Torsional element for steering valves and spring characteristic improving process

A torsion element for a steering valve, said torsion element comprising:

• a torsionally elastic rod member having axially opposite first and second end areas which are rotatable relative to one another, said rod member having a circumferentially spaced plurality of radially and axially extending indentations adjacent said second end area;
• and
• a generally tubular, torsionally stiff sleeve member encircling said rod member, said sleeve member having axially opposite first and second end portions, said first end portion being fixedly attached to said first end area of said rod member,
• said second end portion of said sleeve member including a circumferentially spaced plurality of radially and axially extending grooves which align with and radially overlie said plurality of indentations in said rod member in a neutral steering condition,
• said second end portion of said sleeve member further including a circumferentially spaced plurality of radial slots which extend axially in parallel with said plurality of grooves in said second end portion, said plurality of slots being circumferentially spaced between said plurality of grooves,
• said plurality of grooves in said sleeve member cooperating with said plurality of indentations in said rod member to exert a radially directed centering force on said rod member upon rotation of one of said end areas of said rod member from the neutral steering condition, the magnitude of the centering force being preset by said plurality of slots in said sleeve member.