WO2014133400A1

WO2014133400A1 - A vehicle for operating on steep slopes

Info

Publication number: WO2014133400A1
Application number: PCT/NZ2013/000027
Authority: WO
Inventors: David Robert AITCHISON; Mark LINDBOM; Gary Edward ALLEN; Nigel Joseph Kelly
Original assignee: Kelly Logging Company Ltd
Priority date: 2013-03-01
Filing date: 2013-03-01
Publication date: 2014-09-04

Abstract

A vehicle for operation on steep slopes, such as a tree harvesting vehicle. The vehicle may include a winch mounted for rotational motion about its axis and linear motion parallel to its axis. The vehicle may include various tension control improvements in the winch system. The vehicle may include a rear (downhill) support configured to provide an uphill force by pressing against the ground. The vehicle may include a fuel tank and/or hydraulic fluid tank adapted for improved performance on steep slopes. The vehicle may include a belly plate system allowing its belly plate to be controllable removed and replaced.

Description

A VEHICLE FOR OPERATING ON STEEP SLOPES FIELD OF INVENTION This invention relates to a vehicle for operating on steep slopes. BACKGROUND TO THE INVENTION

To operate an independent vehicle on slopes of substantial incline (typically greater than 20 degrees) is a hazardous operation as it puts the vehicle at risk of losing traction or stability.

Such vehicles are used, among other applications, in harvesting of trees in forestry applications. Tree harvesting vehicles may include a wheeled or tracked vehicle body equipped with a harvesting head. The harvesting head may include a grapple or claw together with a saw for cutting or felling trees. The Applicant devised a tree harvesting vehicle including a winch adapted to assist movement and/or stability of the vehicle via a cable attached to a remote anchor point higher up a slope than the trees to be harvested. That vehicle is described in NZ Patent No. 578476.

The Applicant has made further improvements in such vehicles.

Reference to any prior art in this specification does not constitute an admission that such prior art forms part of the common general knowledge.

It is an object of the invention to provide an improved method and/or apparatus and/or components relating to steep-slope operation of vehicles, or at least to provide the public with a useful choice. SUMMARY OF THE INVENTION

In a first aspect the invention provides a vehicle configured for operation on steep slopes, including: a chassis; a winch mounted to the chassis and adapted, in use, to haul the vehicle via a cable connected to a remote anchor point, wherein the winch includes a winch drum mounted for rotational motion about a winch axis and linear, traversing motion parallel to the winch axis.

The vehicle may be a tree harvesting vehicle and further include a head unit including one or more tools for harvesting trees.

Preferably the vehicle further includes a rotational drive arrangement configured to drive or resist the rotational motion of the winch drum. Preferably the rotational drive arrangement is configured to drive winding of the cable onto the winch drum when the vehicle is moving towards the remote anchor point and to provide a braking force to resist unwinding of the cable from the winch drum when the vehicle is moving away from the remote anchor point. Preferably the vehicle further includes a linear drive arrangement configured to drive the linear, traversing motion parallel of the winch drum.

Preferably the linear drive arrangement includes a linear actuator. Preferably the winch is mounted on one or more shafts for linear, traversing motion parallel to the winch axis.

Preferably the vehicle further includes a controller configured to maintain a desired tension by adjusting a torque applied to the winch drum. Preferably the controller controls the torque to compensate for a cable offset relative to the winch axis. Preferably the rotational and traversing motion are controllable independently of each other.

Preferably the vehicle further includes a rotary encoder configured to sense a rotational position of the winch drum.

Preferably the vehicle further includes a position sensor configured to sense the traversing position of the winch drum.

Preferably the vehicle further includes a controller configured to control the winch drum rotational movement and linear, traversing movement such that the cable remains substantially perpendicular to the winch axis.

In a second aspect the invention provides a vehicle configured for operation on steep slopes, including: a chassis; a winch mounted to the chassis and adapted, in use, to haul the vehicle via a cable connected to a remote anchor point, wherein the winch includes a winch drum mounted for rotational motion about a winch axis; a cable entry point on an uphill side of the vehicle, where cable passes to/from the winch via the cable entry point; a vehicle support mounted on a linkage on a downhill side of the vehicle and controllable to push against the ground to provide a force in an uphill direction.

Preferably the vehicle is a tree harvesting vehicle and further including a head unit including one or more tools for harvesting trees. Preferably the vehicle support is an excavator blade.

Preferably the vehicle support is mounted on a hydraulic linkage. Preferably the vehicle further includes a plurality of tracks or wheels, wherein the vehicle support is operable to be lowered below a plane defined by the bottom surfaces of the tracks or wheels.

In a further aspect the invention provides a hydraulic fluid reservoir including: a hydraulic fluid chamber; a hydraulic fluid inlet opening into the hydraulic fluid chamber and a hydraulic fluid outlet opening out of the hydraulic fluid chamber, for connection to a hydraulic circuit; a further chamber; one or more flow paths allowing fluid flow between the hydraulic fluid chamber and the further chamber; and an opening allowing air to flow into or out of the further chamber.

Preferably the one or more flow paths communicate between one or more ports at or near to the top of the hydraulic fluid chamber and one or more ports at or near to the bottom of the further chamber. Preferably the hydraulic fluid reservoir includes a breather port at the top of the further chamber, allowing gases to vent from the further port.

Preferably the hydraulic fluid reservoir includes a breather valve controlling flow through the breather port, the breather valve allowing flow out of the breather port when pressure in the further chamber exceeds a threshold.

Preferably the hydraulic fluid inlet is at or near to the top of the hydraulic fluid chamber. Preferably the hydraulic fluid outlet is at or near to the bottom of the hydraulic fluid chamber.

Preferably, in use, when net hydraulic fluid flow is out of the reservoir, hydraulic fluid flows from the further chamber through the flow paths into the hydraulic fluid chamber and when net hydraulic fluid flow is into the reservoir, hydraulic fluid flows from the hydraulic fluid chamber through the flow paths into the further chamber.

Preferably, in use, the hydraulic fluid chamber remains substantially full at all times.

Preferably, in use, a level of hydraulic fluid in the further chamber will rise and fall over time.

Preferably the hydraulic fluid reservoir includes an oil level sensor configured to sense the level of hydraulic fluid in the further chamber.

Preferably the hydraulic fluid chamber is formed in two sections that communicate with each other and are positioned on either side of the further chamber. Preferably the two sections communicate with each other in a lower section of the reservoir, but not in an upper section of the reservoir.

