GB2305404A - A moulded structure - Google Patents

Abstract

A moulded structure, such as a non pneumatic tyre, has core holes 19 extending inwardly from a side face 41, the shape of the core hole being defined such that its dimensional characteristics are larger inwardly within the hole than toward the surface of the side face.

Description

A Moulded Structure.

A MOULDED STRUCTURE TECHNICAL FIELD The present invention relates to a moulded structure.

BACKGROUND OF THE INVENTION The invention has been devised particularly, although not solely, as a moulded structure in the form of a non-pneumatic tyre.

Non-pneumatic tyres are well-known and are typically used in industrial applications, such as on forklifts, and other harsh environments where pneumatic tyres would be susceptible to puncturing. Such tyres may be of onepiece construction or of composite construction comprising a plurality of tyre segments assembled on a wheel rim.

Non-pneumatic tyres of one-piece construction and tyre segments which can be assembled onto a wheel rim to form a composite tyre, are often provided with cavities within the bodies of the tyres and tyre segments. The bodies are formed of elastomeric material such as rubber and the cavities serve to enhance the resilient deformation characteristics of the tyre, reduce the volume of elastomeric material required to form the exterior dimensions of the body, and provide ventilation within the body for dissipation of heat.

Typically, each cavity is in the form of a core hole which opens onto a side wall of the tyre or tyre segment and extends sideways into the body of the tyre or tyre segment. In some cases, the core hole extends complete through the body and opens onto opposed side walls of the tyre or tyre segment. In other cases, the core hole terminates within the body and is therefore closed at its inner end.

The tyres and tyres segments are formed in a moulding operation, with the core holes being formed by cores which are subsequently withdrawn. The cores are each slightly tapered in the direction parallel from the core hole, such tapering being known as "draft". The draft in the core provides clearance for the core as it is withdrawn from the core hole.

When the core hole extends entirely through the body of the tyre or tyre segment, the core hole may be formed either by a core composed of two parts positioned in opposed relation and withdrawn from opposed sides of the body, or by a unitary core extending entirely through the body from one side thereof.

Because of the need for tapering of the cores in a manner which provides clearance from the core holes as the cores are withdrawn, the tyres or tyre segments moulded using two-part cores have a region on the radially outer side of the core hole which increases in thickness in the inward direction. This increase in thickness is disadvantageous as it produces a tyre which is stiffer in the inner region of the tyre than at the sides. The problem is made worse by the presence of a crown on the tyre, which is necessary for proper performance of the tyre. In the case of core holes produced by unitary cores which extend entirely through the body, the tapering nature of the core holes result in a tyre which is stiffer at one side than the other.This difference in stiffness at the sides of the tyre is particularly disadvantageous as it can introduce undesirable performance characteristics in the tyre.

The abovementioned disadvantages have in the past been accepted as a necessary and unavoidable consequence of moulding tyres with core holes.

It has, however, now been found (quite unexpectedly and surprisingly) that tyres and indeed other structures with core holes can be moulded from elastomeric or other resiliently deformable material using cores which are not required to taper in a manner to provide clearance from the core holes during withdrawal therefrom.

SUMMARY OF THE INVENTION The invention provides a moulded structure comprising a moulded body of resiliently deformable material and a core hole extending into the body from a face thereof, the core hole being so shaped as to provide an outer dimensional characteristic at an outer zone at or near the face of the body and an intermediate dimensional characteristic of the same character as the outer dimensional characteristic at an intermediate zone disposed inwardly of the outer zone, the intermediate dimensional characteristic being larger than the other dimensional characteristic.

Such an arrangement provides a core hole which is larger at the inner region thereof than at the outer region. This is contrary to conventional moulding practice where a core hole is either tapered inwardly (or is at least straight in its longitudinal direction) so as to facilitate withdrawal of a core forming the core hole from the moulded body.

