Patent Description:
Mobility scooters are an application to which the present invention is particularly applicable and thus the following description makes reference only to mobility scooters, but the invention may have applications to other types of three wheel vehicles with stabilisers which are encompassed within the scope of the claims.

Mobility scooters have been known for over thirty years, with the earlier scooters tending to be three wheel scooters and later scooters tending to be four wheel scooters.

The three wheel scooter and four wheel scooter each have their advantages and disadvantages, particularly when it comes to two major considerations which need to be taken into account when designing such a scooter. These are the posture of the user and the stability of the scooter.

Considering each in turn, posture is important because the person must be comfortable when seated. Generally three wheel scooters tend to be better for posture than four wheel scooters, for they permit a user to place their feet on either side of a single central front wheel. This tends to keep the user in a positive posture with their limbs outstretched in front of them. In contrast, with a four wheel scooter, the front wheels and any wheel guards, which must both accommodate the front wheels and the space swept by the front wheels when turning, together with the space occupied by the steering mechanism, normally means that the feet have to be placed behind the front wheel assembly, often in a space extending forward from immediately below a front edge of the seat, causing the user's posture to be "compressed". Furthermore, it is not desirable to raise the user so that they may position their feet above the front wheels, for this raises the centre of gravity tending to destabilise the scooter, for such scooters have a relatively narrow track width to enable them to pass easily through conventional doorways.

A second consideration when designing a scooter is the stability of the scooter. Four wheel scooters tend to be more stable than three wheel scooters, particularly during cornering, due to the provision of a wheel on each corner of the scooter. In contrast, three wheel scooters can tend to tip during cornering, due to having only a single front wheel. This can be particularly problematic, as a disabled or older person may not be able to put their foot down in time, or with sufficient strength to avoid an accident. Furthermore, they may not tend to shift their weight on the scooter, for example when cornering, as a more able bodied person may do, possibly subconsciously.

Despite the above, a three wheel scooter may have one advantage over a four wheel scooter when it comes to stability. This is because, where the user's feet are placed either side of a single central front wheel, typically twenty five percent of the body weight is over the front wheel. This helps to keep the centre of mass of the scooter forward, which in turn helps with the problem of tipping over backwards on a steep slope, or possibly when mounting a kerb. In contrast, with a four wheel scooter the user tends to have to sit fairly far back on the scooter, in order to be able to place their feet behind the front wheels, thus the centre of mass on a four wheel scooter tends to be significantly further towards the rear of the scooter than on a three wheel scooter and this can tend to cause the scooter to tip over on a steep slope or when mounting a kerb.

Examples of known scooters are described in patent applications bearing <CIT> which discloses the features of the preamble of claim <NUM> and <CIT>.

It is an object of the present invention to provide an improved vehicle.

According to the present invention there is provided a vehicle as recited in claim <NUM>.

The biasing means, adjustable to control the downward force applied by the biasing means on the central steered wheel, may be set to a exert a maximum force to maximise traction between the central steered wheel and the ground when the stabiliser wheels are also supporting the vehicle, but which force is not sufficient, for a given weight of rider, to lift the vehicle off the stop when the stabiliser wheels are not carrying any of the weight of the vehicle.

An advantage of the present invention is that it provides a vehicle having all the advantages that have been described above of a three wheel vehicle. However, a vehicle in accordance with the present invention, by having stabiliser wheels, avoids the stability issues that may otherwise arise.

The stabiliser wheels are not normally used as the main support for the vehicle, as they are only required to act as auxiliary wheels, which provide support (stability) to the vehicle only at those times when it is required, for example when the vehicle is no longer truly upright on the surface over which it is traveling, such as when cornering at speed.

As the stabiliser wheels are not the main wheels of the vehicle (unlike each of the four wheels of a traditional four wheel vehicle), they may be considerably smaller (possibly with solid tyres) than the central steering wheel, and they may be located fairly far forward on the vehicle (which further enhances stability). This may avoid the need for the stabiliser wheels to encroach into the foot space for the rider that is normally provided to either side of the central steered wheel on a three wheel vehicle. Thus the advantages are retained of the traditional three wheel vehicle over the four wheel vehicle, whist addressing the above mentioned stability issues of three wheel vehicles.

