Note: Descriptions are shown in the official language in which they were submitted.
i
CA 02351826 2001-05-18
WO 00/308?3 PCT/GB99/03886
1
TY
The present invention relates to tyres, and in
particular but not exclusively to tyres for vehicles such
as cycles, wheelchairs and the like. One aspect of the
invention relates to a tyre core intended to replace the
inner tube of conventional pneumatic tyres, and to the
composition and method of manufacture thereof. Other
aspects of the invention relate to other features and
elements of tyre construction, composition and fitting.
Pneumatic tyres provide excellent load support and
shock absorbing properties in many applications. For
example, many vehicles, such as automobiles, aircraft,
military vehicles, motorcycles, bicycles, wheelchairs and
the like are provided with pneumatic tyres. Pneumatic
tyres generally comprise an outer tyre casing and an inner
tube which is located between the: wheel rim and the tyre
casing and which is inflated with gas, typically air, to
till the rim-tyre casing space; the inflated inner tube
provides the means for pneumatic support of the vehicle and
retains the tyre casing on the r.it~i. Other tyres, known as
"tubeless" tyres, comprise a gas impermeable tyre casing
the bead of which is sealed to t:he wheel rim. Although
such tubeless tyres are now used in the great majority of
automobile applications, such tyres are unsuitable for
application in which the wheel rim is not readily sealable,
for example, in spoked wheels as commonly used on bicycles.
i
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99103886
2
Although pneumatic tyres provide excellent support and
cushioning they have some drawback:. For example, the tyre
material must have a low permeability to the gas contained
therein but remain flexible to maintain the cushioning
effect of the tyre. The number of materials which fulfil
these requirements tends to be rather limited. Such
materials include butyl rubbers and halogenated butyl
rubbers. These materials are expensive compared to
conventional rubbers, which do not possess the, required
degree of gas impermeability: The valves of such inner
tyres are also required to seal sufficiently well so that
leakage is kept to a minimum.
Although the abovementioned drawbacks may be overcome
by use of particular rubber materials and well engineered
valves, a more fundamental problem exists with respect to
failure of such gas inflated tyre,. For example, sudden
tyre failure, commonly known as a "blow-out", may pose a
serious danger to the occupants of a vehicle. Tyre failure
may be a result of a weak spot ~_n the tyre material, or
puncturing by, for example discarded nails or screws,
shards of glass or metal, or thorxis and the like, as often
found on the ground over which vehicle tyres travel. A
further drawback of gas-filled tyres occurs when a slow
leak exists, either from a small area puncture or through
a poorly sealed valve. Such :slow punctures, or mare
particularly the subsequent loss of pressure, result in an
increased contact area of the gyre with the ground or
contact surface, uneven and ir.~creased tyre wear, and
i
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
3
increased rolling resistance, atzd may adversely affect
vehicle handling.
Previously, the abovementioned disadvantages were
addressed by use of various farms of puncture resistant
liners which, in the case of inner tube containing tyres,
seek to prevent objects passing through the tyre casing
from penetrating the inner tube,, or by use of solid or
semi-solid foam tyres or tyre cores.
A major drawback, however, of certain foam filled
tyres or cores is that the foam is readily flexed or
deformed. In certain materia:Ls, this may result in
excessive heat build-up in the tyre in use, which may lead
to a breakdown of the foam mate?:ial resulting in reduced
support, increased rolling contact and subsequent tyre
damage. A certain degree of flexibility however is
necessary to provide the desired cushioning properties as
provided by the conventional gas-filled pneumatic tyre.
Harder, or less flexible tyre filling materials, such as
the non-foam material of Gomberc~ (US Reissue 29,890) are
claimed to have reduced heat build-up properties. However,,
a reduction in cushioning may occur, and such tyres may be
relatively expensive as more material is required than
those employing foam cores. Moreover harder materials have
the disadvantage of causing exce,~sive vibration within the
wheel which can loosen screws, spokes and the like, and
radically reduce wheel bearing life, thus significantly
increasing the wear and tear on such wheels and the
vehicles housing them.
