Piston guide and seal for dual-tube hydropneumatic shock absorber

Claim 1

A hydropneumatic shock absorber comprising: an outer tube having upper and lower ends and centered on an upright axis; an inner tube inside the outer tube, forming therewith an outer gas/liquid chamber, having upper and lower ends, and itself internally forming an inner chamber; a piston rod inside the inner tube in the inner chamber and generally coaxial with the tubes; a body of liquid filling the inner chamber and partially filling the outer chamber; a piston carried in the inner chamber on the rod, radially outwardly engaging the inner tube, and subdividing the inner chamber into an upper and a lower compartment; a foot valve at the lower ends between the lower compartment and outer chamber and permitting limited liquid flow therebetween; a rigid centering washer having an outer periphery engaged against the upper end of the outer tube and an axially extending ridge engaged directly radially against the upper end of the inner tube; a flexible annular outer lip on the washer, engaged radially against the upper end of the inner tube, and bearing flexibly thereagainst in a direction opposite the direction in which pressure in the upper compartment is effective against the outer lip, whereby the outer lip permits limited fluid flow from the upper compartment to the outer chamber but blocks opposite flow; a flexible annular inner seal underneath the ridge on the washer and engaged radially inwardly against the piston rod, whereby the washer and inner seal upwardly close off the inner chamber; an outer seal on the washer engaged against the outer tube, whereby the washer and outer seal upwardly close off the outer chamber; an element forming in the inner chamber an upwardly open pocket down into which the inner seal projects; and structure forming a passage from the inner chamber axially past the pocket, whereby gas collecting in the inner chamber below the pocket can bleed up past the pocket and then pass by the lip into the outer chamber.