GB2035925A

GB2035925A - Radial carcass pneumatic tyre

Info

Publication number: GB2035925A
Application number: GB7940289A
Authority: GB
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 1978-11-27
Filing date: 1979-11-21
Publication date: 1980-06-25
Also published as: NL7908561A; EP0013194A1; AT377231B; ATA747879A; BR7907692A; FR2442149A1; AU526325B2; AU5318679A; FR2442149B1; JPS5572406A; BE879989A; CA1116502A; GB2035925B; IT7969278A0; EG14591A; DE2947149A1; IT1119548B; AR221514A1; LU81924A1; ES486229A1

Description

1 GB2035925A 1

SPECIFICATION

Radial carcass pneumatic tyre This invention relates to a pneumatic tyre intended to be fitted to medium-sized and large load-carrying vehicles, e.g. vans and lorries, and having a radial carcass reinforcement anchored to at least one beadwire in each bead and a crown reinforcement comprising at least two oblique plies of cords, e.g. wires or cables which are parallel in each ply but cross from one ply to the other.

The invention relates more particularly to such tyres having no independent inner tube, i.e. a tubeless type, and mounted on leaktight rims having frustum-shaped seats for the beads of the tyres. Wheel rims of this kind corresponding to the current standards have seats inclined at about 15 relative to the rotation axis of the wheels. The tyres according to the invention have an aspect ratio H/B of the radial height H of the tyre on the rim to the maximum axial width B of the tyre of from 0.6 to 1.

In an effort to make the loading of mediumsized and large load-carrying vehicles easier and more economical, there has been a tendency to reduce the height of the loading plane of these vehicles. This means that the outer diameter of such tyres has to be main tained or reduced and. that if the number of axles is not to be increased the tyres would be substantially overloaded, by between 30 and 100%, as compared with the nominal load for 100 existing conventional tyres as specified by the manufacturer or in the current standards. This normal load for a conventional tyre has a corresponding nominal inflation pressure.

One solution to the problem of carrying a higher load is to increase the inflation pres sure. However, this solution has an adverse effect on the wear of the tread and also the tension of the carcass reinforcement is increased at the beads and hence the tension on the beadwire to which the carcass rein forcement is anchored, generally by bending, is also increased. To counteract this increase in tensions, the carcass reinforcement and the beadwires have to be made stronger to keep 115 the endurance of such tyres at a satisfactory level. This leads to a considerable increase in the cost price.

The aim of this invention is to provide a tyre which can take an increased load of 30 120 to 100%, preferably of at least 50%, without affecting the tension of the beadwires, i.e.

without having to reinforce the beadwires, and the deflection of the tyre. Further, the increase in the meridian tension of the carcass 125 reinforcement is at most equal to the increase in the inflation pressure necessary to maintain the deflection of the tyre at about its nominal value.

The principle of the solution according to the invention consists in selecting a natural meridian profile of equilibrium for the mean fibre of the carcass reinforcement such that the tension of the beadwires remains more or less equal to the tension of beadwires in conventional tyre under the effect of the nominal pressure and such that the proportional increase in the meridian tension of the carcass reinforcement at the beadwires remains less than the proportional increase in the inflation pressure.

Therefore according to the invention there is provided a tubeless pneumatic tyre for medium- and large-sized load-carrying vehicles having a radial carcass reinforcement anchored to at least one beadwire in each bead and a crown reinforcement comprising at least two oblique plies of cords which are parallel in each ply and cross from one ply to the other, the tyre being intended for use on wheel rims with frustum-shaped bead seats, having an H/B ration of from 0.6 to 1, and when it is mounted and inflated but not loaded, the mean meridian fibre of its carcass reinforcement, between the points of tangency of that reinforcement with the beadwire and the crown reinforcement, follows the natural equilibrium profile so that:

coso = R "12 /R S12 -R "12, the quantity (Rj -R j) being approximately equal to k p,,/p, (RS.2 -R ". 2), p. being the nominal inflation and p, the inflation pressure such that the tyre keeps its nominal deflection under the effect of an overload, k being a positive coefficient of between 1 and the value of the ration p, /p. but not the value 1 and p,/p., the angle P, formed by the tangent to the carcass reinforcement at the point of contact with the beadwire and by the rotation axis of the tyre being such that sinfl, 2 sinp,,/k, and the quantity Rel being equal to R t2_COSPI (R j -R.12).

The natural equilibrium profile of the neutral meridian fibre of a radial carcass reinforcement obeys the law:

(1) cos(p = R 2 -R ',2 /R2- R "2.

