CA1126635A

CA1126635A - Pneumatic safety tire

Info

Publication number: CA1126635A
Application number: CA350,199A
Authority: CA
Inventors: Mark H. Mineur
Original assignee: Goodyear Tire and Rubber Co
Current assignee: Goodyear Tire and Rubber Co
Priority date: 1979-06-06
Filing date: 1980-04-18
Publication date: 1982-06-29
Also published as: AR220839A1; IT8022583A0; JPS55164510A; FR2458407B1; GB2053815A; ATA241480A; AT381476B; DE3017461A1; ZA802710B; AU530898B2; GB2053815B; JPS595444B2; FR2458407A1; IT1131281B; BR8003227A; LU82499A1; AU5812480A

Abstract

Abstract PNEUMATIC SAFETY TIRE

A pneumatic safety tire capable of being used in the uninflated condition at a speed up to a maximum predetermined value for a maximum predetermined dis-tance which can then be repaired and returned to normal service. The sidewalls of the tire have a configuration such that the bending moment stresses experienced in the sidewall when the tire is operated in the uninflated state do not exceed a predetermined value. The portion of the sidewall radially and axially inward of the carcass ply structure is made of an elastomeric material having a dynamic modulus at least equal to or greater than 50 kg/cm2 and has a ratio of hysteresis to dynamic modulus less than or equal to .24%/kg/cm2.

Description

PNEUMATIC SAFETY TIRE

The foreoging abstract is not to be taken as limiting the invention of this application, and in order to understand the full nature and extend of -the technical nature of this applica-tion, reference must be made to the accompanying drawings and the following detailed description.

Background of the Invention This invention relates to a tire; more particularly, to an improved pneumatic tire capable of being used in the uninflated condition.
Various tire constructions have been suggested which are capable of being used in the uninflated condition.
One approach taken is to strengthen the sidewall so that the tire can support the vehicle load by itself when in the uninflated sta-te. The sidewalls are generally strengthened by increasing the cross-sectional thickness of the sidewall members by a substantial amount in relationship to the normal thickness. However, due to the large amount of rubber required to stiffen the side-wall members, heat build-up has become a major factor in early tire failure when the tire is operated in the uninflated condition, and to a lesser exten-t in -the underinflated condition.
Brief Description of the Invention Applicant has discovered an improved -tire construc-tion in which the tire's durability during operation in the uninflated condition is improved while at the same time maintaining the desired tire performance in the inflated condition, and which after being used in theun-inflated condition at a speed up to a maximum predeter-mined value for a distance up to a maximum predetermined distance, can be repaired and returned to normal use.

In accordance with one aspect of the invention there is provided a pneumatic safety tire comprising a circumferentially extending ground-engaging tread portion, a pair of shoulder portions adjacent the axially outer end of said ground-engaging tread portion, a pair of bead portions, a pair of sidewall portions which extend from said shoulder portions to said bead portions, a carcass ply structure which extends from said bead portion to said bead portion, said tire characterized in that said sidewall portions have a predetermined thickness selected to provide that the average maximum stress developed in the elastomeric material does not exceed approximately 8.7 x 105 N/m2 when said tire is operated in the uninflated state, the inner sidewall portions radially inward with respect to the internal cavity of said tire of said carcass structure being made of an elastomeric material having a hysteresis to dynamic modulus ratio not greater than about .24%/kg/cm2 and a dynamic modulus of elasticity not less than about at least 50 kg/cm2.
Descrip-tion of the Drawin~
Fig. 1 is a cross-sectional view of a tire made in accordance with the present invention mounted on a rim for which it is designed and inflated to design inflation pressures;
Fig. 2 in solid lines illustrates a cross-sectional view of a tire made in accordance with the present invention mounted on a rim for whic.h it is designed, in the uninflated state at rated load, and in dash lines there is illustrated a cross-sectional view of the tire as shown in Fig. 1.

