GB2024118A - A puncture resistant pneumatic tyre - Google Patents

Abstract

A puncture resistant pneumatic tyre includes a casing 70 and an inner tube 75 or a base ring of foam rubber (46) (Figure 3 not shown), where the side walls of the casing flex under load, in combination with an elastomeric shield 72 (or 55). The outer surface of the elastomeric shield is contoured to mate with the inside surface of the casing and the inner surface of the shield may be shaped as at 77, 772 or 773. The shield withstands the flexing at the flex zone of the casing by having its edges tapered and that portion where it overlies the tread portion of the tyre creates a massive puncture resistant portion over the tyre thread. The tyre may also be provided with a removable steel belt 80, and instead of being an endless ring the shield may comprise three arcuate segments. <IMAGE>

Description

SPECIFICATION A puncture resistant tyre This invention relates to a puncture resistanttyre and to a method of forming such a tyre.

It is known that considerable expense and time loss is sustained by construction equipment and heavy trucks which employ air-filled tyres when used on rough terrain where sharp rocks stakes and sapling stumps can easily puncture a tyre causing loss while the tyre is replaced or repaired. It is known that liquid plastic material can be injected into a tyre casing when secured to a wheel rim, to set and conform to the inside of the casing and provide a puncture resistant inner core for the tyre.

It has been found that when plastic filled tyres are worn or the casing damaged requiring the discard of the casing, the plastic core must be discarded also since it has been bonded to the casing walls when it was formed in the casing. The cost of filling a tyre with a plastic such as urethane can be a major part of the cost expecially in large tyres when the urethane cannot be saved. There is therefore a great demand and need for a puncture shield core for large tyres that can be salvaged from worn or broken casings.

It is also known that most punctures are caused by objects under three inches in length. It is not necessary therefore to completely fill the tyre to provide puncture protection.

Urethane or high density foam rubber can be injected into a tyre to reduce flats but filled tyres only work well under certain weight restrictions and when driven at speeds under 45 m.p.h. for short distances. When filled tyres are used at highway speeds there is great heat generated by the flexing casing slapping against the fill resulting in the reversion and liquefaction of the rubber or plastic. In the case of solid rubber it will explode or separate the casing from the heat generated within.Although the fill material is injected into the tyre under pressure causing expansion of the casing thereby holding the casing and fill in pressure contact, there is not sufficient resilience and elasticity in the fill to expand at the same rate as the casing as the casing flexes as it rolls on the road surface thereby creating the slapping action, which generates the heat, of the inner wall surface of the casing against the fill. A tube will cling by air pressure to the casing and the airwill dissipate the heat.

Another disadvantage of solid or foam rubber filled tyres is that they add weight to the vehicle and reduce the flexibility of the tyre.

An object of the present invention to provide puncture resistant tyre which is designed to permit the tyre to be run at highway speeds under load without failing from heat cused by frictional action of the casing against a puncture shield during flexing motion of the tyre on the road surface.

According to the present invention a puncture resistanttyre comprises a casing having flexible side walls and a concave inner surface thereon with tread on a peripheral outer edge thereof and an elastomeric shield in the form of a ring concave in crosssection having an outer peripheral surface mating with the concave inner surface of the casing, the outer peripheral surface of the elastomeric shield co-operating and converging with the inner surface of the casing to define a tapered flap along each side wall of the casing.

The invention also includes a method of forming a puncture resistanttyre as defined above comprising the steps of determining the point of greatest side flex in the walls of the casing, determining the point of least side flex in the inside of the surface of the casing, moulding an elastomeric shield in the form of a ring concave in cross-section having an outer peripheral surface mating with the concave inner surface of the casing and having a tapered flap along each side wall of the casing, and tapering the flaps of the elastomeric shield from substantially proximate the greatest flex point downwardly to a point above said point of least flex.

