WO1992002394A1

WO1992002394A1 - Air cushion vehicle

Info

Publication number: WO1992002394A1
Application number: PCT/GB1991/001358
Authority: WO
Inventors: Natale Cantone; Giovanni Cantone; Robert Longley Trillo
Original assignee: Agri-Engineering Di Giovanni Cantone & C S A S
Priority date: 1990-08-10
Filing date: 1991-08-09
Publication date: 1992-02-20
Also published as: AU8336791A; GB9017627D0

Abstract

An air cushion vehicle for agricultural use comprises a platform (1) supported by an air cushion (2) and a traction arrangement comprising a traction arm (5), pivoted to the platform (1) about a transverse axis located adjacent the centre of pressure of the air cushion (2), and a steerable and drivable traction wheel (8) of large diameter and very narrow width. Raisable traction wheels (16) may be mounted on the end of the traction arm (5) pivoted to the platform (1), which traction arm is preferably of A-frame design, to form a tricycle support arrangement with the wheel (8). A longitudinal flexible divider may be provided in the plenum chamber defined by the skirt (2) to give stability in roll to the vehicle.

Description

AIR CUSHION VEHICLE

The invention relates to an air cushion vehicle suitable for use for agricultural work. Our Patent specification GB 2 219 779 describes an air cushion vehicle for agricultural working, particularly in rice fields, with a steerable traction wheel carried by a traction arm which is pivotally connected to the front of the vehicle, the vehicle having, at the rear, at least one retractable guide disc wheel to give directional stability. Retractable auxiliary wheels for use on roads are also provided.

Such a vehicle has proved to be successful particularly on wet or water covered ground, in avoiding formation of the deep and wide wheel furrows which were caused by the tractors and trailers previously used and particularly in avoiding damage to seedlings during the application of fertilizers, herbicides and pest control agents.

Thus, in the Po Valley of Italy, four-wheeled tractors up to 110/120 horse-power towing two-wheeled trailers have been used, not only causing six wheel ruts but being slow in operation, running perhaps at about 5-7 km per hour, and also suffering from being unsteady in roll with the consequence that spray booms tend to operate at varying distance from the ground as they too roll about a longitudinal axis and hence cause variation in the application rate of materials for cultivation. When turning at the end of a rice field the six-wheeled tractor/trailer combination causes quite considerable rutting in the rice field mud and the effect of this is not only to harm the germination of the rice seed and to damage growing rice but also to cause considerable compaction of the soil. Furthermore, the load capacity on the trailer is rather limited so that reloading operations have to be carried out at frequent intervals.

According to one aspect of the invention, there is provided an air cushion vehicle for agricultural working comprising a framework, an inflatable skirt to contain an air cushion to support the framework, a traction arm pivotally mounted at one of its ends to the framework about a transverse axis located approximately at the longitudinal position of the centre of pressure of the air cushion, a wheel leg mounted on the other end of the traction arm and a steerable traction wheel mounted on the wheel leg.

According to another aspect of the invention there is provided an agricultural vehicle in the form of a tricycle tractor comprising a traction arm, a wheel leg at one end of the traction arm, a steerable traction wheel mounted on the wheel leg, a bearing structure at the other end of the traction arm and a pair of support wheels mounted by the bearing structure.

According to yet another aspect of the invention there is provided an air cushion vehicle comprising a framework, an inflatable skirt to define a plenum chamber to contain an air cushion to support the framework and a longitudinal dividing web separating the plenum chamber into two side-by-side compartments.

Advantageously the traction wheel is of large diameter and narrow width, preferably of a diameter equal to approximately 20% to 25 of the overall vehicle length and a width of only 5_. of its diameter. The traction wheel may be provided as two or more narrow traction wheels in a side-by-side arrangement.