Fig. 3 is a cross-sectional view of a modified tire made in accordance with the present invention;
~ig. Ll is a fragmentary side view of the tire of Fig. 3 taken along line 4-4; and Fig. 5 is an enlarged, fragmentary cross-sectional view of the tire of Fig. 3 taken along line 5-5.

Detailed Description of Preferred Embodiment Referring to Fig. 1, there is ill~lstrated a tire 10 made in accordance with the present invention. Tire 10 is provided with a ground-engaging tread portion 12.
A pair of sidewall portions 14,16 extend from the shoulder portions 18,20 of the tread portion 12 and terminate in a pair of bead portions 22,24 having annular inextensible bead cores 26,28, respectively. The tire is further provided with a carcass ply structu.re 30 which extends from bead portion 22 to bead portion 24 and a tread-reinforcing belt structure 32 which e~-tends circumferentially about the carcass ply structure 30 beneath the tread portion 12. The tire may include a conventional inner liner 13 forming the inner surface of the tire 10 if the tire is to be of the +ubeless type.
The ends 34,36 are of the carcass ply structure 30 and are wrapped about the bead cores 26,28, respectively, as shown in Fig. 1.
The carcass ply structure 30 comprises at least one layer of rubber-coated fabric cords and is preferably of the radial type construction, that is, a carcass ply s-tructure in ~hich the cords form an angle from about 75 degrees to 90 degrees with respect to the mid-circumferential centerplane CP of the tire. However, the present invention may also be applied to bias ply tires, that is, tires in which the cords of the carcass ply structure form an angle less than about 75 degrees with respect to the mid-circumferential centerplane CP of the tire. Any number of carcass plies may be used, depending upon the size and load rating of the tire and may be of any suitabIe material used in tire a~ s _L~_ reinforcement, for example, nylon, rayon, aramid, polyester, steel. In the particular embodiment illus-trated, carcass ply structure 30 comprises two ply layers 42,44 having cords made of polyester. The carcass ply structure 30 is located approximately midway between the inner and outer surfaces of the tire in the region A of the sidewall which extends a point spaced from the nominal rim diameter NRD of about 35% of the carcass section height SH of the tire to a second point spaced a dis-tance from the nominal rim diameter NRD of about 90% of the carcass section height SH of the tire.
The carcass aspect ratio may be any conventional ratio used in tire constructions which generally range from 50 to 95, preferably from 55 to ~,5, and in the particular embodiment illustrated, the carcass aspect ratio is approximately 75. For the purpose of this invention, the carcass aspect ratio denotes the relationship of the maximum carcass section heigh SH
divided by the maximum carcass section width CSW as measured on an unloaded tire, inflated to design inflation pressures, mounted on a 70% rim. For the purpose of this invention, a 70% rim is a rim in which the axial distance R70 between the rim flanges is 70%
of the maximum axial section width SD of the tire; the maximum axial section width SD being measured from the axially outer surfaces of the tire, exclusive of indicia, adornment and the like. The carcass aspect ratio is measured using the neutral carcass contour, which in a single radial ply carcass is the ply itself, but in a carcass ply structure having a plurality of plies, is located midway between the outermost and innermost plies. The maximum carcass section width CSW therefore is the maximum axial distance measured parallel to the axis of rotation between the neutral carcass contour of the carcass structure 30. The maximum carcass section height, therefore, is the maximum radial distance between the neutral contour of the carcass structure 30 beneath the tread portion 12 and the nominal rim diameter NRD as contained in the size designation of the tireO
Sidewall portions 14,16 have a cross-sectional configuration, as illustrated in Fig. 1, such tha-t the tire sidewall thickness at the area adjacent the bead areas is at least 65% of the cross-sectional thickness of the sidewall at Rhom. Preferably the sidewall thickness at this area is the thinnest area of the sidewall and proceeding radially outward to the point of maximum tire carcass section width Rhm the tire sidewall portions 14,16 gradually increase in cross-sectional thickness. For the purpose of this invention,the sidewall thickness at any point along the outside surface of the tire is -the distance from -that point to the closest point along the interior surface of the tire, exclusive of indicia, adornmnet or any other markings on the tire sidewall surface.