The intermediate and outer dimensional characteristics may be of any suitable character such as a dimension transverse to the inward extent of the core hole, or a cross-sectional area at a plane transverse to the inward extent of the core hole.

The body may have a second face and the core hole may extend between the first and second faces. With such an arrangement, the core may have a second outer zone at or near the second face of the body, the second outer zone having a second outer dimensional characteristic, the intermediate dimensional character being larger than the second outer dimensional characteristic.

In another arrangement, core holes may extend inwardly from the first and second faces. The core holes in the first face may be aligned with, or staggered in relation to, the core holes in the second face. Where the moulded structure is a tyre, staggering of the core holes may allow the tyre to provide a more even ride. Further, the core holes in the first and second faces may be so dimensioned and arranged to define a central web extending circumferentially within the moulded body between the core holes. The core holes in the first and second sides may be offset in relation to each other and of a length such that the core holes on each side extend into the region between core holes on the other side, thereby producing a zig-zag formation in the central web.

Where the moulded structure is a tyre or a tyre segment, the core holes may extend into the body in a direction which is either generally parallel to the axis of rotation of the tyre or tyre segment or inclined to such axis. In the latter case, the core holes may extend obliquely into the body from one side thereof in a generally parallel arrangement. Alternatively, the holes may extend obliquely into the body from both sides thereof. In such a case, the holes may be in a generally parallel arrangement or they may be arranged in some other fashion such as in a chevron or herringbone pattern.

Preferably, the dimensional characteristics of the core hole change progressively between the or each outer zone and the intermediate zone.

Conveniently, the intermediate zone is centrally located within the moulded body.

The or each core hole may have a ceiling portion adjacent an outer portion of the body and a floor portion adjacent an inner portion of the body, the ceiling portion being shaped to provide the change in dimensional characteristics at the or each outer zone and the intermediate zone. This may be accomplished in various ways, such as by tapering the ceiling portion such that it diverges from the floor portion in the inward direction of the core hole from the or each outer region to the intermediate region. The tapering may be planar or arcuate. Where the tapering is arcuate, the ceiling portion of the core hole may assume a domed formation.

The floor portion may be of a configuration which is constant throughout the core hole or may vary between the or each outer zone and the intermediate zone.

The variation between the outer zones and the intermediate zone may take any suitable form, one such form being a waisted arrangement wherein the floor portion tapers inwardly, but not to an extent which negates the effect of the tapering of the ceiling portion.

It has been found that the increase in the dimensional characteristic of the core hole in the inner direction does not prevent removal of cores from the moulded body during the production process. There is adequate resiliency within the moulded body to allow for the cores to be removed.

In some cases there may be sufficient resiliency for the cores to be removed in unison. In such cases, the cores can be withdrawn on account of the ability of the resiliently deformable material to deform in a direction different to the direction of increase in the size in size of the cores. Removal of the cores in unison does require more force than removal of the cores individually but surprisingly the force has been found to be not as larges as someone skilled in the art might expect.

In other cases, it may be necessary to remove the cores individually or in groups. In the latter case, the first core would generally (but not always) be the most difficult to remove. However, after removal of the first cores there is space created by the vacation of that core into which the elastomeric material can deflect during withdrawal of successive cores thereby reducing the likely force required.

The moulded structure may comprise a one-piece tyre or a tyre segment which along with similar such segments can be assembled onto a wheel rim to provide a composite tyre.

The invention also provides a tyre comprising a resiliently deformable annular body including an inner portion having an inner face for positioning on a support surface, an outer portion having an outer face disposed outwardly of the inner portion for engaging the ground, and opposed side faces extending between the inner and outer faces, and wherein a plurality of core holes are formed in the annular body to extend between the opposed side faces, the core holes each having a cross-sectional configuration which is not constant between the ends thereof and which provides a dimensional characteristic intermediate the ends thereof which is greater than a corresponding dimensional characteristic at or near the ends thereof.