Thus the present invention comprises determining the flex characteristics for the particular tyre casing to be protected and then moulding a shield from high density foam rubber to interfitthetyre casing in a shape which will prevent puncture of a tube while being itself sufficiently flexible within the casing to overcome temperature breakdown to the foam rubber and bulging and pinching of the tube by the shield when the casing flexes and distorts while rolling on a road surface at high speeds. Preferably the tyre also includes an inner tube and the contour of the shield facing the inner tube is rounded upwardly at its edges to thinly contact the casing walls at the point of maximum flex of the casing in flap-like configuration with the mid-section smoothly bulged upwards to provide a depth of rubber shield at least three inches above the casing wall.

The shield is moulded into a ring shape from natural rubber in a small amount of synthetic rubber and a foaming agent such as nitrogen in a mould. The shield is designed with a relatively thin section at the critical flex point for the particular tyre casing to create a hinge-like portion to the point of connection of the flap with the mid-section to prevent overheating and bunching of the shield at the critical flex point.

Where the tyre is to be used only for slow moving vehicles on rough terrain in a one piece of ring of hard rubber or other plastic such as urethane may be fitted against the shield under pressure to provide a reuseable pair of cores resistant to puncture and yet providing a comfortable ride to the operator and protecting the vehicle from undue shock from the terrain.

Where the hard rubber or urethane is to be positioned in the tyre casing additional variations in the methods of installation are employed as follows; a casing is used as a mould; a preformed shield of simple ring like foam rubber is held under pressure next the rim of a wheel holding the casing and the plastic fill is injected between them to harden under pressure in the casing. The shield can be salvaged for reuse after wear of the casing.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 depicts a simple method of fitting a puncture shield to a casing for use on slow speed macbhines; Figure 2 is a sectional view of the tyre and core of Figure 1; Figure 3 is a partially cut away view of a tyre having a rim or inner core of soft easily insertable cellular expansion plastic and a casing engaging shield of hard material which has been formed within the casing after the rim core ring has been interfitted to the wheel rim and in the casing under pressure; Figure 4 is a sectional view taken through the centre of the tyre of Figure 3; and Figure 5 is a cross sectional view of a tyre casing when in the unflexed unloaded condition showing the shield of the present invention situated against the casing wall and showing the shape of the tube protecting flap and the necked portion of the shield at a critical flex point of the tyre.

In Figure 1 numeral 10 designates a large tractor tyre which includes a protective elastomeric shield of urethane plastics material which can be made in a large ring or, as shown, in segments 11, 12 and 13.

For ease in fitting the ring shield to a tyre casing a plug 15 is forced between the segments in the casing. A solid ring of hard rubber or the like 16 is shown fitted between the rims 18, 19 of the casing to assist in holding the sections together when the usual hydraulic fitting means are used. Figure 2 shows how the side and lock means 20 hold the casing 10 to wheel 21.

The method of forming a removeable shield such as shown in Figures 1 and 2 for heavy loads at low speeds is shown in Figures 3 and 4where a tyre casing 40, either new or old, is used as the mould. In the method the inside of the casing is dusted with silica powder to prevent casing bonding to the fill.

Two nylon mesh belts 42,43 are fitted against the inside 41 of the casing to encircle the inside 41 and belt 42,43 has pull tab portions 44,45 extending out from each side of the casing. A base or rim ring 46 of foam rubber is fitted to the casing proximate the rim head and held by wheel member 47 under pressure.

An opening passage 54, is formed through ring 46 or a passage is made by needle means through casing 40 to enter into the cavity between the casing and the ring 46. Liquid urethane is then injected into the cavity under pressure to entirely fill and harden in the cavity. In order to assist the fitting of ring 46 into the casing 40 a slit 48 is made in the ring, and for ease of removal nylon blets 49, 50 encircle the ring.

However if the foam 46 is made of high density foam rubber it will be understood that it can be easily deformed to fit in its place. Belts 49, 50 have pull tabs 51,52 overlying the ring to assist the moulder to pull the foam ring 46 out of the mould casing. The urethane injected under pressure into the casing will harden into a shield 55 pressing against the casing and against the innerfurface of the foam rim ring.