The tread width TW is at least 60% of the maximum axial carcass section width SD and is preferably not greater than 80%. In the particular embodiment illustrated, the tread width TW is approximately 70%.
For the purpose of this inven-tion, the tread width is the axial distance across the tire perpendicular to the mid-circumferential centerplane CP of the tire as measured from the footprint of the -tire inflated to design inflation pressure, at rated load and mounted on a wheel for which it is designed.
In order to provide the support necessary in the uninfla-ted state, the radially inner portions 46,48 of the sidewall portions 14,16, respectively, have a cross-sectional thickness of at least approximately s 30~ of the -total sidewall thickness T at the maximum tire section width Rhom exclusive of any indicia that may be present.
The radially outer ends 50,52 of the inner portions 5 46,48, respectively, terminate beneath the tread portion a distance B from the tread edge which it lies beneath;
'the distance B being not less than 35% of the distance C from the tread edge to the mid-circumferential center-plane CP, preferably not greater than 65%. In the particular embodiment illustrated, the ends 50,52 terminate beneath the tread a distance from the tread edge of approximately 45% of the distance C.
The belt reinforcing structure 32 comprises rubber coated fabric cords made of a material normally used in 15 tires, for example, nylon, polyester, rayon, aramid, glass fiber, steel, and have one or more plies.
In the particular embodiment illustrated, the reinforcing belt structure 32 comprises two reinforcing belt layers 47,49 each having its cords disposed at conventional angles with respect to the mid-circumferential plane CP of the tire which are normally used in conventional pneumatic tires, preferably from about 20 degrees to 25 degrees. In the particular embodiment illustrated the cords of reinforcing belt layers 47,49 for~ an angle of 25 approximately 23 degrees with respect to the circumfer-ential plane of the tire. Preferably, the cords of belt ply layer 47 lie at an angle with respect to the mid-circumferential plane of the tire which is opposite in sign than the angle in which the cords of layer 47 lie with respect to the mid-circumferential plane of the tire.
When the tire is operated in the uninflated condition, as is illustrated in Fig. 2, the sidewall portions 14,16 support the vehicle load such that the internal surface of the tire does not contact any other ~art o~ -tlle internal surface of the tire. The sidewalls 14,16 must be able to withstand the stresses encountered during operation of the tire in -the uninfla-ted condition.
Failure of the tire when run in the uninflated state is primarily due to the chemical breakdown of the elasto-meric material and the breakdown of the bond between the rubber of the elastomeric ma-terial and the reinforcements resulting from the excess heat build-up in the tire sidewall. It is desirable that the sidewall be made of a material that can support the vehicle load in the uninflated or underinflated condition with a minimum amount of heat build-up. Applicant has discovered that the sidewall thickness at the maximum section width SD
of the carcass ply s-tructure 30 should be such that the average maximum stress developed in the sidewall does not exceed approximately 8.7 x 105N/m2 in this area when operated in the uninflated state. In order to minimize the heat build-up in the sidewalls and provide the necess~ry support, the inner portions 46,48 are made of an elastomeric material having a ratio of hysteresis to dynamic modulus not greater than about .24%/kg/cm2, and a dynamic modulus of elasticity of not less than about 50 kg/cm2; preferably at least 85 kg/cm2. The dynamic modulus is obtained from the Goodyear Vibra Tester at about 60 cycles per second (ASTM D-2231) and the hysteresis is obtained from the Goodyear hot rebound test wherein hystersis is equal to 100% minus the percent rebound (ASTM D-1054).
The stresses experienced in the sidewall of the tire are dependent upon the particular load to which the tire will be subjected in the uninflated condition and the configuration of the tire such as the bead spacing of the tire when mounted on a rim for which it is designed and the cross-sectional configuration of the tire sidewalls. The cross-sectional thickness of the tire sidewalls at the point of maximum carcass section width at Rhom of the tire 10 can be determined in accordance with the following relationship:

