Note: Descriptions are shown in the official language in which they were submitted.
S~
The load carrying capacity of a pneumatic tire ls a
function primarily of the width of the tread and the internal
tire pressure. The tire diameter is also a factor as it affects
the area of tread surface in contact with the road, but diameter
is of lesser significance than tread width. Moreover, practical
tire diameters are limited by the size of the vehicles with
which the tire is used. For a given load, a tire within a range
o widths and pressures can be selected. As the tire width is
increased more material-is re~uired and the cost of the tire and
of the rim on which it is mounted increase. It is desirable
~or economic reasons to use a narrow tire and~a high pressure.
Uowever, the "ride cuality" of the tire must also be considered.
It is a subJective measure of the performance of the vehicle and
to some extent individuals will differ in their conclusion as -
to what is a "good" ride. The ride quality is affected both by
tire construction and by the operating pressure. No satisfactory
ob~jective measure has been established. Generally, however, a
maximum pressure of the order of 20 to 30 psi is utilized with
open carcass tires on a passenger vehicl.e. A higher pressure
causes a harsh, uncomfortable ride. Within this pressure range
and the desired tire diameter, a width is selected -to support
the anticipated load.
Grawey U. S. patent 3,606,921 issued September 21,
1971 discloses a pneumatic tube tire which has, among other
features, a capacity of providing a soft, comfortable ride with
little noticeable difference in quality over a pressure range
from 20 psi to as high as 50 or 60 psi. The Grawey tube tire
selected for a given load may be much smaller than a beaded,
open carcass tire for the same load, resulting in a material
cost reduction and a weight saving. The tube tire includes a
' ~
... . . ~ . . _ . ..
z
toroidal. elastomer carcass with an outer tread wall, an inner
rim wall and a pair of side ~alls interconnecting the tread and
rim walls. The carcass is reinforced with a continuous
inextensible filament wound in generally radial planes. A tread
belt has ine~tensible reinforcing ~,enerally parallel with the
Rlane of the tire. It is my present theory that the independence
of ride nuality from tire pressure is due in part to the side
wall construction with uniform radial reinforcing elements, by
virtue of which the incremental side wall deflection at -the rim
and tread is symmetrical as the load on the tire changes. The
tire has a higher torsional spring rate than comparable tires
of open carcass construction and this may also contribute to
~he high quality of the ride.
In contrast to the subJective nature of the ride
quality of the tire, the characteristlcs of a tire which
contribute to vehicle directional control and dynamic stability
in turns have been analyzed objectively. The General Motors
Co~pany has developed Tire Performance Criteria (TPC) which
include force and moment characteristics that provide a measure
of the directional control capability of a vehicle with which
the tire is used. The criteria are described in a publica-tion
entitled "General Motors Tire Performance Criteria (TPC)
Specification System"; and the force and moment characteristics
are defined at pages 74-77. The principal tire characteristics
`~5 affecting the linear directional control performance of the
vehicle is the cornering coefficient, which is defined as the
lateral force produced at a one degree slip angle and 100
percent of the rated load, divided by the rated load
i.
._ _ _ . .. . , . . , . . . ., .. . _ _ ,.. , ____ _ _, _ _ .
S9Z
'
The tires initially made in accordance with the
Grawey patent were typically 64 or 88 inches in diameter and
were used with off-road earthmoving vehicles. The performance
criteria for automobile tires are not of great significance
for such vehicles. A tire having the same construction but
reduced in size to a diameter of 27 inches for use on an
automobile was found to have good ride quality and long life
but to be`deficient in directional control factors important
in the design and operation of passenger vehicles. The
cornering coefficient was too low for satisfactory use on a
passenger vehicle in road service.
This invention is concerned with improvements of
the tire shown in the above-referenced ~rawey patent to
achieve force and moment characteristics which meet or
exceed the General Motors Tire Performance Criteria without
adversely affecting the desired characteristics of the tire of
the Grawey patent, including a low rolling resistance, long life
and soft ride at high inflation pressure.
In a rolling turn the lateral force which provides
the cornering coefficient is developed in that portion of the
tire tread which engages the road surface (the "footprint" of
the tire) and is transmitted from the tread through the side
wall to the rim engaging portion of the tire, and thus to the
wheel and the vehicle where it is effective to change the
direction o vehicle movement.
