Field of the Invention The present invention relates to tracked or wheeled vehicle with a skid device, to facilitate use of the vehicle on soft ground, and in particular to heavy plant vehicles such as tracked excavators, bulldozers and dumpers.

Background to the Invention

The tracked heavy plant vehicles such as excavators are often used on soft, boggy or marshy ground. In wet conditions, the tracks can sink deep into the ground making it difficult to drive the vehicle forward or backwards or, in extreme cases, rendering the vehicle immobile. The same can apply to wheeled vehicles.

It is known to provide small motor vehicles with skis or sleds to enable the vehicle to be driven on snow or ice covered roads. For example, US 2,487,297 discloses a sled apparatus for a car, having apertures through which the car's wheels extend in normal driving conditions. For use in snow or ice, the entire vehicle must be elevated above the level of the sled, to permit shutters to be closed over the apertures, upon which the vehicle then rests. Propulsion of the vehicle is effected by tracks build into the shutters beneath the drive wheels.

Similarly, it is known to provide a vehicle with skis associated with one or more sets of wheels (for example, as shown in US 3,132,873 or US 1 ,733,312) or to provide a platform beneath a vehicle to support a portion of weight of a vehicle (for example as shown in US 1,622,719 or US 4,754,832), so as to reduce the tendency of the wheels from digging, when a vehicle so equipped is driven in snow. However, these arrangements are adapted for comparatively small (and therefore light) vehicles, to enable them to be driven on snow or ice and do not provide a solution to the difficulties encountered when operating heavy plant vehicles on soft, boggy or marshy ground. The invention seeks to provide a solution to this problem. Summary of the Invention

According to a first aspect of the invention there is provided a vehicle having tracks or wheels, the vehicle comprising a skid device having a planar ground facing surface, the skid device operable by way of an actuation mechanism, between a retracted position in which the ground facing surface is spaced apart from the ground, when the vehicle is on level and flat ground;

and a deployed position in which the ground facing surface is at or near the ground, when the vehicle is on level and flat ground;

the skid device operable in the deployed position to support some or all of the weight of the vehicle, in use of the vehicle on soft ground.

In the event that the wheels or tracks (or one or more wheels, or one or more portions of the tracks, as the case may be) sink or dig into soft ground, the ground facing surface of the skid device contacts the ground such that a portion, or all, of the weight of the vehicle is supported by the skid device. Thus, the extent to which the wheels or tracks can sink into or dig into the ground is limited by the skid device and the tendency of the motion of the vehicle to be impeded or restricted when driven on soft ground is reduced. In effect, the skid device is operable to substantially increase the footprint of the vehicle (i.e. the area of the vehicle in contact with the ground), otherwise provided by surfaces of the wheels or tracks only, and so reduce the pressure of the vehicle's weight on the ground. In the deployed position (and typically also in the retracted position), the ground facing surface is preferably parallel to the ground, when the vehicle is on level and flat ground. When the vehicle is on level and flat ground, the ground facing surface may be parallel with the ground across the width of the vehicle (by which we mean in a direction parallel to an axis of rotation of vehicle wheels or tracks) and the ground facing surface is typically also parallel to the ground along the length of the vehicle.

The ground facing surface may be in contact with the ground, when the vehicle is at rest on level and flat ground and the skid device is in the deployed position. In some embodiments, the ground facing surface may be near to the ground, when the vehicle is at rest on level and flat ground and the skid device is in the deployed position; for example separated from the ground by a distance approximately equal to the depth of tread or other traction formations present on the tracks or wheels, in order that the traction formations may engage with the ground (for example, to engage and to some degree dig into soft ground) without the ground facing surface contacting the ground, in use. The separation from the ground of the ground facing surface may be a distance of greater than the depth of tread or other traction formations present on the tracks or wheels, for example approximately equal to two or more times the depth of tread or other traction formations present on the tracks or wheels. Wheeled or tracked vehicles may be provided with suspension, so that the point of contact between one or more of the wheels, or one or more portions of the tracks, may be deflected, so as to enable to the vehicle to move over uneven ground.

