BACKGROUND OF THE INVENTION:

1 . Field of the Invention:

[0001 ] This invention relates to a vehicle.

[0002] The invention particularly relates, but is not limited to, a tri-axle vehicle with a rigid chassis, the vehicle being operable as a powered-vehicle to carry- and/or or tow loads, or as a prime-mover for other machinery e.g. a tree- or cereal harvester.

2. Dictionary:

[0003] Throughout the specification, the terms "wheel" or "wheels" shall be used to include wheel(s), where the wheel(s) may be provided with pneumatic, non-pneumatic or solid tires, or bands around the rim(s) of the wheel(s).

[0004] The discussion of vehicles having "wheels" shall also include so-called "half-track" vehicles, where the drive axles are provided with continuous tracks in substitution for wheels / tires; and the term "wheels" shall include continuous ground-engaging tracks or the like.

[0005] The term "axle" shall include a pair of "half-axles" or "stub-axles" provided on opposite sides of the longitudinal axis of the chassis of the vehicle, where such "half-axles" or "stub-axles" are independently suspended from the chassis of the vehicle or otherwise independently movable relative to the chassis of the vehicle.

[0006] The term "rigid chassis" means a chassis not-articulated, or otherwise interconnected, into two or more chassis sections.

3. Prior Art:

[0007] NB: The following discussion is by way of background information only, and is not to be considered a statement of the common general knowledge (CGK) in the area of technology throughout the world..

[0008] There are many applications for rigid chassis, tri-axle vehicles in operational areas such as agriculture, forestry, mining, quarrying and the military. Such vehicles include those typically identified as "6x6", "6x4", "10x10" or "10x8" vehicles, depending on the number of driven axles and whether or not dual wheels are provided on the non-steering drive axles..

[0009] Typically, a steering axle is provided at, or adjacent, one end of the vehicle chassis - more typically the front end. The wheels on the steering axle may be driven e.g. by hydrostatic hub motors, or via half-shafts from a differential. The remaining (pair of) drive axles are typically provided at, or adjacent, the rear of the vehicle chassis e.g. below a cargo tray or at the load to be transported by the vehicle.

[0010] Alternatively, e.g. in military vehicles, it is known to provide tri-axle rigid chassis vehicles with no steering axle (s); and to employ a skid-steer arrangement, where the wheels on one side of the vehicle are braked, to provide a differential in wheel rotational speeds across the vehicle.

[001 1 ] The sideways skidding of the non-steering axles hereinbefore described absorbs additional power from the vehicle drive system, especially in the alternative embodiment described in paragraph[0010]. Indeed, the required power increase may be of the order of 40-60%, when making a sharp (i.e. small radius) turn, compared with travelling in a straight path, at the same speed.

[0012] The additional requirements, when the vehicle is turning, may require the installation of a more powerful engine (and transmission system), consuming more fuel and adding more weight, than would be required if the additional power requirements during turning where minimized.

[0013] Additional to the increased tire wear, when the vehicle negotiates a sharp turn, the tires can and do inflict considerable damage to the supporting surface e.g. in a cereal paddock or a forest floor, as the tires "scrape" or "laterally drag" across the surface.

[0014] Finally, such rigid vehicles are generally not suitable for making small- diameter turns e.g. at the ends of rows of crops or trees, where adjacent rows are to be harvested side-by-side. As only limited turning space may be available at the ends of the rows, the vehicle may have to make e.g. one or more, "three-point turns" at the ends of the rows to be able to reverse its direction of travel along the rows. The time taken to make such complicated turns adversely affects the operational efficiency of the vehicle.

[0015] The above factors mitigate against the use of a rigid chassis tri-axle vehicle, where such a vehicle may have features which are particularly advantageous e.g. a low-pressure footprint on cultivated or disturbed soil.

OBJECTS OF THE INVENTION:

[0016] It is an object of the present invention to provide a vehicle which overcomes, or at least ameliorates, one or more of the problems with the existing vehicles hereinbefore described.

[0017] Other preferred objects of the present invention will become apparent to the skilled addressee from the following description.