In this equation:

0 is the angle of the tangent to the profile with the rotational axis of the tyre, at a point located at a radial distance R from this axis, with cos4) < 0 for R < R. and coso > 0 for R > R; R, is the radial distance, from the rotation axis, of the point where the profile has a tangent parallel to the rotational axis; and R. is the radial distance, from the rotational axis, of the point where the profile attains its maximum axial width or where the profile has a tangent perpendicular to the rotational axis of the tyre.

Furthermore, the tension T of the beadwire 2 GB 2 035 925A 2 can be expressed by the equation (2) T = p sinfl(R,, 2 R j /2), in this equation:

p is the inflation pressure and 8 is the angle formed by the tangent to the carcass reinforcement at the point of contact of the carcass reinforcement with the beadwire and the 10 rotational axis of the tyre.

Moreover, the meridian tension t (per unit of circumferential length) of the carcass reinforcement at the beadwire is expressed by the equation (3) t = p(R.2_FI.2/2 R,), in which:

Rt is the radial distance of the point of contact of the carcass reinforcement with the beadwire, measured from the rotational axis of the tyre.

At the pressure p. of the nominal tyre specified for a nominal load, the equations 1.2 and 2 above can, for the nominal tyre, be 90 written as follows:

cos4) = R 2 -R.',2 /R.2 -R.',2 (nominal natural equilibrium profile), T. = p. sin#. (R..2 -R.,>2 /2) (nominal ten sion of the beadwire), t. = p. (R..2 -R 'j /2RJ (nominal tension of the carcass reinforcement at the beadwire).

According to the invention, at the pressure p, which is sufficient for the deflection of the tyre when designed for higher loads to be more or less equal to the deflection of the nominal tyre, the tension T, of the beadwire is substantially equal to the nominal tension T,, whereas the tension t, of the carcass reinforcement reaches the value k t., k being between 1 and the value of the ration p,/p.. We have T1/t. = k = p,/p.. ((R.12 -R.12) /(R J_ R..2)), whence we obtain the value of the quantity (R,,,2_R,,,2) to be introduced into the law giving the natural profile of equilibrium of the neutral fibre of the carcass reinforcement according to the invention.

From the equivalence of the tensions T, and T. of the beadwire, we take the value P, of the angle 0 at the beadwire, taking into account the above value for the quantity (R j -R "12) according to the invention: sin#, = (sin#./k). This makes it possible to calculate the quan- tity R ",2 from the term cos P, = (Rt 2 -R.12 /R Re12), noting that cos fl,<O.

In practice, the invention makes it possible to choose a tension, and hence a degree of strengthening, for the carass reinforcement which is less than the increase in the inflation pressure appropriate for maintaining the deflection constant. Preferably, k is between 1. 15 and 1. 30.

The carcass reinforcement is preferably es- sentially made up of a single ply of cords, preferably consisting of steel cords. In this case, the means meridian fibre follows the axis of the cords. In the case of a multi-ply carcass reinforcement, the means fibre is lo- cated halfway between the outer and inner plies.

The invention will now be illustrated, by way of exa-mple, with reference to the accompanying drawing which is a radial half-section through a tyre according to the invention.

The pneumatic tyre 1 is shown mounted on a wheel rim 2 having a frustumshaped bead seat 3 inclined 15 relative to the rotational axis of the tyre and wheel indicated by the line Y-Y'. The mid-circumferential plane X-X is an axis of symmetry of the meridian section of the tyre 1. The maximum axial half-width of the tyre is B/2 and the height H on the rim is measured from the end of the radius R, of the bead seating 3 as defined for the nominal tyre by current standards.

The tyre has a tread 4 beneath which is a crown reinforcement 5 formed by two plies of cords 51 and 52. The tyre has a carcass reinforcement 6 which is at a tangent to the crown reinforcement 5 at the point 8' and which is also at a tangent to a beadwire 7 in the bead 10 at the point 8. The neutral fibre of the cascass reinforcement follows the line defining the carcass 6. Rt is the radius corresponding to the point 8.

The single-ply carcass reinforcement 6 is anchored to the beadwire 7 by means of a terminal portion 6' which is bent-back around the beadwire. Unlike the usual arrangement with a carcass reinforcement formed by a single ply of steel cords, the end C of the bent portion 6' is located radially from the axis Y-Y outside the corresponding end 9' of a stiffening ply 9. The latter is made up of oblique cords and is arranged axially outside the terminal portion 6' of the carcass reinforcement. Thus, with the invention ' the width of the stiffening ply 9 can be reduced. The other end 9", namely the radially inner end, of the stiffening ply 9 is located at an axial spacing A from the plane X-X' which is greater than the minimum axial spacing a of the carcass reinforcement 6 in the bead 10.

This results in increased flexibility of the bead, despite a higher inflation pressure.

Preferably, the radial distance d of the end 6" of the bent portion 6' relative to the crown 11 of the edge of the rim 2' is between 5 and 20% of the height H of the tyre 1.