In another aspect the invention provides a fluid reservoir including: a first chamber and a second chamber; a fluid inlet allowing fluid to be added to either the first chamber or the second chamber; a fluid outlet positioned at or near the bottom of the first chamber; a first flow path between the first chamber and the second chamber, opening into each of the first and second chambers at a point at or near to the bottom of each said chamber; and a valve positioned in the first flow path, allowing fluid flow through the first flow path from the second chamber to the first chamber, but not from the first chamber to the second chamber.

Preferably the fluid inlet is in the first chamber.

Preferably the fluid reservoir includes a second flow path between the first and second chambers, opening into the first chamber at a point spaced above the bottom of the first chamber and opening into the second chamber at a point at or near the bottom of the second chamber.

Preferably the second flow path allows fluid flow in either direction.

Preferably the fluid reservoir includes a gas transfer path connecting the first and second chambers and opening into each chamber at a point at or near the top of that chamber.

In a further aspect the invention provides a belly plate system for a tracked or wheeled heavy vehicle, including: a belly plate arranged to cover an opening in the underside of the vehicle; a releasable mounting arrangement for releasably fixing the belly plate to a chassis of the heavy vehicle; a lowering mechanism operating directly or indirectly between the belly plate and the chassis of the heavy vehicle, the lowering mechanism being: configured to take the weight of the belly plate on release of the releasable mounting arrangement; and operable by a user to lower the belly plate in a controlled manner after release of the releasable mounting arrangement.

Preferably the releasable mounting arrangement includes one or more releasable fasteners. Preferably the releasable mounting arrangement includes a mounting plate configured for permanent attachment to the chassis of the heavy vehicle, the releasable mounting arrangement releasably fixing the belly plate to the mounting plate. Preferably the lowering arrangement operates between the belly plate and the mounting plate.

Preferably the lowering arrangement includes a linear actuator. Preferably the lowering arrangement also allows controlled raising of the belly plate.

Preferably the belly plate is rotatable about the lowering arrangement when in a lowered position, such that it can be rotated away from the opening. In another aspect the invention provides a vehicle configured for operation on steep slopes including: a chassis; a winch mounted to the chassis and adapted, in use, to haul the vehicle via a cable connected to a remote anchor point, wherein the winch includes a winch drum mounted for rotational motion about a winch axis; and a controller configured to adjust a torque applied to the winch drum in order to control the tension applied to the cable.

The vehicle may be a tree harvesting vehicle and further include a head unit including one or more tools for harvesting trees. Preferably the controller is configured to adjust the torque applied to the winch drum to provide a desired braking force when the vehicle is moving downhill against cable tension. Preferably the controller is configured to adjust the torque applied to the winch drum to provide a desired uphill force when the vehicle is moving uphill with the cable tension. Preferably the controller adjusts the torque to compensate for the effect of a cable offset relative to the winch axis on cable tension.

Preferably the controller is configured to adjust the torque applied to the winch drum when the vehicle is moving downhill against the cable tension, to provide: a first constant tension at all cable pay-out speeds up to a first threshold speed; a tension that increases from the first constant tension to a second constant tension for cable payout speeds between the first threshold speed and a second threshold speed; and the second constant tension at speeds above the second threshold speed. Preferably the controller is configured to adjust the torque applied to the winch drum to provide a safety braking force should the vehicle speed exceed a safety limit.

Preferably the vehicle further includes a user input device enabling a user to set one or more of: one or more downhill tension values; and one or more uphill tension values.

In another aspect the invention provides a vehicle configured for operation on steep slopes including: a chassis; a winch mounted to the chassis and adapted, in use, to haul the vehicle via a cable connected to a remote anchor point, wherein the winch includes a winch drum mounted for rotational motion about a winch axis; and two or more feed-out rollers, including at least one powered feed-out roller, the feed-out rollers configured to apply a tension force to the cable to feed the cable off the winch. The vehicle may be a tree harvesting vehicle and further include a head unit including one or more tools for harvesting trees.

Preferably the feed-out rollers include at least one pair of counter-rotating powered pinch rollers.

Preferably at least one of the pinch rollers has a groove formed in its circumference, the cable lying at least partly within the groove such that the groove resists sideways motion of the cable.

Preferably the feed-out rollers are mounted on a feed-out carriage that is free to move horizontally and vertically.

Preferably the vehicle further includes one or more biasing elements tending to force the carriage to move horizontally to a central position.

Preferably the tension force is greater than 100N.

Preferably the tension force is around 200N.

Preferably the feed-out rollers operate to apply a minimum tension to the cable when the cable is being wound in, is being fed out or is static.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a perspective view of a tree harvesting vehicle; Figure 2 shows the winch of the tree harvesting vehicle shown in figure 1 ;

Figure 3 shows the rollers associated with the winch of the tree harvesting vehicle shown in figure 1 ;

Figure 4 shows a schematic diagram of the hydraulic system of the tree harvesting vehicle shown in figure 1 ;

Figure 5 shows a schematic diagram of a method of harvesting trees;

Figure 6 shows a perspective view of a steep slope vehicle according to one embodiment;

Figure 7 illustrates forces in a prior art vehicle;

Figure 8 shows a rear mounted winch set-up;

Figure 9 shows a forward mounted winch set-up;

Figure 10 shows a winch assembly according to one embodiment;

Figure 11 shows a graph of line speed as a function of rope tension in one embodiment;

Figure 12 shows a fuel tank of one embodiment;

Figure 13 shows a hydraulic fluid reservoir according to one embodiment;

Figure 14 is a cross-section through the tank of Figure 13;

Figure 15 shows a belly plate system according to one embodiment;

Figure 16 is a further view of the belly plate system of Figure 15; and

Figure 17 is a cross-section through the belly plate system of Figure 15.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Figures 1 to 5 illustrate an earlier model of the Applicant's machine, as described in NZ Patent No. 578476, the entire contents of which are incorporated by reference herein. Features of that machine may also be used in the inventive machines and components described below. Figures 1 to 4 show a tree harvesting vehicle 1 having an articulated hydraulic arm 2 including a grapple 3 for handling logs and an articulated saw 4 for felling trees. Vehicle 1 is driven by tracks 5 which are driven by hydraulic motors 9 and 10. A winch 6 is provided at one end of the vehicle (either front or rear) having rollers 7 at the other end of the chassis through which a cable from winch 6 exits the vehicle. By winching from a low position good vehicle stability can be maintained.