After the casing is worn it is cutt off from the inner shield and ring which are saved and reused in a new casing. The shield can be slit into segments to fit a new tyre or in the usual case of large tyres the casing is merely expanded open at the rim head and the shield placed inside. The foam ring is then forced in under pressure and held there by the usual rim members. In other cases a pneumatic tube can be used with the shield 55.

The filler components of this embodiment of my invention can all be reused whereas the known fillers cannot, primarily due to their dimensions which don not lend themselves to fitting to a new tyre. The known type of filled tyres cannot keep their height when they become worn whereas the use of a tube under pressure with the urethane fill 55 of tyre 40 can be made to keep the required height so important to earth moving equipment for example. As the tyre 40 expands with use, as all tyres are known to do, the foam 46 compressed by the injected liquid urethane, will expand to hold the shield in pressure contact with the casing thereby avoiding loss of pressure and height of the tyre 40. The known filled tyres will fail to hold the pressure and height because of the lack of a pressure compensation such as that provided by the ring of foam 46.In some applications the foam can be used for shield 55 with urethane in place of foam rubber 46.

The pressure compensator ring 46 can remain in the casing with the shield 55 or alternatively it can be removed and replaced by a tube under pressure.

Also, when the shield 55 is made in a mould for interfitting to a tyre casing a tube can be used instead of the ring since urethane is expensive and where totally filled tyres are required the embodiment and method shown in the drawing is preferred where the urethane is injected into the casing under pressure to compress the foam 46 at least 5% over the required tyre pressure for load carrying. After working expansion of the tyre the foam will compensate for wall growth resulting in the proper pressure.

The use of the foam also providds the equipment and its operator the feel of a pneumatic ride which fact is important for both the comfort of the operator and the shock protection for the equipment.

I use urethane fill having a tear tensile strength of from 1000 to 15000 psi.

In the place of an especially fabricated ring 46 being used for the rim ring it has been found that another tyre casing of smaller size than tyre 40 can be employed as a rim ring. The urethane is injected into the cavity between the casings while a tube keeps the rim ring to proper pressure tension until the urethane sets. The tube being in its natural environment inside a casing will allow the vehicle to operate at highway speeds as well as providing puncture resistance on rough terrain such as junk yark where many sharp objects can pierce the casing 40. In the above method it is noted that before the urethane is injected and pumped between the casing 40 and the smaller casing, the smaller casing and tube must be fitted and held in the holding means or wheel rim at a pressure greater than the pressure with which the urethane will be introduced.

Figure 5 shows a preferred form of shield 72 in use combined with a heavy duty tube 74 in a truck tyre casing 70 for a truck which will be moving at highway speed and carrying a load, and which would also encounter rough terrain. Where the truck or tractor would only be driven at low speeds but on rough terrain the embodiments previously described with reference to Figures 1, 2,3, and 4 would be adequate to protect the tyre from punctures.

The shield 72 is formed in a mould from natural rubber, small amounts of synthetic rubber with nitrogen as the blowing agent to result in a high density foamed rubber product; preferably 70% natural rubber, should be used. Each make of tyre casing will have a shield designed according to the flex characteristics of tis walls. The shield 72 for the casing 70 shown is designed to ensure that the part of the casing experiencing the most side flex is above the top of the shield at the critical flex point 75. The area from dotted line 97 to the outside of the casing 70 encounters the greatest flex and is the flex zone. It is in this area that the shield is worked the most and where the tube puffs out the most when the tyre rolls.Therefore, not only must the shield be the most heat resistant in that zone, as shown by the angle of foam 82, but it must present an even contour to the tube pressing against it from above.

Any sharp corners in the upper side of the shield, expecially in the line 86-75 will provide a discontinuity for the tube to puff out into and eventually loose its elasticity at the point.

Thus, when the side walls of the casing flex outward the tube follows simultaneously to fill the cavity formed but the shield being less elastic lags in time, creating a void between it and the casing wall.

Unless the shield is smoothly contoured with the tube the bunching of the slow moving shield would pinch the tube. It is the overstretching of the segment of the tube where it meets the casing that causes failure unless the shield is designed as herein.