Advantageously a large proportion, preferably at least 40J, of the weight of the unladen vehicle, particularly an engine to drive the steerable traction wheel and an air cushion fan, an hydraulic pump to power hydraulic systems and a fuel tank and hydraulic reservoir, are carried on the traction arm so that the weight thereof is partially applied to the ground and partially applied to the bearing structure adjacent to the centre of pressure of the air cushion; The framework preferably includes a hull platform to receive storage tanks for fluids or granular materials to be dispersed on fields to be worked by the vehicle.

A bearing structure provided at the rear end of the traction arm preferably mounts wheels, the wheels being retractable. Thus, the vehicle may have a tricycle tractor structure, comprising the steerable traction wheel and the retractable rear end wheels mounted on the traction arm, combined with the air cushion supported load bearing platform coupled to the tricycle by means of the bearing structure of the platform. Lateral portions of the vehicle can be raisable to reduce the width of the vehicle and enable it to be transported on a road;

Preferably the skirt of the air cushion vehicle is of loop and segment form and smoothing sheets are provided on the underside of the segments to stop the folds between the segments damaging crops or disrupting the terrain surface.

Locking means, preferably in the form of an hydraulic ram, may be provided to restrain pivoting of the traction arm with respect to the bearing structure of the vehicle when the skirt is not pressurised and the vehicle is operating on the traction wheel and the retractable road wheels.

The steerable traction wheel may be provided within the periphery of the vehicle and particularly within the periphery of the skirt.

A single disc guide wheel, mounted on a strut which is pivoted to allow the wheel to rest on the ground and penetrate it under its own weight, can be fitted towards the rear of the vehicle in order to provide directional stability. The single disc guide wheel can be retractable and upon retraction can be twisted through 90° so as to be stored in a horizontal orientation.

The vehicle thus comprises the combination of a single high ground pressure traction wheel with a low pressure air cushion load-carrying platform.

Stability of the vehicle in roll can be achieved by the basic geometrical form of the air cushion skirt system, as can stability in pitch. Stability in roll can be improved by the longitudinal dividing web particularly if the lower edge of the dividing web is provided at a level below the level of the lower edge of the skirt such that it can extend in to the groove in the ground formed by the traction wheel. The air cushion can operate in a displacement mode and need not be designed to plane on the surface of the water as is the case for a conventional high-speed hovercraft. Because of the low resistance of the air-cushion and skirt system the power required can be considerably less than that for a corresponding tractor/trailer combination and hence a great economy in fuel consumption can be achieved with a consequent reduction in exhaust pollution. The vehicle can be designed to work in ricefields of varying water depth and to be capable of traversing the dams or levees which divide one field from another. In addition, it can be capable of climbing out of ricefields onto road-ways servicing the various fields. A rubber track may be provided to be fitted on the traction wheel for use when the vehicle is to be driven for extended distances over roadway surfaces.

The pivot position for the traction arm is preferably above the centre of pressure of the air cushion but may for operational or other reasons be at a slight forward or aft position in relation to the cushion centre of pressure. When the vehicle is fully risen on an air cushion the traction arm is free to rise and fall depending upon the undulations or irregularities of the ground over which the vehicle is running. When in its lowest position the traction wheel leg is preferably substantially vertical with the bottom edge of the wheel well below, for example 1% of craft length below, the nominal bottom edge of the skirt. The traction wheel is very narrow to minimise the width of the single rut it causes in the field. The wheel may be forced down onto the ground by hydraulic or other means but is preferably allowed freely to bear on the ground under its own weight. By causing the traction arm and the wheel leg thereof to carry much of the machinery weight of the vehicle, the payload that can be carried by the air cushion platform can be increased as can the traction of the wheel depending upon the terrain. Pivoting the traction arm above the centre of pressure of the cushion provides that any extra load applied to the arm will not cause a pitching moment to be applied to the air cushion platform, and hence its trim will remain horizontal. For such a pivot arrangement the torque resulting from the application of power to the traction wheel will similarly apply a download or upload at the centre of the cushion, again avoiding an upset of the trim or horizontal attitude of the air cushion platform. It may be beneficial to apply a torque moment to the air cushion; for instance, should the natural pitching moment resulting from hydrodynamic forces (caused by the air cushion) produce a bow-up trim, then this can be countered by a bow-down trim application coming from the moment on the wheel arm.

