GB1584184A

GB1584184A - Road vehicle wheel

Info

Publication number: GB1584184A
Application number: GB3126877A
Authority: GB
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1976-10-07
Filing date: 1977-07-26
Publication date: 1981-02-11
Also published as: JPS5347603A; CA1081592A; JPS621B2; FR2366944B1; FR2366944A1; IT1084885B

Description

(54) ROAD VEHICLE WHEEL (71) We, CATERPILLAR TRACTOR CO., a corporation organized and existing under the laws of the State of California, United States of America, d 100 N.E. Adams Street, Peoria, Illinois, 61629, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The load carrying capacity of a pneumatic tyre is a function primarily od the width of the tread and the internal tyre pressure. The tyre 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 tyre diameters are limited by the size d the vehicles with which the tyre is used. For a given load, a tyre within a range of widths and pressures can be selected. As the tyre width is increased more material is required and the cost of the tyre and of the rim on which it is mounted increase.

It is desirable for economic reasons therefore to use a narrow tyre and high pressure.

However, rhe "ride quality" of the tyre must also be considered. It is a subjective measure of the performance ob 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 tyre construction and by the operating pressure. No satisfactory objective measure has been established. Generally, however, a maximum pressure d the order of 20 to 30 psi is utilized with open carcass tyres on a passenger vehicle. A higher pressure causes a harsh, uncomfortable ride. Within this pressure range and the desired tyre diameter, a width is selected to support the anticipated load.

Our UK Patent Specfiication No. 1,313,663 (US 3,606,921) discloses a pneumatic tube tyre which has, among other features a capacity of providing a soft, comfort- able ride with little noticeable difference in quality over a pressure range from 20 psi to as high as 50 or 60 psi. Such a tube tyre selected for a given load may be much smaller than a beaded, open carcass tyre for the same load, resulting in a material cost reduction and a weight saving. The tube tyre includes a toroidal elastomeric carcass with an outer tread wall, an inner rim wall and a pair of side walls interconnecting the tread and rim walls. The carcass is reinforced with a continuous inextensible filament wound in generally radial planes. A tread belt has inextensible reinforcement generally parallel with the plane of the tyre. It is our present theory that the independence of ride quality from tyre pressure is due in part to the side wall construction with a uniform array of radial reinforcing elements, by virtue of which the incremental side wall deflection at the rim and tread is symmetrical as the load on the tyre changes. The tyre has a higher torsional spring rate than comparable tyres of open carcass construction and this may also contribute to the high quality of the ride.

In contrast to the subjective nature of the ride quality of the tyre, the characteristics of a tyre which contribute to vehicle directional control and dynamic stability in turns have been analyzed objectively. The General Motors Company has developed Tyre Performance Criteria (TCP) which include force and moment characteristics that provide a measure of the directional control capability of a vehicle with which the tyre is used. The criteria are described in a publication entitled "General Motors Tire Performance Criteria (TCP) Specification System"; and the force and moment characteristics are defined at pages 74-77. The principal tyre characteristics 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.

Tyres initially made in accordance with the above UK patent were typically 64 or 88 inches in diameter and were used with off-road earthmoving vehicles. The performance criteria for automobile tyres are not od great significance for such vehicles.

A tyre 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 pass angler vehicle in road service.

This invention is concerned with the desire to achieve force and moment characteristics which meet or exceed the General Motors Tire Performance Critreia without adversely affecting the desired characteristics of this type of tyre, 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 tyre tread which engages the road surface (the "footprint" of the tyre) and is transmitted from the tread through the side wall to the rim engaging portion of the tyre, and thus to the wheel and the vehicle where is is effective to change the direction of vehicle movement.

According to the invention a road vehicle wheel comprises a rim which carries a tyre, the tyre comprising a tread wall incorporating at least one layer of reinforcing elements to impart lateral stiffness to the tread wall and resist the bending of the tread wall that occurs in the tread footprint during a rolling turn; and, on each side of the mid-circumferential plane of the tyre a side wall extending from the tread wall to a rim engaging wall portion which engages the rim; the side wall containing a uniform array of reinforcing elements which lie substantially in axial planes of the wheel, and having in any axial plane of the wheel a part circular cross section, the incremental lateral distortion upon loading of the tyre of the side wall immediately adjacent to its junction with the tread wall being the same as that immediately adjacent to its junction with the rim engaging wall portion; and the rim engaging wall portion incorporating a respective hoop which is spaced from the junction of the rim engaging portion with each side wall such that two hoops are located on opposite sides of the mid-circumferential plane, the hoops being spaced apart and cooperating with respective annular step portions of the rim to constrain the radially inner peripheral part of the tyre against axial movement relatively to the rim.

