Suspension system for a tilt cab truck

Claim 1

A suspension system for a tilt cab truck, said suspension system comprising: (a) a plunger ending in a first piston; (b) a cylinder which contains a first chamber having a first end and a second end, said plunger being slidably and sealingly received in the first end of said cylinder and said first piston being received in said first chamber, said first chamber having at least two portions having different cross-sections, a first portion adjacent the first end of said cylinder which receives said first piston in a fashion which permits passage of a working fluid around said first piston and a second portion adjacent the second end of said cylinder which slidably and sealingly receives said first piston; (c) first fluid conduit means for conducting working fluid to and from said first portion of said first chamber; (d) second fluid conduit means for conducting working fluid to and from said second portion of said first chamber comprising a first means of fluid communication leading from said second portion of said chamber to a reservoir for working fluid; and (e) third fluid conduit means for blocking said second fluid conduit means, forming a hydraulic lock, when said first piston has seated itself against the end of said second portion of said first chamber comprising a normally open valve in said first means of fluid communication, said valve being opened by fluid pressure when said first piston enters said second portion of said first chamber, being closed when said first piston is seated against the end of said second portion of said first chamber, and being selectively openable when it is desired to break the hydraulic lock formed when said first piston has seated itself against the end of said second portion of said first chamber.