Motorhome levelling apparatus

Abstract

Apparatus for levelling a vehicle, such as a motorhome or recreational vehicle, on uneven ground has an inflatable bag 4 formed from a length of a cylinder of flexible material which is sealed at each

Description

FIELD OF THE INVENTION The present invention relates to apparatus for levelling motorhomes, or "recreational vehicles (RVs)", (vehicles which provide mobile living accommodation) and other vehicles. BACKGROUND ART It is uncomfortable to stay for any length of time in a caravan which is parked on uneven ground. People who move their caravans from site to site cannot rely on the next parking space being even, and so need a way of being able to level their caravans on uneven ground; many conventional caravan levelling devices use ramps, which are heavy, bulky to carry and store, and awkward to use. We have been selling our design of caravan leveller for about 10 years, for use by people who park their caravans on uneven ground and want to make them level. Our products are sold under our trade mark "Lock 'n' Level" (UK trade mark registration No.3025246, in the same name as the present applicant) and, as can be seen from Figure la, these products are inflatable bags 1 comprising a cylinder 3 of flexible, air-impermeable material which is about 60cm in circumference and about 75cm long, and which is sealed at each end by a pair of transverse plates 5 (only one at each end is visible in Figure la). These plates 5 are about 30cm in length and sandwich the material therebetween. This forms the bag 1 which is inflatable by pumping air into the bag through a valve assembly 7 (which is releasable to allow the bag to be deflated). The uninflated bag is placed on the ground valve side up, and a caravan wheel (not shown) is positioned above it using the indicia 9 provided on the upper surface of the bag, with the longitudinal dimension of the bag being aligned with the rolling direction of the caravan wheel. The bag 1 is then inflated enough to raise the wheel by the desired amount to make the caravan level across the axle carrying the wheel. Our products are an improvement on alternative ramp-based designs, they are simple to use, and quick - a caravan of up to 2 ¥2 tonnes can be raised by about 15 cm in about 6 minutes. Moreover, because the air in such a bag need only be at about 18 - 20 psi (0.124 -0.207 MPa), the bags stay inflated without significant leakage for long periods of time, are quite light (about 3 Kg - weight is important for items which are carried in a caravan, because caravans (and motorhomes) have maximum loading limits beyond which they are unsafe to be driven) and, when uninflated, can be rolled up into a compact size. One bag is sufficient to establish a level transversely (i.e. along the axle bearing the wheel supported by the bag. Differently-sized bags are available for different applications. One characteristic of this design is that when fully inflated the bag is largely cylindrical, and it is capable of rolling about its longitudinal axis, as shown in Figure lb. It will be appreciated that this could be problematic, in that a bag supporting a caravan wheel might in theory roll far enough for the wheel to slip off the bag, allowing the caravan to fall; however, in practice this is not a problem because caravans are provided with "stays", normally at each corner - these stays are simply extendable legs which can be lowered to contact the ground. Though they are not strong enough to lift the caravan's weight, they are sufficient to stop the caravan from moving in its horizontal plane, which is sufficient to prevent the caravan from moving horizontally so as to roll off the bag; they also reduce "bouncing" of the caravan on the bag when a person moves inside the caravan. Very few motorhomes are provided with stays similar to those on caravans, this means that the problem of a bag rolling, which is mitigated if not solved by the stays on caravans, is potentially more serious were a bag to our existing designs used for levelling a motorhome. There is a need for a something to address this problem while retaining the advantages of our existing design over other conventional caravan levellers. SUMMARY OF THE INVENTION The present invention is predicated on our realisation that the shape of our existing designs (when inflated) is not completely cylindrical but instead, because of our method of forming the bags, are shaped more like a pillow - that is, cylindrical towards the centre of the bag but deviating from cylindrical towards the ends. The plates at the ends of the bag make the cylindrical shape bend through complex curves to meet along a line, and these complex curves and the movement the bag material goes through to form these curves could, we surmised, be utilised to address the rolling problem. The present invention therefore provides an apparatus for levelling a vehicle on uneven ground comprising an inflatable bag formed from a length of a cylinder of flexible, air-impermeable material which is sealed at each end along a join line by a pair of flat plates which flatten the cylinder and sandwich the cylinder material securely therebetween, the plates at either end being a first, longitudinal distance apart and extending transversely for a second, transverse distance substantially the same as half of the circumference of the cylinder so that on inflating the bag it adopts the shape of a pillow, in which one of the plates at at least one end of the bag extends longitudinally towards the other end of the bag and terminates in two feet, one at each transverse end of the said plate, the longitudinal distance between the feet and the join line being in proportion to the width of the bag such that, on inflating the bag, the material