Conveniently, the dimensional characteristic comprises the cross-sectional area of the core hole. With such an arrangement, the cross-sectional area of the core hole may progressively increase in the inward extent from each end of the hole towards the centre of the length of the core hole.

Conveniently, the increase in the cross-sectional area of the core hole arises at least in part by tapering of the core hole towards the outer face of the tyre in the inward direction of the core hole.

Preferably, the outer face of the tyre has a profile in which the central region is raised with respect to the side regions (commonly referred to as a crown profile), and the tapering of the ceiling portion of the core hole corresponds generally to the profile of the outer surface such that there is a generally uniform thickness between the ceiling portion of the core hole and the outer face of the tyre.

This arrangement is useful as it can assist in providing the tyre with a more even and consistent ride characteristic, and may contribute to lowering rolling resistance of the tyre.

The tyre according to the invention may be a one-piece or a composite tyre assembled from a plurality of tyre segments.

The invention also provides a tyre segment comprising a resiliently deformable body including an inner portion having an inner face for positioning on a support surface, an outer portion having an outer face disposed outwardly of the inner portion for engaging the ground, an opposed side faces extending between the inner and outer faces, and wherein a core hole is formed in the annular body to extend between the opposed side faces, the core hole having a cross-sectional configuration which is not constant between the ends thereof and which provides a dimensional characteristic intermediate the ends thereof which is greater than a corresponding dimensional characteristic at or near the ends thereof.

There may be a plurality of such core holes in the body.

The invention still further provides a tyre comprising an assembly of the tyre segments according to the invention.

The invention still further provides a mould for producing a moulded structure as defined as hereinbefore, the mould having a core for producing a respective core hole in the moulded structure, the core being configured to provide the variation in dimensional characteristics of the core hole as previously described.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood by reference to the following description of various specific embodiments thereof as shown in the accompanying drawings in which: Figure 1 is an isometric view of a tyre according to a first embodiment; Figure 2 is a fragmentary side view of the tyre according to the first embodiment shown fitted onto a wheel rim; Figure 3 is a cross-section view of the tyre fitted onto a wheel rim; Figure 4 is an isometric view of a core for producing a core hole in the tyre of the first embodiment; Figure 5 is a side view of the core of Figure 4; Figure 6 is an end view of the core of Figure 4; Figure 7 is a perspective view of an alternative form of core for forming the core hole of the tyre according to the first embodiment; Figure 8 is a side view of the core shown in Figure 7;; Figure 9 is a cross-sectional view of a tyre according to a second embodiment; Figure 10 is an elevational view of a tyre according to a third embodiment, with a portion cut-away to reveal core holes within the tyre; and Figure 11 is an isomeric view showing the shape (in negative form so as to resemble a solid) of a core hole for a tyre according to a fourth embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to Figures 1 to 6 of the drawings, the first embodiment is directed to a non-pneumatic tyre 10 comprising an inner band 11 having an inner face 12 and an outer face 13, and an outer covering 14 provided on the inner band. The inner band 11 is of substantially rigid construction, being formed of any suitable material such as steel. The band 11 comprises a plurality of band segments 15 in spaced apart relationship to define gaps 17 therebetween. This construction provides the band 11 with a plurality of splits defined by the gaps 17.

The outer covering 14 comprises an annular body formed of an elastomeric material which is bonded onto the inner band 11. The elastomeric material may be of any suitable form such as rubber. The covering 14 is resiliently flexible to provide the tyre with a cushioning characteristic. In this embodiment, the resilient nature of the outer covering 14 is enhanced by the provision of cavities 19 which extend through the tyre between opposed sides 21 thereof. The cavities 19 enhance resilient deformation of the body, reduce the volume of elastomeric material required to form the body, and provide ventilation within the body for the purposes of cooling the tyre.

