The invention relates to technycal and functional improvements related to a tyre, which is puncture proof and has a substantially softer ride in comparison with other non pneumatic tyres, being therefore specially suitable for use in many types of industrial and off-the-road vehicles like: forklift trucks, loaders, backhoes, skid steer loaders and others.

STATE-OF-THE-ART There are many different types of tyres which are used by industrial and off-the-road vehicles. It will be described below the most common types: Tube or tubeless tyres inflated with air or nitrogen, which enable a soft ride, good traction, good load capacity, but are subjected to punctures, having as consequence vehicle downtimes. Another disadvantage, due to the elastomer type utilized in their fabrication, is that such tyres generally make black marks to floors. We may still point out as other disadvantages that such tyres are subjected to explosion due to carcass fatigue, with the possibility of hurting operators, and need frequent inflation pressure checkings.

Tube or tubeless tyres filled with an elastomer resin, which still have the disadvantage of making black marks to the floors where they ride. Their tread thickness is generally smaller when compared with a solid tyre, having therefore a shorter useful life. These tyres have the same advantages of air or nitrogen filled tyres, with the aditional benefits of being puncture proof and avoiding explosions and frequent inflation pressure checkings, as described in the US Patent # Re 29.980 from 01/1979 or in the Brazilian Patent # PI 8325/74. In general, such tyres are elastomer filled after being attached to a vehicle rim.

There are also other elastomer filled pneumatic tyres, where an annular

base member of resilient elastomer extends between and is bonded to the side walls of pneumatic tyres in the vicinity of bead portions so as to define a closed annular space which is then elastomer filled, without the need of being attached to a vehicle rim before the elastomer filling. After the processes cited above, such elastomer filled tyres may be attached to a rim through pressing, exactly the same way as solid tyres usually are attached to rims. These methods suffer from the disadvantage that the bonding between the tyre side walls and the annular base member is subjected to failures that frequently lead to weak bonds, with the consequence of tyre failure during use, being such problem emphasized when the tires have to be inflated with high pressures, which is the case of forklift truck's tyres, where the tyres should be inflated to pressures higher than 100 psi. Example of such a method may be found in the British Patent GB 2215681 A.

Solid rubber tyres-this type of tyre is generally bonded to the vehicle rim and is manufactured with an homogeneous hardness elastomer in the whole tyre structure, offering the advantage of being puncture proof, but suffering from the great disadvantage of supplying a very hard ride to the vehicle, with vibrations and impacts being transmitted more intensely to the vehicle and operator, causing damage for both of them. When subjected to a load, its radial deflection as well as its footprint is smaller than that of a pneumatic tyre, what diminishes its power of traction. These tyres may be manufactured using marking or nonmarking elastomers, but the majorative part of them make black marks to the floor where they ride. Examples of this type of tyres may be found in the brazilian patents # PI9.201.758 e MU7.402.449-3.

Due to their very thick tread, the solid tyres may offer a longer useful life in comparison to pneumatic tyres. Generally the tread thickness of a solid tyre is 2 to 6 times thicker than that of a pneumatic tyre.

Superelastic solid rubber tyres-their construction is of the kind

comprising three layers of rubber compound: one inner radial layer comprising cord or wire reinforcements, made out of a very hard rubber, which will be in contact with the vehicle rim after attachment by pressing; one intermediate radial layer bonded to the inner layer, made out of a softer rubber, whose function is to absorb impacts and give a softer ride; and one outer layer bonded to the intermediate layer, made out of a rubber with high abrasion resistance, which comprises the tread. Such tyres are attached through pressing to common rims, normally used with pneumatic tyres. These tyres remain attached to the rims, without slippage, due to the mechanical interference between the rim and the tyre, what generates a compression force that counteracts the momentum generated during the vehicle ride.

The superelastic solid rubber tyres offer a softer ride, when compared with regular solid rubber tyres. When compared with pneumatic tyres filled with air or elastomer, the superelastic tyre ride is harder. They also offer the advantage of being puncture proof and may be manufactured using non marking elastomers. Examples of such tyres may be found in the patents PI 8402893 (brazilian), US 5.429.165, JP A-61-44005 e JP A-64-83405.