T = ~ I _ V Rhom wherein:
T ls the total sidewall thickness a-t the point of maximum tire section width Rhom exclusive of any indicia measured in millimeters;
L is the load in kilograms at which the tire will : be required to operate;
Rhom is the radius from the axis of rotation of the tire to the point of maximum tire section width SD
measured in millimeters;
S70 is the maximum tire section width SD measured from the radially outer surface of the sidewall exclusive of adornment or other indicia, measured in millimeters when the tire is mounted on a 70% rim; and K is a constant which takes into account the maxlmum stresses that may be developed in the sidewall of the tire and is approximately equal to 8.9 x 10 1.
By taking into account the configuration of the - tire sidewall and the load to which the tire will be subjected in the uninflated or partially uninflated state applicant has discovered a particular tire construction in which the tire's durability during operation in the uninflated condition is improved while at the same time maintaining the desired tire performance in the inflated normal operating condition.
A tire made in accordance with the present invention has been found to have acceptable commercial performance characteristics in the inflated condition while at the same time having satisfactory handling requirements in the uninflated condition. A tire made in accordance with the present invention having a ratio of hysteresis to dynamic modulus of about .16~/kg/cm2 and a dynamic modulus of about 104 kg/cm2 has been found to be capable _9_ of beirlg operated in the uninflated condition for a speed of up to 40 ~iles per hour for a distance of up to approximately 40 miles, which then can be repaired and returned to normal service.
In order to provide the stiffness in the bead area and a smooth transition between the stiff bead cores 26,2~ and the respective sidewalls, stiffening members 38,40 are provided radially outwardly of the bead core 26,28 and between the carcass ply structure 32 and the ends 34,36 of the carcass ply structure. Stiffening members 38 9 40 are made of elastomeric material having a dynamic modulus of at least 125 kg/cm2 and preferably having a maximum ratio of hysteresis loss to dynamic modulus of about .17%/kg/cm2. The dynamic modulus and hysteresis values are determined by Goodyear Vibra Tester and Goodyear hot rebound test per ASTM ~-2231 and ~STM D-1054, respectively.
The operating performance of tire 10 in the uninflated state may be enhanced by the placement of chafer portions 54, 56 in the bead area adjacent the rim flange portions 60,62. When the tire is operated in the uninflated condition, a severe bending action occurs in the bead regions 22,24 about the rim flange portions 60, 62. Chafer portions 54,56 help counteract this bending action and minimize the flexing of the tire adjacent the rim flange portion 60,62. In the embodiment illustrated, the chafer portions 54,56 are made of an elastomeric material. However, chafer portions 54,56 may comprise a rubber-coated fabric. The chafer portions 54,56 are made of a material resistant to chafing and have a dynamic modulus at least equal to the dynamic modulus of the elastomeric material axially outward of the ply structure 30 and adjacent chafer portions 54,56. In the embodiment illustrated, the radially outermost points 64,66, of the chafer portions 54,56 respectively, extend radially outward beyond the flange contact point not less than about ~5 of an inch (12.7 mm) as determined when the tire is mounted on a wheel for which it is designed to be used, and inflated to design inflation pressure. For the ~ 3S