Figure 4 shows a schematic view of the hydraulic system of the vehicle. Hydraulic fluid is supplied to main valve block 1 1 which supplies hydraulic fluid to winch motor 12, hydraulic motors 9 and 10, rope tensioners 13 and valve bank 14 (supplying other hydraulic components). Control valve block 15 manages the power supply to hydraulic loads. This power management system controls the supply of power between the winch motor 12 and the track motors 9 and 10 of the vehicle. Power is preferentially supplied to the winch until a required cable tension is achieved before power is supplied to the traction system. Preferably the required cable tension can be set by an operator via control panel 16 within the harvesting vehicle. This may be via a touch screen or other suitable input. All actuators of the vehicle are preferably powered hydraulically with the traction system, winch, articulated arm, grappling arm and saw all powered hydraulically.

The vehicle may be controlled by an operator within the vehicle or remote controlled via a wire or wireless link.

Referring now to Figure 5, a method of harvesting trees using the tree harvesting vehicle will be described. A cable 20 from winch 6 is secured to an anchor point 21 upslope of the tree harvesting vehicle. A user may control winch 6 to enable the vehicle to ascend or descend the slope in conjunction with the vehicle traction system. Trees may be felled manually or using articulated saw 4 of tree harvesting vehicle 1. Tree harvesting vehicle 1 may be used to collect logs into a pile 22 which may then be hauled up a slope or hauled down a slope using a fixed winch 23 (commonly termed a yarder or skyline hauler) and cable 24 or via a transport vehicle. Felled logs may be picked up using grapple 3 and manipulated using articulated arm 2 to stack the logs into pile 22. Using winch 6 and the vehicle traction system, vehicle 1 may collect logs from various locations up and down the slope and stack them in pile 22.

The method is particularly effective on slopes of greater than 20° where machine stability and traction might otherwise be hazardous without the connecting cable. Figure 6 shows a machine 100 suitable for operation on steep slopes. The machine 100 may include an articulated arm 101, which in preferred embodiments may carry a harvesting head unit for felling or harvesting trees. However, aspects of the machine may be used in other applications. The machine may run on tracks 102, but in some embodiments wheeled vehicles may be suitable.

As shown in Figure 6, a vehicle support 103 may be fitted to the downhill end of the vehicle. The vehicle support is rear mounted and consequently faces down slope when the vehicle is tethered and working on an incline. The vehicle support 103 may be in the form of an excavator blade, bulldozer-type blade or similar. A cable entry point 104 is positioned at the uphill end of the vehicle, opposite from the vehicle support. The cable is wound on a winch mounted to the vehicle chassis and passes from the winch through the cable entry point and can be attached to a remote anchor point.

The vehicle support 103 may be mounted on a hydraulic linkage 105. In use the hydraulic linkage can be operated, either manually be the operator or automatically by the control system, to press against the ground to provide a force on the vehicle in an uphill direction.

The blade 103 can be driven up and down using hydraulic control or may be lowered (under the sole influence of gravity) without the need for hydraulic pressure. The blade 103 provides several potential functions. It can be deployed to stabilize the vehicle chassis during operations such as tree felling. The blade 103 can also be lowered during tracking down-hill to provide resistance to fore-aft tipping. When on steep slopes, the blade 103 can be deployed to skim the ground surface and thus present additional down-hill tracking resistance. In this way the blade can be used to control the rate of vehicle down-hill descent. Preferably the blade can be deployed to a level below the plane defined by the lower surfaces of the vehicle tracks or wheels. In some embodiments a sensor may be provides to report the current blade attitude to the machine operator.

The vehicle support or blade 103 therefore provides a further uphill force to support the vehicle tracks or wheels and the winch system. The operator can engage the ground with the blade to either act as a brake or assist to stabilise the vehicle. The winch in some embodiments has around 380m of 23mm diameter wire rope and a maximum pull rating of 15 tonnes. In some embodiments the winch unit complete with drum, fairlead, housing and wire rope weighs approx. 4.5 tonnes. The positioning of such a significant amount of weight in a machine working on steep slopes up to 55 degrees is critical both for balance and its tractive ability.

One embodiment of the machine described in the Applicant's NZ Patent No. 578476 had the winch positioned at the rear (downhill end) of the machine and the wire traveled underneath to feed out through a fairlead in the front of the machine (see Figure 7). The reason for this was so that level wind technology could be used. This technology consists of a scrolled shaft with a roller carriage sliding on it with a 'knife' inserting into the scroll to move the wire side to side.

With 15 tonnes of tension in the wire rope and a fleet angle F of 8 degrees, as shown schematically in Figure 8, the tension forces in the wire rope induce a 2 tons (max allowable) of side load into the knife/scroll assembly. The closer the winch is to the fairlead, the higher the maximum loading (up to 21 tonnes at 90 degrees).

Further, should the winch be mounted directly behind the fairlead (see Figure 9), the roller sheaves would need to be at least 450mm diameter to take the applied forces, resulting in space issues. This system also uses an alignment system including a knife that follows grooves made in a scroll shaft and the thickness of this knife (12mm in one embodiment) limits how much load can be put into the roller carriage.

The Applicant's winch is preferably positioned the front of the machine. This moves the 4.5 tonne weight of the winch system to the front to help with tractive effort and balance. (Note the generally undesirable position of the centre of gravity C in Figure 7, where the winch is at the downhill end.) Optimum tractive effort is achieved when the entire length of the track is subjected to a uniform load from the weight of the machine, which is more nearly the case with the winch at the uphill end.

In one embodiment the winch is positioned directly behind the fairlead resulting in a best case scenario for tractive effort and balance. In preferred embodiments, the winch drum is mounted on a sliding carriage which is moved side to side by a hydraulic ram so that the wire is always paying off the drum directly behind the opening in the fairlead.

Figure 10 shows a winch drum 1 10 having a winch axis marked by dashed line 11 1. The winch drum is fitted with a planetary drive gearbox on each side driven by a hydraulic motor on each gearbox, with the gearbox and motor together being marked 1 12. The gearbox and motor 1 12 may reside partly or wholly within the inner core of the winch drum. The winch is powered by the hydraulic motors 1 12 when drawing cable in onto the drum. When travelling down hill (i.e. when paying out cable) the winch is not powered out, the motors 1 12 are used as a brake and the cable is pulled off of the drum against that braking force.

Further, as a safety mechanism the internal brake of the planetary gearbox may activate when alarms are triggered.