Non-pneumatic tire with supporting and cushioning members-this type of non pneumatic tyre is integrally molded from a stiff, resilient elastomeric material to form a unitary structure comprising outer and inner cylindrical coaxial and coextensive members ("hoops"). The outer hoop is supported and cushioned by a plurality of circumferentially spaced apart , planar rib members and a planar central web member which connects the hoops at their circumferential center lines. A rubber tread is secured to the outer surface of the outer hoop. Examples of such tyres may be found in the US patents 4,832,098,4,921,029,4,934,425,5,023,040 and 5,265,6 AIMS OF THE INVENTION The aims of the present invention are to provide a tyre that:

-Offers simultaneously a very soft ride and a good side load stability, characteristics very important in forklift: truck applications; -is puncture proof; -has a tread two to six times thicker than the tread of a pneumatic tyre, offering a longer life; -has a unitary structure that avoids leakages and bond failures; -offers a ride softer than superelastic solid rubber tires do and comparable with that of pneumatic tyres, due to its tubular inner core filled and pressurized with elastomer; -does not make marks to the floor where they ride; -may be attached to common rims, normally used with pneumatic tyres, by pressing them; may be bonded to a rim during the manufacturing process, providing a unitary structure that may be attached promptly to the vehicle axle, -may be manufactured in any desired colour.

The development of a tyre that joins all the above characteristics, which are not joined together in any tyre of the present state-of-the-art, is something technycally and economically desirable.

In order to attain the aims above, the present non-pneumatic tyre was created, which comprises a unitary tubular structure made out of a castable non-marking elastomer, preferably polyurethane, having one or more continuous encircling annular space, filled and pressurized with a soft elastomer or foam, in order to sustain the working load, keeping a soft ride, good axial load stability and being puncture proof.

The tyre may have reinforcing elements in the portion of the inside diameter, in order to allow an attachment to a vehicle rim through pressing, just like superelastic solid rubber tyres are usually attached to rims. The said

vehicle rim is a regular one, commonly used with pneumatic or superelastic rubber tyres. The tyre may also be manufactured incorporating a vehicle rim, which is bonded to the inside diameter of the tyre during manufacturing, dispensing the process of pressing the tyre to fit the rim.

DESCRIPTION OF THE DRAWINGS Preferred embodiments of the tyre according to this invention are described below, with reference to the accompanying drawings, wherein: Fig. I A is a cross section through the tyre with reinforcements to allow a press-fit to a vehicle rim; Fig. lB is a cross-section through the tyre according to an embodiment where the cross-section of the encircling continuous annular space, filled and pressurized with a soft elastomer or foam, is not circular; Fig. 2 is a cross-section through a press-fitted tyre and the vehicle rim; Fig. 3 is a cross-section through a tyre with two encircling continuous annular spaces filled and pressurized with a soft elastomer or foam; Fig. 4 is a cross-section through a tyre where the reinforcing elements are steel fabric rings.

Fig. 5 is a cross-section through a tyre where the innertube is covered by a reinforcement of steel or cord fabric; Fig. 6 is a cross-section through a tyre where the vehicle rim is incorporated and bonded to this tyre, there are steel fabric rings covering the innertube, and there are holes molded by the mold's positioning rods.

DESCRIPTION OF THE PREFERED EMBODIMENTS Troughout the description, the same reference numbers have been used to designate the same or functionally equivalent parts.

Referring to Fig. 1-5, the tyre has a unitary tubular structure (1) made out of a castable non-marking elastomer, preferably polyurethane, and a cross-sectional configuration, comprising an inside diameter (2), an outside

diameter (3), which comprises a smooth or provided with profiles tread (7) , reinforcing elements (9) preferably in the form of rings equally distributed in the portion of the inside diameter (2), concave, convex or flat sidewalls (4) and one or more continuous encircling annular spaces (5) filled and pressurized with a soft elastomer or foam, defined through walls in the form of one or more innertubes (6), with any desired cross sectional geometry, being such elastomer or foam filled continuous encircling annular spaces (5), the outside diameter (3) and the inside diameter (2) all concentric, and also being the inside diameter (2) limited in both sides by flat circunferential surfaces (8) intended for attachment to a regular vehicle rim (R) and complements in the form of rings (A) and flanges (B).