When the tyre 70 rolls on the road the tread 73 moves upward and the tyre casing flexes from a point 88 toward the rim. The tread area 73 flattens out and pushes the casing upward and outward as indicated by line 95 with point 86 coming into position 90. The reaction downward of the rim causes point 86 to move out thus becoming the maximum flex point. As will be seen from figure 5, the actual distance of points along line 95 vary dramatically from their unflexed point. Point 88 moves only upward but 86 moves to 90. If the shield were designed to fill an unflexed casing across a line 86-86 with a tube above it pressureized to the recommended 90 psi for a truck tyre under load the ring of foam rubber would make a dense mass in the casing.The tube pressure being equal across the shield surface 77 when the tyre rolls the wall 70 flexes out and the pressure of the tube forces the tube wall 74 to move simultaneously with the tyre.

The dense mass of the slower moving shield at point 86 will pinch the bulge in the tube at the point 86 causing it to fail after continued overstretching and pinching at that point.

The part of the shield 72 above tread 73 moves only upwards but the portion of shield 88-75 goes outwardly creating a hinge-like zone at 75-88 where stress and heat generation will occur in the shieldThe greater the thickness of shield at point 75 the greater the heat generated by high speed driving and the result is a breakdown of the shield. It is therefore the object of this embodiment to provide a shield for use in truck tyres where both tube and shield are protected from fatigue which object is achieved by making the foam rubber shield into a one piece continuous ring concavely shaped to interfit the inside of a tyre casing, on the outside, and generally convexly curved on the inside to accommodate a tube under pressure.In order to give the maximum, preferably at least three inches, of puncture protection for the tyre in the tread region, the inside convex side of the shield can be-bulged upwardly in a continuously smooth contour thereby creating a pair of flap like wings tapering into the outside ring of the shield. Line 77, and line 78 will when combined to create the upper convex and inner side of the shield, provide the ultimate design for a puncture resistant member capable of withstanding heat and also protecting the tube from bellying and pinching as it will be seen the shield is relatively thin in the line of flex hinge zone 75. The line 773 would be an adequate depth of shield where the tread lugs were of unusual depth. In shortthe hinge depth is of critical design depending upon the use of the tyre and the speed with which it will roll.

As additional protection is removeable steel belt 80 can be fitted between the shield 72 and casing 70.

The steel does not require embedding in the casing to hold it in place and to protect the tube from it because the pressure of the shield will hold it in place. When the casing is worn in the present invention the steel belt can be saved with the shield of foam and the tube. In designing a shield for a particular tyre the flex zone line 97 is arrived at as follows; a line parallel with the road is drawn through the point of intersection of the tread outside edge 66 and the outside wall of casing 70, which parallel line will intersect the inside of the casing 70 at point 88 which is the point where the wall begins to flex outwards. In figure 5 a dotted line is shown passing through point 86, the maximum flex point on the casing, which line is substantially tangential to the tyre at 86. The tyre casing shown is a nylon biassed 1000 x 20 truck tyre and the flap dimensions for the shield is found by making angle 82 approximately 60 degrees to give the upper contour of the shield for passage through point 75, the critical flex bend point of the shield 72. A mould is made using the curvature of the inside of the tyre as the bottom of the mould and the limit of the flap the distance to flex point 86 of an unflexed tyre. The dimensions of the flap and thus angle 82 are determined by the desired thickness of the hinge on the critical flex line 97, that is the distance allowable for hinge 88-75.

With the above data for each type of tyre, shields can be made for such tyres from a mould designed especially for each type.

Claims (10)

1. A puncture resistant pneumatic tyre comprising a casing having flexible side walls and a concave inner surface thereon with tread on a peripheral outer edge thereof and an elastomeric shield in the form of a ring concave in cross-section having an outer peripheral surface mating with the concave inner surface of the casing, the outer peripheral surface of the elastomeric shield co-operating and convering with the inner surface of the casing to define a tapered flap along each side wall of the casing.

2. A puncture resistanttyre according to Claim 1 wherein the elastomeric shield is made from high density foam rubber and wherein a pneumatic tube is disposed within the annular space defined by the concave elastomeric shield.