A particular advantage of the present invention is that when the vehicle is on a flat level surface, the suspension stop retains the front of the frame at a height above the surface such that there is a clearance between the stabiliser wheels and the surface. In this way the stabiliser wheels (which may be of a relatively small diameter and which may not have pneumatic tyres) will be prevented from creating unnecessary noise. Furthermore, because the vehicle will then be riding on the suspension stop, this clearance will not depend on the weight of the rider compressing the suspension biasing means, for the weight is transferred to the central steered wheel through the fixed suspension stop. Thus the clearance can be set irrespective of the rider weight.

In addition to the above mentioned advantages, the suspension mechanism of the vehicle of the present invention acts to keep a downward force on the central steered wheel even when, on uneven ground, the stabiliser wheels may otherwise act to lift the steered wheel off the ground, or reduce downward force on the central steered wheel to a point where reliable steerage may be lost. For example, with the present invention the centre steered wheel may be retained in contact with the ground even when the vehicle mounts a kerb at an oblique angle (normally necessary), permitting steerage to be retained at this critical moment in order to force the vehicle to continue its transverse across the kerb, being mounted.

Advantageously the vehicle comprises a steering mechanism that is connected to the central steered wheel but which is not connected to the stabiliser wheels, so that the direction of the stabiliser wheels is controlled only by their contact with the surface. This avoids the cost of providing extra linkages to the stabiliser wheels and avoids such linkages encroaching into the space that should otherwise be provided for the rider's feet. In addition, an advantage of a single steered wheel is retained, in that there are no tracking issues that might otherwise arise with multiple steered wheels. These tracking issues may result from damage occurring to the tracking mechanism due to one steered wheel encountering a hard "knock", for example when the vehicle ascends a kerb at an oblique angle, or they may be inherent, for example arising from the requirement to retain three steered wheels in alignment (in the case of a central steered main wheel and two stabiliser wheels) where two of those wheels (the stabiliser wheels) may not be at the same longitudinal position on the vehicle as the third (main) wheel, which may require multiple component linkages.

In addition to the above, the provision of a single steered wheel, which may be directly steered by a tiller or the like, without the requirement for an indirect track rod linkage, may permit the central steered wheel to be turned through almost <NUM> degrees, thus reducing the turning circle of the vehicle.

Preferably the stabiliser wheels are the wheels of respective castors, with each castor mounted to the frame so that it is generally free to rotate about a substantially vertical axis, the vehicle further comprising a stop associated with each castor to limit rotation of the castor relative to the frame so that each castor is prevented from turning outwardly from the straight ahead position.

Preventing the castors from turning outwardly avoids them rotating outwardly when coming into contact with a kerb at an oblique angle. This is important, because it permits the stabiliser wheel of the castor to be squashed against and to subsequently rise up the kerb. In contrast, if the caster could turn outwardly, then on contacting the kerb the leading edge of the stabiliser wheel of the castor will tend to bite into the kerb and turn into the kerb, thus pushing the vehicle away from the kerb, the leverage of the castor against the fixed kerb being greater than the frictional forces between the steered wheel and the ground. This action tends to become reciprocating, with the castor repeatedly pushing the front end of the vehicle away from the kerb, until eventually a rear wheel of the mobility scoter will also end up against the kerb with the vehicle aligned with the kerb, from where it will normally be impossible to mount the kerb.

Preventing the castors from turning outward does not otherwise impede manoeuvrability to any significant extent, for most of the time the castors will not be in contact with the ground and when they are, the vehicle is likely to be travelling generally straight ahead. The main exception to this will be when cornering, when the stabiliser on the outside of the turn will likely come into contact with the ground to stabilise the vehicle through the turn. However, this castor will need to turn inward to follow the turn, which it is free to do, while the inner castor, which would need to turn outward to follow the turn, will tend to be raised clear of the ground. In any other situation, the far superior grip of the normally larger diameter central steered wheel, with greater downward force on it, will control the direction of travel, with the smaller stabiliser wheel (normally with a solid tyre) being forced to scrub sideways, but this is only likely to occasionally occur.

Each castor may preferably rotate through at least <NUM> degrees relative to the frame. In this manner the castors will simply rotate through <NUM> degrees, if they are in contact with the ground, and the vehicle changes from a forward to reverse direction, thus permitting the stabiliser wheels to remain aligned with the direction of travel.

Each castor may have an associated castor biasing means, arranged to urge that castor to the straight ahead position, such that when a castor is no longer in contact with the surface it will assume the straight ahead position so it is correctly aligned for subsequent contact.