The traction wheel may, for example, be of 1520 mm diameter with spikes of 90 mm giving an overall diameter of 1720 mm. The traction wheel is preferably made of aluminium or other lightweight material so as to maximise the machinery weight that can be carried by the arm. The spikes in steel can be mounted in four segments around the periphery of the traction wheel. Reducing spike length reduces terrain damage. The wheel leg and remainder of the traction arm may also be constructed in aluminium or lightweight material and the traction arm and/or the wheel leg may embody integral fuel and hydraulic oil tanks.

The traction arm may be of triangular form when viewed in plan and may be used for carrying temporary loads, and is especially valuable in this respect because of its central pivoting in that if loads are carried which may vary during a particular operation this variation of load will not upset the trim of the vehicle whereby a very stable platform can be obtained. An air cushion may be provided by one or more fans, motor- driven, preferably with vertical axes and contained within the depth of the air cushion platform. The fan and motor system could instead be carried on the traction arm with suitable flexible ducting carrying air flow to the platform structure and to the air cushion itself. In this manner some useful percentage of the fan system weight and its drive, which could for example be hydraulic or mechanical, can be carried by the wheel rather than taking it all on the air cushion platform but there is a loss of air cushion platform lift associated with this arrangement. The power for the air cushion fan may be taken, preferably hydraulically, from a single main engine or a separate power supply may be provided. The air is fed to an air cushion contained by the skirt. In the particular application of rice field work it is essential that the fan system should have adequate capacity to allow the vehicle to cross dams and other ridges and occasional ditches where air flow loss is at a maximum. While this condition has to be catered for, it is also important that the normal horizontal running condition should call for the minimum of power and therefore a wide volume flow range is required of the fan system. Air cushion rise height may for example be about 7. to 8% of vehicle length.

The two retractable roadwheels are preferably mounted on or in the vicinity of the main pivot mountings of the traction arm . The wheels are preferably mounted in such a way as to secure the maximum track width when deployed and their mounting may incorporate arrangements to enable extra track width (for instance, outside the normal road width limitation of approximately 2 72 metres) to be available when feasible. The wheel system should be able to carry the full loaded weight of the vehicle.

The roadway wheels in their retracted position may be allowed to protrude beneath the hull in order to provide two aft landing pads for the vehicle when at rest. The freely rotatable free-falling disc guide wheel is preferably provided on the longitudinal axis of the vehicle within the cushion and towards the rear of the vehicle. The disc guide wheel may have a diameter of about 10% of vehicle length and can be raised hydraulically or mechanically when required as for instance when the vehicle is to be turned. The disc guide wheel may be mounted in such a way that if excessive side loads are encountered it can turn against a spring loading or other form of variable loading resistance thus avoiding high loads being applied to the disc mounting structures. In addition it could be steerable. The disc guide wheel retracting mechanism may be designed so that upon retraction the wheel plane moves through 90° thus avoiding the necessity for providing a housing for the wheel above the level of the working deck of the vehicle.

If the steerable traction wheel is provided within the periphery of the vehicle and particularly within the periphery of the skirt, provision is made for areas above the traction wheel and its arm and loads to be covered by a sealing structure for retaining the ^"air cushion pressure. In such an arrangement, for the same overall length of vehicle an appreciably greater cushion area (typically approaching 20%) can be achieved. This area may therefore be used to carry extra load at the same cushion pressure or to carry the same load at reduced cushion pressure. Preferably the traction wheel and the traction arm are mounted in the forward area of the cushion with the arm pivot position at or adjacent to the centre of pressure of the cushion. Such a configuration can give a reduced turning circle diameter and reduced traction arm length and weight. Increased safety would also result from the enclosure of the spiked traction wheel. Where the traction wheel is contained within the boundaries of the air cushion the bow skirt may be of semi-circular form at ground level in order to minimise resistance and wave-making. The traction wheel could be positioned substantially at the middle enabling sideways motion of the vehicle to be effected. With the driving wheel within the air cushion boundaries it is possible for the position of a driving cab to be on the centre line of the vehicle.

