Suspension assemblies for vehicles

Claim 1

A vehicle hydro-pneumatic suspension assembly comprising an hydraulic suspension unit of the self-levelling type in combination with a pressure chamber containing air or other gas for supporting the load on a wheel, wherein said unit comprises a cylinder in communication with said pressure chamber, a closure for one end of said cylinder, a piston rod assembly comprising a piston adapted to work in said cylinder, and a piston-rod carrying said piston and adapted to work through said closure, an inlet port for connection to a source of high pressure liquid, an outlet port for connection to a reservoir for liquid, a spool valve responsive to the position of said piston rod assembly for controlling communication between said inlet port and said pressure chamber and between said pressure chamber and said outlet port to maintain the length of the unit at a predetermined value irrespective of the load, and damping means to delay response of said spool valve to movement of said rod assembly, wherein said spool valve comprises a spool, and said cylinder has a bore in which said spool works, and wherein an axial rod located in said cylinder has a first end which carries said spool and a second end, spaced abutments being provided at said second end of said axial rod and at an end of said piston rod remote from said piston, retainers being located in abutment with said abutments, and a spring housed within said piston rod being engaged at opposite ends between said retainers, said spring being caged when said spool is in a neutral position in which both said ports are closed, extension of the unit from said neutral position uncaging the end of said spring which is adjacent to said spool so that said spool can be moved by said axial rod in a corresponding direction to open said outlet port in the event of a decrease in loading, and contraction of said unit from said neutral position uncaging the end of said spring remote from said spool so that said spool can be moved by said axial rod in a corresponding direction to open said inlet port in the event of an increase in loading.