The suspension stop may comprise an adjustment means to permit the clearance to be adjusted. This may then be set to take into account such things as the unevenness of the surface the vehicle is most likely to be used on (if it is totally flat very little clearance will be required), to compensate for a soft tyre on the central steered wheel, or to take into account the assurance a rider may desire. A nervous rider may desire a minimum clearance to provide a maximum feeling of stability, in preference to a quite ride, (which may then be sacrificed because one or more of the stabiliser wheels will then be more likely to be in contact with the ground).

It is preferable that the clearance is either fixed at more than <NUM> or that, if it is adjustable, it may be set to more than <NUM> and more preferably more then <NUM>.

The axis of rotation of each stabiliser wheel may be located forward of the axis of rotation of the central steered wheel. This leaves a larger unimpeded space for the rider's feet and also provides greater stability. In addition the diameter of each stabiliser wheel may be less than two thirds of the diameter of the central steered wheel, reducing the overall bulk of the vehicle and again leaving a larger unimpeded space for the rider's feet.

The biasing means for the central steered wheel may comprise a spring. Such a spring may also define the suspension stop when it is fully compressed, avoiding the need for a separate stop.

Alternatively, the stop may be resilient and permit further downward travel of the frame relative to the steered wheel in order to absorb, or partly absorb, any shock resulting from the steered while striking an obstacle while the frame is supported on the stop. Thus when the frame is riding on the stop, there is still some shock absorption between the steered wheel and the frame.

Preferable the stop is compressible by an amount which is insufficient for the said further downward travel to exceed the said height above the surface. In this manner, on normal impact of an obstacle by the steered wheel on an otherwise flat surface, the compression experienced by the stop will be insufficient to allow the stabiliser wheels to come into contact with the ground. The stiffness of the stop being greater than the stiffness of the biasing means.

The stop may comprises a block of compressible material and, preferably, the biasing means for the steered wheel comprises a compression spring acting between the frame and the steered wheel, the compression spring having a longitudinal axis and being connected at one end, directly or indirectly, by the resilient block of material to one of either the frame or the steered wheel, the block of material having a stiffness in the axial direction greater than that of the compression spring when the compression spring in a state other than a fully compressed state, the stop being formed by the resilient block and the compression spring when the compression spring is in a fully compressed state.

Advantageously the vehicle may further comprising a ride height adjuster for controlling said height above the surface by limiting the maximum expansion of the compressible material.

Two embodiments of the present invention will now be described, by way of example only, with reference to the mobility scooters illustrated in the accompanying figures of which:.

Referring to <FIG> a mobility scooter, indicated generally as <NUM>, is shown as it would be if a rider were present, although the rider is not shown. The mobility scooter <NUM> comprises a frame <NUM>, a pair of rear wheels <NUM> and <NUM> attached to the frame <NUM>, a seat <NUM> attached to the frame <NUM>, a central steered front wheel <NUM>, a tiller <NUM>, handlebars <NUM> for steering the central wheel <NUM> and left and right stabiliser wheels <NUM> and <NUM> mounted at the front of the frame <NUM>.

The mobility scooter <NUM> of <FIG> also has covers <NUM> and <NUM>, cover <NUM> concealing the electric motor battery and various other components found on a mobility scooter, with cover <NUM> covering some components of the steering mechanism and providing a mud guard for the central wheel <NUM>. As can be most clearly from <FIG> the scooter also has two fixed foot rests <NUM> and <NUM> provided to either side of the front wheel <NUM>, which extend over the stabiliser wheels <NUM> and <NUM>.

Referring now to <FIG> and <FIG>, these shows the front portion of the frame <NUM> and the various components that are attached to the front portion of the frame, excluding the cover <NUM> and foot rests <NUM> and <NUM>, omitted for clarity.

With reference to <FIG>, this shows each of the stabiliser wheels <NUM> and <NUM> forming part of respective castor 15a and 15b, which are attached to a front portion of the frame <NUM>. The castors 15a and 15b are described in greater detail below with reference to <FIG>.

Referring to <FIG>, these show how the front central steered wheel <NUM> may be steered by the handlebars <NUM> via tiller <NUM> and that the central steerable wheel <NUM> is supported from a front extension portion <NUM>, of the frame <NUM>, via steerable subframe <NUM>. The steerable subframe <NUM> comprises an upper component 17a rotatable with the tiller <NUM>, relative to the front extension portion <NUM> of frame <NUM>, and a lower component 17b pivotally connected to the upper component 17a via pin <NUM>, to permit the central wheel <NUM> to move from an upper position shown in <FIG> to a lower position shown in <FIG>.

