Type for a motor vehicle having minimized rolling resistance

Abstract

A tyre comprises a casing ply having a meridian profile with a central crown portion and two sidewall portions; in the inflated configuration of the tyre, the crown profile portion has a radius of meridian curvature ρ c in the range from 406 mm to 690 mm and each sidewall profile portion forms an angle α s with the axis of rotation of the tyre in the range from 25° to 30°; additionally, a mould for a tyre has cheek profiles which have a first and a second radius of curvature R fs /R fi whose ratio R fs /R fi ranges from 0.45 to 0.56 and a base profile of one sector having a radius of meridian curvature R≧500 mm and a shoulder angle α 0 ≧42°.

1 . Tyre for a motor vehicle, made from a predetermined viscoelastic material, and comprising 
 a) at least one casing ply,    b) a tread strip placed on the crown of said casing ply,    c) at least one belt strip interposed coaxially between said casing ply and said tread strip,    d) right-hand and left-hand sidewalls, and    e) right-hand and left-hand beads,    f) said casing ply having a profile, in the plane of a meridian section, which has a central crown portion and two sidewall portions, one on the right and one on the left,    g) each of said sidewall profile portions being delimited by two points S and K, where the point S is located substantially at one edge of said at least one belt strip and the point K separates a sidewall from a bead,    h) said tyre assuming, at the operating pressure and in the absence of a load, an inflated configuration having a predetermined outer profile which matches a predetermined enclosing rectangle,    i) said outer profile having a predetermined maximum chord {overscore (C)} and a predetermined maximum height {overscore (H)}, the ratio {overscore (H)}/{overscore (C)} lying in a range from 0.6 to 0.8,     characterized in that,    j) in said inflated configuration, said crown profile portion has a radius of meridian curvature ρ c  lying in a range from 406 mm to 690 mm and each of said sidewall profile portions forms an angle α s  with the axis of rotation of the tyre, at said point S, which lies in a range from 25° to 30°.    
     
     
         2 . Tyre according to  claim 1 , characterized in that each of said sidewall profile portions forms an angle α k  with the axis of rotation of the tyre, at said point K, which is ≧45°.  
     
     
         3 . Tyre according to  claim 1 , characterized in that said crown profile portion is substantially flat.  
     
     
         4 . Mould for producing a tyre made from a predetermined viscoelastic material, said mould having 
 A) a crown formed by radially movable sectors for moulding a tread strip and shoulders of said tyre, and    B) cheeks for moulding sidewalls and beads of said tyre,    C) said mould having a profile, in the plane of the meridian section, which has a predetermined maximum chord C, a predetermined maximum height H and a fitting line I, and is formed centrally by a base profile of one sector and laterally by profiles of said cheeks,    D) said base profile of the sector having a central portion flanked by two connecting portions, which in turn are flanked by two lateral portions,    E) each cheek profile having a total height H g  and having a first portion with a first radius, of curvature R fs  and a second portion with a second radius of curvature R fi , characterized in that    F) the ratio between said first and second radius of curvature R fs /R fi  ranges from 0.45 to 0.56.    
     
     
         5 . Mould according to  claim 4 , characterized in that the ratio between said first and second radius of curvature R fs /R fi  is approximately 0.5.  
     
     
         6 . Mould according to  claim 4 , characterized in that the centres of said first and second radius of curvature R fs  and R fi  lie on said maximum chord C and in that said maximum chord C is located at a distance H lc  from said fitting line  1  equal to approximately ⅔ of said height of the cheek profile H g .  
     
     
         7 . Mould according to  claim 4 , characterized in that said central portion of said base profile of the sector is approximately flat and has a radius of meridian curvature R≧500 mm, and each of said connecting portions has, at the point of junction with one of said lateral portions, an angle α 0  with respect to the longitudinal axis of the mould which is ≧42°.  
     
     
         8 . Mould according to  claim 4 , characterized in that said base profile of the sector, comprising said central portion and said flanking connecting portions, has a camber f of ≦7.5 mm.  
     
     
         9 . Mould for producing a tyre from a predetermined viscoelastic material, said mould having 
 i. a crown formed by radially movable sectors for moulding a tread strip and shoulders of said tyre, and    ii. cheeks for moulding sidewalls and beads of said tyre,    iii. said mould having a profile, in the plane of the meridian section, which has a predetermined maximum chord C, a predetermined maximum height H and a fitting line I, and is formed centrally by a base profile of one sector and laterally by profiles of said cheeks,    iv. said base profile of the sector having a central portion flanked by two connecting portions, which in turn are flanked by two lateral portions,     characterized in that    v. said central portion of said base profile of the sector is substantially flat and has a radius of meridian curvature R≧500 mm, and    vi. each of said connecting portions has, at the point of junction with one of said lateral portions, an angle α 0  with respect to the longitudinal axis of the mould which is ≧42°.    
     
     
         10 . Mould according to  claim 9 , characterized in that said base profile of the sector, comprising said central portion and said flanking connecting portions, has a camber f≦7.5 mm.