI1CAPoflRN608739.doc 12 The secondary suspension 3 also includes damper means 41 for damping movement of the suspension beams 15. The damper means 41 extends directly or indirectly between the suspension beams 15 and vehicle chassis-C, and acts to dampen both pivotal and linea movement of the beams The damper means 41 includes damper members 42 associated with each suspension beam 15. The damper members 42 may be only single acting, so as to damp in one direction of movement of the suspension beams in which case at least a pair of such camper members, each oppositely acting, are provided with each suspension beam 15. At least some of the damper members 42 may be double acting so as to dampen in both directions of movement of the suspension beams, in which case at least one damper member 42 is provided for each suspension beam 15. In these embodiments, a combination of single and double acting damper members 42 are provided, although it will be appreciated that in other embodiments only one form of damper members may be provided.

The damper members 42 include piston-cylinder dampers 43 extending 0 between the suspension beams 15 and chassis rails R. In these embodiments, those dampers 43 are double acting so that a single damper 43 is provided for each beam 15 (as shown). Those dampers 43 extend between the end portions 18 of the suspension beams 15 and the overlying chassis rails R.

The damper members 42 also include pneumatic bag dampers 44, such as air bag dampers, extending between the suspension beams 15 and chassis rails R. Those dampers 44 extend between the beams 15 and rails R, one on either side of the mounting portion 16 of the suspension beams 15. In this way, each damper 44 associated with each respective suspension beam 15 will act to damp movement of the beam 15 in one respective direction.

The damper means 41 includes control means (not shown) operable to vary the pneumatic pressure of the bag dampers 44. Varying the damper pressure permits control of the degree of damping provided to the secondary suspension 3. Varying damper pressure will also enable the chassis C to maintain a constant ride height under varying load conditions.

In the exemplary application of the secondary suspension 3, in an unloaded utility vehicle V having a normal load carrying capacity of 1 tonne the W: teSPECCAPofRN68739.doc 13 bag dampers 44 could be inflated to a pressure of about 5 psi. Increasing the pressure to about 39 psi would enable that vehicle to safely carry about 1.8 tones while retaining the same or similar ride height.

The control means includes a control valve operable to control supply of air or other suitable gas from a supply source to the bag dampers 44, and also control release of the gas from the dampers 44. The control valve may be manually operable, and may be operable remotely from the valve, for example from the vehicle cabin B.

Damping is also provided by the inclusion of a damper member 42 in each mounting unit 21 to assist in damping linear movement of the suspension beam 15. Each such damper member 42 includes one or more spring dampers acting directly or indirectly between the suspension beams 15 and chassis rails R to damp upward linear movement of the beam 15. In these embodiments, each spring damper 45 is a rubber spring, such as an aeon rubber spring, located in the respective mounting bracket 22 so as to be positioned between the suspension beam 15 and chassis rail R. In suspension use, the mounting portions 16 of the suspension beams 15 will bear upwardly **against the springs damper 45, which will in turn deflect under load applied to the vehicle V and to the wheel assembly Ws. That deflection of the springs damper 45 will damp movement of the suspension beams 15 and also transmission of forces, between the wheel assembly Ws and vehicle V during vehicle travel.

The damper means 41 includes various connection brackets 46 for connecting the damper members 42 to the suspension beams 15 and chassis 25 rails R. Those connection brackets 46 are fixed to the suspension beams and chassis rails R in any suitable manner, such as by welding or bolting thereto.

:IIO Use of the secondary suspension 3 may necessitate some modification of the chassis rails R, depending on the vehicle V in which the suspension 3 is installed. By way of example, it may be necessary to rearwardly lengthen the rails R to accommodate the secondary suspension 3, including the mounting of damper members 42 extending between the rails R and the en portion 18 of the beams W:UkateSPECICAPoflRN808739.doc 14 In using the secondary suspension 3 it may also be necessary or desirable to modify the primary suspension 2 in order to optimise vehicle ride and handling. The nature and extent of any modification will vary from make to make of vehicle V. By way of example, it may be appropriate to remove one leaf from each of the multiple leaf springs 4. That will facilitate a softer vehicle ride.

