The present invention relates to retractable wheels and particularly but not exclusively to a steerable wheel for use in amphibious craft such as a boat adapted to be driven on land. In such a craft the wheel would need to be retractable or easily adjustable for height between a lowered position in which it would engage the ground for land use and a retracted position. Whilst amphibious vehicles are not new, most are in the form of amphibious motor cars (or armoured vehicles). One of the main problems with this configuration is that the volume of the car is small in relation to its weight, consequently when in water the vehicle will be deeply immersed. Having little freeboard the vehicle can easily be swamped in any kind of rough water. There is also an insecurity for the occupants in being so low in the water. The design of a car is not appropriate for water travel and therefore a speed only in the region of 5 mph is possible in use. They are nearly always cumbersome on land and sea, are very slow, and are often designed for military use. Those that have a single front wheel, such as that disclosed in U.K. Patent Application No 2024728A do not retract the wheel into the hull of the craft. In this case the front wheel has to be removed when the craft is used on water.

According to the present invention there is provided a vehicle having a steerable wheel and a mechanism for retracting the steerable wheel into a compartment in the vehicle, wherein the mechanism comprises a pillar pivotally mounted to the vehicle within the compartment, a steering arm connected to rotate the pillar about its own axis, a collar slidably mounted on the pillar but rotationally fixed relative thereto, the wheel being attached to the collar so that

it can be raised and lowered in use by sliding the collar on the pillar and steered by movement of the steering arm to rotate the pillar.

Preferably the pillar and collar are of cooperating non-circular section so that rotation of the pillar automatically moves the collar without the use of eyways, splines, or guides. Advantageously the collar supports a pair of wheels. In an amphibious craft these may be arranged one on each side of the keel of the craft. Usually the steerable wheel will be attached to the collar via wheel supports.

In one embodiment the orientation of the wheel supports is altered from an upright position when the wheel is in the lowered position to a substantially horizontal position when the wheel is raised for stowage.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a side view of an amphibious craft according to the invention,

Figure 2 is a schematic section view in plan of the craft of Figure 1

Figure 3 is a schematic front section showing one embodiment of a front wheel retraction mechanism and

Figures 4a_ _r 4b, 4c, and 4d, are schematic partial views of a second retraction mechanism for the front wheels.

The drawings illustrate an amphibious craft in the form of a boat converted so as to provide a means of driving the craft on land on wheels. The operation of the boat in water is substantially unimpaired other than due to the extra weight carried. The profile is unaltered and the drag is not substantially increased. The boat in water is driven either by a large inboard motor normally in an aft position (such as shown

at Y in Figure 2) or by an outboard motor (not shown). Where an inboard motor is used it could also power the wheels for use of the craft on land. If an outboard motor is used on the boat, a secondary motor such as that shown at X would have to be provided to drive the wheels. In either case the boat wheels are driven in a manner similar to those on an automobile through a gear box G, a shaft S, a differential 14 and a shaft 15. Inboard brakes 10 would also be provided. The wheels on the boat comprise a pair of steerable forward or front wheels 11 designed to carry one third of the weight of the boat and set one either side of a keel 12 in the bow of the boat; and two drivable rear wheels 13 designed to carry two thirds of the weight of the boat. The rear wheels 13 are positioned on opposed sides of the boat inside the line of the hull. The use of a pair of forward wheels leaves the keel undisturbed and so does not interfere with the strength of the boat structure. The operation of the rear wheels is described and claimed in my co-pending application of the same date.

The steerable wheels 11 are supported by stub axles 21a_ mounted on a forked wheel support or "forks" 21. The upper end of the forked wheel support 21 is in the form of a square-sectioned collar 22. The collar 22 is slidably mounted on a square-sectioned, rectangular or other cornered section central pillar 23, the upper and lower ends of which pillar are pivotally mounted to the boat structure at 24 and 25. The pillar 23 is pivoted to steer the craft on land by movement of a steering arm 26 which action turns the collar 22 to turn the wheels 11. When the wheels are in the lowered position they can be held in position by security locks (not shown)The wheels are raised and lowered by a hydraulic ram (not shown in

Figure 3) which operates between respective brackets on the pillar and collar. The pillar, the collar and the ram form elements of a retraction mechanism for the wheels.In the raised position the wheels are stowed in a compartment 20 in the bow of the boat.The fitting of the compartment to the hull is entirely watertight so that water entering the compartment does not enter the boat. hen the compartment is closed the profile of the boat is maintained by two doors 27 hinged at 28 which are closed against the bottom 29 of the boat, but need not be watertight. The top of the compartment is situated well above the water line and therefore any water seeping past the doors will remain in the compartment at a level equal to or below the water level outside the hull. The actual portion of the bottom of the boat that is cut away to form the doors 27 is important as sufficient room must be left for the wheel "forks" 21 to turn the wheels in the lowered position without collision or interference with or from the boat structure.