3. A puncture resistanttyre according to Claim 1 or 2 wherein the inner surface of the elastomeric shield includes a flattened portion of a thickness of at least three inches.

4. A puncture resistanttyre according to Claim 1 wherein the shield is urethane plastics material injected into a space within the casing defined between the casing and a smaller former having a convex outer peripheral surface.

5. A puncture resistant tyre according to any oneof the preceding claims wherein the elastomeric shield comprises a plurality of shield segments.

6. A puncture resistant tyre according to Claim 1 or 2 wherein the inner surface of the elastomeric shield includes a central bulged portion above the tread of the casing, said bulged portion having a thickness of at least three inches.

7. A puncture resistant tyre according to any one of the preceding claims wherein a removable steel belt is disposed between the elastomeric shield and the casing.

8. A method of forming a puncture resistanttyre in accordance with any one of the preceding claims comprising the steps of; determining the point of greatest side flex in the walls of the casing, determining the point of least side flex in the inside of the surface of the casing, moulding an elastomeric shield in the form of a ring concave in cross-section having an outer peripheral surface mating with the concave inner surface of the casing and having a tapered flap along each side wall of the casing, and tapering the flaps of the elastomeric shield from substantially proximate the greatest flexpoint downwardly to a point above said point of least flex.

9. A method offorming a puncture resistanttyre according to Claim 8 wherein the inner surface of the shield above the tread of the casing is contoured to create an upward bulge.

10. A method of forming a puncture resistant tyre in accordance with any one of the preceding claims comprising the steps of; determining the point of greatest side flex in the walls of the casing, determining the point of lead side flex in the inside of the surface of the casing, moulding a compressible elastomeric shield of high density foamed material in the form of a ring concave in cross-section having an outer peripheral surface mating with the concave inner surface of the casing and having a tapered flap along each side wall of the casing, tapering the flaps of the elastomeric shield from substantially proximate the greatest flex point downwardly to a point above said point of least flex, and positioning a pneumatic tube within the annular space defined by the concave elastomeric shield.

Original claims 7, and 9 - 13 renumbered and appendancies of original claims 9 - 11 corrected.

10. A method of forming a puncture resistant tyre according to Claim 8 or 9 wherein the shield is moulded so that the depth of the shield at the point of least flex in the casing is no more than two and one half inches since this forms the hinge point of greatest flex in the shield.

11. A method of forming a puncture resistant tyre according to Claim 8 wherein the moulding step comprises, using a tyre casing as a mould, holding a preformed ring former under pressure against the rim of a wheel holding the tyre casing, and injecting plastics filler between the tyre casing and the former to harden under pressure in the tyre casing.

12. A puncture resistanttyre substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

13. A method of forming a puncture resistant tyre substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

New claims or amendments to claims filed on 5 Sept 1979 Superseded claims 1,2 and 8 New or amended claims:

1. A puncture resistant pneumatic tyre comprise ing a casing having flexible side walls and a concave surface thereon with tread on a peripheral outer edge thereof, a compressible elastomeric shield of high density foamed material in the form of a ring concave in cross-section having an outer peripheral surface mating with the concave inner surface of the casing, the outer peripheral surface of the elastomeric shield co-operating and converging with the inner surface of the casing to define a tapered flap along each side wall of the casing, and a pneumatic tube disposed within the annular space defined by the concave elastomeric shield.

2. A puncture tyre wherein the elastomeric shield is made from high density foam rubber material.

7. A puncture resistant tyre according to any one of the preceding claims wherein the tapered flaps extend over only part of the height of the side walls on the tyre.

9. An elastomeric sheild for a puncture resistant tyre in accordance with any one of claims 1 to 8 said shield comprising a ring of compressible high density foamed material concave in cross-section having an outer peripheral surface for mating with the concave inner surface of the tyre casing, the outer peripheral surface of the elastomeric shield merging into tapered flaps along each side of the shield which in use co-operate with the inner surface of the tyre casing and extend only partially over the height of the respective side wall of the casing.