SUMMARY OF THE INVENTION:

[0018] In one aspect, although not necessarily the broadest aspect, the present invention resides in a tri-axle vehicle with a rigid chassis, including: a first, steering, axle at or adjacent one end of the chassis;

second and third, drive, axles, at or adjacent the other end of the chassis, the second axle being intermediate the first and third axles;

respective suspension arms pivotally mounted on the chassis and operably connected, at or adjacent their distal ends, to a respective one of the axles; and

respective lifting means interconnecting the suspension arms to the chassis to selectively raise or lower the axles relative to the chassis.

[0019] Preferably, the second axle is spaced at least 60% of the length of the chassis from the one end.

[0020] Optionally, the first axle is also a drive axle.

[0021 ] Preferably, each axle is formed by a pair of stub-axles, each stub axle being provided at or adjacent the distal end of a respective suspension arm; a respective wheel is rotatably mounted on each stub-axle; and

each wheel is operably connected to a driving source or power transmission.

[0022] Preferably, each lifting means is a hydraulic ram, pneumatic ram, mechanical jack, or hydraulic motor, operable to selectively pivot the suspension arm relative to the chassis.

[0023] Preferably, when the first axle is operated to steer the vehicle around a turn of relatively small radius, the third axle is raised relative to the chassis so that the wheels thereon are disengaged from the surface supporting the vehicle.

{0024} Optionally, when the first axle is operated to steer the vehicle around a turn of relatively large radius, the wheels on the second and third axles on the inside of the turn are differentially driven at a lower rotational speed than the other wheels on the second and third axles on the outside of the turn.

[0025] Optionally, when the vehicle is travelling on, or up or down, an inclined surface, the lifting means are operable to maintain the chassis substantially horizontal.

[0026] Optionally, when the vehicle passes over an obstruction or the surface is undulating, the lifting means are operable to maintain the chassis substantially horizontal, where the wheels operate under a walking beam type effect..

[0027] Preferably, the vehicle is operable in a raised, transport, configuration, with the first axle at the front of the vehicle in the direction of travel; and a lowered, operating configuration, with the first axle at the rear of the vehicle in the direction of travel.

[0028] Preferably, each wheel is driven by a hydrostatic motor mounted on the respective stub axle, each hydrostatic motor being operably connected to a hydraulic pump, in turn driven by an engine;

where each hydrostatic motor, the hydraulic pump, engine and lifting means are selectively controlled by an operator stationed in an operator's compartment mounted on the chassis; and

where the operator's compartment is optionally rotatably mounted on the chassis for rotation between respective transport and operating positions. BRIEF DESCRIPTION OF THE DRAWINGS:

[0029] To enable the invention to be fully understood, and to enable the skilled addressee to put the invention into practice, a number of preferred embodiments will now be described, with reference to the accompanying illustrations, in which:

FIG. 1 is a side view of a tri-axle rigid chassis vehicle of a first embodiment, in accordance with the present invention, with parts shown in dashed lines;

FIG. 2 is a top plan view thereof;

FIG. 3 is a side view of a second embodiment of the invention in a raised, transport configuration;

FIG. 4 is a similar view to FIG. 3, in a lowered, operational configuration;

FIG. 5 is a similar view showing the vehicle "walking" over an obstruction or uneven surface;

FIG. 6 is a front view of the vehicle negotiating an inclined or sloped surface;

FIG. 7 is a side view, corresponding to FIG. 3, with the wheels omitted;

FIG. 8 is a top plan view of the vehicle of the first embodiment, with the steering wheels turned to the right and the third axle raised;

FIG. 9 is an isometric view of the vehicle of FIG. 8, taken from the right-hand-side (RHS) of the vehicle;

FIG. 10 is a side view, from the left-hand-side (LHS) of the vehicle;

FIG. 1 1 is a top plan view of the vehicle of the second embodiment, with the steering wheels turned to the left and the third axle raised;

FIG. 12 is a side view, from the left-hand-side (LHS) of the vehicle; FIG. 13 is a schematic circuit diagram of the vehicle of FIG. 5;

FIG. 14 is a similar circuit diagram of the vehicle of FIG. 6; and

FIG. 15 is a similar circuit diagram of the vehicle of FIG. 8.

[0030] NB: Any annotations on the drawings are by way of illustration only, and are not limiting to, the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

[0031 ] NB: The same feature of the first embodiment of FIGS. 1 , 2, 8 to10 and 15; and of the second embodiment of FIGS. 3 to 7, and 1 1 to 14; shall be identified by the reference numerals "xx" and "1xx" respectively.