In ricefield operations it is essential that the skirt system should cause the minimum disturbance to the rice plants. A smoothing sheet is advantageously incorporated beneath the segments of the skirt particularly the rear segments to prevent their snagging on rice plants and hence disturbing the roots or damaging the growth. This smoothing sheet may be restrained by ties to prevent flapping and consequent terrain surface damage.

If a closed loop/segment skirt configuration is provided the loop is preferably fed directly by the fan or fans and is of a closed form with holes for feeding the air on into the cushion. In this manner the loop can be maintained at a higher pressure than the cushion pressure and then offers greater resistance to deformation and increased stability of the skirt system in roll and pitch.

A cab may be provided with a filter system and forced ventilation enabling clean air operating conditions to be provided for the driver when the vehicle is operating over dusty conditions or water when spray may be generated.

To enable the vehicle to operate on its three wheels (the traction wheel and the two road wheels) the traction arm can be locked to the platform structure by a hydraulic jack operating in a vertical sense and mounted at a forward position on the craft platform. In normal off-road operations this hydraulic jack has unrestrained motion and hence transfers no loads between the traction wheel arm and the platform structure of the vehicle. When the vehicle is to travel on roads or lanes the jack is hydraulically locked at a position which will provide a substantially horizontal attitude for the platform. When locked in this position the three wheels and the traction wheel arm structure form a tricycle and this may be considered for use as an independent vehicle for specific tasks when not attached to the air cushion platform.

The hull platform structure may contain tanks or spaces for tanks for the carriage of fluids and granular materials such as pesticides and herbicides. The tanks are preferably situated in the lower part of the platform structure in order to reduce the centre of gravity height and improve stability for the vehicle. In one embodiment of this tank arrangement a tank for fluids may surround a tank for granular materials, so allowing alternative loads to be carried while still maintaining their centre of gravity over or near the centre of pressure of the air cushion, either when full or partially full.

Lateral portions of the vehicle may be capable of being raised so that the vehicle width does not exceed road transport limitations. Retraction of the lateral portions may be performed mechanically or hydraulically by the driver. The engine is preferably mounted in the lowest position on the traction arm and may, when the arm is at its lowest position, protrude downwards into the vehicle platform structure in order to minimise centre of gravity height.

To reduce weight the platform sides may be fabric-covered, carrying only the cushion pressure upward load.

An air cushion vehicle according to the invention may have a substantially increased work capacity (speed x payload) compared with the existing tractor/trailer systems. The work capacity is increased because of additional speed capability, typically the craft may operate at speeds of 10-12 km per hour, about twice that of a tractor undertaking the same^'task, and in addition if loads of 1¹/2 to 2 times that of the conventional trailer system are carried a very substantial increase in work capacity results.

Various types of traction wheel may be fitted to the vehicle according to terrain, for example for working over very wet peat bog conditions a low-ground-pressure wheel may be required.

The invention is diagrammatically illustrated by way of example in the accompanying drawings in which:-

Figure 1 is a perspective view from above, the front and one side of an air cushion vehicle for agricultural work according to the invention;

Figure 2 is a schematic side view showing the basic components of the vehicle of Figure 1;

Figure 3 is a transverse sectional view through an air cushion portion of the vehicle of Figure 1;

Figure 4 is a schematic longitudinal sectional view corresponding to Figure 3; Figure 5 is a perspective view from below of a platform and air cushion portion of the vehicle of Figure 1;

Figure 6 is a rear view corresponding to Figure 5; and

Figure 7 is a schematic sectional view showing the arrangement of smoothing sheets for segments of the skirt of the vehicle of Figure 1.

