Automatically recharging air spring

An air spring assembly to assist in movement of a movable member including a cylinder formed by a housing having a chamber therein, cap means for closing opposite ends of said cylinder and sealing said chamber from ambient conditions, a piston, a rod extending through one of said cap means to a first end outside said chamber, means attaching the second end of said rod to said piston so that said piston and rod move conjointly upon relative movement of said housing and piston through each complete cycle of movement between limit positions, said piston serving to divide said chamber into a first subchamber on one side of said piston and a second subchamber on the other side of said piston, a first checkvalve means connected between said first subchamber and the atmosphere, and a second checkvalve means in said piston and connecting said first and second subchambers, said second checkvalve means and said piston cooperating with said chamber in said housing to retain gas in said second subchamber under pressure elevated with respect to the pressure in the first subchamber under normal circumstances, said first and second checkvalve means being automatically operable for both pressurizing said second subchamber to a pressure level to balance the force to be exerted on said movable member and restoring pressure to said second subchamber previously charged in the maintenance of said pressure level under circumstances of leakage of pressure from said second subchamber, initial pressurization of said second subchamber and the restoration of pressure in said second subchamber being carried out by flow of a compressible fluid from said first to said second subchamber through said second checkvalve upon movement of said piston in one direction with respect to said housing through at least one cycle of movement, and means for connecting one of said housing and rod at first end to a support and the other of said housing and rod to said movable member requiring assistance in movement by one of a pushing and a pulling force.