Hydraulic power steering gear with noise attenuation

In a hydraulic power steering apparatus having:

• a rotatable input member;
• a rotatable output member;
• a housing supporting said input member and said output member for rotation about an axis relative to each other;
• and
• hydraulic valve means comprising a valve core and a valve sleeve;
• said valve core having a cylindrical surface and being supported in said housing to rotate with said input member relative to said output member and said valve sleeve;
• said valve sleeve being supported in said housing to rotate with said output member relative to said input member and said valve core, said valve sleeve having a cylindrical surface adjoining said cylindrical surface of said valve core;
• the improvement comprising:
• means for attenuating noise caused by vibrations of said valve core relative to said valve sleeve, said noise attenuating means comprising an elastomeric damping ring extending circumferentially between said adjoining cylindrical surfaces of said valve core and said valve sleeve, said damping ring being compressibly deformed by said valve core and said valve sleeve in an interference fit between said adjoining cylindrical surfaces, said interference fit continuously maintaining frictional contact of said damping ring with said adjoining cylindrical surfaces whenever said valve core and said valve sleeve rotate relative to each other;
• said frictional contact providing static friction which is great enough to cause said damping ring to undergo cyclic deformation in shear between said adjoining cylindrical surfaces when said vibrations occur, said static friction thus being great enough to cause said damping ring to experience hysteretic energy loss which dissipates energy of said vibrations;
• and
• said damping ring being formed of an elastomeric material having a loss tangent of at least 0.5 when subjected to vibrations at frequencies of approximately 100-300 Hertz, whereby said damping ring experiences said hysteretic energy loss in an amount which substantially eliminates noise caused by said vibrations at said frequencies.