Referring to the drawings, an air cushion vehicle comprises a platform framework 1 carrying an inflatable skirt 2 and defining upstanding bearing members 3 and 4 to receive trunnions of a traction arm 5. Thus the traction arm 5 is mounted for pivotal movement about a transverse horizontal axis provided at approximately the centre of pressure of the vehicle air cushion. The traction arm 5 is generally triangular when viewed in plan and at its free forward end has a bearing pin 6 which defines a generally upright axis about which a wheel leg 7 is pivotable. The wheel leg 7 at its lower end carries a traction wheel 8 which is rotatable by means of a hydraulic motor 9. The traction wheel 8 is in diameter approximately equal to a quarter of the length of the platform 1 and is of very narrow width, only a few centimetres, so that it will cause minimum damage to crops and minimum soil compaction. The bearing members 3, 4 may be longitudinally movable on the platform framework 1 so that longitudinal trim is adjustable.

A main engine 10 is carried by the traction arm 5 to drive a hydraulic pump for transmitting power to the traction wheel hydraulic motor 9, to hydraulic rams for control of the vehicle and to vehicle services. An additional hydraulic pump supplies power to a hydraulic motor driving an air cushion fan 5a.. A driver's cab 11 is provided alongside the traction arm 5 with a protective enclosure thereover.

At the rear of the vehicle a housing 12 is provided to cover a guide disc wheel provided on a retractable arm and rotatable around a transverse horizontal axis to maintain the direction of travel of the platform 1 in line with the direction of the traction wheel 8.

Lateral portions 1ei and 1JJ of the platform are raisable about hinges 13 and 14 respectively to allow the overall width of the vehicle to be reduced for road travel. Road wheels which are retractable are provided beneath the rear end of the platform 1.

Figure 2 shows the platform 1, the bearing support 4, the traction arm 5, the wheel leg 7 and the traction wheel 8 and also indicates a hydraulic connection 15 which may be provided between the platform 1 and the traction arm 5 to lock pivotal movement of the traction arm 5 in the bearing members 3, 4 when required.

The bearing members 3, 4 also carry road-wheel arms 17 for retractable road wheels 16, that is to say movable between a lowered full down position (shown in full line) and a raised full up position (shown in dotted line).

Figure 2 also shows, at the rear end, the mounting of a disc guide wheel 18 on an arm 19 pivotally connected to the bearing structure 1 and movable between a lowered full line position and a raised dotted line position. In the dotted line position the wheel 18 is housed within the housing 12 shown in Figure 1.

As shown in Figures 3 to 5 the skirt 2 surrounds the platform 1 and is of loop and segment form. A central longitudinal divider 20 is provided as a flexible web secured at its upper edge to the platform 1 and connected at its ends to the skirt 2, preferably to two segments 2a of the skirt 2 at each end. The divider 20 separates the compartments 21 each of which is equally pressurised by the fan 5a since a rigid upward extension 20a_^ of the divider 20 bisects an outlet duct 22 of the fan 5 _,. If desired, and an indicated by dotted lines at 20b in Figure 5, the divider 20 may be extended downwardly beyond the bottom edge of the skirt 2 so that in operation it will extend into a groove in the ground made by the traction wheel 8 so as even more effectively to prevent movement of air from one side 22 of the plenum chamber to the other side 22, thereby stabilising the vehicle against roll. This is particularly important when spraybooms are in use extending for example for 10 metres to each side of the vehicle. Flaps shown at 23 in Figure 3 may be provided to prevent air flow back into the duct 22 of the fan from the plenum chambers 21. The upper edges of the rigid divider 20a may be shaped as shown at 2θ in Figure 3 so as to be aligned with the angle of fan discharge air flow.