A principal object of the invention is to stiffen the
tread of the tire with respect to lateral forces and to transmit
efficiently to the wheel rim the lateral force developed in the
` tread.
~0~3~S9Z
According to the invention a radially reinforced
pneumatic tire and rim assembly therefor, with a ratio of
lateral force to load in a rolling turn sufficient to
establish a cornering coefficient satisfactory for vehicle
road use, comprises a pneumatic tire having an elastomer
carcass with a peripheral inextensible annular tread wall,
a pair of annular rim wall portions and a pair of opposed
annular side walls each joining a lateral edge of the
tread wall with a lateral edge of the respective rim wall
portion, a pair of roll restraining hoops each connected
to one of the rim wall portions, radial reinforcing in
the side walls, the rim wall portions, and the tread wall,
the construction of the tire being such that incremental
deformation of the side walls at their ~unctures with the
tread wall and rim wall portions is substantially
symmetrical under load in the plane of the tire; a rim
having a pair of annular surfaces on which the tire rim
wall portions are received; means in said tire tread wall
for imparting lateral stiffness thereto to resist bending
of the footprint of the tire so that a substantial lateral
force is developed in the tread wall in a rolling turn;
and means for securing the tire rim wall portions to the
annular surfaces of the rim to restrain movement there-
between in a direction axial of the tire and rim so that
the lateral force developed in the tire tread wall and
transmitted through the side walls to the rim wall portions
is transmitted from the rim wall portions to the rim, said
securing means including a pair of radially outwardly
extending annular rim surfaces provided on the rim each
being positioned in motion restraining relation to the
respective roll restraining hoop, preventing lateral
~ -5-
. .
- ~o~s~z
movement thereof relative to the rim as a result of
lateral force developed in a rolling turn, the radially
outwardly extending annular rim surfaces and the roll
restraining hoops being spaced axially inwardly of the
juncture of the respective side wall and rim wall portion.
The invention provides stiffness in the tread
of the tire with respect to lateral forces and enables
the force to be transmitted efficiently to the wheel rim.
The tread wall of the tire may be laterally
stiffened by a pair of complementary bias reinforcing
strips which have substantial lateral stiffness.
The tire may include annular bodies between the
lateral edges of the tread wall and/or each hoop and the
respective side walls, ~nhancing the transfer of force
through the tire in a rolling turn between the roll restrain-
ing hoops, to prevent lateral inward movement of the hoops
with respect to the surface of the wheel rim.
Further features and advantages will readily be
apparent from the following specification and from the
drawings, in which:
Figure 1 is a broken perspective of a prior art
tire illustrated in said Grawey U. S. Patent 3,606,921i
Figure 2 is a diagram of forces on a tire in a
rolling turn;
Figures 3a, 3b and 3c are diagrams illustrating a
series of tire footprints in idealized form;
Figure 4 is a cross-section of a tire embodying
the invention;
Figure 5 is a broken perspective of the tire of
Figure 4; and
-5a-
~. I
lOB~S92
Figure 6 is a diagrammatic illustration of a
test useful in comparing materials used in stiffening
the tread of the tire.
A prior art tube tire will be considered briefly
to illustrate the problems solved by the present invention.
Figure 1 is a broken perspective view of the tire of
Figure 7 of Grawey U. S. patent 3,606,921. The elastomer
carcass 20 has a tread wall 21, a rim wall 22 and side
walls 23, 24. The carcass is reinforced by a single layer
wrapped filament 25 with turns lying substantially in
radial planes. A unitary circumferential tread 27
surrounds the carcass and includes reinforcing elements 28
which are arranged in planes generally parallel with the
plane of the tread so that the tire is effectively
inextensible peripherally. Reinforcing elements 25, 28
may, for example, be steel wires. Rim wall 22 has at its
outer edges a pair of roll restraining hoops 29, 30 prefer-
ably wound of steel wire.
The rim wall 22 has a centrally located radial
rib 31 received in a centering recess 32 between the split
sections 33, 34 of the rim. Further details of the tire
construction and its manufacture may be found in the above-
referenced Grawey patent. The tire of Figure 1 has many
desirable features including a soft ride characteristic
over a wide range of inflation pressures, long life and a
low rolling resistance which contributes to low fuel con-
sumption. The prior art tire, however, has shortcomings
which affect its suitability for a road-service passenger
vehicle as an automobile or truck.