Thus, the skid device may similarly be provided with resilient biasing means, such as one or more shocks or dampers or other suitable apparatus known for use in vehicle suspension, to enable the ground facing surface to be deflected over uneven ground. The actuation mechanism may comprise resilient biasing means.

Alternatively, or in addition, deviation or deflection of the position or orientation of the ground facing surface of the skid device responsive to contact or a part of the ground facing surface with uneven ground, may be possible. For example, the skid device may comprise a resilient portion having a ground facing surface, such as a metal plate.

In some conditions, when the skid device is deployed it may be acceptable or desirable for the wheels or tracks of the vehicle to dig or sink into soft ground to a limited degree, so as to provide traction, before the skid device engages with the ground and supports some or all of the weight of the vehicle. Whereas, in other conditions, optimal traction may be provided if the wheels or tracks are prevented from digging into soft ground. Accordingly, the skid device may be operable to move between a retracted position and one or more than one deployed position, wherein in a first deployed position, the distance between the ground and the ground facing surface is greater than the distance between the ground and the ground facing surface in a second deployed position, when the vehicle is on flat and level ground (the said distance in the or each deployed position being small in comparison to the distance between the ground facing surface and the ground, in the retracted position). The wheels or tracks of the vehicle are typically provided in parallel arrays along the length of the vehicle. For example, a vehicle having tracks is typically supported and driven by two tracks, one along each side of the vehicle. A wheeled vehicle is typically provided with two or more pairs of wheels spaced along the length of the vehicle. The skid device is preferably positioned between the tracks or wheels of the vehicle. A skid device so positioned has minimal effect on normal operation of the vehicle (for example, does not impede access to the vehicle for loading or for occupants) and optimally positioned to support some or all of the weight of the vehicle evenly, in a deployed position in use of the vehicle on soft ground.

The vehicle is preferably supported and driven by tracks, any may for example be a heavy plant vehicle such as a digger, excavator or bulldozer, or may be a farm vehicle. In the (or each) deployed position, the ground facing surface may extend along substantially the entire length of the vehicle, between the tracks or wheels. In some embodiments, the ground facing surface extends beyond (i.e. in front of and/or behind) the wheels or tracks. The ground facing surface may extend across substantially the entire width of the vehicle between the tracks or wheels, so as to most evenly distribute pressure on soft ground resulting from the weight of the vehicle. Thus the ground facing surface extends to support substantially all of the area described by the contact between the wheels or tracks and the ground.

In a preferred embodiment, the ground facing surface extends to an excurvate end surface, at one or both ends thereof (i.e. towards the front and/or rear of the vehicle). In use, the distance between the ground and the excurvate end surface increases gradually with distance from the ground engaging surface, thereby reducing the tendency of the skid device to dig into, or jam against, uneven ground in use. The excurvate end surfaces may be provided with a curvature substantially similar to (or the same as) the curvature of the leading and/or trailing surfaces of the tracks or wheels of the vehicle, and are preferably in alignment therewith. Vehicles (such as heavy plant vehicles) for use on soft ground are commonly also required to travel up or down steep slopes, or over uneven ground. Thus the leading edges (in relation to the direction of travel of the vehicle) may encounter sloped or other obstacles in the ground. Excurvate ends surfaces which have a substantially similar curvature, and are in alignment with, the leading and/or trailing ends of the tracks or wheels of the vehicle, ^• enable the wheels or tracks to engage with or ride over obstacles or slopes, whilst also preventing the leading edges, or front wheels (in relation to the direction of travel) from digging into soft ground.

In contrast, some previously known devices to enable small vehicles to travel on snow or ice either extend beyond the front wheels of the vehicle (as for example disclosed in US 4,754,832) and prevent the vehicle from travelling up steep slopes or over sudden obstacles, or extend along only a part of the length of the vehicle (as for example disclosed in US 1 ,622,719) and so could not prevent the front wheels of the vehicle from becoming embedded, should the vehicle encounter a steep slopes or sudden obstacles. In an alternative embodiment, the end surfaces may be planar and may extend at an angle from the ground facing surface.