Figures 6 and 7 show a smoothing sheet 24 extending beneath the segments 2ji of the skirt 2. The smoothing sheet 24 extends from a position A to a position B, is secured at the outside of the skirt 2 by ties 25 and at the inside of the skirt by ties 26.

Claims

1. An air cushion vehicle for agricultural working comprising a framework (1), an inflatable skirt (2) to contain an air cushion to support the framework (1), a traction arm (5) pivotally mounted at one of its ends to the framework (1) about a transverse axis located approximately at the longitudinal position of the centre of pressure of the air cushion, a wheel leg (7) mounted on the other end of the traction arm (5) and a steerable traction wheel (8) mounted on the wheel leg (7).

2. An air cushion vehicle according to claim 1, in which the traction wheel (8) is of large diameter and narrow width having a diameter equal to at lest 20% of overall vehicle length and a width of not more than 5% of its diameter.

3. An air cushion vehicle according to claim 1 or claim 2, in which at least 40% of the unladen weight of the vehicle is carried on the traction arm (5).

4. An air cushion vehicle according to claim 3, in which an engine (10) to drive the steerable traction wheel (8), an air cushion fan (5a), a hydraulic pump, a fuel tank and a hydraulic reservoir are mounted on the traction arm (5).

5. An air cushion vehicle according to any one of claims 1 to 4, in which the framework (1) mounts a hull platform to receive storage tanks for fluids or granular material.

6. An air cushion vehicle according to any one of claims 1 to 5, in which a bearing structure (3, 4) at said one of the ends of the traction arm (5) mounts retractable wheels (16).

7. An air cushion vehicle according to any one of claims 1 to 6, in which lateral portions of the framework (1) and the skirt (2) can be raised to reduce overall vehicle width.

8. An air cushion vehicle according to any one of claims 1 to 7, in which the inflatable skirt (2) is of loop and segment form and smoothing sheets are provided on the underside of the segments to stop the folds between the segments damaging crops or disrupting the terrain surface.

9. An air cushion vehicle according to claim 6, including locking means to restrain pivoting of the traction arm (5) with respect to the framework (1) when the skirt (2) is not pressurised and the vehicle is supported on the traction wheel (8) and the retractable road wheels (16).

10. An air cushion vehicle according to any one of claims 1 to 9_f in which the steerable traction wheel (8) is provided within the periphery of the skirt (2).

11. An air cushion vehicle according to any one of claims 1 to 10, including a single disc guide wheel (18), mounted on a strut (19) which is pivoted to allow the wheel (18) to rest on the ground and penetrate it under its own weight and located adjacent an end of the vehicle opposite to that at which the traction wheel (8) is provided in order to provide directional stability.

12. An air cushion vehicle according to claim 11, in which the single isc guide wheel (18) is retractable and upon retraction is twisted through 90° so as to be stored in a horizontal orientation.

13. An agricultural vehicle in the form of a tricycle tractor comprising a traction arm (5), a wheel leg (7) at one end of the traction arm (5), a steerable traction wheel (8) mounted on the wheel leg (7), a bearing structure (3, 4) at the other end of the traction arm (5) and a pair of support wheels (16) mounted by the bearing structure (3, 4).

14. An agricultural vehicle according to claim 13, in which the traction arm (5) is of A-frame form with the wheel leg (7) mounted at the apex of the side arms of the A-frame and the bearing structure (3, 4) provided at the free ends of the side arms of the A-frame.

15. An air cushion vehicle comprising a framework (1), an inflatable skirt (2) to define a plenum chamber to contain an air cushion to support the framework (2) and a longitudinal dividing web separating the plenum chamber into two side-by-side compartments.

16. An air cushion according to claim 15, in which the lower edge of the longitudinal dividing web extends downwardly below the level of the underside of the inflatable skirt (2).