Tire for motor vehicle wheels having a tread producing a low rolling noise

Abstract

A tread for motor-vehicle tires has a raised pattern formed of a plurality of shaped blocks 7 distributed in circumferential rows 3, 4, 5, 6 disposed in parallel and in side by side relation. The number of the shaped blocks 7 arranged in each row gradually increases while moving from the equatorial plane X-X to the axial outer side edges 1 a of the tread 1. Thus a gradual increase in the longitudinal stiffness of the shaped blocks 7 is achieved on passing from the side edges 1 a of the tread 1 to the equatorial plane X-X, which brings about a reduction in the mobility of said blocks on the road contact patch and lower rolling noise.

1 . A tire for motor-vehicle wheels provided with a tread producing a low rolling noise, comprising: 
 a raised pattern formed of a plurality of shaped blocks distributed in parallel circumferential rows bounded by longitudinal grooves extending circumferentially of the tire each row comprising a plurality of shaped blocks circumferentially separated from each other by respective transverse cuts with each of said rows having a number of shaped blocks greater than the number of shaped blocks present in the adjacent axially inner row towards the equatorial plane of the tread, the arrangement being such to give the tread a gradually increasing longitudinal stiffness from the axial outer side edges thereof towards said equatorial plane.    
     
     
         2 . A tire according to  claim 1 , in which the number of said rows of blocks on each axial side of the center line of the tread is not smaller than three and not greater than five.  
     
     
         3 . A tire according to  claim 1 , in which at least one continuous circumferential rib is disposed close to the equatorial plane, said rib being defined between two of said longitudinal grooves.  
     
     
         4 . A tire according to  claim 3 , in which there are two of said circumferential ribs disposed symmetrically with respect to the equatorial plane of the tread and mutually separated by a central groove.  
     
     
         5 . A tire according to  claim 1 , in which the number of said shaped blocks in the axially innermost row is in the range of 20 to 40.  
     
     
         6 . A tire according to  claim 1 , in which the number of said shaped blocks in one row is double the number of shaped blocks in an axially inner adjacent row.  
     
     
         7 . A tire according to  claim 1 , in which in each row of said shaped blocks the transverse cuts define an impact angle with the adjacent longitudinal grooves, the value of said angle being greater than the value of an impact angle formed with the transverse cuts of the adjacent row of block disposed axially inward thereof towards the equatorial plane.  
     
     
         8 . A tire according to  claim 7 , in which the value of the impact angle in the block rows that are closest to the equatorial plane is in the range of 15° to 25°.  
     
     
         9 . A tire according to  claim 7 , in which the value of the impact angle in the rows of blocks closest to each of the axial outer side edges of the tread is in the range of 70° to 105°.  
     
     
         10 . A tire according to  claim 1 , in which each of said rows has first transverse cuts which are in alignment with one of the first transverse cuts of an adjacent block row.  
     
     
         11 . A tire according to  claim 10 , in which said aligned first cuts define continuous transverse grooves each extending from an outer side edge of the tread to a position adjacent said equatorial plane.  
     
     
         12 . A tire according to  claim 10 , in which each of said transverse grooves, starting from an outer side edge has one straight portion substantially perpendicular to the longitudinal grooves, a curved union portion and a second straight portion disposed obliquely relative to said longitudinal grooves.  
     
     
         13 . A tire according to  claim 11 , in which said longitudinal grooves have a smaller width than the first transverse cuts.  
     
     
         14 . A tire according to  claim 12 , in which a ratio between a width of the longitudinal grooves and a width of the first transverse cuts ranges between 0.6 and 0.2.  
     
     
         15 . A tire according to  claim 10 , in which at least one of said rows of blocks has second transverse cuts each being intermediate between two of said first cuts.  
     
     
         16 . A tire according to  claim 15 , in which the second transverse cuts are associated with outer shoulder rows, adjacent to the outer side edges of the tread, and inner shoulder rows disposed adjacent to the outer shoulder rows towards the equatorial plane.  
     
     
         17 . A tire according to  claim 15 , in which the width of the second cuts is smaller than the width of the first cuts.  
     
     
         18 . A tire according to  claim 17 , in which a ratio between a width of the second cuts and a width of the first cuts ranges between 0.5 and 1.  
     
     
         19 . A tire according to  claim 15 , in which the shaped blocks of at least one of said rows each have at least one transverse slot extending towards said equatorial plane over a portion of a smaller width than the width of that block.  
     
     
         20 . A tire according to  claim 19 , in which said transverse slots are associated with outer center rows disposed adjacent the inner shoulder rows towards the equatorial plane of the tread.  
     
     
         21 . A tire according to  claim 15 , in which at least one of said rows of blocks further comprises third transverse cuts extending parallel to said first and second transverse cuts.  
     
     
         22 . A tire according to  claim 21 , in which said third transverse cuts are associated with outer shoulder rows adjacent to the outer side edges of the tread.