US 5,628,496 AGranted

Pneumatic spring

AssigneeAVM, Inc.

InventorJames Chamberlin

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Abstract

A pneumatic counterbalance spring includes a hollow cylinder defining a first internal chamber divided into a compression compartment and an extension compartment by a piston movably mounted in the chamber. The compression compartment contains pressurized gas and a seal assembly mounted on the piston prevents the gas from escaping into the extension compartmint. A piston rod is slibably mounted in the open end of the cylinder and has its inner end connected to the piston. The piston rod includes a hollow portion defining a second internal chamber which is fluidly connected to the compression compartment by a flow passage. As a result, the compression compartment has an effective volume of A+B, where A represents the volume of the compression compartment and B represents the volume of the piston rod internal chamber. This design is advantageous in applications where a low spring rate is desired and where the length of the spring needs to be minimized. A gas permeable insert may be positioned in the flow passage to provide restricted rate flow of gas through the flow passage. Alternatively, a check valve may be provided for providing restricted rate flow of gas through the flow passage during the extension stroke and a tree, by-pass flow of gas through the flow passage during the compression stroke.

Claims21

Dependent claims

A pneumatic spring, comprising:

a hollow cylinder having an open end and a closed end, and defining a first internal chamber;
a piston rod slidable mounted in the open end of the cylinder, the piston rod defining a second internal chamber and having a first end extending into the first internal chamber and a second end projecting from the open end of the cylinder;
a piston slidable positioned in the cylinder and dividing the first internal chamber into a compression compartment adjacent the closed end of the cylinder and an extension compartment adjacent the open end of the cylinder, the volumes of the compression and extension compartments varying in accordance with the position of the piston, the piston being connected to the first end of the piston rod for movement away from the cylinder closed end during an extension stroke and toward the cylinder closed end during a compression stroke;
a predetermined quantity of gas in the compression compartment under a pressure in excess of atmospheric pressure;
a seal assembly mounted on the piston and adapted to prevent gas flow between the compression and extension compartments;
a flow passage extending through the piston between the compression compartment and the second internal chamber and permitting gas flow therebetween;
and
a gas permeable insert of a predetermined porosity positioned in the flow passage and adapted to provide restricted flow rate of gas through the flow passage.

5 more elements

Dependencies are inferred from the claim text.