A suspension unit, indicated generally as <NUM>, is pivotally connected by pin <NUM> to a bracket <NUM> of the lower component 17b of the steerable subframe <NUM>. The suspension unit comprises a spring <NUM> acting between the bracket <NUM> and a plate <NUM>, which sits under the upper component 17a of the moveable frame <NUM>, as shown.

The spring <NUM> is retained in position by a shaft <NUM> passing through its centre and which is anchored at its lower end to the pin <NUM>. Coaxially located internally of the spring, but external of the shaft <NUM> is a cylindrical tube <NUM> which is free to slide on the shaft <NUM>.

<FIG>, show the central steered front wheel <NUM> in the vertical position that it will adopt under the weight of the mobility scooter with a rider thereon. With reference to <FIG>, when the central wheel <NUM> is in the position shown, the cylindrical tube <NUM> extends between the top of the bracket <NUM> and the plate <NUM> and thus acts a stop, preventing the central wheel <NUM> moving upwards against the action of the spring <NUM> towards the upper component 17a of the steerable subframe <NUM>. Thus, the cylindrical tube <NUM> retains the steerable wheel <NUM> in the position shown in <FIG>, regardless of the weight of the rider and any upward forces placed on the wheel during operation of the mobility scooter <NUM>. The cylindrical tube <NUM> is of such a length that, as can be most clearly seen from <FIG>, it maintains the central wheel <NUM> in a position such that, when a tire on the central wheel <NUM> is correctly inflated, there is a clearance <NUM> of <NUM> between the bottom of the stabiliser wheels <NUM> and <NUM> and the ground <NUM>.

On level ground, with a rider on board, the suspension unit <NUM> adopts the position shown in <FIG>, such that the stabiliser wheels <NUM> and <NUM> only come into contact with the ground should the mobility scooter <NUM> start to lean excessively, for example on cornering or on the shifting of the weight from side to side of the rider both during use and when getting on and off the mobility scooter <NUM>.

As will be appreciated from <FIG>, if one the stabiliser wheels <NUM> or <NUM> were to mount a kerb for example, or the central steered wheel <NUM> were to pass over a trough more than <NUM> deep, then without any vertical movement of the central wheel <NUM> relative to the frame <NUM>, the central steered front wheel <NUM> would be lifted clear of the ground <NUM> so that the steerage would be lost, or the pressure exerted on the ground by the central steerable front wheel <NUM> would be so reduced that it would no longer be sufficient to steer the mobility scooter <NUM>. This is avoided with the mobility scooter in accordance with the present invention, for as shown in <FIG>, in a situation where the frame <NUM> becomes supported by the stabiliser wheels <NUM> and <NUM>, the spring <NUM> forces the central steered wheel <NUM> downwards, as shown, to keep it firmly in contact with the ground <NUM>, until eventually it reaches such a position where plate <NUM>, mounted to the top of the shaft <NUM>, comes into contact with a top surface of the upper component 17a of steerable subframe <NUM> to retain the shaft <NUM> in the upper component 17a of the steerable subframe <NUM>. This vertical travel of the central steered front wheel <NUM> acts to keep the central steered front wheel <NUM> in contact with the ground, even when the ground is uneven and the stabiliser wheels <NUM> and <NUM> are in contact with the ground and partly supporting the mobility scooter <NUM>, thus maintaining steerage for the mobility scooter <NUM>.

Although not shown, adjustment means may be included in the suspension unit <NUM> in order to adjust the position of the suspension stop formed by the top of the cylindrical tube <NUM>, in order to adjust the clearance <NUM> shown in <FIG>. This may be used to compensate for the type of ground the mobility scooter will typically be used on, by setting a greater clearance <NUM> for rough ground, to compensate for any unexpected softness in the front tire of the central steered wheel <NUM>, or tailor the characteristics of the mobility scooter <NUM> to the rider, by setting the stabiliser wheels <NUM> and <NUM> close to the ground in the case of a more nervous or new rider in order to enhance the feeling of stability of the mobility scooter <NUM>. Similarly, also not shown, the spring <NUM> is adjustable to control the downward force applied by the biasing means on the central steered wheel. In this manner the spring <NUM> may be set to a exert a maximum force to maximise traction between the central steered wheel <NUM> and the ground <NUM> when the stabiliser wheels <NUM>, <NUM> are also supporting the scooter <NUM>, but which force is not sufficient, for a given weight of rider, to lift the scooter <NUM> off the stop formed by the plate <NUM> and cylindrical tube <NUM> when the stabiliser wheels <NUM>, <NUM> are not carrying any of the weight of the scooter <NUM>. Adjustable springs of this type are readily available and are commonly found on some older models of motor bikes.

