Patent Application
20070158154
The subject invention relates to piston assembly for a gas spring or damper that includes a resilient member that reduces shuttling of piston components between extension and compression positions.
Gas spring assemblies and dampers are used to control movement of one component relative to another component. A damper or gas spring assembly is used to control movement of a movable vehicle component relative to a fixed vehicle component. The damper or gas spring assembly is moveable between a fully extended position and a fully compressed position. A gas spring assembly assists an operator with movement of the movable vehicle component. A damper is used to dampen input loads to a vehicle chassis.
Gas springs and dampers each include a rod and piston assembly that is received within a cylinder. One rod end is coupled to the piston assembly to move the piston assembly back and forth within the cylinder. An opposite rod end is mounted to one of the movable vehicle component or the fixed vehicle component. The cylinder is mounted to the other of the movable vehicle component or the fixed vehicle component. The piston includes multiple orifice plates that cooperate with washers to restrict fluid flow during compression and extension to dampen or assist movement depending on a desired application.
In one known configuration, the piston assembly comprises a dual dampening piston that includes first and second orifice plates that are separated by a spacer. Located between the first and second orifice plates is an o-ring positioned between first and second washers. When compressed or extended, friction on the o-ring forces one of the first and second washers to move axially against a respective one of the first and second orifice plates depending upon direction of movement. This provides a restrictive flow path in an opposite direction to the direction of movement.
One disadvantage with this traditional configuration is that a dead band of operation occurs as the first and second washers and o-ring shuttle back and forth between the first and second orifice plates. This “slop” reduces the operating efficiency of the piston assembly.
Thus, there is a need for a piston assembly that eliminates slop between internal piston components as the rod moves the piston assembly back and forth between extended and retracted positions.
A piston assembly includes first and second orifice plates that are axially spaced apart from each other. First and second rings made from a low-friction material are positioned between the first and second orifice plates. A resilient member reacts between the first and second rings. The piston assembly could be utilized in a gas spring assembly or a damper, each of which includes a cylinder. The piston assembly is mounted within an internal cavity of the cylinder and is connected to a rod. The rod moves the piston assembly back and forth within the cylinder between extension and compression positions.
A biasing force exerted by the resilient member on the first and second rings eliminates dead-band operation as the piston assembly moves between extension and compression. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
The damper or gas spring assembly 10 is typically used to control movement between a fixed member and a movable member. A first connector 22 is attached to the rod 14 and a second connector 24 is attached to the cylinder 12. One of the first 22 and second 24 connectors is connected to one of the fixed member and movable member. The other of the first 22 and second 24 connectors is connected to the other of the fixed member and the movable member.
The piston assembly 16 includes a first orifice plate 30 and a second orifice plate 32 that are separated from each other by a spacer 34. Each of the first 30 and second 32 orifice plates includes at least one orifice hole 35, schematically shown, to facilitate fluid flow as needed. In the example shown the orifice holes 35 are formed at side surface of the first 30 and second 32 orifice plates, however, the shape, configuration, and location of the orifice holes 35 can vary depending on specific applications. The subject piston assembly 16 can be used with any configuration of orifice holes 35. The spacer 34 is mounted on a reduced diameter portion 36 of the rod 14. A rivet 38 is used to secure and hold the first orifice plate 30, second orifice plate 32, and spacer 34 together on the rod. The rivet 38 can be integrally formed with the rod 14 or can be installed as a separate piece.
One end 40 of the spacer 34 holds the first orifice plate 30 against an end face 42 of the rivet 38. An opposite end 44 of the spacer 34 holds the second orifice plate 32 against a shoulder portion 46 of the rod 14. The spacer 34 maintains a fixed distance between the first 30 and second 32 orifice plates.
A first ring 50 is positioned adjacent the first orifice plate 30. A second ring 52 is positioned adjacent the second orifice plate 32. Both the first 50 and second 52 rings are positioned axially between the first 30 and second 32 orifice plates. The first 50 and second 52 rings are formed as solid bands of a low-friction material, such as polytetrafluoroethylene (PTFE) or Teflon®, for example. One example of this type of ring is a Rulon® ring.
The first 50 and second 52 rings each include an outer peripheral edge 54 that is in abutting, sliding contact with an inner wall surface 56 of the cylinder 12. A resilient member 60, shown schematically in
Optionally, the piston assembly 16 could also include first 70 and second 72 washers positioned between the first 30 and second 32 orifice plates, as shown in
During compression, the first washer 70 and first ring 50 are forced away from the first orifice plate 30 producing a non-restrictive flow path on the rivet side. On the opposite side of the resilient member 60, the second ring 52 and second washer 72 are forced against the second orifice plate 32 producing a restricted flow path through the second orifice plate 32.
The piston assembly 16 could be utilized in various different applications to reduce shuttling of piston components including gas springs, dampers, shock absorbers, etc. Further, the piston assembly 16 could also be used in a hydraulic cylinder or fluid flow application to reduce free play.
Preferably, the piston assembly 16 is used in a damper application for a lawn mower 150 shown in
The piston assembly 16 could also be used in a damper assembly 90 as shown in
The piston assembly 16 can also be used in a gas spring in a vehicle 80 as shown in
It should be understood that while the piston assembly 16 of
In either configuration, i.e. with or without the first 70 and second 72 washers, the resilient member 60 forces one of the first 50 and second 52 rings against a respective one of the first 30 and second 32 orifice plates (depending upon direction of movement). By forcing the rings against the orifice plates, a dead-band operation area normally caused by shuttling of internal piston components is eliminated.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