Cable 1 13 passes from the winch drum 1 10 to a fairlead 1 14. In one embodiment the fairlead may comprise four heavy rollers, two on vertical axes and two on horizontal axes. The rollers may be positioned in a rectangular arrangement to provide a central rectangular opening through which the cable passes. The fairlead thus constrains the cable movement to within the inner opening of the four rollers. As the cable passes over the fairlead rollers they freely rotate and therefore help prevent damage to the cable.

The winch drum 1 10 is mounted on one or more slide shafts 1 15 (preferably two or more traversing shafts) by sliding mounts 1 16. In this way the winch . carriage, including the winch drum 1 10, gearboxes and motors 112 and sliding mounts 116 is mounted for transverse sliding motion parallel to the winch axis 1 11. In other words, the winch drum 1 10 is mounted for linear traversing motion along the winch axis 1 1 1. This traversing motion may be driven by a linear actuator 1 17 acting against the winch carriage. In preferred embodiments the linear actuator 1 17 is a hydraulic cylinder. The traversing motion is controllable independently of the winch drum rotation.

A position sensor 1 19 may be used to sense the winch carriage transverse position. In the embodiment shown the sensor 1 19 includes an ultrasonic range finder sensor 1 16, with an ultrasonic sensor target 120 mounted at a centre point of the winch assembly.

A rotary encoder (not shown in Figure 10) may be provided to sense rotational position of the winch drum.

As shown in Figure 10, the cable 1 13 is generally perpendicular to the winch axis. As the cable is wound onto (or pulled off) the winch drum 1 10, the drum is driven by the linear actuator 1 17 along its axis 1 1 1 in order to maintain the substantially perpendicular relationship between cable 1 13 and winch axis 1 1 1. The extent of this traversing motion should be sufficient to allow the perpendicular relationship to be maintained at all points along the length of the winch drum 1 10.

This traversing motion enables the cable 1 13 to be wound onto the drum 1 10 in an orderly fashion such that coils are laid consecutively next to each other. In this way a layer is wound on progressing from one side of the drum 1 10 to the other. Once the layer is complete and the rope has reached the extreme end of the drum the rope then naturally winds up onto the next layer and progressively returns across the traversing drum, laying down one coil at a time. Consequently the rate of drum traversal is linked directly to the rate of winch drum rotation. In one embodiment a software based control system receives data from the sensors detecting rotational and transverse position of the winch and controls the movements of the winch (both rotational and transverse motion) in accordance with that data and with the vehicle motion.

The drum rotation quantifies the corresponding amount of drum traverse and direction.

The controller also monitors and controls the rope tension within system defined values, or to an operator defined value within the system defined limits.

Different tension limits may be applied for up slope and down slope movement. These rope tension values are defined and controlled independently of each other. The vehicle drive system pressure may be monitored and used to synchronize the winch tension with the vehicle motion, when travelling up slope.

Further, as the cable offset (i.e. radius) relative to the winch axis 1 1 1 changes the relationship between winch torque and tension also changes. The greater the number of cable layers on the winch drum, the greater the offset/radius and the greater the torque needed to apply the same tension. The controller takes this into account and alters the torque applied to the winch drum 1 10 in order to keep the wind on tension constant. A maximum tension limit may be applied. For example, in one embodiment the rope tension is limited to a maximum of 15 Tonnes. In the absence of any other settings, the winch controller can be manipulated to deliver 15 tonnes of tension, upon demand, when heading up slope. Within the safe operational limits of rope tension, a reduced upper limit can be set by the operator. This can be set for up slope and down slope operation.

When the vehicle is stationary the winch may provide a rope tension to help prevent vehicle movement or tipping down the slope.

The winch controller can also be manipulated to deliver a minimal tonnage in rope tension if desired. Unlike a conventional winch drive system, the operational up slope rope tension and down slope rope tension may be set at different magnitudes.

The controller may also monitor the winch drum and thus rope speed are monitored for over-speed (i.e. a speed greater than a threshold). If the drum over-speed condition is detected then the winch drum brake is applied.

The fairlead 1 14 may consist of a number of rollers mounted to provide a cable entry / exit point to the winch assembly. The fairlead is preferably centrally mounted with respect to the vehicle chassis. The fairlead rollers may be sized to ensure that the rope is not curved around too sharp a radius when it is placed under tension, at an angle to the vehicle axis (the vehicle axis being perpendicular to the winch axis 1 11).

The fairlead rollers may rotate freely if the rope rides over them so as to prevent abrasion on the outer strands of the rope. Any horizontal or vertical loads, generated by the rope arriving at the machine from any angle other than straight ahead are 'neutralized' by the fairlead rollers prior to the rope entering the winch bay.

Figure 10 also shows a feedout assembly 125. The feedout assembly is configured to apply a tension to the cable, tending to draw the cable off the winch drum when the cable is being fed out. This is important when there is no or minimal external load applied to the cable, as it helps to ensure proper feeding out of the cable and prevents tangling of the cable on the winch drum. The rollers maintain a low level of tension in the rope between the drum and the feed-out roller system. This ensures that the spooled rope is always held in tight wraps on the drum.

The feedout assembly 125 may include a number of feed out rollers 126. A pair of opposing feedout pinch rollers may be used. One or both of the pinch rollers may be formed with a circumferential groove, such as a semi-circular annular groove, the groove being dimensioned to match the cable 1 13. This groove resists sideways motion of the cable off the roller.

As shown, the feed-out assembly is positioned between the fairlead 1 14 and the winch drum 1 10. Rope passes between the feedout rollers and is constrained laterally by the two grooves.

The feed-out rollers may be mounted on a carriage that is free to slide vertically and horizontally (laterally), within the physical constraints of the machine. Any side-to- side, lateral movement is made against the resistive force of biasing elements, such as mechanical coil springs 127. The spring arrangement biases the carriage to naturally default to a central position. The horizontal degree of freedom of the carriage may be around +/-50mm but this is dictated by the opening size in the fairlead.

The direction of the rope feed-out is essentially not influenced by the feed-out roller system. The direction of the rope within the winch bay is solely governed by the drum peel-off point (i.e. the point where the cable is coming off the winch drum 1 10) and the inner opening confines of the fairlead 1 14. A holding force may be applied by a hydraulic ram, causing the feed-out rollers to clamp onto the rope. As the winch drum pays rope out, the feed-out rollers are powered to rotate as a coupled pair and generate resistance so as to maintain a nominal feed-out rope tension.