I
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
4
A further major drawback of many "puncture-proof"
tyres is that many such tyres a~:e constructed integrally
with the wheel , and thus specia7.ly produced, or adapted,
wheel rims are required. Spec:i.alist equipment is also
necessary for constructing and fixing such puncture-proof
tyres on the wheel rims. Furthermore, integral tyre-wheel
constructions have the disadvantage that, should damage to
the tyre occur, complete removal and replacement of the
wheel would be required.
ZO US 4,416,844, US 4, &83,929 and US Re 29,890 describe
foam-filled deflation-proof pnE:umatic tyres which are
produced by injecting the filling material into the outer
tyre casing and wheel rim cavity, to create an integral
arrangement as described above.
US 3,348,597 describes a polyurethane foamed rubber
tyre which is formed directly on the axle. US 3,987,832
describes a solid wheel which comprises a hard radially
extending core enclosing a hub sleeve. US 4,033,395
describes a tyre wherein the outer tyre casing and core are
integral.
It is further noted that many known foam cores have a
skin covering the surface of the core which is intended to
reduce abrasion and damage to the core. In EP 0057927 A1
the skin also protects the open-cell core from filling with
water in wet conditions. This document describes the core
as being 10% larger in cross section than the tube cavity
in which it is housed, it is believed this would make the
fitting of such a tyre difficult. Furthermore, since such
CA 02351826 2001-05-18
WO 00130873 PCT/GB99/03886
a core is not circumferentially symmetrical - having a
portion for extending into the ri.m and engaging the spoke
ends - orientation of such a core on fitting to a wheel
would be necessary, which may increase the fitting
5 difficulty.
A number of polyurethane "puncture-proof" tyres are
currently available. This material has the considerable
disadvantage of producing toxic emissions of isocyanates
and dense black smoke when ignited, thus posing
environmental problems on disposal.
Other problems associated with polyurethane and rubber
materials include, for a non-pneumatic tyre construction:
- marked extreme vibration of the wheel;
- lack of grip of the tyre on the contact surface;
- occurrence of flat spots on the tyre due to
abrasion during skidding of the tyre on the
contact surface;
- considerable drag and high rolling resistance;
- static build-up which results in sparking, thus
use in flame-free areas or where sparking is
undesirable would be prohibited;
- slippage from wheel r~_m when side pressure is
applied to the tyre, fc~r example when a vehicle
is cornering.
It is anticipated that a puncture-resistant inner core
of similar palyurethane or rubber materials would encounter
i
CA 02351826 2001-05-18
WO 00/30873 PCTlGB99/03886
6
similar problems.
The above problems cont5~ibute to provide, in the
case of vehicular application of such tyres, a poor ride
quality. Safety may also be comp:ramised.
It is an object of embodiments of certain aspects of
the present invention to obviate or mitigate the
abovementioned disadvantages of gas-filled pneumatic tyres
and existing so-called solid puncture or deflation-proof
tyres described in the art. It is a particular object of
one embodiment of the present invention to provide a tyre
core or insert which may be used in place of or in
combination with conventional inflatable inner tubes. It
is intended that the advantages provided by conventional
pneumatic inner tubes are retained, such as superior
cushioning support, without risk of deflation to provide a
reliable alternative or complement to pneumatic tyres.
According to a first aspect ~cf the present invention,
there is provided a composition for use in the manufacture
of a tyre core, wherein said composition comprises a
copolymer of ethene with a vinyl acetate. The copolymer
thus formed is known as an ,ethylene vinyl acetate copolymer
hereinafter described as EVA).
Preferably, the vinyl acetate is un-substituted.
It should be noted that a number of physical
properties have been established. for a material tan EVA)
found to be suitable for use as a tyre core in accordance
with an embodiment of the present invention. Some
properties of this material which may be advantageous are
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
7
represented as follows and the properties of other
materials employed in tyre cores according to aspects of
the present invention should preferably be within the
ranges or values shown.