Referring now to <FIG>, here stabiliser wheel <NUM> is shown to a larger scale, where it is seen that the wheel <NUM> forms part of the castor 15a of <FIG>. The castor 15a comprises a top plate <NUM> welded to the frame <NUM> (not seen in <FIG> and <FIG>) and a wheel support bracket <NUM> pivotally connecting the stabiliser wheel <NUM> to the fixed top plate <NUM> so that it may rotate about a vertical pivot axis <NUM>. As can be seen from <FIG>, the rotation axis of the stabiliser wheel <NUM> is a set back from the vertical pivot axis <NUM> of the castor 15a, so that when the castor 15a moves forward in the direction of the arrow <NUM> it will adopt the position shown in side elevation in <FIG>, (and as also shown in the plan view of <FIG>). A small spring (not shown) in a bush <NUM> between the top plate <NUM> and the support bracket <NUM> also acts to bias the stabiliser wheel <NUM> to the position shown, so that when the stabiliser wheel is clear of the ground it will be retained in this position ready for it returns into contact with the ground.

With further reference to <FIG>, two wheel support bracket stops <NUM> and <NUM> extend downwardly from the fixed top plate <NUM> and limit rotation of the castor about the vertical pivot axis <NUM>. As can be seen most clearly in <FIG>, when travelling in a forward direction, as represented by arrow <NUM>, the stop <NUM> prevents the stabiliser wheel <NUM> turning outwards, whilst permitting it to turn inwards and to rotate <NUM>° to the position shown in <FIG>. This position would be adopted by the wheel when in contact with the ground and the mobility scooter <NUM> was reversed such that the stabiliser wheel <NUM> moved in the direction of arrow <NUM> of <FIG>. However, in this "reverse" position the wheel <NUM> is prevented from turning outwards again, while reversing in the direction of arrow <NUM>, by stop <NUM>. The stops <NUM> and <NUM> thus prevent the stabiliser wheel <NUM> turning outwards if it should come into contact with a fixed object such as a kerb. In such a situation the stops <NUM> or <NUM> would retain the stabiliser wheel <NUM> in a forward facing direction, or let it be deflected inwards until it was aligned with the kerb. However the stops <NUM>, <NUM> prevent the stabiliser wheel <NUM> snatching on the kerb and turning sharply into the kerb, which would deflect the front of the mobility scooter <NUM> away from the kerb and prevent it from climbing the kerb.

The castor 15b of <FIG> is an exact mirror image of the castor 15a described above and functions in an identical manner.

With reference to <FIG>, this is schematic in nature and for clarity only shows the frame <NUM> stopping short of the respective top plates <NUM>. However the top plates <NUM> are each welded to the frame <NUM>. Similarly, for simplicity, the centre steered wheel <NUM> is shown directly pivoted on the frame <NUM>.

<FIG> illustrates the position adopted by the castors 15a, 15b when they are either clear of the ground (regardless of the direction of travel of the mobility scooter <NUM>) or when they are in contact with the ground and moving straight ahead.

<FIG> corresponds to <FIG>, but shows the position the castors 15a, 15b adopt during a sharp right turn that places the left hand castor <NUM> in contact with the ground.

<FIG> shows the position of the castor 15a, 15b would adopt when the mobility scooter <NUM> is being reversed.

Referring now to <FIG>, these schematically illustrate a mobility scooter, indicated generally as <NUM>. This is very similar to the mobility scooter <NUM> previously described with reference to <FIG>, with only the steered wheel <NUM> and immediate related components differing to those shown in, (and described with reference to), the previous figures. Thus only these related components are described again here. Additionally, for reasons of clarity, in <FIG> the foot rest, stabiliser wheels and those sections of the frame which retain the stabiliser wheels in place have been omitted, these being the same as those of the mobility scooter <NUM> of <FIG>.