The pneumatic tyre 1 shown in the drawings has a size known as 9.5-17.5 (in inches).

The radius R, of the bead seat 3 of a rim 2 for this tyre is 222 mm, and the seat 3 has a 1 1 r f 1 3 GB2035925A 3 conicity of 15 to the rotational axis of the tyre.

Under the nominal conditions specified in the current standards for a conventional or nominal tyre of this size, it is expected to be able to withstand a load of 1,700 kg under a pressure of 6.75 bars with a static deflection of about 33 mm.

The point of tangency 8 of the carcass reinforcement 6 with the beadwire 7 is located at a distance Rt of 238 mm from the rotational axis Y-Y' of the tyre. Moreover, this tyre has a H/B ratio of 0.9.

For a load equal to 2,665 kg, the tyre of the present invention has to be inflated to a pressure of 8.5 bars in order to obtain a deflection of 36 mm, which is close to the deflection of the nominal tyre although the load has been increased by 57% 20 In the case of the 9.5-17.5 tyre chosen as an example, the coefficient k should be between 1 and 8.5/6.75 = 1.26: it is equal to 1.20. For the nominal tyre appropriate for carry- ing the nominal load:

R, = 393 mm R.. = 320 mm and & = 43'.

From this, we obtain the value of the quantity (R j -R.12) = 49,600 MM2, corresponding to the tyre according to the invention. Similarly P, in the tyre of the invention is 34.

Noting that, for two points of the natural equilibrium profile corresponding to the radii R, and R2, we have:

coso, = Rll-R.12 /(R j -R j) and COS02 = R2 2 -R.12 /(R.12 -R j) the natural equilibrium profile of the neutral fibre of the carcass reinforcement according to the invention can easily be traced, step by step, using a computer from the equation:

COS01-COS02 = R 2 -R2 2 /(R '12 -R '12) starting from the value 8, = 34' for R, 238 mm.

On this trace, the calcuated values:

R,, = 384 mm R., = 313 mm are read off.

According to the invention, the tension of the beadwire has virtually not changed at all:

T,, = 1198 kg, and T, = 1179 kg.

According to the invention, the tension of the carcass reinforcement has increased by about 20%:

t. = 7.38 kg/mm t, = 8.86 kg/mm whereas the inflation pressure has increased by 26%.

Moreover, in spite of a 57% increase in the load in relation to the nominal load, it should be pointed out that the resistance to rolling of the tyre according to the invention, per 1000 kg of load at a speed of 70 km/h, is 8% lower than that of the known or nominal tyre.

Claims

1. A tubeless pneumatic tyre for medium and large-sized load-carrying vehicles having a radial carcass reinforcement anchored to at least one beadwire in each bead and a crown reinforcement comprising at least two oblique plies of cords which are parallel in each ply and cross from one ply to the other, the tyre being intended for use on wheel rims with frustum-shaped bead seats, having an H/B ration of from 0.6 to 1, and when it is mounted and inflated but not loaded, the mean meridian fibre of its carcass reinforcement between the points of tangency of that reinforcement with the beadwire and the crown reinforcement, follows the natural equilibrium pofile so that:

cos(p = R 2 -R,2 /R j -R "'2.

the quantity (R j -R j) being approximately equal to k p"/p, (R"2-R "02), p. being the nominal inflation pressure and p, the inflation pressure such that the tyre keeps the deflection of the nominal tyre under the effect of an overload k being a positive coefficient of between 1 and the value of the ratio p,/po but excluding the value 1 and p,/p., the angle 8, formed by the tangent to the carcass reinforcement at the point of contact with the beadwire and by the rotational axis of the tyre being such that sinfl, = sinp./k, and the quantity R,2 being equal to R '2-COSP, (R j -Re,2).

2. A pneumatic tyre as claimed in Claim 1 in which the coefficient k is from 1. 15 to 1.30.

3. A pneumatic tyre as claimed in Claim 1 or Claim 2 in which the end portion of the carcass reinforcement is bent around the beadwire and this portion is located radially from the rotational axis of the tyre outside the corresponding end of a stiffening ply for the bead, this stiffening ply being arranged axially outside the end portion of the carcass reinforcement.

4 GB2035925A 4 4. A pneumatic tyre as claimed in Claim 1 in which the end portion of the carcass reinforcement is located at a spacing of from 5 to 20% of the height of the tyre, relative to the crown of the edge of the nominal rim.

5. A pneumatic tyre of medium- and large-sized load-carrying vehicles substantially as herein described with reference to the accompanying drawing.

Printed for Her Majesty's Stationery Office by Burgess Et Son (Abingdon) Ltd-1 980. Published at The Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies may be obtained.

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