Note: Descriptions are shown in the official language in which they were submitted.
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Description
Improvement in Tire Constructlon
for Decreasin~ Rolling Reslstance
Technical Field
This invention relates génerally to tire
construction and more particularly to means Eor
improving the interference fit between a beadless tire
and a rim upon which it is mounted.
Background Art
It is well known that the rolling resistance
of the wheels of a moving vehicle constitutes a
significant portion of the resistive force that must be
overcome by that vehicle. This is especially tLue for
those veh:icles having pneumatic tires. The losses
owing to the rolling resistance in the pneumatic wheels
of a vehicle often amount to as much as 15% of the
power ~roduced by the vehicle's engine. A decrease in
this rolling resistance would result in increased fuel
efficiency and a decrease in the strain imposed upon
the engine.
One of the sources of this rolling resistance
is the aerodynamic drag on the tire. The aerodynamic
losses typically are insignificant, amounting to no
more than a few percent of the total rolling resistance
losses. Additionally, in light of design constraints
on tires, little can be d~ne to significantly decrease
this loss.
A second source of rolling resistance is
tire-to-ground frictional loss. This is generally
10-30% of the rolling resistance losses of a tire.
Certain decreases in -this loss can be achieved by means
of the use of a 0 belt as has been implemented in
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certain existing tires. Additional decreases can
actually be disadvantageous, owing to the fact that
traction, which yields necessary safety and motive
advantages, is a concomitant of tire-to-ground friction.
A third, and by far the most significant,
source of rolling resistance in pneumatic tires
includes those losses which are internal to the wheel.
As a tire rolls, the loading of each differential unit
of the elastomeric material of which the tire is formed
is cyclically altered. As a result, a~jacent portions
of the tire periodically move relative to one another,
expending energy in the process. Such losses, common
to both standard and closed torus (beadless) tires, are
termed "hysteresis losses".
This deformation also tends to result in
movement of the tire across the rim which supports it.
This motion occurs cyclically, with the greatest motion
across the tire-rim interface occurring at the point at
which the tire is most greatl~ loaded. ThiS motion can
be either circumferential or axial and results in both
cases in chaffing friction between the rim and tire.
Not only does this movement of the tire across
the rim result in highly disadvantageous rolling
resistance, but the energy wasted theLeby is
transformed into heat and erosion of that portion of
the tire in contact with the rim. The buildup of heat
in a tire is especially disadvantageous in that tires
operating at an elevated temperature are reduced in
load carrying capacity and suffer decreased durability.
This problem of movement of discrete portions
of the tire across the rim appears to be somewhat more
pronounced in closed to~us tires tha~ it is in standard
beaded tires. Certain of the advantages of beadless
(closed torus and the like) tires are derived from
their having a certain degree of flexibility in the
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tire at a location adjacent the point where the tire
contacts the rim. It is believed that it is this
flexibility in existing closed torus tires that tends
to accentuate the undesirable chaffing. It would be
advantageous to eliminate this chaffing without
decreasing the beneficial sidewall flexibility. It is
further believed that mitigation of this chaffing will
also decrease hysteresis losses in the shoulder.
Existing tires generally incorporate some type
on inextensible band, e.g. a bead restraining band or a
roll restraining hoop, for providing an interference
fit between the tire and the rim on which it is
mounted. On certain types of tires, expecially closed
torus tires, there is a substantial area of contact
between the tire and rim intermediate each rim edge and
the corresponding roll restraining hoop. Consequently,
most closed torus tires have a flexible rim contact
area outboard from and not under compression from the
roll restraining hoop. See, for example, U.S. Patent
4,043,370 issued to Urwin et al. on August 23, 1977
disclosing a large shoulder area on a closed torus tire
including portions significantly separated from the
roll restraining hoop. It is believed that such areas
are particularly prone to suffer the previously
discussed tire-rim motion the elimination of which
would be highly advantageous.
~ he present invention is directed to
overcoming one or more of the problems as set forth
above.
Disclosure of the Invention
In one aspect of the present invention, a
closed torus tire adapted to be mounted on a rim
includes sidewalls, an inner surface and an outer
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surface with said outer surface having a rim contacting surface, a radial
ply intermediate said inner and outer surfaces, at least one shoulder
portion positïoned exterior said radial ply and forming a junction
between one of said sidewalls and said rim contacting surface, and at
least one roll restraining hoop positioned within said radial ply and
adjacent said shoulder portion. A means is provided for increasing the
resistance to relative motion between the shoulder portion and the rim
so that the rolling resistance of the closed torus tire is reduced, said
means including at least one substantially inextensible circumferentially
extending strengthening member positioned intermediate said rim contact-
ing surface and said radial ply and being positioned in said shoulder
portion, said strengthening member being free of having any radial plies
outside thereof and being so constructed and arranged that compression
of the material between the strengthening member and the rim is lnduced.