The skid device may comprise a foot member, having a ground facing surface and, in some embodiments, the or each end surface (which may be excurvate). The foot member is typically operably connected to a body of the vehicle (for example the vehicle chassis, or other portion of the vehicle underside) by the actuation mechanism. The foot member may comprise or consist of a metal plate, which may be resilient, so as to enable to the ground facing surface to be deflected when the vehicle is driven over uneven ground.

The skid device may further comprise one or more support members, which may operably connect the skid device to the vehicle (typically the underside of the vehicle) and through which some or all of the weight of the vehicle may be supported, in use of the vehicle on soft ground.

The actuation mechanism may comprise one or more support members, which may operably connect the skid device to the vehicle. The actuation mechanism may comprise or consist of one or more telescopic shafts (which may in some embodiments function as support members), by which the skid device may be moved between retracted and deployed positions. The actuation mechanism may comprise one or more pivotal linkages (which may in some embodiments function as support members), by which the skid device may be swung between deployed and retracted positions. In embodiments wherein the ends of the ground facing surface (or the end surfaces) extend beyond, or are in alignment with, the leading edges of the tracks, or the front wheels, in the deployed position, the skid device may be advantageously swung from the deployed position to the retracted position, so that the leading edges of the tracks, or the front wheels, extend beyond the skid device. Thus, the ground facing surface and/or the end surfaces of the skid device are moved away from alignment with the leading edges of the tracks or wheels and are less prone to contact the ground when the front of the vehicle encounters uneven or sloped ground.

The actuation mechanism may comprise any suitable mechanism for operating the skid device between deployed and retracted positions, for example an electromechanical mechanism and/or a hydraulically actuated mechanism.

The actuation mechanism is preferably operable from within the vehicle, for example by the vehicle operator or driver.

The skid device may comprise one, or two, or more ground facing surfaces. The skid device may comprise a foot or more than one foot, each having a ground facing surface. One or more ground facing surfaces may be associated with each said wheel or track of the vehicle. The vehicle may comprise one, or more than one skid device.

In the (or each) deployed position, the ground facing surfaces may together extend along substantially the entire length and/or width of the vehicle, between the tracks or wheels (in alignment with, or extending beyond, i.e. front and/or behind, the wheels or tracks). The ground facing surface may extend across substantially the entire width of the vehicle between the tracks or wheels, so as to most evenly distribute pressure on soft ground resulting from the weight of the vehicle. Thus the ground facing surface extends to support substantially all of the area described by the contact between the wheels or tracks and the ground.

According to a second aspect of the invention, there is provided a skid device for mounting a vehicle having tracks or wheels, the skid device having a planar ground facing surface and an actuation mechanism; when mounted to a said vehicle positioned on level and flat ground, the skid device operable between a retracted position in which the ground facing surface is spaced apart from the ground, when the vehicle is on level and flat ground; and a deployed position in which the ground facing surface is at or near the ground;

the skid device operable in the deployed position to support some or all of the weight of the vehicle, when mounted to a vehicle in use on soft ground.

The skid device may be provided with one or more resilient biasing means, such as shocks or dampers or other suitable apparatus known for use in vehicle suspension, to enable the ground facing surface to be deflected over uneven ground. The actuation mechanism may comprise one or more resilient biasing means.

The skid device may comprise a resilient portion having a ground facing surface, such as a metal plate.

In some embodiments, the ground facing surface extends to an excurvate and surface (at one or both ends thereof). In a deployed position in use, the distance between the ground and the excurvate end surface increases gradually with distance from the ground engaging surface, thereby reducing the tendency of the skid device to dig into, or jam against, uneven ground. In an alterative embodiment, the end surfaces may be planar and may extend at an angle from the ground facing surface.