The invention provides stiffness in the tread d the tyre with respect to lateral forces and enables the force to be transmitted efficiently to the wheel rim.

The tread wall of the tyre may be laterally stiffened by a pair of complementary bias reinforcing strips which have substantial lateral stiffness.

The tyre may include annular bodies of elastomer between the lateral edges of each tread wall and/or each hoop and the respective side walls, enhancing the transfer of force through the tyre in a rolling turn between the roll restraining hoops, to prevent lateral inward movement of hoops with respect to the surface of the wheel rim.

Examples of wheels of the prior art and according to the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a broken perspective of a prior art tyre such as illustrated in UK Patent Specification No. 1,313,663; Figure 2 is a diagram of forces on a tyre in a rolling turn; Figure 3a, 3b and 3c are diagrams illustrating a series of tyre footprints in idealized form; Figure 4 is a cross-section of a tyre of the invention; Figure 5 is a broken perspective of the tyre of Figure 4; and, Figure 6 is a diagrammatic illustration of a test useful in comparing materials used in stiffening the tread of the tyre.

A prior art tube tyre will be considered briefly to illustrate the problems solved by the present invention. Figure 1 is a broken persepective view of the tyre of Figure 7 of Specification 1,313,663. 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 tyre 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 preferably wound of steel wire.

The rim wall 22 has a centrally located radial rib 31 received in a centering recess 32 between split sections 33, 34 of the rim. Further details of the tyre construction and its manufacture may be found in the above specification. The tyre 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 consumption. The prior art tyre, however, has shortcomings which affect its suitability for a road-service passenger vehicle as an automobile or truck.

A consideration of the tyre 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 tyre and wheel 38 are illustrated on a road plane 39. The mid-circumferential or 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 la. 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 centre 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 negative 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 load and slip angle affect the handling characteristics of the vehicle. If the lateral force is tuo great, the vehicle will respond violently and be difficult to control. If the lateral force is small, vehicle response is sluggish. The structure of the tyre and the interconnection of the tyre and the wheel are major factors in establishing the lateral force 44.

In a turn a force is generated by interaction between the tyre tread and the road surface. The dynamics of the generation of the force in the tread are complex. A simpllified qualitative discussion is sufficient for an explanation of the invention. The portion of the periphery of the tyre which engages the road surface, sometimes referred to as the footprint of the tyre, is illustrated diagrammatically in Figure 3a for a tyre travelling in the direction of its heading. The longitudinal axis 51 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, respectively. The extent of the deformation, which may be measured by the angle ld between the segments of longitudinal axes 54, 55, is determined principally by the slip angle a and the resistance of the tread to lateral deformation. If the tread has little lateral stiffness, the footprint deformation is greater, Figure 3b, than if the tyre is stiff, Figure 3c.

The General Motors Tire Performance Criteria discussed above identifies the ability of a tyre to generate a lateral force 44 in a turn by a cornering coefficient, defined as the lateral force which is generated at a 10 slip angle and rated tyre load, divided by the rated load.

The first tyres built in accordance with Patent No. 1,313,663 in a size for use on passenger vehicles for road operation (sometimes referred to herein as "automotive tyres") were found to have a cornering coefficient insufficient for passenger vehicles.

We believe that this low cornering coefficient results from the fact that the peripheral tread with reinforcing elements 28 parallel with the plane of the tyre has little resistance to lateral deformation. The footprint deforms in a turn as illustrated in Figure 3b.

Two principal changes have now been proposed to overcome this problem. First, the tread is provided with at least one layer of reinforcing elements which, contrary to the elements 28 of the prior art of Figure 1, are specifically arranged to impart lateral stiffness to the tread wall. This reduces deformation of the footprint, Figure 3c, and results in the generation within the tread of a higher lateral force. Second, the tyre is interconnected with the wheel rim to minimize relative movement so that the lateral force developed in the tyre tread is efficiently transferred from the tyre to the wheel.