purpose of -this invention, -the flange contact poin-l shall be the point at which the tire sidewall first contacts the rim proceeding from the tread portion to the bead portion.
The performance of the tire in the uninflated state 5 may be further enhanced by providing the bead portions 22,24 with narrow reinforcing strips 58,59 axially outwardly of bead cores 26,28 extending circumferentially about the tire 10. In the embodiment illustrated reinforcing strip 58,59 are located axially outwardly of the ends 34,36 of the carcass ply structure 30.
Reinforcing strips 58,59 enhance the bead area's resistance to compressive forces resulting from the tire bending about the rim flange during operation in the uninflated or par-tially uninflated condition. The reinforcing strips 58,59 further provide an imporved transition of stiffness from the stiff bead cores 26,28 to the softer sidewall compound. Reinforcing strips 58,59 comprise a plurality of parallel reinforcing cords, the cords being made from a highly compressive resistant material, for example, and not for the purpose of limitation, fiberglass or any metal. In the embodiment illustrated, the strips 58,59 comprise a plurality of reinforcing cords made from steel.
To ensure continuity, the radially inner ends 68,70 should be located radially inward of the radially outer-most point of the bead cores 26,28, respectively.
Applicant has discovered that when the radially inner point of the reinforcing strips is above the radially outermost point of the bead core, stress concentrations may result and cause premature failure. The radially outer endings 72,74 of reinforcing strips 58,59 are preferably located radially outward from the rim flange contact point by at least about . 2 of an inch (5.4 mm)-In order -co assure that lhe bead portions 22,24 do not move from their respective rim bead seats 65,67 when tl~e -tire is opera-ted in the uninflated stat,e, some l,ype of bead re-tention feature is preferably used. It has been found that the standard safety hump used on the JJ and JB rim, as specified by the Tire and Rim Association, provide the necessary support to retain the beads in their bead seat.
Prolonged use of the tire in -the uninflated condition may be provided by providing a coolant in the tire cavity. The coolant may be present in the tire cavity during normal operating conditions or may be dispensed into the tire cavity when the tire goes into the underinflated or uninflated state. A tire made in accordance with the present invention having a ratio of hysteresis to dynamic modulus of about .16%/kg/cm2 and a dynamic modulus of about 104 kg/cm2 and with the introduction of one pint of polyethyleneglycol into the tire cavity, has been found to be capable of traveling upward of 190 miles at 40 miles per hour which could then be inflated to normal operating pressures and returned to normal service. This is an increase of approximately 150 miles of additional travel of the tire as opposed to opera-ting the tire wi-thout a coolant. The amount of coolant necessary will, of course, be dependent upon the size of the tire and the physical properties of the particular coolant chosen.
Referring to Figs. 3, 4 and 5, there is illustrated a modified tire 110 made in accordance with the present invention. The radially inner surface 111 of the tire is shaped to have a plurality of substantially identically shaped corrugations 113 which extend in a substantially radial direction with respect to the mid-circumferential plane of the tire and are spaced apart about the circumference of the tire 110. The cross-sectional configuration of the corrugations 113 may be sinusoidal as illustrated in Fig. 4 or may take a variety of forms such as saw-toothed or stepped tj;~5 (not illus-trated). Adclitionally, the configurations need not be equally spaced about the circumference of the tire. In the embodiment illustrated, the corrugations 111 113 ha~e a substantially sinusoidal cross-sectional configuration, and are spaced substantially equidistant from each other about the circumference of the tire and extend substantially radially with respect to the mid-circumferential centerplane of the tire, starting from a point adjacent the bead area radially outward along the interior surface of the tire to a point beneath the tread portion terminating prior to reaching the mid-circumferential centerplane CP of the tire 110.
Preferably the ends of the corrugations 113 beneath the tread portion terminate at a point spaced a distance from the tread edge equal to at least 35% of the distance C from the tread edge to -the mid-circumferential plane o~ the tire. The tire 110, Figs. 3 4 and 5 is similar to tire 10 of Fig. 1, except that the sidewall thickness of the tire 110 takes into consideration the thickness of the corrugations 113. m e sidewalls of the tire 110 follow the same relationship as the sidewalls 14,16 of the tire 10, except that the total sidewall thickness T of tire 110 is the sum of the mean corrugation height H and the interior sidewall thickness G. The interior sidewall thickness ~ being the distance from the base of the corrugation axially outward to the outer surface of the tire e~clusive of any indicia that may be present. The mean corru~ation height H as is sho~Jn in Fig. 5, is the height from the base of the corrugation to the point wherein half of the cross-sectional area of the corrugation is above and half of the cross-sectional area of the corrugation is below.
While certain representative embodiments and details have been shown for purposes of illustrating the inven-tion, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A pneumatic safety tire comprising a circumferentially extending ground-engaging tread portion, a pair of shoulder portions adjacent the axially outer end of said ground-engaging tread portion, a pair of bead portions, a pair of sidewall portions which extend from said shoulder portions to said bead portions, a carcass ply structure which extends from said bead portion to said bead portion, said tire characterized in that said sidewall portions have a predetermined thickness selected to provide that the average maximum stress developed in the elastomeric material does not exceed approximately 8.7 x 105 N/m2 when said tire is operated in the uninflated state, the inner sidewall portions radially inward with respect to the internal cavity of said tire of said carcass structure being made of an elastomeric material having a hysteresis to dynamic modulus ratio not greater than about .24%/kg/cm2 and a dynamic modulus of elasticity not less than about at least 50 kg/cm2.