As the winch drum draws rope in, the feed-out rollers resist rotation, as a coupled pair and thus generate resistance, so as to maintain a nominal feed-in rope tension, to ensure that the windings on the winch drum stay tight. The feed-out rollers can be separated to allow for easy rope replacement.

In one embodiment two driven feed-out pinch rollers exert tension on the wire coming off the drum and this tension is maintained in both directions. In one embodiment the pinch rollers may squeeze the rope with a pinch force via a hydraulic ram.

Each feed-out pinch roller may be fitted with a torque arm-mounted hydraulic motor 128. The effective diameter of the pinch roller may be around 100mm. In one embodiment a maximum rotational speed of the pinch roller may be around 160rpm.

The feed-out rollers will feed slack rope out of the fairlead when required. The feed out system also keeps the line firm/tight on the winch drum at all times to eliminate poor rope spooling causing rope damage.

In a Winch and Tracks mode the winch system works in unison with the tracks to provide improved stability and traction on steep terrain. For example, when tracking downhill, the wire rope tension creates an uphill force on the vehicle chassis and consequently helps to resist track slippage and/or vehicle tipping down the slope. The rope tension can be set by the operator independently for uphill and downhill tracking. The downhill tension has calculated default values when in specific modes of operation, the operator can also set these values in other modes if desired. The operator set downhill tension is termed the 'Downhill Preset Tension' value. Utilization of the Downhill Preset Tension value is actively applied by the dedicated control system for downhill tracking. However, the Downhill Preset Tension utility is constrained and adapted - based upon the speed at which the wire rope is being paid out (line speed). In this way an Adaptive holdback tension is achieved, as described below.

Whilst tracking downhill in Winch and Tracks mode an adaptive system has been developed which only utilizes the Downhill Preset Tension at lower line speeds. However, within this mode, once a threshold line speed is reached the holdback tension increases as a function of increasing line speed. This ramped rope tension escalation extends up to a Ramp Speed Limit. Further line speed increases then occur at constant rope tension (at the Rope Tension Limit) up to a point where the brake is automatically applied and the machine brought to rest. This absolute speed limit is termed the Vehicle Speed Limit. The behavior described herein is illustrated in the graph of Figure 1 1. This system is designed to mitigate the possibility of a vehicle runaway situation.

The rope tension is maintained at a preset or desired level across all winch drum wound layers.

As a winch pays out rope the effective diameter of the drum decreases and, conversely, as a winch hauls in rope the effective diameter increases. If a constant winching torque is applied to the drum by a drive motor (as is normally the case) then the varying effective diameter results in a changing rope tension. A constant rope tension is achieved by modulating the drive motor torque in harmony with the rope layers. This is an important feature that aids vehicle stability and provides consistent control characteristics for the operator's benefit. Beyond these benefits the constant tension system helps to maintain a safe working load on the rope whilst providing optimal machine performance.

A further feature of the Applicant's winch system is the fact that the pay out tension and haul in tension are most often set and controlled at different levels. The rope tension magnitude is dependent upon system-defined values and/or operator-defined values. The uphill or downhill tension may dominate. The tension levels may be set based on the machine function, incline of operation and ground conditions for example. The implementation of these values is transparent to the operator as the control system is configured to drive the winch appropriately when the track pedals are depressed (for forward/backwards/left/right/ stationary vehicle motion).

Normally a winch is driven directly by a prime mover (e.g. a motor) and moves synchronously with the prime mover drive shaft. In the case of the Applicant's machine the winch and track operations are coordinated but not physically synchronized. For example, when the machine is travelling down a slope the rope may be pulled off the drum whilst the drum offers turning resistance, thus creating a tension in the rope. Similarly, when the machine is travelling up hill the winch drum experiences a desired level of torque from the prime mover but will only wind on the rope as the tension permits, e.g. as the tracks propels the vehicle forward (up the slope). When the vehicle moves up the slope the winch winds on the rope and maintains a constant preset tension as it does so. The vehicle is described as track driven. However, under certain circumstances, it is apparent that enhanced performance could be achieved by using wheels instead of tracks, and such variations are intended to fall within the scope of the invention. This is particularly the case when minimal ground disturbance (damage) is required - a scenario which is being pursued in the international logging sector and is anticipated to be implemented in New Zealand in due course.

A wheeled vehicle configuration would differ from a tracked configuration in the following ways.

Tracks typically provide around 2/3 of the required tractive force to propel the vehicle up a slope and the winch provides the balance of force (up to 1/3). A wheeled vehicle cannot attain equivalent traction and therefore relies more heavily on the winch system. Therefore it is anticipated that a wheeled vehicle would develop around 1/3 of the tractive force to climb an incline through the wheels with the winch developing 2/3 of the required force. Consequently the wheeled vehicle would be capable of moving around on low gradient independently of the winch but would essentially act as a maneuverable platform, raised by the winch, when used in conjunction with the winch on steeper gradients.

The optimum shape for a fuel tank on steep slopes is circular in plan view and with a high height to diameter ratio (ie. the tank should be tall and thin). The fuel pickup can be situated in the centre of the tank at the bottom so that the fuel level remains above the pickup regardless of angle, for fuel levels greater than about 5% of tank capacity. Square cross-section tanks may be acceptable is alright and rectangular is bad.

In one embodiment the Applicant's vehicle has a fuel tank capacity of about 1000 litres and for space reasons a non-ideal rectangular cross-section was desirable. The Applicant's fuel tank is shown in Figure 12. The tank 130 includes a first chamber 131 and a second chamber 132. A fluid inlet 133 allows fluid to be added. Preferably the inlet is placed in the first chamber 131, but in some embodiments may be in the second chamber 132. In some embodiments the fluid inlet 133 may also allow gases to escape from the tank. A fluid outlet 134 may be positioned at or near the bottom of the first chamber. A first flow path 135 is connected between the first chamber 131 and the second chamber 132, opening into each of the first and second chambers at a point at or near to the bottom of each said chamber. A check valve 136 is positioned in the first flow path, allowing fluid flow through the first flow path from the second chamber to the first chamber, but not from the first chamber to the second chamber.

In the embodiment shown a further flow path 138 is provided between the first and second chambers. This further flow path opens into first chamber at point 139 spaced above the bottom of the chamber, while it opens into second chamber 132 at or near the bottom of the chamber. The second flow path may allow flow in either direction, or in some embodiments may allow flow only from the first chamber into the second chamber.

Finally, the fuel tank 130 may include an gas transfer path 140 allowing gas flow between the two chambers 131, 132. As shown, the gas transfer path may connect to each chamber 131, 132 at or near the top of each chamber.