The resiliently flexible outer covering 14 provides a flexible link between the band segments 15 thereby allowing the inner band 11 to be resiliently expanded and contracted to allow fitting of the tyre onto a tyre rim 23 as will be explained later. The band is provided with a plurality of mounting holes 25 for releasably retaining the tyre onto the rim 23, as will also be explained later. The mounting holes are positioned so as to open onto the cavities 19. This provides access to the mounting holes from the outer side of the band 11.

The rim 23 has an outer circumferential face 27 against which the inner face 12 of the band 11 bears when the tyre is fitted onto the rim.

The band 11 is dimensioned such that the inner circumference of the tyre is marginally smaller than the outer circumference of the rim 23. With this arrangement, it is necessary to marginally expand the band 11 by increasing the size of the gaps 17 to allow it to be fitted onto the rim 23. This expansion of the band 11 can be accomplished by forcing the band 11 onto the rim 23, possibly with the aid of a tool such as a rubber mallet. The resilient nature of the outer covering 14 allows the band 11 to expand for fitment on the rim 23. The band 11 is positioned on the rim 23 such that the mounting holes 25 register with the corresponding mounting holes 28 in the rim whereby fixing elements 29 such as bolts can be fitted to secure the band to the rim.The use of bolts 29 to secure the band to the rim is particularly convenient and allows the tyre to be readily removed from the rim if necessary.

A guide means 31 is provided for properly aligning the inner band 11 of the tyre 10 with respect to the rim 23 to ensure that the mounting holes 25 in the band 11 register with the mounting holes 28 in the rim. The guide means 31 comprises a protrusion on the outer face 27 of the rim. The protrusion 31 is so positioned that the tyre 10 is properly aligned with the rim when one of the gaps 17 in the band 11 is aligned with the protrusion. During fitting of the tyre, the protrusion 33 enters the particular gap 17 with which it is aligned and guides the tyre 10 into the correct position on the rim 23 such that the moulding holes 25 register with the moulding holes 28.

A convenient way of producing the tyre would be to incorporate the tyre segments 15 into a mould in which the outer covering 14 is formed, and thereby mould the outer covering 14 directly onto the band segments 15. In this way, the splits 17 in the band 11 are formed prior to moulding of the outer covering 14 onto the band. It may, however, also be possible to mould the outer covering 14 onto a band 11 which has not been split and then form the splits in the band after the moulding process.

When the splits 17 are present in the inner band 11 during the moulding operation, the gap provided by the split would be occupied by the elastomeric material forming the outer covering 14.

The annular body which provides the outer covering 14 comprises an outer portion 35 having an outer face 37 for engagement with the ground, and an inner portion 39 having an inner face 40 bonded to the inner band 11. The annular body 14 also has a pair of opposed side faces 41 which extend between the outer face 37 and the inner face 40 and which provide the sides 21 of the covering.

The outer portion 35 incorporates a tread formation 43 forming part of the outer face 37.

The tread formation 43 is of a crowned profile such that the inner region 45 thereof extends radially outwardly further than the side regions 47, as is convention practice with tyres. The crowning of the tread formation 43 enhances ride comfort and provides improved steering.

The cavities 19 are provided by core holes which extend between and open onto the side faces 41 of the annular body.

Each core hole 19 comprises a ceiling portion 49 adjacent the outer portion 35, a floor portion 51 adjacent the inner portion 21 and side portions 53 extending between the inner and outer portions.

Each core hole 19 is of a cross-section which is not constant throughout the length of the core hole between the ends thereof. More particularly, each core hole 19 within the outer covering 14 has a cross-sectional area transverse to the inward extent of the core hole 19 which progressively increases from each end thereof towards the centre of the length of the core hole.

The increasing cross-sectional area is provided by tapering the ceiling portion 49 such that the spacing between the ceiling portion and the floor portion 51 progressively increases from each end of the core hole 19 to the centre of the length thereof, as best seen in Figure 3 of the drawings. This tapering may be planar or arcuate so as to provide a somewhat domed formation within the core hole.