[0032] The vehicle 10 of the first embodiment (of FIGS. 1 , 2, 8 to 10, and 15) has a chassis 20 formed of side rails 22, 23 and cross-members 24, which are typically of C-, H-, I-, Z- or box-section, or of circular or elliptical section, or metal castings, for high-tensile steel, aluminium alloys or the like. The forward sections 22a, 23a of the chassis side rails 22, 23 are inwardly offset to allow for the steering mechanism (to be hereinafter described), while allowing all the axles to have their wheels with the same track.

[0033] As indicated in dashed lines, the vehicle 10 may have an operator's cabin 1 1 , engine 12, and power transmission 13. In the embodiment illustrated in FIG. 1 , the vehicle 10 is configured as a self-propelled tree harvester, with a chipper drum 14 and rotary saw(s) 15.

[0034] For consistency, the "forward end" or "front" of the vehicle 10 shall be the front of the vehicle 10 when in the vehicle 10 is the (front-steer) transport configuration.

[0035] The vehicle 10 has a first, steered (and driving) axle 30, a second, driving axle 40, and a third, driving axle 50, to be hereinafter described. Each axle 30, 40, 50 is provided by pairs of stub-axles 31 , 32, 41 , 42, 51 , 52 respectively, to which are fitted pneumatic tire / wheel assemblies 33, 34, 43, 44, 53, 54 respectively. The second axle 40 is preferably arranged at least 60% of the length of the chassis 20, measured from the "front" of the vehicle 10.:

[0036] Each stub-axle is mounted at the distal end of a suspension arm 35, 36, 45, 46, 55, 56; with the proximal ends of the suspension arms being pivotally mounted pivot blocks 37, 38, 47, 48, 57, 58 on the outer-sides of the chassis side rails 22, 23. Respective lifting rams 61 to 66 are mounted, via brackets 25, 26 on the chassis side rails 22, 23, and operably connected to brackets intermediate the length of the respective suspension arm 35, 36, 45, 46, 55, 56, so arranged that by extension, or retraction, of the lifting rams 61 -66, the suspension arms can be pivoted relative to the chassis 22 to raise, or lower, the chassis 22 relative to the supporting surface. (This suspension system is illustrated for the vehicle 1 10 of the second embodiment in FIG. 7, where the tire / wheel assemblies have been omitted for clarity.),

[0037] A hydrostatic drive motor 71 -76 is provided on each stub-axle to provide drive to a respective tire / wheel assembly; with respective steering mechanisms 77, 78 interposed between the suspension arms 35, 36 and the drive motors 71 , 72 to provide steering for the first axle 30. Each drive motor 71 -76 is operably connected to the power transmission 13; and each steering mechanism 77, 78 has a respective steering ram 79 operably connected to the operator's cabin 1 1 .

[0038] FIGS. 3 and 4 illustrate the vehicle 1 10 of the second embodiment; where, in FIG. 3, the lifting rams 161 -166 are all extended, so that the suspension arms 135, 136, 145, 146, 155, 156 are all swung downwardly relative to the chassis 120 so that the vehicle 1 10 is in the raised, transport configuration; while in FIG. 4, the lifting rams 161 -166 are retracted, so that the vehicle 1 10 is in the lowered, operational configuration.

[0039] When the vehicle 1 10 is passing over an obstacle, or undulation U, in the support surface SS, the lifting rams 161 -166 may be selectively retracted / extended so that the chassis 120 is maintained substantially horizontal at all times.

[0040] Referring to FIG. 6, when the vehicle 1 10 is travelling along an incline I (e.g. at an angle β to the horizontal, the lifting rams 162, 164, 166 can extended and/or lifting rams 161 , 163, 165 retracted, to maintain the vehicle 1 10 substantially horizontal. By maintaining the vehicle 1 10 substantially horizontal, the center-of-gravity CG (see FIG. 2) remains well within the stability zone SZ.

[0041 ] As illustrated in FIG. 7, the lifting rams 161 -166 are connected to brackets 167, 168 intermediate the lengths of the suspension arms 1 35, 136, 145, 146, 155, 156, where the brackets are formed integrally with, or attached to, the suspension arms.