The present invention provides increased preloading to the rim
contacting portion of the tire resulting in a stronger interference fit
between the tire and the rim. This is achieved by placing a circum-
ferentially extending band, loop or coil of metal or some other sub-
stantially inextensible material adjacent or abutting the rim contacting
portion of the tire. The improvement achieved in this interference fit
serves to improve the resistance to relative motion between the tire
and rim.
Brief Description of the Drawings
Fig. 1 shows in cross section a tire incorporating an embodiment
of the present invention, the tire being mounted on a two-piece rim;
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Fig. 2 shows in cross section through a tire a
second embodiment of the present invention used in
conjunction with a one-piece rim; and
FigO 3 shows a detail of the segmented band of
the embodiment shown in Fig. 2; this segmented band is
shown in top view relative to the cross section of Fig.
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Best Mode for Carrying Out the Invention
Referring to Fig. 1, a wheel 10 has a tire 12
mounted on a rim 14. ThiS tire 12 is shown for the
purposes of example as a closed torus tire (that is, a
beadless tire) but it should be understood -that the
present invention may also be applied -to certain types
of beaded tires.
The closed torus tire 12 has inner and outer
surfaces 16,18, separated by the tire carcass 20. A
radial ply 22 passes through the carcass 20 and is
positioned intermediate the inner and outer surfaces
16,18.
The outer surface 18 has an outer surface
outer diameter 24 abutting a tread portion 25 o~ the
tire 12, and an outer surface inner diameter 26 which
includes a rim contacting surface 28. Corresponding to
the inner diameter outer surface 26 and separated
therefrom by the tire carcass 20 is an inner diameter
inner surface 30, which forms a portion of the tire
inner surface 16.
~ pair of roll restraining hoops 32 are
positioned to restrain the closed torus tire 12 from
becoming dislocated with respect to the rim 140 The
roll restraining hoops 32 are fashioned of
substantially inextensi~le members such as
rubber-imbedded wire and are so sized that when the
tire 12 is correctly positioned on the rim 16 the
carcass material intermediate each roll restraining
hoop 32 and that portion of the rim 14 nearest it is in
compression. That is, the roll restraining hoops 32
are sized to provide an interference fit between the
tire 12 and the rim 14. The purpose of this
interference fit is twofold. First, it is intended to
prevent circumferential rotation of the tire 12
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relative the rim 14. Second, this interference fit,
coupled with the angled rim 14, prevents significant
axial movement of the tire 12 relative the rim 14.
The roll restraining hoops 32 are positioned
inward from a rim edge 36. This permits the radial ply
22 to flex in a portion of the tire 12 where a sidewall
35 of the tire 12 joins the rim contacting portion of
the tire 12. Due to the roll restraining hoops 32
being offset inwardly from this boundary of tire 12-rim
14 contact, this flexing is not deleteriously
restrained by the roll restraining hoops 32. As will
be appreciated by those skilled in the art, were the
roll-restraining hoops 32 located outward from their
proper positions so as to be adjacent the rim edge 36,
the required flex of the radial ply 22 would be limited
to a smaller portion of this radial ply 22. This
concentration of strain could result in overstrain
damage to this ply 22. Consequently, it is preferable,
as shown in Figs. 1 and 2, that the roll restraining
hoops 32 overlie the radial ply 22 at a position
significantly inward from the boundary of tire 12-rim
14 contact.
The carcass 20 of the closed torus tire 12 has
a shoulder 34 extending from each roll resisting hoop
32 to the adjacent rim edge 36 and being intermediate
the rim 14 and the radial ply 22. In one aspect of the
present invention, these shoulders 34 each contain at
least one strengthening member 38. The strengthening
members 38 are preferably substantially inextensible
elements positioned within the shoulder 34 and
extending circumferentially through the tire 12. These
substantially inextensible elements 38 are preferably
formed of a coil of metal or cord passing throu~h each
shoulder 34 as shown in Fig. 1. This coil has a
plurality of continuous loops extending
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circumferentially through each shoulder 34 and being
substantially coaxial with the tire 12. Alternatively,
these strengthening members 38 can be a plurality of
coaxial closed loops of such material. It should also
be understood that the strengthening member 38 can be a
single closed loop of metal or cord passing through
each shoulder 34.
Preferably, the strengthening members 38 are
located intermediate the radial ply 22 and the rim
contacting surface 28 of each shoulder 34. The term
"intermediate" is intended to mean "between or in
contact with." Thusly, a portion of each strengthening
member 38 may form a portion of the rim contacting
surface 28 of the tire 12. The strengthening members
38, irrespective of their configuration, should be of a
construction sufficient ~o establish an improved
interference fit between the rim 14 conta~ting portion
of the shoulder 34 and the rim 14. More particularly,
these strengthening members 38 are adopted to render
2~ the rim contacting portion of the shoulder less
susceptible to circumferential e~pansion, and be sized
to induce compression of the carcass material
intermediate the strengthening members 38 and the rim.