The arrangement of the steering arm above the water line of the boat makes for a simpler mechanism. Moreover with this sliding collar arrangement the wheels can be steered successfully in any position of the collar on the pillar.The steering for the boat is not moveable with the wheel but instead stays in one place.

In some boats there may not be sufficient room for a large front wheel compartment with the wheel "forks" 21 stored substantially vertically. Figure 4 shows an alternative arrangement to cater for storage in a smaller deck to keel depth. Each drawing shows only part of the arrangement and it may be necessary to refer to Figure 3 to understand the whole.

Figure 4a_ is a front view of the lower part of the mechanism showing the wheel forks 21 and one wheel 11. The wheel "forks" 21 are pivotally mounted at 31 to the

collar 22 and are connected together by a bar 32. Respective bars 33 are pivotally mounted to opposed sides of the bar 32 at one end and at the other end 30 are pivotally mounted to opposed sides of the central pillar 23. A shoulder 34 on the collar 22 provides a lower mounting point for the ram now shown at 35 and the pivotal mounting 25 of the central pillar 23 to the keel 12 is also shown. If desired the section of the keel on which the pillar is mounted can be removed and replaced by an equivalent section of different and preferably stronger material from the rest of the keel , such as a casting or fabrication. The movement of the collar up and down the pillar in either embodiment can equally be controlled by any suitable alternative to hydraulic rams, such as screw, cables,chain, compressed air etc. Slots can be machined into the pillar to allow the moving force to be applied from inside if desired for example by an internal ball screw.

Figure 4b is a side view of Figure 4a_ showing the central area of the mechanism with the wheels in the lowered position. It will be noted that as the ram 35 draws the collar 22 up until it abuts the pivotal mounting 30 the pivoted bars operate as a lever mechanism to lift the wheels until the "forks" 21 lie along the line of the boat substantially horizontally.

Figure 4c illustrates the connection of the central pillar 23 at the upper end of the pillar. The same pivotal connection and height adjustment pieces and fillers may be used at the lower pivotal mounting 25. The connection comprises a sub-assembly of a mounting block 36, a thrust bearing 37 and a nut 41. The upper race of the thrust bearing 37 has a pivot mounting 38 for attachment to the deck. The lower race of the bearing 38 is located by a threaded bolt portion 39. The bolt 39 is threaded through the centre of the mounting block 36 and is screw threaded into the nut 41. This

sub-assembly is then fitted into the top end of the pillar 23 to which it is bolted via holes 43 in the block and 44 in the pillar. The length of the pillar 23 is selected in accordance with the distance between the deck and the keel on any particular boat and any fine adjustment to the fitting is achieved using shims (not shown) .

In each case the hydraulic rams are connected to a hydraulic pump powered by the motor X or Y or an electrically powered pump. The hydraulic ram 35 is operable from a remote position in the cockpit of the vehicle to raise or lower the wheels by the required amount instantly. The steering is also operable by remote control from the cockpit, the wheels being steerable throughout the height range. The steering arm 26 and levers connecting the steering arm to the remote steering mechanism in the cockpit have constant geometry with the angles only changing in one plane. It is envisaged that the craft will not be expected to travel more than 25 miles per hour on land. In this case floatation tyres can be used absolving the need for suspension. If a greater land speed is required then higher pressure road tyres will be needed and probably some springing or other suspension. Both embodiments could accommodate suspension. This would be interposed between the sliding collar and the mechanism for moving the collar up and down the pillar. The front wheel could be driven by a motor mounted on the collar or the pillar, or remote from the pillar through chains or shafts to the wheels. Hydraulic drive to the wheels themselves could be used. Although the retractable wheels are described in relation to an amphibious craft it will be appreciated that the same mechanism could be used in other applications.