[0042] FIGS. 8 to 10 illustrate the vehicle 10 making a sharp right- hand turn in a forward direction of travel.. [0043] With a conventional vehicle, the tires on the second and third axles 40, 50 would be "dragged" or "scraped" sideways over the supporting surface. However, as better illustrated in FIGS. 9 and 10, the lifting rams 65 and 66 are retracted to raise the tire / wheel assemblies 53, 54 clear of the supporting surface. The tire / wheel assemblies 43, 44 of the second axle 40 support the rear of the vehicle 10 until the turn is completed.

[0044] As will be hereinafter described, sensors in the steering mechanism can operate to raise the third axle 50 when the steered tire / wheel assemblies 33, 34 are turned e.g. more than 2° or 5° from the straight-ahead position and/or lower the third axle when the steering angle is reduced below those limits. In addition, the inner tire / wheel assembly 44 on the second axle 40 may be "braked" to provide a differential rotational speed with the outer tire / wheel assembly 43 on the second axle 40. In addition, the steering mechanism can also automatically be adjusted from one operating with Ackermann-type steering about an axis intermediate the second and third axles 40, 50 to one steering about an axis aligned with the second axle 40.

[0045] The skilled addressee will appreciate that when the vehicle 10 is in the operational configuration, the steered tire / wheel assemblies 33, 34 of the first axle 30 are at the rear of the vehiclel O, and the vehicle 10 will be making a sharp left-hand turn with the tire / wheel assemblies as shown.

[0046] FIGS. 1 1 and 12 illustrate the vehicle 1 10 of the second embodiment, having a rotary saw 1 15 of a tree harvester. In these illustrations, the tire wheel assemblies 133, 134 are steered in the opposite direction for a sharp left-hand turn in the transport configuration or a sharp right-hand turn in the operational configuration. Again, the tire / wheel assemblies 153, 154 of the third axle 150 are raised from the support surface during the sharp turn.

[0047] By being able to make such sharp turns, the vehicle 10, 1 10, when configured as a harvester, can travel along adjacent rows up-and-back in the cereal crop or rows of trees (or other crops) to be harvested; and only minimal turning space is required at the ends of the rows to enable the vehicle 10, 1 10 to turn though 180° in a single movement. [0048] While raising the third axle 50, 150 will increase the footprint pressure on the supporting surface when the vehicle 10, 1 10 is turning; the vehicle 10, 1 10 will operate with all three axles 30, 40, 50 or 130, 140, 150 in their operational positions as the vehicle 10, 1 10 moves along the rows, with the minimum footprint pressure. In addition, as will be hereinafter described, sensors on the lifting rams 61 -66, 161 -166 can be connected to a CPU and hydraulic valves in the hydraulic lines to the lifting rams to extend / retract the lifting rams to equalize the footprint pressures of the tire / wheel assemblies along the vehicle.

[0049] FIG. 13 illustrates a schematic circuit diagram for the vehicle 1 10 of FIG. 5.

[0050] The operation of the vehicle 1 10 is controlled from an operator's cabin 1 1 1 , rotatably mounted on the chassis 120 so that the operator at the Operator's Station is able to face in the direction of travel of the vehicle. A diesel engine M (12) drives a hydraulic pump P, which is part of the power transmission 1 1 3.

[0051 ] Valve V is a first order valve, and hydraulic fluid is supplied under pressure, in parallel, via two second order solenoid valves Vs to each of the lifting rams 161 -166. When the CPU holds both valves V _s open, only the valve V is controlling nominal extension / retraction of the lifting rams 161 - 166, providing a walking beam effect. However, when full independence is required, the valve V is held open, and the valves Vs will independently supply hydraulic oil to each lifting ram 161 -166.

[0052] The sensors SL, are linear displacement sensors. An example of operation, when in walking beam mode to give the foot print shown in FIG.2, is as follows. The CPU will determine its current height of the vehicle 1 10 via the S _L sensors, and sets a new height by directing oil or out of the two lifting rams 163 and -164 via valve V. In the walking beam mode, both valves Vs will stay open, thereby creating equal footprint pressure to the ground, as shown in FIG.2. Trying to sense differences in hydraulic pressure in the lifting rams 161 -166 would be very difficult. The present arrangement is both simple and robust. [0053] Whilst in walking beam mode, if the cylinder of one lifting ram 161 -166 is leaking past the piston, the CPU will register this imbalance of linear distance expected from each S _L sensor, i.e. if the lifting rams 161 -166 were expected to be nominally at half extension, the CPU should expect each lifting ram to be retracted or extended an equal amount from the set nominal distance. So as one wheel rises over an obstruction U e.g. a mound, and retracts its lifting ram, the other will extend an equal value. If the CPU does not register the linear sensor S _L to be where it should be, it will shut off the opposite Vs valve to the lifting ram that needs topping up with oil and extending. In this event, a warning message will go to the operator to tell them which lifting ram is faulty and needs repair, but does not stop the harvester from working. This is effectively a self-diagnosis and temporary repair system.