S PROPERTY UNIT ~'T_ METHQD VALUE ( S
)
HARDNESS (SHORE A) DEGREE AST:M D2240 30 to 75
TENSILE STRENGTH Kg/cms ASTM D1623 25 to 30
ELONGATION % ASTM D1623 200 to 300
TEAR STRENGTH Kg/cm ASTM 1623 10 to 15
FOAMING RATE TIMES U.S.I. 2 to 5
ADHESION STRENGTH Kg/cm U.S.I 2.2 to 3.2
SHRINKAGE o ASTM D955 2 to S
Most preferably, the properties are:
PROPERTY UNIT T METHOD VALUES)
HARDNESS (SHORE A) DEGREE AST'M D2240 35 to 55
TENSILE STRENGTH Kg/cmZ AST'M D1623 27
ELONGAT I ON ~ AST'M D 16 2 2 5 0
3
TEAR STRENGTH Kg/cm AST'M 1623 11
FOAMING RATE TIMES U.S.I. 3
ADHESION STRENGTH Kg/cm U.S.I 2.8
SHRINKAGE o AST'M D955 3
It is believed that perhaps the most important of
these properties is the hardnes~~, due to the significant
bearing on rider comfort, for cycle applications, vehicle
handling and rolling resistance.
Certain EVA campositions have been found to possess
such properties. EVA compositions are preferred because
they are relatively light weight, that is of a lower
density compared to existing polyurethane compositions.
i
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
8
EVA tyre cores, tyre inserts and gyres have also been found
to provide relatively low rolling resistance which, without
wishing to be bound by theory, is believed to be due to
lower absorption of. energy than polyurethane, as hysteresis
lasses are lower. This may also contribute to the superior
low heating properties of EVA when flexed and deformed,
unlike polyurethane foams which rapidly heat up in use.
EVA also provides the required hardness, while
retaining the desirable flexural properties of tyre cores,
for example memory properties, which ensure good shape
recovery following removal of ~E deforming f force . This
ensures good replication of the desirable properties of
conventional pneumatic tyres.
EVA also desirably does not, in general, contain ozone
depleting substances nor heavy metals, thus conferring
additional environmental benefits in EVA product
manufacture or disposal.
Ln other aspects of the invention, materials other
than EVA may be utilised to form tyre cores having such
desirable properties. For example, it is anticipated that
formulations of ethylene-propylene rubbers (EPR and EPDM)
containing low polypropylene (in the region of 15%), and
also Hytei rubber may be utilised.
The amount of vinyl acetate monomer incorporated into
the preferred EVA copolymer in. relation to the ethene
content by weight (w/w) may be between 30% and 60%.
Preferably the amount of vinyl acetate is between 30% and
500, more preferably between 30o and 40%. A most preferred
i
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
9
amount of vinyl acetate is 33%.
Advantageously, said EVA m.ay be cross-linked EVA,
wherein the cross-linking is achieved by any suitable
method.
The composition may be in the form of a foam. Foaming
may be achieved by any suitable method in the art, for
example mechanical agitation or chemical means. The foam
is preferably of closed cell construct, the closed cel l
construct offering the advantage that liquid, typically
water, will not be taken up by the tyre, and an outer
"skin" is not required. In other embodiments a "skin" may
be desirable, for example to protect the core from abrasion
or to facilitate fitting, anal may be formed as a
consequence of the manufacturing or forming method.
The composition may contain are or more agents
independently selected from the following classess
lubricants, cross-linking agents, foaming agents and
fillers. It is to be understood that more than one agent
may be selected from each of the: above classes.
Any suitable lubricant may be used. Typical
lubricants include long chain carboxylic acids, for example
stearic acid.
Any suitable cross-linking .agent commonly known in the
art may be used, such as dicumyl peroxide (DCP).
Suitable foaming agents include those commonly known
in the art such as azodicarbonamide (ADCA).
Suitable fillers include an.y suitable calcium salt and
those fillers commonly known in the art such as mica,
i
CA 02351826 2001-05-18
W~ 00/30873 PCT/GB99/03886
silica, calcium carbonate, carbon black and clay.