The skid device may comprise a foot member, the foot member having a ground facing surface and, in some embodiments, the or each end surface (which may be excurvate). The foot member is typically operably connectable to a body of the vehicle (for example the vehicle chassis, or other portion of the vehicle underside) by one or more support members, so as to mount the skid device to the vehicle. The foot member may comprise or consist of a metal plate, which may be resilient, so as to enable to the ground facing surface to be deflected over uneven ground, when the skid device is mounted to a vehicle.

The skid device may further comprise one or more support members, which be adapted to operably connect the skid device to the vehicle (typically the underside of the vehicle) and through which some or all of the weight of the vehicle may be supported, in use of the vehicle on soft ground. The actuation mechanism may comprise one or more support members. The actuation mechanism may comprise or consist of one or more telescopic shafts (which may in some embodiments function as support members), by which the skid device may be moved between retracted and deployed positions, when the skid device is mounted to a vehicle. The actuation mechanism may comprise one or more pivotal linkages (which may in some embodiments function as support members), by which the ground facing surface may be swung between deployed and retracted positions, when the skid device is mounted to a vehicle.

Further preferred and optional features of the second aspect correspond to preferred and optional features of the first aspect.

By soft ground we include muddy or boggy ground, and sand or gravel covered ground.

Relative terms such as "end", "side", "front" "in front of, "behind", of the vehicle, the skid device or features thereof, are defined in relation to the direction of motion of the vehicle, when propelled by the tracks or wheels in normal use. However the invention relates in some embodiments to vehicles operable to be propelled equally well in more than one direction and it will be understood that such relative terms as applied to vehicles of this type may be interchangeable.

The invention extends to a skid device suitable for use on a wheeled or tracked vehicle (and to a wheeled or tracked vehicle comprising at least one skid device), wherein the skid devices includes: a) an elongated skid portion formed and arranged to extend along the longitudinal axis of a vehicle in use of the skid device; b) skid support means formed and arranged to be mounted to the underside of a vehicle in use thereof and means for moving the skid portion from a first raised position to a second lowered position levelled with the bottom of the wheels/tracks; whereby the skid portion engages the ground on which a vehicle in use thereof is positioned, therefore reducing the pressure exerted onto the ground by the vehicle.

The skid portion may have a turned up portion at each end. The said means for moving the skid portion is powered by hydraulic or electro/mechanical means. The invention further extends to a vehicle comprising: a) a vehicle body, b) spaced tracks and/or wheels projecting below the vehicle body to engage the ground, and c) at least one skid between the tracks and/or wheels, the or each skid being moveable from a first upper position above the ground to a second lower position to engage the ground, in use, the or each skid in the second lower position reducing the ground pressure on the tracks and/or wheels and skidding along the ground as the tracks and/or wheels drive the vehicle body.

The or each skid may be moved from the first to the second position by a hydraulic or mechanical device. The or each skid may be connected to the vehicle body by at least one telescopic shaft allowing the skid to be moved from the first to the second position and vice versa. The or each skid may have turned up ends to ride over undulations in the ground surface. Description of the Drawings

An example embodiment of invention will now be described with reference to the following figures in which: Figure 1 shows a rear view of a tracked excavator with a skid device in a retracted position;

Figure 2 shows a rear view of a tracked excavator with a skid device in a deployed position;

Figure 3 shows side view of the skid device shown in Figures 1 and 2; and

Figure 4 shows a schematic side view of a further embodiment of a skid device of the present invention (a) in a deployed position (b) in a retracted position.

Detailed Description of an Example Embodiment

Referring to Figures 1 and 2 there is shown a vehicle in the form of a tracked excavator 1. Excavator 1 has a vehicle body 2 with a chassis 3. A pair of spaced tracks 4A.4B project below the vehicle body 2 to engage the ground. The external surfaces of tracks of vehicle of this type are typically provided with plurality of traction formations, such as the parallel ridges 14 shown in Figures 1 and 2.

A skid device 100 is provided between the tracks, comprising a foot or skid 10 having a planar ground facing surface 10A. Skid 10 is moveable from a retracted upper position, wherein the skid is close to the underside of the chassis and the ground facing surface is spaced apart from, and above the ground (as shown in Figure 1) to a deployed lower position wherein the ground facing surface of the skid is generally parallel to and close to the ground, (as shown in Figure 2).