Referring now to <FIG>, as with the previous embodiment, the steerable wheel <NUM> is mounted to a steerable subframe, indicated generally as <NUM>, this comprises a lower component 39b pivotally mounted to an upper component 39a, the pivotable lower component 39b retaining the steerable wheel <NUM> in position within the steerable subframe <NUM>, whilst permitting the steerable wheel <NUM> to move up and down relative to the steerable subframe <NUM>.

A shaft <NUM> extends through a hole in a mounting plate <NUM> of the steerable subframe <NUM> and connects to a distal end of the lower component 39b of the steerable subframe <NUM>. The top of the mounting plate <NUM> has a flange <NUM>, to limit downward travel of the shaft <NUM> through the mounting plate <NUM>.

Positioned on the shaft <NUM>, below the mounting plate <NUM>, is a compressible rubber bush <NUM> and a compression spring <NUM>. Additionally, between the rubber bush <NUM> and the compression spring <NUM>, there is located an adjustment plate <NUM>. This is retained in the substantially horizontal position as shown, by being mounted on the shaft <NUM> at its distal end by means of a collar (not shown) fixed in an aperture (not shown) in the proximal end of the adjustment plate <NUM>. The collar has an inner diameter just slightly larger than the outer diameter of the shaft <NUM>, thus enabling the adjustment plate <NUM> to slide and up and down the shaft <NUM>, whilst retaining the adjustment plate in the horizontal position shown. Thus, the rubber bush <NUM> is sandwiched between the mounting plate <NUM> and the adjustment plate <NUM>.

Also sandwiched between the mounting plate <NUM> and the adjustment plate <NUM> is an adjustment spring <NUM>, which is also a compression spring. This has a threaded shaft <NUM> passing through it and retaining it in place. The threaded shaft <NUM> can be adjusted to alter the length of the adjustment spring <NUM>.

Although in <FIG> (and subsequent <FIG> and <FIG>), the rider has been omitted, the components are shown in the position they would adopt with the weight of a rider present.

As with the previous embodiment illustrated and described with reference to <FIG>, when the mobility scooter <NUM> of <FIG> is on a flat level surface, as shown in <FIG>, it is desirable that the steerable wheel <NUM> is located vertically relative to the front of the frame <NUM> of the mobility scooter <NUM>, at a position such that stabiliser wheels <NUM> have a clearance above the ground of about <NUM>, with the compression spring <NUM> fully compressed by the weight of the rider and the scooter. Thus when riding over flat or gently undulating ground, the compression spring <NUM> maintains a constant (fully compressed) length and thus acts to maintain the stabiliser wheels <NUM> above the surface of the ground. However, where the ground undulates greatly and where the steerable wheel <NUM> should then run on a surface lower than the surface on which the two stabiliser wheels <NUM> are running, the compression spring <NUM> will then expand to maintain downward pressure on the steerable wheel <NUM> as it falls away from the frame <NUM>, when the front of the frame <NUM> is supported by the stabiliser wheels <NUM>. The compression spring <NUM>, urging the steerable wheel <NUM> downwards into firm contact with the ground, thus ensures the steerable wheel <NUM> is still able to steer the scooter <NUM>.

However, when the compression spring <NUM> is fully compressed, as for example when travelling over fairly level ground, it may be desirable that some limited vertical travel of the steerable wheel <NUM> relative to the front of the frame <NUM> to be possible, in order to absorb shocks that may be otherwise transmitted to the frame <NUM> by the steerable wheel <NUM> encountering an obstacle, or running over a rough surface. This is addressed by the embodiment shown in <FIG> by the rubber bush <NUM>, which is arranged to absorb such shocks whilst supporting the frame <NUM>.

Although it may be desirable to employ the rubber bush <NUM> to absorb shocks, it is also necessary to maintain the clearance between the ground and the stabiliser wheels <NUM>. As previously described, the compression spring <NUM> may be arranged to be fully compressed by riders of a certain weight range that the mobility scooter <NUM> is designed to carry, or is set up to carry. However it is not possible to similarly fully compress the rubber bush <NUM>, or its ability to absorb shocks will be lost.

It is possible, to select and fit a rubber bush of the correct dimensions and stiffness for a given weight of rider, in order to retain the desired clearance between the stabiliser wheels <NUM> and the ground. However it is desirable that that the weight range of riders the scooter is designed to carry be relatively large, without the need to change components of the scooter <NUM>.