A preferred formulation has the following
constituents:
EVA 0 - 120 parts by weight
5 (w/w) of the total formulation
Stearic Acid 1 5 parts (w/w)
DCP 1 - 5 parts (w/w)
ADCA 2 - 6 parts (w/w)
Calcium carbonate 30 - 60 parts (w/w)
10 Preferably the amounts of each component are:
EVA 100 parts (w/w)
Stearic Acid 1 part (w/w)
DCP 1 part (w/w)
ADCA 2 parts (w/w)
Calcium carbonate 40 - 50 parts (w/w)
According to a second aspect of the present invention
there is provided a tyre core or insert having a Shore (A)
hardness of 30° - 70°, preferably 35° - 60°. The
most
preferred Shore hardness will depe=nd on the intended use of
the core, for example most preferably 38° to 40° for a
leisure and commuting cycle, and 48° to 50° for a
wheelchair.
The tyre core may be formed for fitting within a tyre
i;
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
m
casing, or may be formed within a tyre casing, or the tyre
casing formed around the core, or the casing and tyre core
formed simultaneously.
According to a third aspect of the present invention
there is provided a tyre produced using the composition
according to the first aspect.
It is to be understood that: the tyre may be of the
type which is moulded as a unit piece containing a core
made using the composition of the first aspect and an
outer, abrasion resistant skin or casing. Alternatively
and preferably, the composition may be used to make a tyre
core which may be inserted into a conventional pneumatic
tyre casing in place of or in combination with a pneumatic
inner tube. Such a core may be any suitable shape,
Z5 including a torus shaped core. Such a torus shaped core
has a circular cross-section, how~wer other cross-sectional
shapes may be desirable in certain circumstances, such as
half-moon or crescent shapes, whE:re a pneumatic tube is to
be retained. The core may have a smooth, irregular or
20 discontinuous surface or profiJ_e; a smooth surface may
facilitate'fitting while a rougher surface may facilitate
grip between the tyre elements and prevent or limit
relative movement therebetween. The characteristics of
different areas or sections of the core may differ, for
25 example the core may include a relatively stiff or hard
central element, to minimise rol:Ling resistance, and softer
side portions, to provide great°r grip when cornering, or
a similar effect may be possible by providing a triangular
i,
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
12
core profile. The core may also be configured such that by
reversing the core orientation within the tyre casing it is
possible to provide the tyre with different
characteristics; each half of the core section may be
formed from a material having different properties, for
example a relatively soft material and a relatively hard
material. The core may also be configured to facilitate
contact with the spoke nuts within the rim, to support the
nuts and also to assist in preventing the nuts vibrating
loose from the spokes. This may be achieved by providing
the core with an appropriate profile, or by forming the
inner surface of the core in a softer material which will
readily deform to extend into the rim. The core may
contain one or more cavities of gas such as air, or such
cavities may be filled with gels, foams or other materials
possessing particular desirable properties. For example a
torus shaped core having a central cavity may be provided,
resulting in a tubular configuration.
The core may not necessarily fill the entire wheel rim
- tyre casing cavity, for -example a pneumatic tube or
element may be provided, or separate elements may be
provided to engage and support the spoke nuts. Where a
core is used in conjunction with a pneumatic inner tube it
may be preferred that the core is'. located directly beneath
2S the tyre casing, with the inner tube sandwiched between the
wheel rim and the core. Tyres of this arrangement have
been found to retain the desirable properties of solely
pneumatic tyres while being eff=ectively puncture proof.
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
13
This mode of construction may be particularly applicable to
half-moon or crescent shaped cores.
According to a fourth aspect of the present invention
there is provided a method of .producing a tyre core, the
method comprising the steps of:
providing an EVA composition;
mixing said composition;
moulding said mixed composition under pressure; and
shaping said moulded composition to form a tyre core.
Tt is to be understood that any suitable mixing method
may be used and the components of the EVA composition may
be mixed in any suitable order. A preferred mixing
apparatus is a two roll mill which is commonly known in the
art. Preferably the EVA composition is introduced into the
mill in the order of: EVA, lubricant, cross-linking agent,
foaming agent, filler.
The roll mixing may be conducted at any suitable
temperature conveniently provided by controlling the
temperature of the rolls. Tt ha;s been conveniently found
that good mixing is achieved with one roll set at a
temperature in the region of 100°C and the other roll at the
lower temperature of about 60°C.
Moulding may be achieved using any suitable method.
Conveniently this is achieved by injection moulding.