When the vehicle is driven over soft ground (as commonly encountered during building or engineering works), the track may sink or dig into the ground, hampering movement of the vehicle. However, when the skid is in the deployed position as shown in Figure 2, it is in position to contact the ground when the tracks begin to sink or dig, such that some (or in extreme cases all) of the weight of the vehicle is supported through the skid device. Thus, the skid device reduces the ground pressure on the tracks preventing the tracks from sinking into the ground (or further into the ground). In the deployed position, and when some or all of the weight of the vehicle is suppored by the skid device, the skid device effectively increases the footprint of the vehicle on the ground. Additionally by virtue of the planar ground facing surface, which is generally parallel to the ground, skid 10 slides along the ground as the tracks drive the vehicle body 2.

Referring now to Figure 3, skid 10 has turned-up, curved ends 1 1A,1 1 B, the ground facing surface 10A extending to excurvate end surfaces 0B. In use, the end surfaces 10B taper towards the ground and enable the skid 10 to ride over undulations in the ground surface, and reduces the risk of the skid digging in or being caught in uneven surfaces over which the vehicle is driven.

Skid 10 is connected to chassis 3 by four telescopic shafts 12A, 12B, 12C, 12D (12C not shown); together functioning as an actuation mechanism, which may be mechanically or hydraulically operated. The telescopic shafts are operable to move the skid 10 between the retracted and deployed positions. Any number of telescopic shafts may be used. The shafts may function as support members, to mount the skid device to the chassis and typically also to bear some or all of the weight of the vehicle, in use on soft ground. Optionally, the shafts comprise a damping mechanism, to allow small deflections in the position of the skid an facilitate movement of the skid over undulations in the ground surface, and reduce the risk of the skid digging in or being caught in uneven surfaces over which the vehicle is driven.

The skid device could be built into new vehicles or retro-fitted to existing vehicles.

The invention may take a form different to that specifically described above. For example more than one skid may be provided. Also the vehicle could be a wheeled vehicle. A further embodiment of the invention is shown in Figure 4. The actuation mechanism of skid device 101 comprises a set of pivotal members 120 (which, in the example shown, additionally function as support members) connected to the chassis 3 and the skid 10 by pivots 121 and 122, respectively. In the deployed position shown in Figure 4(a), the ground facing surface 10A is positioned slightly above the ground, when the vehicle is on flat firm ground, such that the surface 10A is spaced from the ground by a distance approximately equal to the depth of the raised traction formations 14 (the path of which is shown by dotted line 124). The traction formations may thus dig into soft ground to provide the vehicle with traction, but further sinking of digging of the tracks 4A,B into the ground which would otherwise hinder movement of the vehicle, is prevented by skid 10 contacting the ground and supporting some or all of the weight of the vehicle.

The curvature or end surfaces 0B is similar the curvature of the leading and trailing ends of the tracks 4A.B, and the curved ends 1 1 A,1 1 B of the skid are aligned with the ends of the tracks. By this arrangement, the skid device reduces the tendency of the vehicle i.e. the front or rear ends of the tracks, to dig into soft ground, when driven over undulations, or from level to steeply sloping ground. The skid device 101 may be swung from the deployed position to the retracted position shown in Figure 4(b), by rotation of the apparatus around the pivots 121 ,122. The actuation mechanism typically further comprises hydraulic or electromechanical members (not shown), preferably operable by the driver of the vehicle, to move the skid device between the retracted and deployed positions.

In the retracted position shown in Figure 4(b), the leading end 123 of the tracks extend beyond (i.e. in front of) leading curved end 1 1A (in relation to the vehicle when driven in the direction of arrow A). Accordingly, when the vehicle is driven over rough ground, for example from generally level ground up a steep incline, or over such irregular surfaces as are typically encountered on construction sites, the skid device is less prone to contact rocks or other obstacles, when in the retracted position.

Further modifications will be apparent to those skilled in the art without departing from the scope of the present invention.