towards the end of the bag adjacent the said plate in adopting the pillow shape pushes the plate away from the axis of the cylinder and to pivot about the join line until the feet come into contact with the ground to prevent rotation of the inflated bag around the axis of the cylinder. With such an arrangement, on inflating the bag the shape of the end of the bag acts on the plate which is underneath the bag (the "bottom plate"), causing it to rotate downwardly about the join line until the feet come into contact with the ground. Because the feet are located at opposite ends of the transverse bottom plate, this contact is sufficient to prevent the bag from rolling as in Figure lb, and this will persist for as long as the bag remains inflated. The design is just as easy to use as our existing products, and is not significantly heavier or bulky to store. The ratio of the longitudinal distance between the feet and the join line to the second distance is preferably 100: 300. Although the general concept of our invention was simple, we found that there are several factors that have to be taken into account for the products to work effectively. The degree of rotation of the bottom plate must be sufficient to prevent rolling, but the force rotating the bottom plate imparted by the air inflating the bag needs to be spread over a significant proportion of the bottom plate to bear the weight of the motorhome, and spreading this force effectively depends on the curvature of the bag where it abuts the bottom plate. When first trying to put the invention into practice, it became clear that simply adjusting the sizes of the bag and plates to take account of the different size of motorhome wheels compared to caravan wheels and the different weights of the two was suboptimal, and that it would be necessary also to adjust the proportions of the bag; after many iterations we found that a ratio of the first to the second distance of 500 : 300to be the best (varying this ratio between about 450 : 300 and about 550 :300 would still allow the apparatus to work, but sub-optimally; with a shorter bag length there is a tendency for the feet to dig in to the ground or mat underneath so that on deflation of the bag the bottom plate levels out in uncomfortably discontinuous steps rather than at a constant state, and with a longer bag there is a greater tendency for the motorhome to "bounce" on the inflated bag). Because the length of the bag is shorter than that of our caravan levelling products, so that a wheel supported by the bag is close to the bottom plates supporting the ends of the bag, the tendency for a motorhome to "bounce" on the inflated bag when someone moves inside the motorhome is reduced compared to our existing products. There may be a bottom plate at each end of the bag (both on the same bottom surface of the bag) so as to stabilise both ends of the bag against rolling, and / or the or each bottom plate between the two feet may extend longitudinally towards the other end of the bag by a third distance which is less than the longitudinal distance between the join line and the feet. This latter arrangement allows the feet to come into contact with the ground as desired, and prevents an upstanding piece of ground in between these contact points from becoming the sole point of contact with the bottom plate - which would otherwise allow rolling around that contact point. There may be a plurality of apertures provided in the plate; this reduces the weight of the plate but without reducing its strength (provided the apertures are suitably sized / shaped and disposed). Preferably there remains a sufficient area of plate between the apertures to support the curved surface of the bag material as it inflates and presses the bottom plate downwardly. A region of the plate adjacent an edge of the plate at the third distance from the join line and extending in the transverse direction between the feet may be solid, forming a solid spar of plate joining the feet together. This is important to prevent the bottom plate from bending when a motorhome is driven over the end of the bag before it is inflated, and it allows the ends of the plate to rotate together when the bag is inflated. The plate forming a pair with one of the said plates may extend longitudinally away from the other pair of plates, and be shaped and configured to extend longitudinally beyond the length of the cylinder material and to extend towards the ground. This is advantageous because this plate can serve as a ramp, lifting a rolling motorhome wheel onto the bag and protecting the end of the bag material from damage. As with our existing products, indicia may be provided on the outer surface of the cylinder of material on the side opposite that on which the bottom plate(s) is / are located, to assist in positioning a vehicle wheel on the cylinder of material. The present invention extends to a kit of one or more of the above apparatuses together with a mat to go between the apparatus and the ground to protect the bag from damage. The protective mat may have a number of load spreading pads located so as to underlie the feet; these pads (or the mat, where there are no pads) reduce friction and allow the feet to slide more easily as the bottom plate is caused to pivot by the inflation of the bag. Unlike a caravan, all motorhomes have at least four wheels and four points of contact with the ground which are separated far apart. For motorhomes, therefore two or three bags may be used in order to level the motorhome longitudinally as well as transversely. Accordingly the present invention extends to a kit of two or three of the above apparatuses. The kit may have an electric pump associated with each apparatus and may be operatively connected to a controller which is adapted to sense the amount by which a motorhome deviates from the level, horizontal plane, to determine the number and identity of motorhome wheels which should be raised to correct the deviation from the horizontal, and to determine the pressure to which each apparatus, when located under the identified motorhome wheels, needs to be inflated to raise the motorhome until it is at an acceptable horizontal level. With such an arrangement, a user inside the motorhome can establish which wheels should be raised, and so where and how many apparatuses should be placed for the motorhome to be levelled, and under which wheels. The motorhome can then be driven onto the apparatuses for levelling. Advantageously, the controller is adapted to control each pump to inflate the associated apparatus to raise the motorhome until it is at an acceptable horizontal level. Additionally or alternatively, the controller can monitor the level of the motorhome, continuously or intermittently, and, if its level goes past one which is deemed unacceptable, actuate the pump(s) to inflate one or more bags to return the motorhome to a comfortable level. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example and with reference to the accompanying figures, in which; Figure la is a view from above of a known caravan levelling apparatus in an uninflated state, and Figure lb is an end view of the apparatus in an inflated state; Figure 2a is view from below a motorhome levelling apparatus in accordance with the invention, Figure 2b is a plan view of a protective mat for use with the apparatus of Figure 2a, and Figure 2c is a side view of the apparatus of Figure 2a located on the protective mat of Figure 2b, and Figures 3a to 3d are views of the arrangement of Figure 2c showing the operation of the apparatus to raise the wheel of a motorhome at different stages: Figure 3a is a side view showing the apparatus of Figure 2a in a part-inflated state, Figure 3b is front three-quarters view showing the apparatus in part in a fully inflated state, and Figures 3c and 3d are front and side views of the apparatus as shown in Figure 3b. DETAILED DESCRIPTION OF THE EMBODIMENT Figure la shows a known caravan levelling apparatus and is described above (and is the subject of UK design registration No.4030336, in the same name as the present applicant). Figure 1 b shows how the apparatus of Figure la may roll undesirably when inflated. Figures 2a to 2c show the apparatus in accordance with the invention and its protective mat, and will be used to identify the elements of the apparatus and of the mat; Figures 3a to 3d will be used to illustrate how the apparatus operates. The apparatus 2 in Figure 2a comprises a length of a cylindrical piece of reinforced PVC (the reinforcement being single ply polyester yarn) which is formed into a bag 4; in Figures 2a and 2c the bag 4 is in a flattened state. The ends of the bag are sealed by transverse metal plates 6, 12 similar to those in our known design (as shown in Figure la) which sandwich the PVC between them and are joined by a line of flange bolts 16 which define a "join line"; however, the plate 6 on the bottom of the bag 4 comprises two parts, namely a transverse metal plate 8 the same as that shown in Figure la, and a bottom plate 10 which has substantially the same transverse length as the metal plate 8, but which extends for a significantly greater distance in the direction towards the transverse metal plate 6 at the other end of the bag 4. Each bottom plate 10 has a foot 14 at each transverse end of the bottom plate, and has a number of apertures 18 passing through it. Apertures 18 are intended to reduce the weight of the bottom plate 10 whilst retaining a sufficiently large area of metal for the material of the bag to press against when inflated, as described below. Each bottom plate 10 also has a solid spar portion 20 which extends transversely between the feet 14, and the solid spar portions 20 have an edge 22 which is a shorter distance from the join line than are the distal edges of the feet 14. In the example shown, the transverse width of the flattened bag 4 is 30cm (substantially the same as the transvers length of the metal plates 6, 12), and its length (the distance between opposite join lines) is about 50cm. The bottom plates 10 extend for 10 cm from the join line towards the opposite end of the bag. Edges 22 are about 1cm closer to the join line than are the distal edges of the feet 14. The metal is 3mm mild steel plate, and there are 7 flange bolts in total, spaced 48mm apart (we have found that the spacing of these bolts is important: spaced too widely and, as they bend when a motorhome is driven onto the bag, the sandwiched bag material can be contorted and lose its seal, but spaced too close together and the weight of the apparatus increases) Turning now to the protective mat 30 shown in Figure 2b, this is formed of a rubberised fabric or other flexible material which in use is placed beneath the apparatus 2 so as to protect the material of the bag 4 from being damaged or pierced by stones or other sharp items protruding from the ground surface. There are also four pads 32 of a UHMWPE (Ultra-high-molecular-weight polyethylene) material which act to spread the load of the feet 14 during operation and present a low friction surface for the feet to slide over. The pads 32 are sized and located so as to complement the shape of the metal plate 6 as will now be described with reference to Figure 2c; the thickness of the pads 32 (the vertical dimension in Figure 3c) is such that with the bag 4 uninflated the bottom plate 10 lies flat against the surface of the associated pad 32 and the bottom surface of the transverse metal plate 8 lies flat against the top surface of the mat 30. The pads 32 are positioned at either end of the bag so that they have an edge 34 running transversely against which an edge of the transverse metal plate 8 is able to abut; this allows the apparatus 2 to be accurately placed on the mat 30 and prevents the apparatus from moving off the mat whilst the bag is uninflated (which might happen when a motorhome is driven onto the bag, for example). Also shown in more detail in Figure 2c is the upper metal plate 12, which extends downwardly and outwardly from the join line to form a ramp section 26; this protects the edges of the bag 4 from damage as a motorhome is driven onto the apparatus, and eases a wheel upwardly when a motorhome is driven onto the apparatus. There is also a valve assembly 24 exactly the same as in the Figure la arrangement, for inflating and deflating the bag. The valve assembly has a standard one-way valve for inflating the apparatus, and there is a second, semi-restricted valve for deflating, so the apparatus will deflate quickly with the weight of a motorhome on top. The semi-restricted valve is designed to release air at a specific rate so that the motorhome will come down gently, but still in a fast enough time that is not inconvenient for the user. With the apparatus 2 supported on the protective mat 30 as shown in Figure 2c, a motorhome can be driven over the ramp section 26 and onto the bag 4, and accurately positioned using the indicia 42 for the levelling process to be carried out, as is now illustrated in Figures 3a to 3d, which show the motorhome wheel 40 only (not the motorhome itself). As the bag 4 is inflated, it lifts the wheel 40 to the desired height to level the motorhome as with the prior art devices of Figures la and lb (usually this levelling process is measured with a spirit level or the like measuring the horizontality of the caravan floor; exactly the same process is used with a motorhome). For clarity, Figure 3a shows the bag 4 partially inflated, and Figures 3b, 3c and 3d show the bag 4 fully inflated; it will be understood that in use the bag is inflated only to the extent necessary to raise the motorhome wheel 40 to the right height to level the motorhome. As the bag 4 is inflated, its pillow-like shape raises the transverse metal plates 8, 10, 12 upwardly, and the length of the bag 4 shortens, drawing the two join lines together; this causes the bottom plates 10 to pivot and to rest at an angle to the horizontal with the feet 14 forming the only contact with the pads 32. The motion of the join line during inflation has both upward and longitudinally inward components; it is desirable that the bottom plate pivot along the line where the feet 14 meet the pads 32 (so that the feet do not drag along the surface of the pad, which would cause damage to them), and this is achieved with the appropriate ratios of the longitudinal distance between the feet and the join line to the first distance and to the second distance being as described above. The bottom plates 10 are also urged outwardly by the bag material abutting the bottom plates (i.e. the parts of the bag 4 which abut the bottom plate around the apertures 18. It will be understood that when the bag 4 is inflated in use, the major force applied to the bottom plate 10 will, at its transverse ends adjacent the feet, be a bending moment around an axis parallel to the join line. Towards the centre of the plate (in the transverse direction) there will be less of a bending moment about the join line axis, but there will also be an appreciable bending moment about the longitudinal axis along the plate; it is for this reason that the spar portion 20 of the bottom plate 10 is provided, because it prevents the ends of the bottom plate 10 adjacent the feet from bending out of alignment and allowing the apparatus to roll. Placing the edge 22 closer to the join line than the feet 14 are to the join line allows for the mat 30 to conform to the shape of the underlying ground and so that it does not come into contact with an edge 22, which potentially could give the bottom plate 8 a single point of contact with the mat 30 rather than two points of contact at the feet 14. A single point of contact might allow the bottom plate 10 to roll about that point of contact. It will of course be understood that many variations may be made to the abovedescribed embodiment without departing from the scope of the present invention. For example, the metal plates which we made of mild steel could be made of any material sufficiently strong to withstand the point force loading at the feet and the bending moments, such as carbon fibre reinforced plastic; the bag could be formed of any suitably strong, flexible and air-impermeable material or coated fabric. We have described a two-part lower transverse metal plate, but this could be formed in one piece of a suitable material or composite material. The metal plates could be shorter or longer than the width of the flattened bag, provided a shorter plate would still effectively seal the end of the bag, and that a longer plate did not protrude too far as to present a trip hazard in use or be too bulky to store. The apparatus has been described as using flange bolts to join the metal plates, but other mechanical fixings could be used (such as ordinary nuts and bolts, rivets and the like) or the plates could be welded together at their ends and / or bonded (with heat or an adhesive) to the bag material. The drawings show one particular arrangement of apertures in the bottom plate, but there could be any number and disposition of apertures provided these retain the spar portion adjacent the feet and the remaining part of the bottom plate in between the apertures is strong enough to withstand the expected bending moments when the apparatus is in use.

Claims

1. Apparatus for levelling a vehicle on uneven ground comprising an inflatable bag formed from a length of a cylinder of flexible, air-impermeable material which is sealed at each end along a join line by a pair of flat plates which flatten the cylinder and sandwich the cylinder material securely therebetween, the plates at either end being a first, longitudinal distance apart and extending transversely for a second, transverse distance substantially the same as half of the circumference of the cylinder so that on inflating the bag it adopts the shape of a pillow, in which one of the plates at at least one end of the bag extends longitudinally towards the other end of the bag and terminates in two feet, one at each transverse end of the said plate, the longitudinal distance between the feet and the join line being in proportion to the width of the bag such that, on inflating the bag, the material towards the end of the bag adjacent the said plate in adopting the pillow shape pushes the plate away from the axis of the cylinder and to pivot about the join line until the feet come into contact with the ground to prevent rotation of the inflated bag around the axis of the cylinder.Apparatus according to Claim 1, in which the ratio of the longitudinal distance between the feet and the join line to the second distance is 100 : 300.

2. Apparatus according to Claim 1 or Claim 2 in which the ratio of the first distance to the second distance is 500 : 300.

3. Apparatus according to Claim 1, Claim 2 or Claim 3 comprising one of said plates at each end of the bag.

4. Apparatus according to any preceding claim, in which the or each said plate between the two feet extends longitudinally towards the other end of the bag by a third distance which is less than the longitudinal distance between the join line and the feet5. Apparatus according to any preceding claim, in which a plurality of apertures is provided in the plate.

6. Apparatus according to Claim 5, in which a region of the plate adjacent an edge of the plate at the third distance from the join line and extending in the transverse direction between the feet is solid.

7. Apparatus according to any preceding claim, in which the plate forming a pair with one of the said plates extends longitudinally away from the other pair of plates, and is shaped and configured to extend longitudinally beyond the length of the cylinder material and to extend towards the ground.

8. Apparatus according to any preceding claim, in which indicia are provided on the outer surface of the cylinder of material on the side opposite that on which the said plate(s) is / are located, to assist in positioning a vehicle wheel on the cylinder of material.

9. A kit comprising one or more apparatuses according to any preceding claim and a protective sheet of flexible material.

10. A kit according to Claim 9, in which the protective sheet has a number of load spreading pads located so as to underlie the feet.

11. A kit according to Claim 9 or Claim 10 comprising two or more apparatuses according to any of Claims 1 to 8, further comprising an electric pump associated with each apparatus and operatively connected to a controller which is adapted to sense the amount by which a motorhome deviates from the level, horizontal plane, to determine the number and identity of motorhome wheels which should be raised to correct the deviation from the horizontal, and to determine the pressure to which each apparatus, when located under the identified motorhome wheels, needs to be inflated to raise the motorhome until it is at an acceptable horizontal level.

12. A kit according to Claim 11, in which the controller is adapted to control each pump to inflate the associated apparatus to raise the motorhome until it is at an acceptable horizontal level.

13. A kit according to Claim 11 or Claim 12, in which the controller is adapted to monitor the orientation of the motorhome and, if it deviates from the level, horizontal plane by more than a predetermined amount, to control each pump to inflate the associated apparatus to raise the motorhome until it is at an acceptable horizontal level.13

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