Regressive hydraulic damper

Abstract

A damper of shock and vibration. In one embodiment there is a hydraulic damper with a regressive damping characteristic in both compression and extension, such that damping forces decrease with increased stroking velocity within a predetermined range of stroking velocity. Outside of this range, damping forces are progressive, such that the damping force increases with increased stroking velocity. In another embodiment, there is a hydraulic damper with a second, slidable piston within one of the internal chambers defined by the main piston. This secondary piston is spring loaded and hydraulically latchable at either a first position or a second position based on the pressure differential across the main piston.

What is claimed is: 
     
         1 . A hydraulic damper, comprising:
 a first housing defining a cavity for hydraulic fluid;   a first piston slidable within the cavity and dividing the cavity into a first volume and a second volume;   a rod extending from the cavity, said first piston being attached to said rod, said rod including an internal passageway for flow of hydraulic fluid between said first volume and said second volume;   a second housing in fluid communication with the first volume and attached to said rod, said second housing including an internal chamber and a second piston slidable within the chamber between a first position and a second position;   wherein in the first position there is a first flow path for the flow of hydraulic fluid from the first volume through the internal passageway and into the second volume, in the second position there is a second flow path for the flow of hydraulic fluid from the first volume through the internal passageway and into the second volume, and the first flow path is more restrictive than the second flow path.   
     
     
         2 . the damper of  claim 1  wherein said second piston includes a first aperture in the first flow path and the second flow path, said second piston includes a second aperture in the second flow path, and in the first position hydraulic fluid flows through the first aperture and the second aperture is substantially blocked off, and in the second position hydraulic fluid flows through the first aperture and the second aperture. 
     
     
         3 . The damper of  claim 1  which further comprises a spring biasing said second piston to the first position. 
     
     
         4 . The damper of  claim 1  wherein said second piston is in the second position when pressure in the first volume is higher by a predetermined amount than pressure in the second volume. 
     
     
         5 . The damper of  claim 1  wherein said second piston is in the first position when pressure in the second volume is higher than pressure in the first volume. 
     
     
         6 . The damper of  claim 1  wherein said first piston includes a third flow path for the flow of hydraulic fluid from the first volume to the second volume. 
     
     
         7 . The damper of  claim 1  wherein said damper provides a damping force that opposes compression and rebound, and said second piston moves to the second position during rebound. 
     
     
         8 . The damper of  claim 1  wherein said damper provides a damping force that opposes compression and rebound, and said second piston moves to the second position during compression. 
     
     
         9 . The damper of  claim 1  wherein said damper provides a damping force that opposes compression and rebound, and the second flow path is not operable during rebound, and the first flowpath is operable during compression and rebound. 
     
     
         10 . The damper of  claim 1  wherein said damper provides a damping force that opposes compression and rebound, and the second flow path is not operable during compression, and the first flowpath is operable during compression and rebound. 
     
     
         11 . A hydraulic damper, comprising:
 a first housing defining a cavity for hydraulic fluid;   a first piston slidable within the cavity and dividing the cavity into a first volume and a second volume;   a rod extending from the cavity, said first piston being attached to said rod, said rod including an internal passageway for flow of hydraulic fluid between said first volume and said second volume;   a second housing in fluid communication with the first volume and attached to said rod, said second housing including an internal chamber and a second piston slidable within the chamber between a first position and a second position, said second piston providing a flow path for the flow of hydraulic fluid from the first volume through the internal passageway and into the second volume in the second position, said second piston having a surface area; and   a spring biasing said second piston toward the first position;   wherein in the first position a portion of the surface area is exposed to pressure in the first volume and the remainder of the surface area is not exposed to pressure in the first volume, the portion coacting with pressure above a predetermined value in the first volume to move said second piston toward the second position.   
     
     
         12 . The damper of  claim 11  wherein in the second position pressure above the predetermined value in the first volume coacts with the surface area to maintain said second piston in the second position. 
     
     
         13 . The damper of  claim 11  wherein said second housing includes internal walls and the surface area and the internal walls define a third volume, said second housing includes an orifice providing fluid communication between the third volume and the first volume, and said second piston is adapted and configured to discourage flow from the first volume to the third volume when said second piston is in the first position. 
     
     
         14 . The damper of  claim 11  wherein said second housing includes internal walls and the surface area and the internal walls define a third volume, said second housing includes an orifice providing fluid communication between the third volume and the first volume, and the portion of the surface area is substantially the same as the area of the orifice. 
     
     
         15 . The damper of  claim 11  wherein the flow path is a first flow path, said first piston includes a second flow path for the flow of hydraulic fluid from the first volume to the second volume, and the first flow path and the second flow path operate in parallel when hydraulic pressure in the first volume exceeds a predetermined value. 
     
     
         16 . The damper of  claim 11  wherein the flow path is a first flow path, said first piston includes a second flow path for the flow of hydraulic fluid from the first volume to the second volume, and the first flow path and the second flow path operate in parallel when said second piston is in the second position. 
     
     
         17 . The damper of  claim 11  wherein the flow path is a first flow path, said second piston providing a second flow path for the flow of hydraulic fluid from the first volume through the internal passageway and into the second volume in the first position, and the second flow path is more restrictive than the first flow path. 
     
     
         18 . The damper of  claim 11  wherein the remainder of the surface area is greater than the portion of the surface area. 
     
     
         19 . The damper of  claim 11  wherein the flow path is a first flow path, and said first piston includes a second flow path for the flow of hydraulic fluid from the first volume to the second volume. 
     
     
         20 . An apparatus for a hydraulic damper having a rod with an internal flowpath for hydraulic fluid and a threaded end, comprising:
 a housing including a first part coupled to a second part and defining an internal chamber therebetween, said housing being adapted and configured for threadably coupling to the rod;   a piston slidable within the internal chamber, said piston including an aperture adapted and configured to be in flow communication with the internal flowpath; and   a spring biasing said piston toward one end of the chamber.