Oil-type vibration damper

Claim 1

A shock absorber of the oil damper type, for use in automotive vehicles having bodies supported on axles through springs, and capable of damping efficiently both the natural low frequency primary vibrations occurring above the springs and the natural high frequency secondary vibrations occurring beneath the springs, said shock absorber comprising, in combination, a cylinder element; a piston element slidable in said cylinder element, one element being constructed for connection to a vehicle axle and the other element being constructed for connection to a vehicle body; two pressure control valves each mounted on one of said elements; one of said valves constituting a primary valve having high damping characteristics effective to dampen said primary vibrations, and the other of said valves constituting a secondary valve having lower damping characteristics effective to dampen said secondary vibrations; and frequency responsive switching means operatively associated with said secondary valve and operable, responsive to occurrence of said primary vibrations, to render said secondary valve ineffective and operable, responsive to termination of said primary vibrations, to render said secondary valve effective again; said piston element comprising a piston rod formed with an axial duct therein opening into said high pressure chamber, at one end, and opening through a piston, on said piston rod, at the other end; a transverse duct in said piston rod connecting said axial duct to one of said pressure control valves; said switching means comprising a switch valve mechanism including a plungerlike valve member having a sliding fit in said axial duct and movable therealong to open and close said transverse duct; said plungerlike valve member including a pushup piston at its lower end slidable in a cylinder; said valve member being formed with an axial working fluid passage for maintaining communication between said high pressure chamber and a chamber beneath said pushup piston; a working fluid chamber above said pushup piston having a working fluid discharge port; said valve member being formed with a duct for introducing fluid to said pushup piston; either said discharge port or said introducing duct serving to throttle the flow of working fluid; a biasing spring urging said pushup piston to a position in which said plungerlike valve member opens said transverse duct; whereby said one pressure control valve is opened by the throttling effect wheN a change in the pressure in said high pressure chamber is caused by external forces of higher frequency, and said plungerlike valve member is moved upwardly to close said transverse duct when the change in in the pressure in said high pressure chamber is caused by external forces of low frequencies.