Hydrapneumatic suspension unit and valving structure

A hydrapneumatic suspension unit, comprising:

• (a) a first chamber,
• (b) a piston movable longitudinally in the first chamber,
• (c) a piston rod extending from one side of the piston through one end of the first chamber,
• (d) the piston end of the chamber containing an hydraulic liquid, there being no restricted flow of said liquid to opposite sides of the piston to cause restricted movement of the piston,
• (e) a second chamber,
• (f) movable separator means in the second chamber dividing the latter into a first compartment containing the same liquid as the first chamber and a second compartment containing compressible means for resiliently resisting movement of the separator means in the direction of the second compartment,
• (g) check valve means between the piston end of the first chamber and first compartment for permitting rapid flow of liquid only from the first chamber to the first compartment,
• (h) damper valve means between the piston end of the first chamber and the first compartment for permitting restricted flow of liquid from the first compartment to the first chamber,
• (i) bypass valve means between the piston end of the first chamber and the first compartment for permitting flow of liquid from the first compartment to the first chamber at a rate substantially greater than the rate of flow through the damper valve means,
• (j) one end of the bypass valve means communicating with the piston end of the first chamber and the liquid contained therein, and
• (k) resilient means engaging the end of the bypass valve means opposite the end communicating with the first chamber and providing a reference pressure independent of the liquid pressure in the first compartment and the only pressure opposing the liquid pressure in the first chamber, whereby when the liquid pressure in the first chamber is lower than the reference pressure provided by the resilient means the bypass valve means is moved to open communication between the first chamber and first compartment, and when the liquid pressure in the first chamber is higher than the reference pressure provided by the resilient means the bypass valve means is moved to close communication between the first chamber and first compartment.