Referring to Fig. 6, in another embodiment, the inside diameter of the tyre (2) is bonded to a vehicle rim (Rr), forming a single unitary structure comprising tyre and rim. The rim (Rr) is preferably symetrical and with drilled holes (12) which have conical countersinks in both sides (13), being such holes drilled in the inside disc (E) and intended for attachment of the bolts and nuts used for fixation of the rim in the vehicle axle, being such rim manufactured using regular steel tubes available for oil pipes (T), without the need of inside or outside tube machining.

Still referring to Fig. 6 the tyre may have many molded holes (16) extending inwardly from the the tread portion (7) and sidewalls (4) and terminating in the innertube wall (6), in such a manner that in the intersection between these molded holes and the innertube wall, there are inserts (l5) of any material or geometry, whose function is to protect the innertube (6) against punctures promoted by the mold's removable rods, used for prepositioning the said innertube (6) during the manufacturing process. The holes (16) are molded through the mold's removable positioning rods.

The tyre according to the invention may have more than one continuous

encircling annular space (5) filled and pressurized with a soft elastomer or foam. In another embodiment, where the carrying load is small, the said spaces may be filled with air at atmospheric pressure, since the load may be supported by the sidewalls (4), without the need of inside pressure.

The innertube (6) is preferably a piece of vulcanized rubber, like those used with pneumatic tyres. The innertube may also be an elastomeric extruded tube.

The reinforcing elements (9) are metalic rings with any cross-section or steel fabric rings, whose function is to enable a good attachment between the tyre and the rim (R). The tyre and rim are attached through pressing one against the other. The inside diameter of the tyre (2) is fitted on the outside diameter of the rim (R).

The innertube (6) may be covered by a reinforcement of steel or cord fabric (l 1), in order to allow a high pressurization of the continuous encircling annular space (5) by filling it with a soft elastomer or foam, without an expressive change of the tyre's external dimensions.

The tyre's tread thickness, measured from the tyre's outside diameter (3) till the innertube's outside diameter, is two to six times thicker than that of a regular pneumatic tyre used in the same vehicle, allowing a longer useful life, comparable to those obtained by superelastic tyres.

The tyre's innertube (6) may be covered by steel fabric rings (14) or any other cut resistant material, being such rings centralized with the innertube (6).

The purpose of such rings is to protect the tyre's structure against cuts and to allow a high pressurization of the continuous encircling annular space (5) by filling it with a soft elastomer or foam, without an expressive growing of the tyre's external dimensions.

The tyre's sidewalls (4) may be concave, flat or convex, depending on the axial load stability desired.

The castable elastomer used for molding the unitary tubular structure of the tyre (1) may have any desired colour, without changing its properties.

The unitary tubular structure of the tyre (1), having continuous encircling annular spaces (5), filled and pressurized with a soft elastomer or foam, supports the working loads in such a manner that the tyre will keep its performance even after being subjected to punctures and cuts. Obviously, depending on the cuts dimensions, the tyre's structure may suffer a irreversible deformation. This invention's tyre, when riding loaded, will suffer a reversible deformation, thanks to the good hysteresis of the castable elastomer used for its manufacturing and to the soft elastomer or foam pressure inside the continuous encircling annular spaces (5). The said reversible deformation is responsible for the energy's absorption caused by the impacts between the tyre and the floor where it rides, allowing therefore a very soft ride, very close to the obtained by a pneumatic tyre, and much softer than that obtained by a regular or superelastic solid tyre. As a consequence, the rolling resistance and heat generation of this invention's tyre are much lower than those of superelastic or regular solid tyres.

Regular and superelastic tyres offer low side load stability, since all the load is supported by the elastomer's compression resistance. There is no inside pressure in the tyre to counteract the load.

In the case of air filled pneumatics, the load is supported by the pressurized carcass structure. Since the carcass has thin walls, the side load stability is low.

In the case of elastomer or foam filled pneumatics, the load is supported by the pressurized carcass structure and by the filling elastomer's compression resistance, allowing a better side load stability than that of an air filled tyre, but worse than that of a solid elastomer.