The lateral stiffness of the tread section of the tyre is provided 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 layers, each made up of an elastomer strip, with reinforcing elements in the two strips arranged at complementary bias angles with respect to the plane of the tyre, 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 developed in the tyre tread. The force must be efficiently transmitted through the side wall to the rim wall and from the rim wall to the rim of the wheel. The interconnection of the tyre rim wall and the wheel rim will be considered next. A lateral force applied to the tread wall of the prior art tube tyre shifts the tread wall sideways and increases the force tending to move the roll restraining hoop on the outside of the turn of the wheel rim. Any movement of the hoop results in a shear force in the rim wall that dissipares some of the lateral force, reducing the force which is effective to turn the vehicle.

Figure 4 and 5 illustrate a construction in which the rim surface 76 on which the rim wall 77 of the tyre 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 the roll restraining hoops 81, 82. The interlocking connection between the tyre rim wall and the mounting surface of the rim restricts relative movement of the tyre and rim for efficient force transfer.

The rim surface 76 may be a transversely split ring with an expander and. mounting member 84, both described in more detail in U.K. Specification No.

1,478,427. Tyre rim wall 77 has a generally straight inner surface in unstressed condition. Expansion of annular rim surface 76 against the tyre causes the rim step 78 to deform the tyre 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 ob 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 to Figure 4, the elastomeric body of the tyre 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 od elastomer incorporated in the composite tyre structure prior to vulcanization.

Automotive tyres are made in many different sizes to accommodate different loads, with a diameter and width which complement the styling of the vehicle. The physical dimensions and other tyre characteristics, including the Tyre Performance Criteria, are related to the tyre size. Some of the dimensions and component characteristics of the tube tyres od Figures 4, 5 corresponding to an open carcass beaded tyre size HR78-15 will be given by way of example. It will be understood that different combinations of materials and dimensions may be used in constructing other forms of this tyre and other sizes of tyre.

The HR78-15 at a maximum pressure of 32 psi is rated for a load of 1770 pounds. The General Motors Tyre Performance Criteria establishes a nominal cornering coefficient of 0.160 for this tyre. Other tyres 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 8.45 inches and a height from bead to tread of 6.6 inches.

A lighter weight tyre is illustrated in Figures 4 and 5. The section width is 8 inches but the tyre 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 wall 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 filaments 98 per inch. Roll restraining hoops 81, 82 are of 6 X 5 X .037 steel wire. Rim step 78 has a radial dimension of 0.01 inch and a width of 1.95 inches.

Suitable elastomer compounds for the tyre are identified by code number in Table A. The principal constituents and physical characteristics of the elastomer compounds are given in Table B.

TABLE A Tire Part Tire Figures 4, 5 Tube Stock (inside the T208 radial reinforcing) Bond Stock B320 Sidewall C657 Tread C657 Hoop Filler V904 TABLE B Hardness Tensile Elasticity Tear (Shore A) Strength Strength Compound Composition (Durometer) psi Elongation Stress psi Elongation Die C B306 Natural Rubber 55 2900 550% 1250 100% 300 lb./in.

B320 Natural Rubber 75 3000 375% 2300 300% 350 lb./in.

C657 90% Natural Rubber 59 3750 100% 1049 100% 414 lb./in.

10% Polybutadiene T208 Bromobutyl Rubber 53 3750 300% 822 573% 158 lb./in.

T215 75% Bromobutyl Rubber 54 1462 610% 718 300% 196 lb./in.

25% Low Viscosity Natural Rubber V904 Filled Styrene- 85 1800 100% 1100 100% Butadiene Rubber The tyre of Figures 4 and 5 has a cornering coefficient of .159. The tyre can be operated at substantially higher pressures than 30 psi with good ride characteristics.

The cornering coefficient increases with inflation pressure. Accordingly, the tyre can accommodate a significantly greater load than the HR78-15 tyre. Conversely, a smaller tyre incorporating the invention could be selected for service with a load capability of the HR78-15.