[0054] A gyroscope G can be connected to the CPU to measure the attitude of the vehicle chassis 120 relative to the horizontal (in both the longitudinal- and transverse-axes), and the CPU can operate the valves V and V _s to maintain the chassis 120 substantially horizontal at all times, including traversing an incline as illustrated in FIG. 14.

[0055] Referring to FIG. 15, the rotational speed of the tire / wheel assemblies are monitored by sensors Sw; and the steering angles of the tire / wheel assemblies 133, 134 of the first axles 130 are monitored by sensors Ss, in addition to the position of the lifting rams 161 -166, and the CPU may operate the valves V connected to the steering rams 169 to change the respective steering angles of the tire / wheel assemblies depending on whether or not the third axle 150 is raised; and/or to automatically raise and/or lower the third axle 150 when the steered tire / wheel assemblies exceed a preset steering angle. The CPU may also limit the steering angles, and prevent the raising of the third axle, when the vehicle 1 10 is travelling above a preset speed.

[0056] Many of the components for the vehicle 10, 1 10 can be sourced as "off-the-shelf" items, including the engine, power transmission, hydrostatic drive motors, suspension arms, lifting rams, steering rams, and the like, to minimize costs and "back-up" repair and maintenance services .For example, the engine and associated cooling pack may be a Caterpillar® C18, C27 or C32 unit; and the reversible operator's cabin can be of the type on the Caterpillar® 584 Forwarder.

[0057] If preferred, the second and third axles 40, 50 or 140, 150 can be provided by bogie chain drive axles CDB of the type used in modern road graders e.g. of the types sold by Caterpillar® or Oerlikon®. These types of drive axles are less expensive than individual drive motors for each tire / wheel assembly; but may restrict the ability of the vehicle to overcome obstructions and/or absorb very large torque loads.

[0058] Advantages of the vehicle of the present invention, include, but are not limited to:

a) The chassis is designed to overcome several challenges. To keep the drive train between the engine and chipper drum in a tree harvester in constant alignment, there is a need for a solid chassis where all parts of the harvester are commonly mounted. While mounted common, the chassis also needs the freedom to lift, tilt fore-aft and tilt side-to-side;

b) In forestry operations, the distance available to turn vehicles is very limited, therefore any 6-wheel skid steer vehicle would be required to perform near zero point turns at the end of rows. Research indicates that this would incur significant energy loss and create excessive soil disturbance. The present vehicle combines skid steer principles with rear steer. In practice, the vehicle reaches the end of row, the chassis is lifted, with the wheels closest to the saw lifted off the ground. This reduces the wheel base length between the centre (second) axle and rear (first) steer axle;

c) In combination with the rear (first) steer axle, the wheels on the centre (second) axle can be individually controlled to provide differential speed, to further reduce the steering circle. This will make the vehicle feel to the operator to have turning brakes, i.e. forcing the outside turning wheels to drive faster.

[0059] The present invention provides a vehicle which incorporates a chassis design and function which is unique, as it combines the principles of skid steer, wheel base reduction, rear steer function (when in the operational configuration) and front steer function ( in the transport configuration) simultaneously. The present invention provides a vehicle that offers:

1 . A chassis that is extremely well suited to the sloping terrain of forestry;

2. Able to shorten the wheel base to perform near zero-point turns;

3. Combines rear steering function with skid steer;

4. Can facilitate both fore-aft angle (for saw) and side-to-side angle (for side slope); and

5. Can vertically lower the vehicle on a transport deck to lower height and centre of gravity.

[0060] Various changes and modifications may be made to the embodiments described and illustrated without departing from the present invention.

[0061 ] In this specification, the terms 'comprises', 'comprising', 'includes', 'including', or similar terms are intended to mean a non-exclusive inclusion, such that a method, system or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed.