GB2513834A

GB2513834A - Improved vehicle floor

Info

Publication number: GB2513834A
Application number: GB1304097.7A
Authority: GB
Inventors: Ashwyn Dhir
Original assignee: Swift Group Ltd
Current assignee: Swift Group Ltd
Priority date: 2013-03-07
Filing date: 2013-03-07
Publication date: 2014-11-12
Anticipated expiration: 2033-03-07
Also published as: GB201304097D0; GB2513834B

Abstract

A caravan or a motor home floor comprises a lay-up 100 of a composite skin 200, a honeycomb 300 and a foam 400, wherein the layers are retained together. The skin 200 can be a glass fibre reinforced polymer (GRP) where the fibres filaments are arranged as a roven-woven to provide high stiffness along the length or width of the caravan. The honeycomb 300 comprises hexagonal cells whose cross section extends in the thickness direction of the floor and may be aluminium, GRP or a polypropylene. The foam 400 comprises expanded or extruded polystyrene foam. The layers 200, 300, 400 are retained together by a bonded adhesive such as a polyurethane adhesive and may be impermeable to water. Paper separating layers 600 can be provided to prevent adhesive entering the honeycomb cells. Stiffeners (700, fig 2) can be provided around the floor to add rigidity, and may extend around any cut-outs. Honeycomb layers 310,320 can be adjacent the composite skin 210,220 and sandwich a foam layer 400; alternatively foam layers can be adjacent the composite skin 210,220 and sandwich a honeycomb layer 400.

Description

IMPROVED VEHICLE FLOOR

FIELD OF INVENTION

The invention relates to a vehicle floor, in particular to a caravan or a motor home with an improved floor and to a method of forming the floor.

BACKGROUND OF THE INVENTION

A floor of a caravan or motor home is required to provide structural rigidity to the caravan or motor home since it interconnects the chassis with other primary structural components. It is also required to absorb impact from users within the caravan or motor home and from debris external to the caravan or motor home. In addition to the above, the material of the floor must be selected to provide an insulating effect such that heat is retained within the caravan or motor home. It is also desirable to make the floor as light as possible such that fuel consumption during towing or driving is minimised.

As a result of these requirements conventional floors are generally made from a lay-up of wood, such as plywood, metal and polystyrene.

It is an object of the invention to provide an improved floor.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a caravan or a motor home floor, which is configured to cover a substantial portion of the bottom of the caravan or motor home, wherein the floor comprises a lay-up of the following materials: a composite skin; a honeycomb; a foam, wherein the layers are retained together by retaining means.

Advantageously the first objective is solved since; the composite skin acts to provide a high torsional and bending stiffness for a given weight; the honeycomb can act to separate the composite skin from a centreline of the lay-up thus positioning the skin for optimum torsional and bending stiffness, the honeycomb also increases the compressive strength and resistance of the lay-up to impact and reduce the thermal conductivity of the lay-up; the foam acts in a similar manner to the honeycomb, but is primarily to reduce the thermal conductivity of the lay-up.

Preferably, the composite skin is arranged on an outer layer of the lay-up. More preferably, there are two composite skin layers, a first composite skin layer arranged on an upper outer layer and a second composite skin layer arranged on a lower outer layer.

Advantageously, by positioning the composite skin on an outer layer the bending and torsional stiffness of the lay-up is increased.

Optionally, the honeycomb layer is arranged adjacent the composite skin layer. More preferably, there are two honeycomb layers, a first honeycomb layer being adjacent the first composite skin, and a second honeycomb layer being arranged adjacent the second composite skin. Preferably, the foam layer is arranged adjacent the honeycomb layer, more preferably, the foam layer is sandwiched between the first and second honeycomb layer.

Alternatively, there are two foam layers, a first foam layer being adjacent the first composite layer and a second foam layer being adjacent the second composite layer.

Preferably, the honeycomb layer is sandwiched between the first and second foam layers.

Preferably, the composite skin comprises a glass fibre material. Preferably the glass fibre material is a glass fibre reinforced polymer that comprises a plastic matrix reinforced by fibres of glass. Preferably, the plastic matrix is one of the following or other suitable materials: epoxy; a thermosetting plastic, such as polyester or vinylester; or a thermoplastic.

Advantageously, the composite skin is relatively cheap and is easily formed by moulding.

Preferably, the fibres of the composite comprise a plurality of filaments arranged in a bundle to provide a roving. Preferably, the rovings are woven to provide a roven-woven arrangement within the skin. Preferably, the rovings are arranged to provide high stiffness along one or more axes, preferably, in a direction, which in use extends along a length and/or width of a caravan or a motor home. Advantageously, the roven-woven arrangement can support high loads and is hard wearing such that the upper surface can be walked on and the lower surface can resist damage from impact caused by debris from the road.

Alternatively, the composite skin comprises a carbon fibre reinforced polymer.

Preferably, the honeycomb comprises a plurality of substantially hexagonal cells, the cross section of which preferably extending in a through thickness direction. Preferably, the cells are composed of one of the following or other suitable materials: aluminium; Glass reinforced polymer; polymer, preferably polypropylene.

Advantageously, the honeycomb is able to retain a portion of air between the cells thereby increasing the thermal resistance of the caravan or motor home floor. Advantageously, the honeycomb has a high compressive strength for resisting load caused by users walking on the floor.

Preferably, the foam comprises a polystyrene foam. Preferably the foam is expanded or extruded. Preferably, the foam is a closed-cell foam. Preferably the foam is styrofoamk.

Preferably, the layers are bonded together by an adhesive retaining means. Preferably, the adhesive is a polyurethane adhesive.

Preferably, one or more of the layers of the lay-up are impermeable to water.

Advantageously, the floor does not absorb water.

Preferably, the or each composite skin is 1.5mm in the through thickness direction, preferably, ± 20%. Preferably, the or each honeycomb layer is 8mm in the through thickness direction, preferably ± 20%. Preferably, the or each foam layer is 30mm in the through thickness direction, preferably ± 20%.

Advantageously, it has been found that the specific combination of these materials and their geometries leads to a floor which has optimum stiffness: a floor which is too stiff is susceptible to stress failure from shock loads; a floor which is too flexible is susceptible to excessive movement and hence failure by fatigue. Furthermore, it has been found that the specific combination of these materials and geometries leads to a floor with the correct thermal properties: the floor has a low equivalent coefficient of thermal expansion so that the caravan can operate at high temperatures; the floor has low thermal conductivity, which also enables it to operate at high temperatures and helps to retain heat within the body of the caravan.

Preferably, the or each composite skin layers have a tensile strength of 90 N/mm2, preferably a tensile modulus of 9750 N/mm2. and preferably a flexural modulus of 8700 N/mm2 wherein the aforementioned material properties preferably vary by ± 20%.

Preferably, the or each foam layers have a tensile strength of 0.45 N/mm2, preferably a tensile modulus of 10 N/mm2, preferably a shear modulus of 7 N/mm2, preferably a coefficient of thermal expansion of 0.07 mm/rn K, preferably a thermal conductivity at 10° C of 0.035, wherein the aforementioned material properties preferably vary by ± 20%.

Preferably, the or each honeycomb layers have a cell size of 3, or 8, or 10mm, preferably a compression modulus of 40 M Pa, preferably a shear modulus of 6 -15 M Pa, preferably a thermal conductivity of about 0.065 W/m K, wherein the aforementioned material properties preferably vary by ± 20%.

Preferably, the floor is about 1.5m wide and 2-Sm in length.

Preferably, the floor comprises two cut-outs, which in use enable the floor to extend around the wheels of the caravan.

Preferably, the floor comprises one or more stiffeners arranged to increase the stiffness at locations where the floor experiences high stress concentration, for example, at proximate the wheels or chassis mounting points.

Preferably, the floor comprises one or more edge stiffeners which extend around an edge of the floor for fixing structural components to the floor, such as the vertical side of the vehicle.

Preferably, the stiffeners are bonded to the floor by an adhesive. Preferably, the stiffeners extend around the cut-outs.

Preferably, the floor comprises one or more embedded stiffeners which are embedded in one or more of the layers. Preferably, the embedded stiffeners comprise elongate members.

Preferably, the stiffeners extend on or through the lay-up in a lateral and for longitudinal direction.

In this way the floor acts to distribute the majority of the loads which are experienced in the structural components of the caravan through the caravan.

Preferably, the stiffeners are made from metal or are made from a polymer such as polyurethane.

Preferably, the floor comprises a conduit that extends through one or more of the layers, the conduit being for the transmission of wiring or heating.

Preferably, the composite skin is suitable for receiving a layer of carpet material.

Preferably, the floor comprises one or more vents, that comprise apertures which extend through one or more of the layers.

Preferably, a separating layer is arranged on one of more sides of the or each honeycomb layer, the separating layer to prevent material used to bond the layers together from entering the cells of the honeycomb. Preferably, the separating layer comprises a paper based material, such as Scrirn TM According to a second aspect of the invention there is provided a caravan or a motor home comprising a floor according to the first aspect of the invention.

According to a third aspect of the invention there is provided a method of assembling a caravan or a motor home floor, the method comprising: fixing a honeycomb layer, a foam layer and a composite skin layer together to form a lay-up by retaining means.

Preferably, the method includes a step of bonding one or more of the layers together by an adhesive retaining means, which is preferably a polyurethane adhesive.

Preferably, the method includes a step of attaching a separating layer to one or more sides of the or each honeycomb layer prior to fixing the honeycomb layer to the foam layer and / or the composite skin.

Preferably, the method comprises arranging a first layer of the composite skin on an upper surface of the lay-up and arranging a second layer of the composite skin on a lower surface of the lay-up.

Optionally, the method includes sandwiching the foam layer between a first and a second honeycomb layer, and thereafter fixing a first layer of composite skin to the first layer of honeycomb, and fixing a second layer of composite skin to the second layer of honeycomb.

Alternatively, the method includes sandwiching the honeycomb layer between a first and a second foam layer, and thereafter fixing a first layer of composite skin to the first layer of foam, and fixing a second layer of composite skin to the second layer of foam.

Preferably, the method includes a step of pressing the lay-up whilst curing of the adhesive retaining means occurs. Preferably, the lay-up is hot or cold pressed. Preferably, the lay-up is pressed when it is vertically suspended from a support such that each layer in the lay-up experiences the same pressure.

According to a fourth aspect of the invention there is provided a method of assembling a caravan or a motor home comprising connecting a chassis and side panels of the caravan to a floor formed in accordance with the third aspect of the invention.

All of the features described herein may be combined with any of the above aspects, in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 shows a side cross-sectional view of a floor of a caravan according to an exemplary embodiment of the invention; Figure 2 shows a perspective view of the floor of figure 1;

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Figures 1 and 2 show a caravan floor which comprises a lay-up 100 having: a composite skin 200; a honeycomb layer 300 and a foam layer 400, wherein the layers are retained together by retaining means 500. In this embodiment the retaining means 500 comprise an adhesive positioned between adjoining layers, although in other embodiments it will be appreciated that they may alternatively or in addition comprise a pin which extends the through thickness of the lay-up.

Firstly considering the composite skin 200; in this embodiment there are two composite skin layers, a first layer 210 is arranged on an upper surface of the lay-up which defines an interior surface of the floor of the caravan, and a second layer 220 arranged on a lower surface of the lay-up which defines an exterior surface of the caravan. By positioning the composite skin 200 away from a centreline 110 of the lay-up 100 the bending and torsional stiffness of the lay-up is increased. In this embodiment the composite skin 200 comprises a GRP material, with a matrix through which glass fibres extend. In this way the composite skin is relatively cheap and is easily formed by moulding.

In this embodiment the fibres comprise a plurality of filaments arranged in a bundle to provide a roving. The rovings are woven to provide a roven-woven arrangement within the skin which comprises a series of interleaved, laterally extending and horizontally extending rovings.

With such an arrangement the composite skin can support high loads and is hard wearing such that the upper surface can be walked on and the lower surface can resist damage from impact caused by debris from the road.

In this embodiment the composite skin is about 1.5mm in the through thickness direction. The matrix and fibres combine to give the following equivalent material properties: a tensile strength of about 90 N/mm2 tensile modulus of about 9750 N/mm2, and a flexural modulus of about 8700 N/mm2.

Now considering the honeycomb layer 300; in this embodiment there are two honeycomb layers a first honeycomb layer 310 being arranged adjacent the first composite skin 210, and a second honeycomb 320 layer being arranged adjacent the second composite skin 220. Each honeycomb layer is about 8mm in the through thickness direction. The honeycomb layers are composed of substantially hexagonal cells, the cross section of which extending in a through thickness direction. In this embodiment the cells are composed from polypropylene, and the cell size is about 8mm between parallel sides of the cells.

The material of the honeycomb is selected such that it has a compression modulus of about 40 M Pa, a shear modulus of about 6-15 M Pa, a thermal conductivity of about 0.065 W/m K. An advantage of the honeycomb is that it is able to retain a portion of air between the cells thereby increasing the thermal resistance of the caravan floor. The honeycomb also has a high compressive strength such that it is able to absorb compressive loads, for instance, when a user walks on the floor. A further advantage of the honeycomb is that it acts as a light weight spacer between the composite skins, that allows the skins to be placed as far apart as possible to increase the bending stiffness of the lay-up.

Now considering the foam layer 400: in this embodiment there is a single foam layer 400, which is sandwiched between the first 310 and second 320 honeycomb layers. However, in another embodiment there may be two foam layers that sandwich a single honeycomb layer.

Other embodiments may comprise other variations/combinations of the above embodiments that will be appreciated by the skilled person.

In this embodiment the foam is a closed-cell extruded polystyrene foam, such as Stryofoam., The foam layer is about 30mm in the through thickness direction.

The material of the foam is selected such that it has a tensile strength of about 0.45 N/mm2 a tensile modulus of about 10 N/mm2. a shear modulus of about 7 N/mm2, a coefficient of thermal expansion of about 0.07 mm/rn K, and a thermal conductivity at 10° C of about 0.035.

It will be appreciated that from the above materials, the foam and honeycomb layers are selected to be impermeable to water, in this way the floor does not absorb water.

Now considering how the layers are bonded together: initially a separating layer 600 is positioned on either side of the honey comb layers 310, 320. The separating layer 600 is to prevent material used to bond the layers together from entering the cells of the honeycomb. In this embodiment the separating layers comprise a paper based material, referred to as ScrimTM. The separating layer 600 is adhesively bonded to the honeycomb layer 300 by means of a foaming water based Polyurethane adhesive.

Thereafter, the honeycomb layers 310, 320 are fixed on either side of the foam layer 400 by means of an adhesive. In this embodiment the adhesive is sprayed finely through a nozzle to ensure a thin uniform film is provided to one or both of the adjoining surfaces. In this embodiment the adhesive is a polyurethane adhesive. The honeycomb layers 310, 320 and foam layer 400 are then pressed together.

The first 210 and second 220 composite layers are then bonded to the respective first 310 and second 320 honeycomb layers in the same way as for the foam and honeycomb layers.

The assembled lay-up is next sized to fit the caravan by means of a cutting element (not shown). In a preferred embodiment, the cutting element is a water jet cutter. As best seen in figure 2, the cutting element may also be used to machine two cut-outs 120A, B, which enable the floor to extend around the wheels (not shown) of the caravan. Furthermore, the cutting element may be used to machine one or more vents 130 into the floor.

The cut lay-up is then cured. In a preferred embodiment the lay-up is allowed to cure in a zero gravity press such that each layer in the lay-up experiences the same pressure. The zero gravity press is achieved by attaching the lay-up to a support such that it is vertically suspended, thereafter, the lay-up is pressed. An advantage of cutting before curing is that subsequent curing removes any residual stresses caused by cutting.

It will be appreciated that the lay-up may alternatively be cut following curing, for instance by a CNC machine.

Due to the above materials, and their arrangement a floor is achieved which has optimum stiffness: a floor which is too stiff is susceptible to stress failure from shock loads; a floor which is too flexible is susceptible to excessive movement and hence failure by fatigue.

Furthermore, it has been found that the specific combination of these materials and geometries leads to a floor with the correct thermal properties: the floor has a low equivalent coefficient of thermal expansion so that the caravan can operate at high temperatures; the floor has low thermal conductivity, which also enables it to operate at high temperatures, and helps to retain heat within the body of the caravan.

As best seen in figure 2, the lay-up includes stiffeners 700 that in one example comprise a plate 710 which extends around the edge of the lay-up at one or more points. In this embodiment the stiffener comprises a metal extrusion, which is bonded to the lay-up. The plate 710 can be used to reduce delamination of the lay-up. Structural components can be attached to the stiffeners 700, such as the chassis and vehicle side faces and I or vehicle front and rear faces of the caravan, to aid transmission of load between these components through the floor. In this example the plate 710 is used to interconnect the floor with the vehicle sides (not shown).

Further stiffeners 720 may be embedded in the lay-up during assembly of the layup. The stiffeners 720 comprise elongate members, which in a preferred embodiment are made from polyurethane. The stiffeners can be embedded into the honeycomb layer and extend in a longitudinal or lateral direction. Alternatively, or additionally, the stiffeners can extend through the lay-up in the through thickness direction. In a preferred example of stiffeners that extend in the through thickness direction, the stiffeners extend through all layers other than the composite outer skins 200. In this way the areas of the floor which, in use, are subject to stress concentrations can be reinforced by the stiffeners. Such an arrangement enables a lighter more efficient floor structure.

Sections of the layers can be cut out or omitted to define conduits (not shown) for the transmission of wiring and/or heating.

The upper surface of the first layer 210 of composite material is smoothly finished such that a carpet or other interior decoration can be added to it.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS1. A caravan or a motor home floor, which is configured to cover a substantial portion of the bottom of the caravan or motor home, wherein the floor comprises a lay-up of the following materials: a composite skin; a honeycomb; and a foam, wherein the layers are retained together by retaining means.
2. The caravan or a motor home floor as claimed in claim 1, in which the composite skin is arranged on an outer layer of the lay-up.
3. The caravan or a motor home floor as claimed in claim 2, in which there are two composite skin layers, a first composite skin layer arranged on an upper outer layer and a second composite skin layer arranged on a lower outer layer.
4. The caravan or a motor home floor as claimed in any preceding claim, in which, the honeycomb layer is arranged adjacent the composite skin layer.
5. The caravan or a motor home floor as claimed in claim 4, in which there are two honeycomb layers, a first honeycomb layer being adjacent the first composite skin, and a second honeycomb layer being arranged adjacent the second composite skin.

0
6. The caravan or a motor home floor as claimed in any preceding claim in which the foam layer is arranged adjacent the or each honeycomb layer.
7. The caravan or a motor home floor as claimed in claims 3, in which there are two foam layers, a first foam layer being adjacent the first composite layer and a second foam layer being adjacent the second composite layer.
8. The caravan or a motor home floor as claimed in any preceding claim, in which the composite skin comprises a glass fibre material.
9. The caravan or a motor home floor as claimed in any preceding claim, in which one or more of the layers of the lay-up are impermeable to water.
10. The caravan or a motor home floor as claimed in any preceding claim, in which the or each honeycomb layer has a cell size of approximately 3, orB, or 10mm,
11. The caravan or a motor home floor as claimed in any preceding claim, in which the floor comprises two cut-outs, which in use enable the floor to extend around the wheels of the caravan.
12. The caravan or a motor home floor as claimed in any preceding claim, in which the floor comprises one or more stiffeners arranged to increase the stiffness at locations where the floor experiences high stress concentration.
13. The caravan or a motor home floor as claimed in any preceding claim, in which the floor comprises a conduit that extends through one or more of the layers, the conduit being for the transmission of wiring or heating.
14. The caravan or a motor home floor as claimed in any preceding claim, in which the floor comprises one or more vents that comprise apertures which extend through one or more of the layers.
15. The caravan or a motor home floor as claimed in any preceding claim, in which a separating layer is arranged on one of more sides of the or each honeycomb layer, the separating layer operating to prevent material used to bond the layers together from entering the cells of the honeycomb.
16. A caravan or a motor home comprising a floor according any one of claims 1 to 15.
17. A method of assembling a caravan or a motor home floor, the method comprising: fixing a honeycomb layer, a foam layer and a composite skin layer together to form a lay-up by retaining means.
18. The method of claim 17 including a step of bonding one or more of the layers together by an adhesive retaining means, which is preferably a polyurethane adhesive.C)
19. The method of claim 17 or claim 18 including a step of attaching a separating layer to one or more sides of the or each honeycomb layer prior to fixing the honeycomb layer to the foam layer and for the composite skin.
20. The method of any one of claims 17 to 19 including arranging a first layer of the composite skin on an upper surface of the lay-up and arranging a second layer of the composite skin on a lower surface of the lay-up.
21. The method of any one of claims 17 to 20 including sandwiching the foam layer between a first and a second honeycomb layer, and thereafter fixing a first layer of composite skin to the first layer of honeycomb, and fixing a second layer of composite skin to the second layer of honeycomb.
22. The method of any one of claims 17 to 20 including sandwiching the honeycomb layer between a first and a second foam layer, and thereafter fixing a first layer of composite skin to the first layer of foam, and fixing a second layer of composite skin to the second layer of foam.
23. The method of any one of claims 17 to 22 including a step of pressing the lay-up whilst curing of the adhesive retaining means occurs.
24. The method of any one of claims 17 to 22 wherein the lay-up is pressed when it is vertically suspended from a support such that each layer in the lay-up experiences the same pressure.
25. A method of assembling a caravan or a motor home comprising connecting a chassis and side panels of the caravan to a floor formed in accordance with any one of claims 1 to 24.
26. A caravan or a motor home floor substantially as described herein with reference to the accompanying drawings.
27. A method of assembling a caravan or a motor home floor substantially as described herein with reference to the accompanying drawings. C?)N