Some riders may thus be significantly heavier than others and although all of these may fully compress the compression spring <NUM> they will compress the rubber bush <NUM> by different amount depending on the weight of rider. The rubber bush <NUM> needs to have a vertical stiffness greater than that of the compression spring <NUM>, to ensure that the compression spring <NUM> is fully compressed prior to the rubber bush being compressed by any significant amount. The rubber bush <NUM> could have a stiffness that would retain stabiliser wheels <NUM> at a desired height above the ground, for the heaviest of intended riders, but this would then provide little in the way of shock absorption for a lighter rider. In order to address this, the adjustment spring <NUM> is located effectively in parallel with the rubber bush <NUM> and it is the combined stiffness of the rubber bush <NUM> and the adjustment spring <NUM> which determines the separation between the mounting plate <NUM> and the adjustment plate <NUM> and thus the clearance of the stabiliser wheels <NUM>. The threaded shaft <NUM> permits the compression of the adjustment spring <NUM> to be adjusted and thus this can be adjusted for a rider of a particular weight, so as to trim the stiffness of the combined rubber bush <NUM> and adjustment spring <NUM>, in order to provide the desired clearance for the stabiliser wheels <NUM> for a rider of any selected weight within a permissible range, as shown in <FIG>.

Referring now to <FIG>, this shows how the rubber bush <NUM> will be compressed as a result of the steerable wheel <NUM> encountering an obstacle <NUM>, acting to absorb the impact while the compression spring <NUM> acts to maintain the front of the frame <NUM> at a set level above the ground, thus retaining a clearance between the stabiliser wheels <NUM> and the ground. However, as with the embodiment previously described with reference to <FIG>, should the ground <NUM> below the steerable wheel <NUM> be lower than the ground <NUM> below the stabiliser wheels <NUM>, as shown in <FIG>, then the compression spring <NUM> will expand, as shown in <FIG>, to retain a load on the steerable wheel <NUM> and thus maintain the steering of the mobility scooter <NUM>.

Claim 1:
A vehicle (<NUM>) comprising:
a frame (<NUM>);
two wheels (<NUM>, <NUM>) mounted at or towards a rear end of the frame;
a steered wheel (<NUM>) centrally mounted at or towards a front end of the frame;
two stabiliser wheels (<NUM>, <NUM>) mounted at or towards the front end of the frame to respective sides of the steered wheel (<NUM>); and
a suspension mechanism (<NUM>) between the frame (<NUM>) and the steered wheel (<NUM>) to permit vertical travel of the steered wheel (<NUM>) relative to the frame (<NUM>), the suspension mechanism (<NUM>) comprising biasing means (<NUM>) for the steered wheel (<NUM>), the biasing means (<NUM>) acting directly or indirectly between the frame (<NUM>) and the steered wheel (<NUM>) to urge the steered wheel downwards relative to the frame (<NUM>), wherein the biasing means (<NUM>) is arranged and selected such that in use, when the vehicle (<NUM>) is on an uneven surface, where the stabiliser wheels (<NUM>, <NUM>) come into contact with the ground so that the frame (<NUM>) is supported at least partially by the stabiliser wheels (<NUM>, <NUM>), the biasing means (<NUM>) urges the steered wheel (<NUM>) downwards into contact with the surface to act to maintain the steered wheel (<NUM>) in contact with the surface, to retain steerage as the vehicle (<NUM>) becomes partially supported by the stabiliser wheels (<NUM>, <NUM>),
the vehicle (<NUM>) being characterised in that the suspension mechanism (<NUM>) further comprises a suspension stop (<NUM>) arranged to limit upward travel of the steered wheel (<NUM>) against the biasing means (<NUM>) relative to the frame (<NUM>), wherein the biasing means (<NUM>) is arranged to be adjusted for the weight of a given rider to control the downward force applied by the biasing means (<NUM>) on the steered wheel (<NUM>) such that in normal use, when the vehicle (<NUM>) is on a flat level surface, the weight of the vehicle and weight of a rider urge the frame (<NUM>) downwards relative to the steered wheel (<NUM>), against the biasing means (<NUM>), until the suspension stop (<NUM>) limits further downward travel of the frame (<NUM>) relative to the steered wheel (<NUM>), where the front of the frame (<NUM>) is then supported by the steered wheel (<NUM>) and the suspension stop (<NUM>), with the suspension stop (<NUM>) retaining the front of the frame (<NUM>) at a height above the surface such that there is a clearance between the stabiliser wheels (<NUM>, <NUM>) and the flat level surface.