This arrangement allows the tank 130 to be filled and breathe from one point 133 but does not let the first chamber drain into the second chamber when the fuel level drops below the level of the second flow path inlet 139. This ensures fluid flow to the outlet 134 even when fuel level is low on a steep slope. This fuel tank configuration may be used in other fluid reservoirs, such as vehicle coolant tanks etc.

The Applicant has also found that conventional hydraulic fluid tanks are problematic when used on steep slopes. In a conventional tank, suitable for use on level ground, the hydraulic fluid level is typically around 75% on average of the tank capacity. This allows the hydraulic fluid level to rise or fall within the tank while maintaining a fluid level that is acceptable for most applications. When a conventional hydraulic fluid tank is used on steep slopes the fluid surface remains horizontal, while the tank itself is angled parallel to the slope. This leads to several problems. The hydraulic fluid outlet may be positioned near or even above the fluid surface, such that air rather than hydraulic fluid, or a mix of air and hydraulic fluid, is pumped into the hydraulic circuit. Further, the fluid level may be near or above a breather opening, intended to allow air to flow into or out of the tank. This may cause undesirable flow of hydraulic fluid out of the breather opening.

These problems may be exacerbated by the shape of the tank. For example, long tanks may suffer worse problems than generally square or round tanks, depending on the orientation of the tank to the slope.

In one embodiment the Applicant's hydraulic fluid reservoir holds 800 litres of hydraulic fluid in a relatively long rectangular space. Figure 13 is a perspective view of the tank showing internal and external features. Figure 14 is a cross-section along the line 14'-14' in Figure 13.

The tank, or reservoir, 150 includes a main hydraulic fluid chamber 151 which, in use, remains substantially full of hydraulic fluid. In practice, some air may enter the main chamber 151 and will be removed from the main chamber 151 by a mechanism discussed below.

In one embodiment the main chamber 151 may be formed in two sections or sub- chambers 152, 153. The two sections 152, 153 communicate with each other via a flow path. In the embodiment shown the flow path is provided by a region 154.

The two sections 152, 153 of the main chamber 151 are separated by a further chamber, or expansion chamber, 155, which will be described in detail below.

A hydraulic fluid inlet 156 opens into the top of the main chamber 151. A hydraulic fluid outlet 157 opens from the bottom of the main chamber 151. The expansion chamber 155 in the embodiment shown also acts as a baffle limiting the effect of turbulence at the inlet 156 on flow through the outlet 157.

The inlet 156 and outlet 157 can be connected to a hydraulic circuit in a known manner, as will be well understood by the skilled reader.

A breather outlet 159 is provided at the top of the expansion chamber 155. This outlet allow s gas to escape form the expansion chamber. A breather valve 160 may be fitted to the outlet, to allow gas flow out of the chamber when the pressure within the expansion chamber exceeds a threshold (e.g. 6 psi).

Expansion flow paths 162 allow flow between the main chamber 151 and the expansion chamber 155. Preferably these flow paths connect the top of the main chamber 151 to the bottom of the expansion chamber 155. In the embodiment shown one expansion flow path 162 opens into the top of each chamber 152, 153. When net hydraulic fluid flow (i.e. taking into account both oil flow out of the outlet and oil flow into the inlet) is out of reservoir 150, fluid will flow from the expansion chamber 155 through the expansion flow paths 162 into the main hydraulic fluid chamber 151. When net hydraulic fluid flow is into the reservoir 150, fluid will flow from the main hydraulic fluid chamber 151 into the expansion chamber 155. In this way the changes in hydraulic fluid level are kept within the expansion chamber, isolated from the hydraulic fluid outlet 157. The fluid level 158 in the expansion chamber will rise and fall with changes in net fluid flow. The main tank 151 remains substantially full at all times.

Further, when fluid flows from the main chamber 151 into the further chamber 155, gases trapped at the top of the main chamber 151 will flow into the expansion chamber and exit the tank 150 through the breather outlet 159. The region 154 that joins the two sub-chambers 152, 153 does not extend all the way to the top of the reservoir 150 (see Figure 14). Air is therefore trapped in a region at the top of each sub-chamber. As shown in Figure 13, when the tank 150 is at an angle to the horizontal, air will tend to rise to region near an intake of the expansion flow path 162 (where the fluid level is marked 165). The hydraulic fluid reservoir 151 may also include a fluid level sensor (not shown) arranged in the expansion chamber 155, to monitor fluid level within that chamber. The fluid level may change due to actuator movements on the machine or due to the thermal expansion of the oil, particularly as the machine heats up after standing idle (overnight for example). A low fluid level may indicate that further fluid needs to be added. The positioning of the sensor within the expansion chamber 155 minimizes reading variations due to tilting of the tank (when on steep slopes).

Figures 15 to 17 show a belly plate system 170. Belly plates are used to close openings on the underside of heavy vehicles, including tracked or wheeled heavy vehicles, in order to protect the vehicle from damage. Belly plates are heavy and unwieldy, and removing a belly plate to access the opening is difficult, particularly in the field. The Applicant has devised a belly plate system that attaches to the underside of the vehicle chassis. The system includes a belly plate 171. A mounting plate 172 is configured for attachment to the vehicle chassis, either by a permanent connection (e.g. welding) or temporary connection (e.g. bolts). The mounting plate includes an opening 173, which will align with the opening on the underside of the vehicle. In some embodiments a mounting plate may not be required, with the belly plate system being attached directly to the vehicle chassis.

The belly plate system 170 also includes a lowering / raising mechanism 174. The lowering / raising mechanism 174 may connect between the belly plate 171 and mounting plate 172, or directly between the belly plate 171 and the vehicle chassis. The lowering / raising mechanism allows controlled lowering of the belly plate, with the load being transferred by the belly plate system to the vehicles chassis. The lowering / raising mechanism also allows controlled raising of the belly plate. Further, when the belly plate 171 is in a lowered position (Figure 15) it is allowed to rotate about the lowering mechanism 174 to swing away from the opening, allowing operator access.

Figure 17 is a cross-section showing the workings of the lowering mechanism 174. The lowering mechanism may be a suitable linear actuator, such as a hydraulic cylinder or, in the embodiment shown, a threaded rod arrangement. The threaded rod arrangement includes a fixed nut 175 and a threaded rod 176. One end of the threaded rod 176 acts against a fixed element 177 attached to the belly plate 171. Concentric tubes 178, 179 slide with respect to each other, maintaining the rigidity and alignment of the system 170. The lowering mechanism 174 may be actuated by hand cranking of the threaded rod 176, or by a built in motor (not shown) or an external motor such as a batter drill or rattle gun.