59~
A consideration of the tire force and moment diagram
of Figure 2 will aid in the following discussion. This diagram
is adapted from the conventions recommended by the Society of
Automotive Engineers. The tire and wheel 38 are illustrated
on a road plane 39. The longitudinal plane of the wheel 40
corresponds with the direction of wheel heading, arrow 41. The
direction of wheel travel, arrow 42, is displaced from the wheel
direction by a slip angle ~. The displacement between the wheel
heading and wheel travel results in establishment of a lateral
force indicated by arrow 44 in the plane 45 through the center
of the wheel and at right angles to the wheel plane 40. For
the positive slip angle shown, the lateral force will be in the
ne~ative direction. The load on the wheel is represented by a
normal force, arrow 46. An aligning torque, arrow 47, tends
to rotate the wheel to align the wheel heading with the wheel
travel.
In a moving vehicle it is the lateral force 44 which
causes a change in vehicle direction when the steering wheels
are turned. The relationship of the lateral force to the wheel
~0 load and slip angle affect the handling characteristics of the
vehicle. If the lateral force is too great, the vehicle will
respond violently and be difficult to control. If the la-teral
force is small, vehicle response is sluggish. The structure of
the tire and the interconnection of the tire and the wheel are
~5 major factors in establishing the lateral force 44.
In a turn a force is generated by interaction between
the tire tread and the road surface. The dynamics of the genera-
tion of the force in the tread are complex. A simplified
qualitative discussion is sufficient for an explanation of the
lnvention. The portion of the periphery of the tire which en-
gages the road surface, sometimes referred to as the footprint
~611i3~L5~Z
of the tire, is illustrated diagrammatically in Figure 3a for
a tire traveling in the direction of its heading. l`he longitu-
dinal axis 5-1 of the footprint 50 is a straight line. When wheel
heading and direction of travel differ, the footprint is deformed
as shown at 52 and 53, Figures 3b and 3c, respecti.vely. The ex-
tent of the deformation, which mày be measured by the angle ~
between the segments of longitudinal axes ~l, 55, is determined
principally by the slip angle a and the resistance of the tread
to lateral deformation. If the tread has little lateral stiff-
ness, the footprint deformation is greater, Figure 3b, than if '
the tire is stif, Figure 3c.
The General Motors Tire Performance Criteria discussed
above identifies the ability of a tire to generate a lateral
force 4~ in a turn by a cornering coefficient, defined as the
lateral force which is generated at a 1 slip an~,le and rated
tire load, divided by the rated load.
The first tires built in accordance with the above-
referenced U.S. patent 3,606,921 in a size for use on passenger
vehicles for road operation (sometimes referred to herein as
"automotive tires") were found to have a cornering coefficient
insufficient for passenger vehicles. ~e believe that this low
cornering coefficient results from the fact that the peripheral
tread with reinforcing. elements 28 parallel with the plane of the
tire has little resistance to lateral deformation. The footprint
deforms in a turn as illustrated in ~igure 3b.
Two principal changes have been made to overcome this
problem. First, the tread is stiffened laterally. This reduces
deformation of the footprint, Fi~ure 3c, and results in the gen-
eration within the tread of-a higher lateral force. Second, ~he
tire is interconnected with the wheel rim to minimize relative
~movement so that the lateral force developed in the tire tread
...... _ _.. _ . . __ _ . . _ __ .__ . _ . .. .
. .
55~Z
is efficiently transferred from the tire to the wheel.
The lateral stiffness of the tread section of
the tire is preferably increased by incorporating in the
tread wall a layer or layers of material which resist the
bending that occurs in the footprint during a rolling turn.
A construction which has been found satisfactory is
illustrated in Figures 4 and 5. In this construction,
two radially spaced elastomer strips with reinforcing
elements arranged at complementary bias angles with respect
to the plane of the tire underlie the inextensible
peripheral reinforcing belt. More particularly, lateral
reinforcing breaker strips 63, 64 underlie and are of
greater width than peripheral belt 65 and enhance the
lateral stiffness of the tread. The strip 64 is wider
than the strip 63. Further details of these reinforcing
strips are discussed below.