The moulded composition, on~~e removed from the mould
may then be shaped using any suit<~ble method to form a tyre
core. For example pieces of the moulded composition may be
cut to form rods of the composition. The offcuts may be
i:
CA 02351826 2001-05-18
WO 00/30873 PCTIGB99/03886
14
used for other purposes, for example for location in a tyre
rim adjacent to the spoke nuts. The ends of the rods may
then be joined to form the tyre core. Joining may be
accomplished using adhesive applied to each end of the rod.
The rod ends are preferably flat cut, however other
profiles suitable for bonding may be used. In an
alternative embodiment, the ends of the rods remain free,
to facilitate fitting; this-may allow a rod to be fitted
to, for example, a bicycle wheel without having to remove
l0 the wheel from the bicycle.
It should be understood that one or more of the above
process steps may be carried out by utilizing an extrusion
technique. For example a screw exaruder may be used to mix
the composition prior to injection moulding thereof.
According to a fifth aspect of the present invention
there is provided an apparatus for forming a puncture
resistant tyre core comprising means for shaping an EVA
composition into a rod configuration.
This may be achieved by u~~ing a suitably arranged
cutting head. Conveniently the surface of such a tyre core
is relatively rough and therefore: grips the wheel rim and
inside tyre surface, thus reducing slippage and
disengagement of the tyre from the wheel.
According to a further aspect: of the present invention
there is provided a tyre core fo:r location in the volume
deffined between a tyre casing and a wheel rim, the tyre
core comprising a resilient rod having free ends, the rod
length being selected to conform to the length of the
i:
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
volume between the casing and rim.
The invention also relates to a method of fitting such
a core to a tyre.
As noted above, fitting of the core may be facilitated
5 by providing the core in rod form. Also, stock keeping,
and production of tyre cores may be simplified, as a
retailer may be supplied with long lengths of rod which may
be cut to size in accordance wii~h individual customers'
requirements. Such tyre cores also facilitate
10 accommodation of variations in rim and tyre casing
dimensions; rims and tyre casings tend to be provided in a
range of "standard" diameters and widths, however different
manufacturers tend to produce different rim and tyre
configurations, and the ends of ityre cores in accordance
15 with this aspect of the invention may be trimmed or
shortened accordingly to provide a "perfect" fit.
The various aspects of the present invention will now
be described by way of example, with reference to the
accompanying drawings, in which:
Figure 1 is a sectional view of a tyre core in
accordance with an embodiment of an aspect of the present
invention;
Figure 2 is a sectional view of a tyre core in
accordance with a further embodiment of the present
invention; and
Figure 3 is a sectional view of a tyre core in
accordance with a still further embodiment of the present
invention.
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
is
Reference is first made to Figure 1 of the drawings,
which illustrates a section of a tyre core 10 in accordance
with an embodiment of the present: invention. The core 10
is circular in cross section and is intended to replace a
conventional pneumatic inner tube;, that is the core 10 is
located between a tyre rim and tree tyre casing. The core
is of an EVA foam composition, as will be described in due
course.
Figure 2 of the drawings i17_ustrates a section of an
EVA tyre core or insert 20 in accordance with a further
embodiment of the present invention. The core 20 is part-
circular in section and is intended to be inserted in the
crown of a tyre, between an existing pneumatic tube and
tyre casing. It has been found that, when the tube is
inflated to its normal recommended pressure, as used in the
absence of the core 20, the ty~:-e retains the desirable
properties of a solely pneumatic tyre, but is effectively
puncture proof. It has also been found that the core 20 is
easier to fit than the core 10 described above.
Figure 3 of the drawings i13_ustrates a section of an
EVA tyre core 30 in accordance with a still further
embodiment of the present invention. The core 30 is
rectangular in section and is intended to be inserted in
the crown of a relatively small diameter "balloon" tyre;
such as utilised in electrically-powered wheelchairs,
between an existing pneumatic tube and tyre casing. As
with the core 20 described above,. it has been found that,
when the tube is inflated to its normal recommended
CA 02351826 2001-05-18
WO 00!30873 PCT/GB99/03886
17
pressure, as used in the absence of the core 30, the tyre
retains the desirable properties of a solely pneumatic
tyre, but is effectively puncture proof. Surprisingly, it
has been found that the rectangular form of the core 30
does not have an adverse effect on the tyre performance; it
appears that the properties of the preferred EVA
composition, as described below, a.re such that the core 30
may deform to fill the tyre casing, and in doing so does
not lose the advantageous propertues of the composition.
to The manufacture and testing of the core 10 will now be
described in some detail, and it will be apparent to those
of skill in the art that the manufacturing process may be
adapted as required in order to produce the other cores 20,
30 described above.