In normal use, the belly plate will be attached to the vehicle chassis, either directly or indirectly via the mounting plate, by a releasable mounting arrangement. In the embodiment shown fasteners (e.g. bolts) 180 engage through holes 181 in the belly plate 171 into holes 182 in the mounting plate 172. When access is needed to the covered opening, the releasable mounting arrangement can be released (e.g. by undoing the bolts 180). The belly plate system then takes the load of the belly plate through the lowering mechanism 174. A user can operate the lowering mechanism to lower the belly plate and swing it out of the way. Once work is complete these steps can be reversed to reattach the belly plate.

In this way, the removal and reattachment of the belly plate is made an easy and safe job for a single worker.

There is thus provided a tree harvesting vehicle capable of operating safely and productively on steep slopes (typically over 20 degrees). The vehicle can perform felling, gathering and transport operations. The vehicle has improved stability due to its low winching point. The method of harvesting provides a faster and safe method of harvesting on steep slopes that can also be highly productive.

Various features of the Applicant's vehicle have been discussed above. These features may be used independently of each other, or any combination of the above features may be used. The Applicant's systems are particularly suited to tree harvesting vehicles for operating on steep slopes, but may be used in other vehicles, particularly vehicles for operating on steep slopes. While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of the Applicant's general inventive concept.

Claims

CLAIMS:

1. A vehicle configured for operation on steep slopes, including:

a) a chassis;

b) a winch mounted to the chassis and adapted, in use, to haul the vehicle via a cable connected to a remote anchor point, wherein the winch includes a winch drum mounted for rotational motion about a winch axis and linear, traversing motion parallel to the winch axis.

2. A vehicle as claimed in claim 1 , being a tree harvesting vehicle and further including a head unit including one or more tools for harvesting trees.

3. A vehicle as claimed in any preceding claim, further including a rotational drive arrangement configured to drive or resist the rotational motion of the winch drum.

4. A vehicle as claimed in claim 3 wherein the rotational drive arrangement is configured to drive winding of the cable onto the winch drum when the vehicle is moving towards the remote anchor point and to provide a braking force to resist unwinding of the cable from the winch drum when the vehicle is moving away from the remote anchor point.

5. A vehicle as claimed in any preceding claim further including a linear drive arrangement configured to drive the linear, traversing motion parallel of the winch drum.

6. A vehicle as claimed in claim 5, wherein the linear drive arrangement includes a linear actuator.

7. A vehicle as claimed in any preceding claim, wherein the winch is mounted on one or more shafts for linear, traversing motion parallel to the winch axis.

8. A vehicle as claimed in any preceding claim, including a controller configured to maintain a desired tension by adjusting a torque applied to the winch drum.

9. A vehicle as claimed in claim 7 wherein the controller controls the torque to compensate for a cable offset relative to the winch axis.

10. A vehicle as claimed in any preceding claim wherein the rotational and traversing motion are controllable independently of each other.

1 1. A vehicle as claimed in any preceding claim including a rotary encoder configured to sense a rotational position of the winch drum.

12. A vehicle as claimed in any preceding claim including a position sensor configured to sense the traversing position of the winch drum.

13. A vehicle as claimed in any preceding claim, including a controller configured to control the winch drum rotational movement and linear, traversing movement such that the cable remains substantially perpendicular to the winch axis.

14. A vehicle configured for operation on steep slopes, including:

a) a chassis;

b) a winch mounted to the chassis and adapted, in use, to haul the vehicle via a cable connected to a remote anchor point, wherein the winch includes a winch drum mounted for rotational motion about a winch axis; c) a cable entry point on an uphill side of the vehicle, where cable passes to/from the winch via the cable entry point; d) a vehicle support mounted on a linkage on a downhill side of the vehicle and controllable to push against the ground to provide a force in an uphill direction.

15. A vehicle as claimed in claim 14, being a tree harvesting vehicle and further including a head unit including one or more tools for harvesting trees.

16. A vehicle as claimed in claim 14 or 15 wherein the vehicle support is an excavator blade.

17. A vehicle as claimed in any one of claims 14 to 16 wherein the vehicle support is mounted on a hydraulic linkage.

18. A vehicle as claimed in any one of claims 14 to 17, including a plurality of tracks or wheels, wherein the vehicle support is operable to be lowered below a plane defined by the bottom surfaces of the tracks or wheels.

19. A hydraulic fluid reservoir including:

a) a hydraulic fluid chamber;

b) a hydraulic fluid inlet opening into the hydraulic fluid chamber and a hydraulic fluid outlet opening out of the hydraulic fluid chamber, for connection to a hydraulic circuit;

c) a further chamber;

d) one or more flow paths allowing fluid flow between the hydraulic fluid chamber and the further chamber; and

e) an opening allowing air to flow into or out of the further chamber.

20. A hydraulic fluid reservoir as claimed in claim 19, wherein the one or more flow paths communicate between one or more ports at or near to the top of the hydraulic fluid chamber and one or more ports at or near to the bottom of the further chamber.

21. A hydraulic fluid reservoir as claimed in claim 19 or 20, including a breather port at the top of the further chamber, allowing gases to vent from the further port.

22. A hydraulic fluid reservoir as claimed in claim 21 , including a breather valve controlling flow through the breather port, the breather valve allowing flow out of the breather port when pressure in the further chamber exceeds a threshold.

23. A hydraulic fluid reservoir as claimed in any one of claims 19 to 22, wherein the hydraulic fluid inlet is at or near to the top of the hydraulic fluid chamber.

24. A hydraulic fluid reservoir as claimed in any one of claims 19 to 23, wherein the hydraulic fluid outlet is at or near to the bottom of the hydraulic fluid chamber.

25. A hydraulic fluid reservoir as claimed in any one of claims 19 to 24, wherein, in use, when net hydraulic fluid flow is out of the reservoir, hydraulic fluid flows from the further chamber through the flow paths into the hydraulic fluid chamber and when net hydraulic fluid flow is into the reservoir, hydraulic fluid flows from the hydraulic fluid chamber through the flow paths into the further chamber.

26. A hydraulic fluid reservoir as claimed in any one of claims 19 to 25, wherein, in use, the hydraulic fluid chamber remains substantially full at all times.