The pressurized unitary tubular structure (1) according to this

invention's tyre offers simultaneously a very soft ride and a good side load stability, which is very important in curves and when the forklift trucks are carrying highly elevated loads. The load is also supported by the pressurized carcass structure and by the filling elastomer's compression resistance. Since the tyre's structure is unitary and the sidewalls (4) and the tread (7) are very thick, the side load stability is better than that of solid and elastomer filled pneumatics.

The deformation of this invention's tyre when loaded occurs in such a manner that the cross-section's height of the continuous encircling annular space (5) is diminished, and the cross-section's width is enlarged, recovering the original dimensions when deloaded. The same type of deformation occurs in pneumatics and is responsible for the good impact's absorption and soft ride.

The deformation of solid superelastic tyres when loaded occurs in such a manner that the intermediate radial soft layer is compressed, having its cross- section's height diminished and its width enlarged. Since a regular solid tyre is made out of an homogeneous elastomer, harder than that used in the superelastic's intermediate radial layer, its ride is much harder. The regular or superelastic solid tyre's rides are harder and worse than that of this invention's tyre.

When compared with a pneumatic tyre, where an annular base member of resilient elastomer extends between and is bonded tothe side walls of such tyre in the vicinity of bead portions so asto define a closed annular space which is then elastomer filled, this invention's tyre offers the following advantages: -Has a unitary structure, dispensing the bonding process of the annular base member, avoiding leakages and the possibility of bond failure, mainly when the tyre is subjected to high pressures, like those necessary in forlift truck's applications.

-Is manufactured using a floor non-marking elastomer.

-Has a tread two to six times thicker, allowing a longer life.

-Has thicker sidewalls, allowing better side load stability.

The elastomer used in this invention's tyre manufacturing is castable and will be preferably a polyurethane, floor non-marking, having for example the following properties: HARDNESS (ASTM 224): 40 ShA to 50 ShD TEAR RESISTANCE (ASTM-D470): MINIMUM 20 PLI.

HYSTERESIS (ASTM 2235): Tan delta, Degrees @ 100 C: 0,10 max.

ELONGATION: (ASTM D 412): 100 TO 900 %.

MANUFACTURING METHOD In the manufacture of this invention's tyre, a castable elastomer resin is poured inside an open mold, where the innertube or elastomer tube (6), the reinforcing elements (9) already sandblasted and treated with a bonding agent for perfect adhesion to the casting resin, the reinforcement of steel or cord fabric (l 1), and eventually the steel fabric rings (14), are all prepositioned inside the above mentioned mold, in such a manner that the elastomer resin, after being poured, covers and adheres to all the prepositioned elements mentioned above, forming a unitary tubular structure (1), that will be subjected in the mold to a cure for the complete reaction of the elastomer resin and afterwards will be demoulded.

The innertube (6) may be positioned inside the mold through removable position rods, having inserts (I 5) on its ends, for protecting said innertube against punctures caused by said rods during the manufacturing process.

Besides all the prepositioned elements inside the mold, in another embodiment , the vehicle rim (Rr), sandblasted and treated with a bonding agent for perfect adhesion to the casting elastomer resin, may also be prepositioned inside the mold and covered by the elastomer resin, becoming part of the unitary

structure.

After curing and demolding of the unitary tubular structured) of the tyre, with or without a bonded rim (Rr), a soft elastomeric or foam resin in the liquid form is injected inside the innertube or elastomeric tube (6) that defines the continuous encircling annular space (5), filling it totally while the air is drained out, being said resin pressurized as desired and allowed to react, forming after some hours a pressurized solid soft elastomer or foam core, inside the inertube or elastomer tube (6).

In the case of low load capability tyres, there is no need to fill the tyres with a soft elastomer or foam. The continuous encircling annular spaces may be left with air at atmospheric pressure.

After the soft elastomer or foam filling is reacted, the rim bonded tyre is ready for attachment to a vehicle axle.

In the case of the other embodiment, where there is no rim bonded to the tyre's unitary structure (1), the tyre must be press-fitted to the vehicle rim (R) and then attached to a vehicle axle.