The secondary suspension of the present invention can be easily and quickly installed in utility vehicles after manufacture. The installation requires minimal, if any, modification to the existing vehicle. In particular, the secondary suspension is able to continue to utilise the existing primary suspension of the vehicle. As such, the suspension can be economically installed in individual utility vehicles in order to increase their load carrying capacity.

The accessory nature of the secondary suspension increases the application and uses of utility vehicles. The market available to such vehicles will therefore be broadened through the provision of the present invention.

Finally, it is to be understood that various alterations, modifications and/or additions may be made to the secondary suspension without departing from the ambit of the present invention as defined in the claims appended hereto.

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Claims (24)

1. A secondary suspension for a road vehicle having a primary suspension supporting a primary road engaging wheel assembly, the second suspension including: a pair of suspension assemblies for mounting to a vehicle chassis in spaced apart relation, each assembly having an elongate suspension member mountable to the vehicle chassis and connectable to the primary suspension, the suspension members in use of the secondary suspension supporting a secondary road engaging wheel assembly therebetween so that the second suspension operates in tandem with the primary suspension and the primary and secondary wheel assemblies cooperate with one another to support the vehicle.

2. A secondary suspension as claimed in claim 1, wherein each suspension member has opposed end portions, and a mounting portion intermediate the end portions and at which the suspension member is mountable to the vehicle chassis so as to extend longitudinally of the vehicle.

3. A secondary suspension as claimed in claim 2, wherein the suspension members are mountable at the mounting portions for limited movement relative to the vehicle chassis.

4. A secondary suspension as claimed in claim 3, wherein the suspension 20 members are mountable for limited pivotal movement about an axis extending parallel to an axle unit of the secondary wheel assembly. A secondary suspension as claimed in claim 3 or 4, wherein the suspension members are mountable for limited linear movement toward and away from the overlying vehicle chassis. 25 6. A secondary suspension as claimed in any one of claims 3 to 5, wherein each suspension assembly includes a mounting unit for mounting the suspension members to the vehicle chassis for the limited movement thereof.

7. A secondary suspension as claimed in claim 6, wherein each mounting unit includes a mounting bracket mountable to a respective chassis rail so as to depend therefrom, and a connection member connecting the respective suspension member to the mounting bracket.

8. A secondary suspension as claimed in claim 7, wherein each mounting bracket includes a pair of spaced apart bracket plates accommodating a respective mounting portion therebetween, and each connection member W:~kate\SPECICAPoflRN608739.doc 16 includes a connection pin extending through aligned holes in the mounting plate and mounting portion for connecting the respective suspension member to the mounting bracket.

9. A secondary suspension as claimed in claim 8 when appended to claims 5 and 6, wherein the connection pins are journalled in holes through the suspension members to enable the pivotal movement of the suspension members, and the holes in the mounting plates are elongate to enable sliding movement of the connection pins therealong and thus the linear movement of the suspension members.

10. A secondary suspension as claimed in any one of claims 2 to 9, wherein each suspension member is connectable at one end portion thereof to the primary wheel assembly, and is mountable at the other end portion thereof to the secondary wheel assembly, the one end portions being forward of the other end portions, relative to the direction of forward travel of the vehicle, so that in use the secondary wheel assembly is positioned behind the primary wheel assembly.

11. A secondary suspension as claimed in claim 10, wherein each suspension member is pivotably connectable at the one end portion to an axle o.unit of the primary wheel assembly. 20 12. A secondary suspension as claimed in claim 11, wherein each o-o suspension assembly includes at least one connection bracket rigidly mountable to the axle unit, and a pivot pin pivotably connecting the connection bracket to the one end portion of the respective suspension member.

13. A secondary suspension as claimed in any one of claims 10 to 12, o 25 wherein each suspension member is rigidly mountable at the other end portion thereof to an axle unit of the secondary wheel assembly.

14. A secondary suspension as claimed in any one of claims 10 to 12, lo": wherein each suspension member is mountable at the other end portion thereof to an axle unit of the secondary wheel assembly to allow relative movement between the suspension member and secondary wheel assembly. A secondary suspension as claimed in claim 14, wherein the other end portions of the suspension members are mountable to the axle unit for pivotal movement about axes extending perpendicular to a longitudinal axis of the W:Wkate\SPECI\CAPoflRN608739.doc second wheel assembly, enabling the primary and secondary wheel assemblies to twist relative to one another about a central longitudinal axis of the vehicle.

