CA1168135A - Tire construction for decreasing rolling resistance - Google Patents

Abstract

Improvement in Tire Construction for Decreasing Rolling Resistance Abstract A wheel having a rim and a tire mounted thereon. The tire has a rim contacting portion and a bead or roll resisting hoop. A circumferentially extending substantially inextensible strengthening member is mounted in said tire adjacent said rim contacting portion for increasing the interference fit between the rim contacting portion and the rim and for stiffening the rim contacting portion.
Many existing tires suffer movement of their rim contacting portion with respect to the rim. In many cases this abrasion is not pronounced and/or localized. This serves to erode the rim contacting portion, increase tire rolling resistance, and permit the build-up of heat. By stiffening the rubber adjacent the rim and by improving the interference fit between the tire and rim as achieved by the present invention, this relative motion is decreased or eliminated.

Description

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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 l ~ 6~13~
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-2-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 ~ 1~8~ 3~

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 ~ :~68~35 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;

1 ~8135 -4a-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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~ 3 ~i$~35 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

3 5 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 3 ~

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, 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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g 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 I ~ 6~ 1 ~5 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

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a closed torus tire adapted to be mounted on a rim, said tire having sidewalls, an inner surface and an outer surface with said outer surface having a rim contacting surface, a radial ply intermediate said inner and outer surfaces, at least one shoulder portion positioned 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, the improvement comprising:
means 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 contacting surface and said radial ply and being positioned in said shoulder portion, said strengthen-ing 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 induced.

2. The closed torus tire as set forth in claim 1 wherein said circumferentially extending strengthening member is of a coiled configuration.

3. The closed torus tire as set forth in claim 1 wherein said circumferentially strengthening member comprises at least one closed loop.