A benefit of this arrangement is that a substantially uniform thickness can be attained in the region 55 of the outer portion 35 between the outer face 37 and the core hole 19. This uniform thickness is beneficial as it can enhance the evenness and consistency of the ride characteristics of the tyre and can also contribute to lowering of the rolling resistance of the tyre.

Figures 4, 5 and 6 show a core 60 which can be used for producing core holes 19 in the tyre according to this embodiment.

The annular body which provides the outer covering 14 is moulded using conventional techniques with the cores 60 being located in the moulds to produce the core holes 19. After the moulding operation has been completed, the cores 60 are removed from the mould. It is conventional wisdom that with such moulding procedures it is necessary for the cores 60 to have a profile such that the side walls thereof either taper inwardly towards each other (or are substantially straight) to facilitate removal of the core from the moulded article.

The core holes 19 and the cores 60 are not constructed in accordance with such conventional wisdom but nevertheless it has surprisingly and unexpectedly been found that the cores can be conveniently and readily removed in unison from the moulded body because of the resilient nature of the material from which it is made.

There are situations where it may be advantageous or convenient to utilise cores which are of two-part construction which can be removed from opposed sides of the tyre. An example of such a two-part core 61 is illustrated in Figs. 7 and 8 of the accompanying drawings. The use of two-part cores allows the tyre to be moulded with core holes which do not extend completely through the body of the tyre. This can be of benefit as it allows the tyre to be formed with a continuous central web extending circumferentially within the tyre.

Referring now to Fig. 9 of the drawings, there is shown a second embodiment of a tyre according to the invention which is somewhat similar to the first embodiment with the exception that the floor portion 51 of each core hole 19 is also shaped to extend away from the ceiling portion in the inward direction of the tyre so as to enhance the increase in cross-sectional area of the tyre in the inward direction from each end to the middle of the core.

In the third embodiment, which is shown in Fig 10, the progressive increase in cross-sectional area in the inward direction of each core hole 19 is provided by tapering of the side portions 53 of the core hole such that the spacing between the side wall portions varies in the circumferential direction of the tyre. With the tapering of the side portions 53 of the core holes 19, there is a reduction in the amount of elastomeric material occupying the central region of the tyre where such material is least required.

Fig. 9 illustrated an arrangement where the floor portion 51 is tapered so as to enhance the increase in cross- sectional area of the core hole 19 in the direction from the ends thereof to the middle. Fig 10 illustrated an arrangement where the side portions 53 are tapered for a similar purpose. There may be situations where the floor portion 51 and the adjacent region of the side portions 53 are shaped in some other fashion, such as the waisted formation illustrated in Fig.

11 of the drawings which depicts a core hole 19 as a negative so as to resemble a solid. In this embodiment, the floor portion 51 and the adjacent region of the side portions 53 taper inwardly towards the middle of the core so as to provide a waist 65. As a result of the waist 65, the spacing between the regions of the side portions 53 adjacent the floor portion 51 decreases towards the centre of the core but the resultant reduction in cross-sectional area does not negate the increase in cross-sectional area developed by the tapering of the ceiling portion 49. This arrangement is useful in that it allows the ceiling portion 49 to be profiled so as to provide a substantially uniform thickness in the region 55 of the outer portion 35 between the outer face 37 thereof and the core 31 without significantly varying the cross-sectional area of the core hole.

From the foregoing, it is evident that the present invention may provide a nonpneumatic tyre which can be moulded with core holes and which has improved ride characteristics.

It should be appreciated that the scope of the invention is not limited to the scope of the various embodiments described.

Claims (18)

The Claims defining the invention are as follows:

1. A moulded structure comprising a moulded body of resiliently deformable material and a core hole extending into the body from a face thereof, the core hole being so shaped as to provide an outer dimensional characteristic at an outer zone at or near the face of the body and an intermediate dimensional characteristic of the same character as the outer dimensional characteristic at an intermediate zone disposed inwardly of the outer zone, the intermediate dimensional characteristics being larger than the outer dimensional characteristic.