Mixing of formulate-on
100 parts (w/w} of ethylene vinyl acetate copolymer
(available under the tradename EVATHENE VE 630) having a
vinyl acetate monomer unit content of 33% w/w compared to
the ethylene monomer Content was added to a two roll mill.
Stearic acid 1 part (w/w), DCP 1 part (w/w), ADCA 2 parts
(w/w) and calcium carbonate 40 - 50 parts (w/w) were then
added to the mill in that order.
The rolls of the mill were set at temperature of 100°C
and 60°C.
Once mixed, the formulation was then removed from the
mill and then introduced into a 6 ounce - 150 ton
i
CA 02351826 2001-05-18
WO 00/30873 PCTIGB99/03886
18
injection moulding machine.
Mouldir~,g of formulation
Injection moulding was conducted using a mould at 170°C
and an injection pressure of T00 kg cm-a. Following
injection, the material contained within the mould was
cooled by cooling the mould with v~rater. The cooling water
had a temperature of 20°C on input to the mould. The
cylinder temperatures of the injection moulding machine
were 140°C and 180°C. The mouldir~g timing was as follows:
Injection: 10 to 20 seconds
Cooling: 40 to 90 seconds
Mould open and closer 20 seconds
Moulding Cycle therefor: 70 to 130 seconds.
The resultant moulded EVA composition was removed from
the mould. The dimensions of tree sheet depended on the
mould used, but typically were 40 - 41" x 64 - 65" x 40 mm
and 42 - 43" x 65 - 66" x 50 mm.
The moulded EVA compasition, following removal from
the mould, was then cut into strips using a band saw. The
strips were then fed into a cutting machine to produce
cylindrical rods.
Various diameters of rod could be made by using
different cutting heads in the cutting machine. Typical
sizes of rod have the following diameters:
CA 02351826 2001-05-18
WO 00130873 PCT/GB99/03886
19
1. . 75" - 1. 95" ;
2.0" - 2.10";
1.25" - 1.375".
These three size ranges are' suitable for insertion
into a multitude of outer tyre casing sizes.
A rod was then cut to the required length for the
particular wheel to which it was to be fitted, and the ends
glued together using impact glue' containing Tolve:ne and
Polene R.C. to form a torus shape. The torus could then be
inserted directly into a conventional wheel, for example a
bicycle wheel in place of the inner tube therein.
The tyre core had a shore hardness of 50° (ASTM
D2240) .
Details of testing of such a tyre core are set out
below.
Example 1
A company based on a large site uses a fleet of 24
bicycles to facilitate movement of personnel around the
site. Half of the fleet of bicyc:Les were fitted with tyre
cores 10 as described above and u;~ed over a 12 month trial
period. Users found that the 12 test cycles performed in
a similar manner to the bicycles fitted with conventional
pneumatic tubes, providing comparable rider comfort,
handling capabilities and tyre casing wear, and of course
did not experience any punctures or other tyre failures'.
CA 02351826 2001-05-18
WO 00/30873 PCTIGB99/03886
At the end of the trial period the company selected to
abandon pneumatic tubes and fitted the tyre cores 10 to the
remainder of their fleet of bicycles.
Ex~ple 2
S A wheel builder, who builds wheels by hand for cycles
and wheelchairs, was supplied with a number of 26" tyre
cores 10. Over a six month period cycles fitted with the
tyre core were ridden over a variety of terrain, giving a
comfortable ride, and exhibiting no problems. In
i0 particular, it was noted that no tyres were forced off the
rim, even under extreme pressure a.nd stress, in contrast to
the behaviour of existing "solid" polyurethane tyres.
Further, the wheels to which the cores were fitted
experienced no adverse effects, notably no hub damage, no
15 loosening of spokes, and no effect on the trueness of the
wheels.