; It is not enough that the lateral force be develop-
ed in the tire tread. The force must be efficiently trans-
mitted through the side wall to the rim wall and from the
~0 rim wall to the rim of the wheel. The interconnection of
the tire rim wall and the wheel rim will be considered
next. A lateral force applied to the tread wall of the
Grawey tube tire shifts the tread wall sideways and increases
the force tending to move the roll restraining hoop on the
outside of the turn inwardly on the wheel rim. Any
; movement of the hoop results in a shear force in the rim
wall that dissipates some of the lateral force, reducing
the force which is effective to turn the vehicle.
_g_
S9;2
Figures 4 and 5 illustrate a construction in
which the rim surface 76 on which the rim wall 77 of the
tire is seated is provided with a centrally located radial
step 78 which extends outwardly and has a lateral
dimension corresponding with the spacing between the
inner surfaces 79, 80 of roll restraining hoops 81, 82.
Again, the interlocking connection between the tire rim
wall and the mounting surface of the rim restricts
relative movement of the tire and rim for efficient force .
transfer.
The rim surface 76 may be a transversely split
ring with an expander and mounting member 84, both describ-
ed in moxe detail in U. S. Patent No. 3,998,258 issued
December 21, 1976 to Grawey and Groezinger. Tire rim wall
77 has a generally straight inner surface in unstressed
condition. Expansion of annular rim surface 76 against
the tire causes the rim step 78 to deform the tire rim
wall outwardly between the roll restraining hoops 81, 82.
The dynamic mechanical action which occurs at
the junctures of the side walls with the tread wall and
the rim wall during a rolling turn, transferring the
lateral force from the tread wall to the rim wall is complex
and not fully understood. It is believed that the principal
action takes place in the vicinity of the lateral edges of
the inextensible peripheral reinforcing belt 65 and at
the axially outer surfaces 75 of the roll restraining
hoops 81, 82. The force transfer from the tread wall to
the side walls and from the side walls to the rim wall is
enhanced by restricting lateral deformation of the side
walls in these areas. More specifically, with reference
-la-
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to Figure 4, the elastomeric body of the tire is thickened
at shoulders 88 in the sidewall regions adjoining the
edges of the tread wall and elastomeric fillers 89 are
provided between the axially outer surfaces 75 of roll
restraining hoops 81, 82 and the inner surface of the side
walls. The shoulders and fillers 88, 89 are formed by
annular bodies of elastomer incorporated in the composite
tire structure prior to vulcanization.
Automotive tires are made in many different
sizes to accommodate different loads, with a diameter and
width ~hich complement the styling of the vehicle. The
physical dimensions and other tire characteristics,
including the Tire Performance Criteria, are related to
the tire size. Some of the dimensions and component
characteristics of the tube tires of Figures 4, 5
corresponding to an open carcass beaded tire size HR78-15
will be given by way of examples. It will be understood
that different combinations of materials and dimensions
may be used in constructing other forms of this tire and
other sizes of tire.
The HR78-15 at a maximum pressure of 32 psi is
rated for a load of 1770 pounds. The General Motors Tire
Performance Criteria establishes a nominal cornering
coefficient of 0.160 for this tire. Other tires for
which General Motors has issued specifications have
nominal cornering coefficients from 0.150 to 0.195. The
HR78-15 on a 6.00 inch rim has a section width of 8.~5
inches and a height from bead to tread of 6.6 inches.
--11--
`
.
~08~S9~
A lighter weight tire is illustrated in
Figures 4 and 5. The section ~idth is 8 inches but the
tire has a side wall thickness of 0.23 inches. The
radius of the outer side wall surface is 2.6 inches.
Tread width is 5~1 inches. The radial side ~all
reinforcement 96 is 3 x .010 steel cable with 7 filaments
per inch. Lateral reinforcing sheets 63, 64 are 4.60
and 4.90 inches wide, respectively, and each has
4 x 4 x .007 steel cable reinforcing with 14 filaments
97 per inch. Inextensible belt 65 is 4 inches wide and
reinforced with 5 x .010 inch steel cable with 16
~ilaments 98 per inch. Roll restraining hoops 81, 82
are of 6 x 5 x .037 steel ~-re. Rim step 78 has a
radial dimension of 0.10 inch and a width of 1.95
inches.
Suitable elastomer compounds fnr the tire are
identified by code number in Table A. The principal
constituents and physical characteristics of the elastomer
compounds are given in Table B.
... . . .. . . .. . .... .
s9~
TABLE A
. Tire Part Tire Figures 4,5
Tube Stock t.inside the T208
radial reinforcing)
Bond Stock B320
.