2. A moulded structure according to claim 2 wherein the core hole is so shaped as to provide an outer dimensional characteristic at an outer zone at or near the face of the moulded body and an intermediate dimensional characteristic of the same character as the outer dimensional characteristic at an intermediate zone disposed inwardly of the outer zone, the intermediate dimensional characteristic being larger than the outer dimensional characteristic.

3. A moulded structure according to claim 2 wherein the intermediate and outer dimension characteristics comprise a dimension transverse to the inward extent of the core hole.

4. A moulded structure according to claim 2 wherein the intermediate and outer dimensional characteristics comprise a cross-sectional area at a plane transverse to the inward extent of the core hole.

5. A moulded structure according to any one of the preceding claims wherein the body has a second face and the core hole extends between the first and second faces, the core hole having a second outer zone at or near the second face of the body, the second outer zone having a second outer dimensional characteristic, at an outer zone at or near the second face and an intermediate dimensional characteristic of the same character as the outer dimensional characteristic at an intermediate zone disposed inwardly of the outer zone, the intermediate dimensional characteristic being larger than the second outer dimensional characteristic.

6. A moulded structure according to any one of the preceding claims wherein the dimensional characteristics of the core hole change progressively between the or each outer zone and the intermediate zone.

7. A moulded structure according to any one of the preceding claims wherein the intermediate zone is centrally located within the moulded body.

8. A moulded structure according to any one the preceding claims wherein the or each core hole has a ceiling portion adjacent an outer portion of the body and a floor portion adjacent an inner portion of the body, the ceiling portion being shaped to provide the change in dimensional characteristics at the or each outer zone and the intermediate zone.

9. A moulded structure according to claim 8 wherein the ceiling portion is shaped so that it diverges from the floor portion in the inward direction of the core hole from the or each outer zone to the intermediate zone.

10. A moulded structure according to any one of the preceding claims wherein the moulded structure comprises a tyre or a tyre segment.

11. A moulded structure according to claim 10 wherein the tyre or tyre segment has an outer face for engagement with the ground, the outer face having a profile with a central region thereof raised with respect to side regions thereof, the ceiling portion of the or each core hole being shaped to correspond generally to the profile of the outer face such that there is a generally uniform thickness between the ceiling portion of the core hole and the outer face of the tyre.

12. A mould for producing a moulded structure according to any one of the preceding claims, the mould having a core for producing a respective core hole in the moulded structure, the core being configured to provide the variation in dimensional characteristics of the core hole described.

13. A tyre comprising a resiliently deformable annular body including an inner portion having an inner face for positioning on a support surface, an outer portion having an outer face disposed outwardly of the inner portion for engaging the ground, and opposed side faces extending between the inner and outer faces, and wherein a plurality of core holes are formed in the annular body to extend between the opposed side faces, the core holes each having a cross-sectional configuration which is not constant between the ends thereof and which provides a dimensional characteristic intermediate the ends thereof which is greater than a corresponding dimensional characteristic at or near the ends thereof.

14. A tyre segment comprising a resiliently deformable body including an inner portion having an inner face for positioning on a support surface, an outer portion having an outer face disposed outwardly of the inner portion for engaging the ground, and opposed side faces extending between the inner and outer faces, and wherein a core hole is formed in the annular body to extend between the opposed side faces, the core hole having a cross sectional configuration which is not constant between the ends thereof and which provides a dimensional characteristic intermediate the ends thereof which is greater than a corresponding dimensional characteristic at or near the ends thereof.

15. A tyre comprising an assembly of tyre segments, at least one of the tyre segments being in accordance with claim 14.

16. A tyre comprising a plurality of tyre segments assembled on a wheel rim, each tyre segment being in accordance with claim 14.

17. A tyre substantially as herein described with reference to the accompanying drawings.

18. A tyre segment substantially as herein described with reference to the accompanying drawings.