Exa le 3
A number of tyre cores 10 were supplied to a cycle
road racing team, who carried out a number of tests and
20 comparisons with existing products, as described below.
A rolling resistance test was carried out at Quarry
Hill, Stanton by Dale, Derbyshire, England.
From a standing start, at a :fixed point, the exercise
was carried out to find and compare the distance travelled,
t:he maximum speed gained and the average speed, using a
normal leisure "mountain bike" cycle and measured by Cateye
i
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/0388b
21
(trade mark) Computer.
The reasoning for using Quarry Hill was because of its
long "straight" when it flattened out. The weather and
road conditions were good.
Comparisons were made between:
1. A normal Continental (trade mark) "Cross Country" tyre
with pneumatic inner tube @ 50 lbs psi.
2_ A narmal Continental "Cross country" tyre with a tyre
insert or core, as the core .LO, in accordance with an
embodiment of the invention.
3. A Green (trade mark) tyre (a "solid" polyurethane
tyre}.
The same cycle and rider, whose weight was 12 st 2 lbs, was
used throughout the test to maintain continuity and
therefore giving no advantage to any one product.
RESUL~,~
Normal Continental Cross Country Tyre
And Pneumatic TuI2e Size - 26 x 1 _9"~1,.__
Average speed 15.3 mph.
Maximum speed 28.5 mph.
Distance travelled 0.68 miles
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
22
Tyre Insert Tnside A Normal Continental
Cross Countrv Tvre - Size 26 ~c 1 90
Average speed 14.0 mph
Maximum speed 23.0 mph
Distance travelled 0.58 milE~s
GrPP~ Tvre ~iz_e 26 x 1 90
Average speed 12.4 mph
Maximum speed 19.0 mph
Distance travelled 0.46 mils~s
A rolling road test was conducted, in conjunction with
Sturmey Archer, Nottingham, England using their test
equipment.
The tyre insert was fitted to a 26" ATB wheel, with a
payload of 72.5 kg and run continuously for 100 hours; at
a continuous speed of 15 mph therefore covering 1,500 miles
non-stop.
Throughout the test the wheel was monitored for friction or
excessive heating, which was not over-apparent throughout.
On completion, the wheel was taken apart and the tyre and
tyre insert were examined for damage.
There was visible wear to the tyx-e but no more than would
normally be expected after 1,500 miles.
i
CA 02351826 2001-05-18
WO 00/30873 PCT/GB99/03886
23
The tyre insert showed signs of vuear as follows:
Dust particles were present which. indicated the insert had
settled into the wheel rim. Again, this was to be expected
and would not be so prominent under normal conditions.
It will be apparent to those of skill in the art that
the tyre cores demonstrated excellent roll, resilience and
cushioning properties, until n~~w only associated with
conventional pneumatic tyres. I:n particular there was a
lack of vibration with minimum friction- and hence road
drag. The wheels remained light-weight and the tyres
demonstrated full memory capabilities. Furthermore, the
tyres did not absorb water in wet conditions and exhibited
good road holding capabilities. The tyres also did not
generate static electricity thus enabling use in flammable
vapour areas or where sparks\electric discharges are
prohibited. These road tests demonstrate that the required
degree of hardness and resilience in a foam tyre may be
achieved while maintaining the desirable flexibility and
hence cushioning effects, until n.ow only seen in. pneumatic
tyres, thus demonstrating superiority over existing
polyurethane foam tyres.
It should be understood that the above examples are
not limiting on the scope of the present invention and
variations within the scope are allowed. For example the
hardness of the final composition may be chosen for
particular applications such that simulation of differing
i,
CA 02351826 2001-05-18
WO 00/30873 PCTIGB99/03886
24
conventional tyre pressures is achieved. For example a
shore hardness of 48 to 50° has been found to be
particularly suitable for wheelchair use, whereas a shore
hardness of 38 to 40° has been found to be particularly
suitable for leisure and commuting bicycles.
Alternative methods of moulding the EVA composition
may be chosen without departing from the scope of the
present invention. For example tube-shaped moulds which
give a rod shape of composition, or tarus shapes, may be
used. Moulding may also be accomplished by extruding the
composition through a suitably sized die orifice.