;;` Sidewall C657
Tread C657
Hoop Filler V904
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- 14 -
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The tire of Figures 4 and 5 has a cornering
coefficient of .159. The tires can be operated at sub-
stantially higher pressures than 30 psi with good ride
characteristics. The cornering coefficient increases
with inflation pressure. Accordingly, the tire can
accommodate a significantly greater load than the
HR78-15 tire. Conversely, a smaller tire incorporating
the invention could be selected for service with a load
capability of the HR78-15.
The open carcass HR78-15 tire weighs approxi-
mately 32 pounds. The comparable tire of Figures 4 and
5 weighs 25 pounds.
The almost unlimited selection of elastomer
materials and reinforcing available for the tire tread
wall enables fabrication of tires of various sizes with a
desired cornering coefficient. However, it is both
expensive and time consuming to build and test a complete
tire. We have determined that samples of tread material
may be tested in simple beam deflection, providing
information regarding stiffness which correlates predict-
ably with the cornering coefficient of the tire using the
material in the tread. This greatly simplifies the
analysis of tread material and the design of tires. Figure
6 illustrates a section of tread material prepared for a
beam deflection test. The dimension 115 of the sample
116 corresponds with the peripheral dimension of the
tire tread. Dimension 117 corresponds with the transverse
dimension of the tread. Three holes 118, 119 and 120
are spaced along the axis of the sample 116 parallel with
-15-
., , .. . ~, .,:.. ~ ... . .
~0~3~5~
dimension 115. The specimen is suspended from holes 118
and 120 and a deflecting force is applied to hole 119.
The deflection of the specimen is a measure of its
resistance to lateral deformation.
The incremental deflection of the side walls of
the tire is related to its multipressure, good ride
performance. AS the tire is loaded, the incremental
deflections at the junctures of the side walls with the
rim and at the junctures of the side walls with the tread
wall are uniform. This is to be contrasted with a
conventional open carcass, beaded tire where the side
wall is stiff in the area of the beads and the principal
deflection occurs at the side wall-rim wall juncture.
So long as the tire side wall6 have this capacity for
symmetric incremental deflection at the tread wall and
rim wall, the multipressure, soft ride and the advantages
of the invention in establishing the desired cornering
coefficient are achieved. These side wall characteristics
do not require the tube tire construction on a core as
described in the Grawey patent. While this construction
is desirable because it provides tire uniformity and
lower cost, similar performance can be achieved with a
crown overlap construction if the overlap is buried in
the rim wall which is not subject to flexure or even in
the tread wall where flexure is minimized. Moreover, it
is not necessary that the side wall reinforcement be
precisely in radial planes. A deviation of up to 10 is
tolerable.
-16-
~o~s9%
It is preferable that the tread have the two
bias reinforcing layers inside the inextensible 0 belt
to eliminate the effect of the bias reinforcing on steer-
ing. However, where the bias layers have sufficient
resistance to peripheral expansion, as permitting a
circumferential expansion of no more than 5%, the 0 belt
may be omitted.
There are other characteristics of the tire
which contribute to the cornering coefficient but to a
lesser extent than the lateral tread reinforcement tire
to rim connection and side wall fillers.
The tread width and elasticity of the tread
material affect tread stiffness. The cornering coefficient
is higher for a wider tread or stiffer material. However,
excessive heat is generated in a stiff material and this
is detrimental to tire life. The angle between the edge
of the tread and the side wall, sometimes described as
the tread shoulder angle, may vary substantially. The
cornering coefficient is higher for a square relationship
~ than for a smaller angle ~2 .
The tube tires illustrated in Figures 4 and 5,
may be manufactured with the procedures described in
Grawey 3,776,792, a division of 3,606,921.
While preferred embodiments of the invention
have herein been illustrated and described, this has been
done by way of illustration and not limitation, and the
invention should not be limited except as required by the
scope of the appended claims.
s~z
The tube tires illustrated in Figures 4, 5, 6 and 7
may be manufactured with the procedures described in Grawey
3,776,792, a division of 3,606,921.
While preferred embodiments of the invention have
herein been illustrated and described, this has been done by
way o illustration and not limitation, and the invention
should not be limite~ except as required by the scope of the
appended claims.
.. .. . . ... ...
