Vehicle suspensions

Claim 1

A VEHICLE AXLE SUSPENSION HAVING A MAXIMUM STIFFNESS UNDER A DESIGNED FULL BUMP LOAD CONDITION AND A MINIMUM STIFFNESS UNDER A DESIGNED TARE LOAD CONDITION, THE SUSPENSION COMPRISING, IN COMBINATION, A MAIN LEAF SPRING SYSTEM AND AN AUXILIARY SPRING SYSTEM, THE MAIN LEAF SPRING SYSTEM HAVING A SUBSTANTIALLY CONSTANT STIFFNESS THROUGHOUT THE DEFLECTION RANGE OF THE AXLE WHICH SUBSTANTIALLY CONSTANT STIFFNESS IS GREATER THAN SAID MINIMUM STIFFNESS, THE MAIN LEAF SPRING SYSTEM SUPPORTING THE AXLE CASING FROM A FRAME OF THE VEHICLE, AND THE AUXILIARY SPRING SYSTEM LIKEWISE SUPPORTING THE AXLE CASING FROM SAID FRAME BUT HAVING A VARIABLE STIFFNESS THROUGHOUT THE DEFLECTION RANGE OF THE AXLE WHICH, UNDER SAID TARE LOAD CONDITION, IS NEGATIVE SO AS TO REDUCE THE OVERALL STIFFNESS OF THE SUSPENSION TO SAID MINIMUM VALUE, THE AUXILIARY SPRING SYSTEM COMPRISING A PAIR OF LINKS EXTENDING ONE ON EACH SIDE OF THE AXLE CASING GENERALLY FOREAND-AFT OF THE VEHICLE, A PIVOT MEMBER AT THE INNER END OF EACH LINK CONNECTING THE LINK TO THE AXLE CASING, AND A PIVOT MEMBER AT THE OUTER END OF EACH LINK CONNECTING THE LINK TO SAID FRAME, ONE AT LEAST OF SAID PIVOT MEMBERS ASSOCIATED WITH EACH LINK BEING OF RUBBER AND PROVIDING, UP TO A PREDETERMINED LOADING CONDITION GREATER THAN TARE LOAD, A TORSIONAL REACTION ACTING TO LOAD THE MAIN LEAF SPRING SYSTEM, SAID LINKS BEING DISPOSED HORIZONTALLY IN LINE UNDER SAID TARE LOAD CONDITION AND EACH BEING OF A LENGTH SUCH THAT, UNDER SAID TARE LOAD CONDITION, WHEN THEY ARE HORIZONTALLY IN LINE, EACH LINK IS HELD IN LENGTH WISE COMPRESSION BETWEEN THE AXLE CASING AND SAID FRAME, WHEREBY THE RUBBER PIVOT MEMBERS ARE COMPRESSED LENGTHWISE OF THE LINKS, AND AT SAID FULL BUMP LOAD CONDITION THE LINKS ARE IN TENSION, VERTICAL LOADS ON THE AXLE CASING ABOVE SAID PREDETERMINED LOAD BEING RESISTED BY THE RUBBER PIVOT MEMBERS ACTING IN TORSION AND BY COMPRESSION THEREOF LENGTHWISE OF THE LINKS.