16. A secondary suspension as claimed in claim 15, wherein each suspension assembly includes a mounting bracket pivotably connected to the other end region of the respective suspension member and rigidly connectable to the axle unit.

17. A secondary suspension as claimed in claim 16, wherein each suspension assembly further includes a pivot bolt for extending through aligned holes in the axle unit, mounting bracket, and other end portion of the respective suspension member, to mount the axle unit to the suspension member.

18. A secondary suspension as claimed in any one of claims 2 to 17, wherein each suspension member is connectable at the one end portion thereof to the primary wheel assembly at or adjacent a mounting of an axle unit of the primary wheel assembly to a leaf spring.

19. A secondary suspension as claimed in claim 18, wherein each suspension member extends in the same vertical plane as its associated leaf spring upon installation of the secondary suspension, the suspension member 0* being shaped to clear the spring for unimpeded movement of the suspension member. 20 20. A secondary suspension as claimed in claim 19, wherein each suspension member has an access opening through which the respective spring passes with clearance upon installation of the secondary suspension. •21. A secondary suspension as claimed in claim 20, wherein each access opening is elongate, extending along the respective suspension member S 25 between the mounting portion and the one end portion thereof.

22. A secondary suspension as claimed in claim 3 or any claim appended thereto, and further including damper means for damping movement of the suspension members relative to the chassis.

23. A secondary suspension as claimed in claim 22, wherein the damper means includes at least one damper member associated with each suspension member for acting between the suspension member and vehicle chassis.

24. A secondary suspension as claimed in claim 23, wherein the damper members include at least one hydraulic or pneumatic piston and cylinder W:\kate\SPECftCAPoflRN08739.doc 18 damper for extending between each suspension member at or adjacent the other end portion thereof and the vehicle chassis. A secondary suspension as claimed in claim 23 or 24, wherein the damper members include hydraulic or pneumatic bag dampers for extending between the suspension members, one on either side of the mounting portion, and the vehicle chassis.

26. A secondary suspension as claimed in claim 25, wherein the damper means includes control means to vary the pressure of the bag dampers and thereby control the degree of damping provided to the secondary suspension.

27. A secondary suspension as claimed in any one of claims 23 to 26, when appended to claim 6 or any claim appended thereto, wherein the damper members include one or more spring members for location between the mounting portions and vehicle chassis to damp upward linear movement of the suspension members.

28. A secondary suspension as claimed in claim 27, wherein the or each spring damper is a rubber spring.

29. A secondary suspension as claimed in any one of claims 2 to 28, wherein each suspension member is a rigid suspension beam. A secondary suspension as claimed in claim 29, wherein each mounting portion is located closer to the one end portion, providing each suspension S.beam with unequal beam sections extending from the mounting portion to a respective end portion. S31. A secondary suspension as claimed in claim 30, wherein the beam sections of each suspension beam are angled relative to one another. 25 32. A secondary suspension as claimed in claim 31, wherein the beam sections of each suspension beam extend downwardly from the mounting portion in a common vertical plane so that each beam has a generally inverted .0 V-shape. bas

33. A secondary suspension for a road vehicle having a primary suspension supporting a primary road engaging wheel assembly, the secondary suspension substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings.

34. In combination, a secondary suspension as claimed in any preceding claim, and a secondary wheel assembly supported thereby. W: .ate\SPECICAPoflRN608739.doc 19 A suspension system for a road vehicle having a tandem rear wheel assembly, the suspension system including: a primary suspension supporting a primary road engaging wheel assembly; and, a secondary suspension as claimed in any one of claims 1 to 33 supporting a secondary road engaging wheel assembly in trailing relation to the primary wheel assembly, relative to the direction of forward travel of the vehicle. DATED: 9 February 2001 PHILLIPS ORMONDE FITZPATRICK Attorneys for: TRANSIT ENGINEERING PTY. LTD. 00 *0 0 00 Si 0 00 0 S* @005 W:\kate\SPECI\CAPoflRN608739.doc