The open carcass HR78-15 tyre weighs approximately 32 pounds. The com Parable tyre of Figures 4 and 5 weighs 25 pounds.

The almost unlimited selection of elastomer materials and reinforcing available for the tyre tread wall enables fabrication of tyres of various sizes with a desired cornering coefficient. However, it is both expensive and time consuming to build and test a complete tyre. We have determined that samples of tread material may be tested in simple beam deflection, providing information regarding stiffness which correlates predictably with the cornering coefficient of the tyre using the material in the tread. This greatly simplifies the analysis of tread material and the design of tyres.

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 tyre 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 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 tyre is related to its multipressure, good ride performance. As the tyre 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 tyre where the side wall is stiff in the area of the beads and the principal deflection occurs at the side wall-rim juncture. So long as the tyre side walls have this capacity for symmetrical 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. The side wall characteristics do not require the tube tyre construction on a core as described in the specification No.

1,313,663. While this construction is desirable because it provides tyre 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 100 is tolerable.

It is preferable that the tread has the two bias reinforcing layers inside the inextensible 0 belt to eliminate the effect of the bias reinforcing on steering. However, where the bias layers have sufficient resistance to peripheral expansion, as permitting a circumferential expansion of no more than 5%, the 00 belt may be omitted.

There are other characteristics of the tyre which contribute to the cornering coefficient but to a lesser extent than the lateral tread reinforcement tyre to rim con nection 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 Cis generated in a stiff material and this is detrimental to tyre 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 yl than for a smaller angle 72.

The tube tyres illustrates in Figures 4 and 5 may be manufactured with the procedures described in U.S. Patent Specication 3,776,792, a division of 3,606,921 (U.S. equivalent of UK 1,313,663). Improvements in some of the manufacturing procedures and apparatus are disclosed in our UK Patent Applications Nos. 1,445,490; 25,405/76 and 20,193/77 and in US Patent Specification No. 3,998,918.

Claims

WHAT WE CLAIM IS:-

1. A road vehicle wheel comprising a rim which carries a tyre, the tyre comprising a tread wall incorporating at least one layer of reinforcing elements to impart lateral stiffness to the tread wall and resist the bending of the tread wall that occurs in the tread footprint during a rolling turn; and, on each side of the mid-circumferential plane of the tyre, a side wall extending from the tread wall to a rim engaging wall portion which engages the rim; the side wall containing a uniform array of reinforcing elements which lie substantially in axial planes of the wheel, and having in any axial plane of the wheel a part circular cross section, the incremental lateral distortion upon loading of the tyre of the side wall immediately adjacent to its junction with the tread wall being the same as that immediately adjacent to its junction with the rim engaging wall portion; and the rim engaging wall portion incorporating a respective hoop which is spaced from the junction of rhe rim engaging portion with each side wall such that two hoops are located on opposite sides of the mid-circumferential plane, the hoops being spaced apart and cooperating with respective annular step portions of the rim to constrain the radially inner peripheral part of the tyre against axial movement relatively to the rim.

2. A wheel according to claim 1, in which the tread wall includes a peripheral inextensible belt with reinforcing elements substantially parallel to the plane of the tyre.

3. A wheel according to claim 1 or claim 2, in which the reinforcing elements incorporated in the tread wall to impart lateral stiffness are provided by a pair of radially spaced peripheral breaker strips providing reinforcing elements disposed at a bias angle, the bias angles of the two strips being equal and displaced in opposite directions from the mid-circumferential plane od the tyre.

4. A wheel according to claim 3 when dependent on claim 2, in which the inextensible belt is spaced radially outside the breaker strips.

5. A wheel according to claim 4, or to claim 3 when dependent on claim 2, in which the width of the inextensible belt is less than the width of the breaker strips.

6. A wheel according to any one of claims 3 to 5, in which the width of the outer breaker strip is less than the width of the inner breaker strip.

7. A wheel according to any one of the preceding claims, in which the tyre has an annular body of elastomer between the lateral edges of each tread wall and the outer surface of the respective side wall.

8. A wheel according to any one of the preceding claims, in which the tyre has an annular body of elastomer between the outer edge of each hoop and the inner surface of the respective side wall.

9. A wheel according to claim 1, substanually as described with reference to Figures 4 and 5 od the accompanying drawings.