Additionally, they stiffen the carcass material
adjacent the rim 14 minimize or eliminate
circumferential and axial buckling. Furthermore, they
are sized~ tensioned and positioned so as to avoid
deleterious restraint on the radial ply 22. It is
preferably to size the strengthening members 38 so that
the interference fit they impose between the rim 14 and
the tire 12 ls less than that imposed by the roll
restraining hoops 32.
As an alternative embodiment, shown in Fig. 2,
the strengthening member 38 can include a segmented
band 40. This segmented band 40, best seen in Fig. 3,
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is a band of metal or some other substantially
inextensible substance having periodic slits on
alternate sides thereof. One such segmented band 40 is
bonded into each shoulder 34 with one face exposed and
forming at least a portion of the rim contacting
surface 28 of the tire 12. Owing to the segmentation,
the band 40 is slightly extensible in diameter when
placed in tension which facilitates mounting of the
tire 12 on the rimt improves interference fit, and
decreases the area of rubber-to-metal interface.
Alternatively, the segmented band may be set totally
within the shoulder 34 eliminating the area of
metal to-metal contact.
The strengthening members 38 may be
incorporated in tires to be mounted on a variety of
rims 14. For example, the present invention may be
utilized in conjunction with a two-piece rim 14 as
shown in Fig. 1, or in conjunction with a one-piece rim
as shown in Fig~ 2. The use of a rim 14 having an
outer lip 46 to physically restrain the shoulder 34
from outward axial motion is especially advantageous.
Such an embodiment is shown in Fig. l. Note that as
shown in Fig~ l, this physical restraint of the
shoulder 34 is achieved by the outer lip 46 contacting
the sidewall 35 at a region adjacen~ the shoulder 34.
This point of contact is indicated by the reference
numeral 48 on Fig. l.
Industrial_Applicability
It is believed that in the operation of many
types of tires, especially those with a large shoulder
or bead in contact with the rim, there is significant
localized circumferential and axial chafing of portions
of the tire relative to the rim on which it is
mounted. Such chafing has numerous harmful effects.
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In a closed torus tire, a roll restraining
hoop 32 establishes an interference fit between the
inner diameter of the tire 12 and the rim 14. This
interferenc~ fit must be substantial since any
significant axial slippage of the entire tire 12 on the
rim 14 could permit the tire 12 to become dislodged
from the rim 14. Furthermore, any substantial
circumferential slippage could result in damage to the
tire 12 as by damaging the valve stem.
~here are certain design limitations relating
to the placement of roll restraining hoops in closed
torus tires which limit their use in immobilization of
the rim contacting surface 28 of the tire 12~ Carcass
material, especially carcass material containing plies,
lS is superior in compression than it is in tension,
assuming an application of force perpendicular to the
plane of the plies. Because of this, it is preferable
that the radial ply 22 be positioned intermediate the
roll resisting hoop 32 and the rim contacting surface
28. This prevents potential tensile forces from being
placed on the tire material posit:ioned between the roll
resisting hoop 32 and the radial ply 22. Additionally,
as discussed at some length above, the roll resisting
hoop 32 should be positioned a significant axial
distance inward from the rim edge 36. Unaer these
limitations, a substantial portion of the shoulder 34
is removed from compression by the roll resisting hoop
32 and, hence, is in an inadequate interference fit
with the ri~ 14 it abuts. This inadequ~te compLession
of the shoulder 34 is compounded by the fact that the
rirn contacting surface 28 of the tire 12 is prefera'oly,
due to the exigencies of molding, straight or convex in
axial cross section. As the tire is inflated this rim
contacting surface 28 tends to pull away from the rim
14 decreasing the force applied by this surface 23 to
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the rim 14. It is believed that it is this
inadequately compressed region in which the most
significant abrasion, resulting in increased rolling
resistance, heat buildup, etc.
By adding the strengthening members 38,40
detailed above, the interference fit between the rim 14
and the shoulder 34 is improved. This compresses the
underlying rim contacting surface 2~ of the shoulders
34 more firmly against the rim and more effectively
limits relative motion therebetween. This is
accomplished without the utili2ation of reinforcing
elements diametrically outboard of the radial ply 22.
~ence, restraint upon this radial ply 22 is minimally
increased, preventing undue stress from being imposed
upon this ply 22.
Other aspects, objects and advantages of this
invention can be obtained from a study of the drawings,
the disclosure and the appended claimsO