2. A pneumatic safety tire according to claim 1 further characterized in that the mean thickness of said sidewall portions measured at the maximum tire section width of said tire corresponds to the follow-ing relationship:

T = wherein, T is the total sidewall thickness at the point of maximum tire section width Rhom exclusive of any indicia measured in millimeters;
L is the load in kilograms at which the tire will be required to operate;
Rhom is the radius from the axis of rotation of said tire to the point of maximum tire section width SD
measured in millimeters;
S70 is the maximum tire section width SD measured from the radially outer surfaces of the sidewall, exclusive of any adornment or indicia that may be present and measured parallel to the axis of rotation, measured in millimeters when said tire is mounted on a rim which has the axial flange surface spaced 70% of the maximum section width SD of the tire; and K is equal to approximately 8.9 x 10 1.

3. A pneumatic tire according to claim 1 wherein the inner sidewall portion radially inward with respect to the internal cavity of said tire of said carcass structure being made of an elastomeric material having a dynamic modulus of elasticity not less than about 85 kg/cm2.

4. A tire according to claim 1 wherein each of said sidewall portions have a cross-sectional configuration such that the mean thickness of said sidewall portion at the area adjacent said bead portions being at least 65% of the mean sidewall thickness at Rhom, the mean thickness of said sidewall portion proceeding from said point of maximum tire section width radially outward toward its respective shoulder portion being equal to or greater than the thickness of said sidewall portions at said maximum tire section width.

5. A tire according to claim 2 wherein the radially inner portion of each of said sidewall portions radially inward of said carcass ply structure having a cross-sectional mean thickness at the maximum tire section width of said tire of at least 30% of the total thickness of said sidewall portion at said point exclusive of said carcass ply structure or inner liner that may be present.

6. A tire according to claim 1 wherein the radially outer ends of said inner portion of each of said sidewall portions terminate at a point spaced a distance from the tread edge which it lies beneath of at least 35% of the distance from the tread edge to the mid-circumferential centerplane of said tire.

7. A tire according to claim 1 wherein said bead portions are each reinforced with a stiffening member located radially outward of each of said bead cores and between said carcass ply structure and the ends of said carcass ply structure, said stiffening members having a dynamic modulus of 125 kg/cm2 and a maximum ratio of hysteresis loss to dynamic modulus of .15%/kg/cm2.

8. A tire according to claim 1 wherein said bead portions are each provided with a chafer portion adjacent the rim flange contact area, said chafer portion having a dynamic modulus of at least 125 kg/cm2.

9. A tire according to claim 1 wherein each of said bead portions of said tire being further provided with a narrow reinforcing strip located axially outward of said respective bead core and said end of said carcass ply structure extending circumferentially about the tire.

10. A tire according to claim 1 wherein said tire is provided with a coolant in the tire cavity when operated in the underinflated or uninflated state.