27. A hydraulic fluid reservoir as claimed in any one of claims 19 to 26, wherein, in use, a level of hydraulic fluid in the further chamber will rise and fall over time.

28. A hydraulic fluid reservoir as claimed in any one of claims 19 to 27, further including an oil level sensor configured to sense the level of hydraulic fluid in the further chamber.

29. A hydraulic fluid reservoir as claimed in any one of claims 19 to 28, wherein the hydraulic fluid chamber is formed in two sections that communicate with each other and are positioned on either side of the further chamber.

30. A hydraulic fluid reservoir as claimed in claim 29, wherein the two sections communicate with each other in a lower section of the reservoir, but not in an upper section of the reservoir.

31. A fluid reservoir including:

a) a first chamber and a second chamber;

b) a fluid inlet allowing fluid to be added to either the first chamber or the second chamber;

c) a fluid outlet positioned at or near the bottom of the first chamber;

d) a first flow path between the first chamber and the second chamber, opening into each of the first and second chambers at a point at or near to the bottom of each said chamber; and

e) a valve positioned in the first flow path, allowing fluid flow through the first flow path from the second chamber to the first chamber, but not from the first chamber to the second chamber.

32. A fluid reservoir as claimed in claim 31 wherein the fluid inlet is in the first chamber.

33. A fluid reservoir as claimed in claim 31 or 32 including a second flow path between the first and second chambers, opening into the first chamber at a point spaced above the bottom of the first chamber and opening into the second chamber at a point at or near the bottom of the second chamber.

34. A fluid reservoir as claimed in claim 33 wherein the second flow path allows fluid flow in either direction.

35. A fluid reservoir as claimed in any one of claims 31 to 34 including a gas transfer path connecting the first and second chambers and opening into each chamber at a point at or near the top of that chamber.

36. A belly plate system for a tracked or wheeled heavy vehicle, including:

a) a belly plate arranged to cover an opening in the underside of the vehicle; b) a releasable mounting arrangement for releasably fixing the belly plate to a chassis of the heavy vehicle;

c) a lowering mechanism operating directly or indirectly between the belly plate and the chassis of the heavy vehicle, the lowering mechanism being: configured to take the weight of the belly plate on release of the releasable mounting arrangement; and operable by a user to lower the belly plate in a controlled manner after release of the releasable mounting arrangement.

37. A belly plate system as claimed in claim 36 wherein the releasable mounting arrangement includes one or more releasable fasteners.

38. A belly plate system as claimed in claim 36 or 37 wherein the releasable mounting arrangement includes a mounting plate configured for permanent attachment to the chassis of the heavy vehicle, the releasable mounting arrangement releasably fixing the belly plate to the mounting plate.

39. A belly plate system as claimed in claim 38 wherein the lowering arrangement operates between the belly plate and the mounting plate.

40. A belly plate system as claimed in any one of claims 36 to 39 wherein the lowering arrangement includes a linear actuator.

41. A belly plate system as claimed in any one of claims 36 to 40 wherein the lowering arrangement also allows controlled raising of the belly plate.

42. A belly plate system as claimed in any one of claims 36 to 41 wherein the belly plate is rotatable about the lowering arrangement when in a lowered position, such that it can be rotated away from the opening.

43. A vehicle configured for operation on steep slopes including:

a) a chassis;

b) a winch mounted to the chassis and adapted, in use, to haul the vehicle via a cable connected to a remote anchor point, wherein the winch includes a winch drum mounted for rotational motion about a winch axis; and c) a controller configured to adjust a torque applied to the winch drum in order to control the tension applied to the cable.

44. A vehicle as claimed in claim 43, being a tree harvesting vehicle and further including a head unit including one or more tools for harvesting trees.

45. A vehicle as claimed in claim 43 or 44 wherein the controller is configured to adjust the torque applied to the winch drum to provide a desired braking force when the vehicle is moving downhill against cable tension.

46. A vehicle as claimed in any one of claims 43 to 45 wherein the controller is configured to adjust the torque applied to the winch drum to provide a desired uphill force when the vehicle is moving uphill with the cable tension.

47. A vehicle as claimed in any one of claims 43 to 46 wherein the controller adjusts the torque to compensate for the effect of a cable offset relative to the winch axis on cable tension.

48. A vehicle as claimed in any one of claims 43 to 47 wherein the controller is configured to adjust the torque applied to the winch drum when the vehicle is moving downhill against the cable tension, to provide:

a. a first constant tension at all cable pay-out speeds up to a first threshold speed;

b. a tension that increases from the first constant tension to a second constant tension for cable payout speeds between the first threshold speed and a second threshold speed; and

c. the second constant tension at speeds above the second threshold speed.

49. A vehicle as claimed in any one of claims 43 to 48 wherein the controller is configured to adjust the torque applied to the winch drum to provide a safety braking force should the vehicle speed exceed a safety limit.

50. A vehicle as claimed in any one of claims 43 to 49 including a user input device enabling a user to set one or more of: one or more downhill tension values; and one or more uphill tension values.

51. A vehicle configured for operation on steep slopes including:

a) a chassis; b) a winch mounted to the chassis and adapted, in use, to haul the vehicle via a cable connected to a remote anchor point, wherein the winch includes a winch drum mounted for rotational motion about a winch axis; and c) two or more feed-out rollers, including at least one powered feed-out roller, the feed-out rollers configured to apply a tension force to the cable to feed the cable off the winch.

52. A vehicle as claimed in claim 51 , being a tree harvesting vehicle and further including a head unit including one or more tools for harvesting trees.

53. A vehicle as claimed in claim 51 or 52, wherein the feed-out rollers include at least one pair of counter-rotating powered pinch rollers.

54. A vehicle as claimed in claim 53 wherein at least one of the pinch rollers has a groove formed in its circumference, the cable lying at least partly within the groove such that the groove resists sideways motion of the cable.

55. A vehicle as claimed in any one of claims 51 to 54 wherein the feed-out rollers are mounted on a feed-out carriage that is free to move horizontally and vertically.

56. A vehicle as claimed in claim 55 including one or more biasing elements tending to force the carriage to move horizontally to a central position.

57. A vehicle as claimed in any one of claims 51 to 56 wherein the tension force is greater than 100N.

58. A vehicle as claimed in any one of claims 5 1 to 57 wherein the tension force is around 200N.

59. A vehicle as claimed in any one of claims 51 to 58 wherein the feed-out rollers operate to apply a minimum tension to the cable when the cable is being wound in, is being fed out or is static.