Gas spring with automatic locking mechanism

A gas spring, comprising:

• (a) a cylinder member having an axis of elongation, a closed, axially inner end wall and an annular, axially outer end wall and defining therein a sealed cavity, said cylinder including means defining a first transverse cross section over an axially inner portion of said cavity and means defining a second, smaller transverse cross section over an axially outer portion of said cavity;
• (b) a piston rod member received through said annular outer end wall in sealing engagement therewith for axial movement within said cavity;
• (c) first and second axially spaced piston means carried by said piston rod within said cavity, with said first piston means being located axially inwardly of said second piston means, for movement between an axially inner position at which at least said second piston means is located within said axially inner cavity portion and an axially outer position at which said first piston means is located within said axially inner cavity portion and said second piston means is located within said axially outer cavity portion;
• (d) said first and second piston means having transverse cross sections which match the transverse cross sections of said axially inner and axially outer cavity portions, respectively, for slidable sealing engagement therewith, said means defining said second transverse cross section over said axially outer cavity portion including an annular member located within said cylinder member, said annular member defining internally thereof said second transverse cross section and having an axial length sufficient to extend axially beyond said second piston means in both axial directions when said second piston means is at said axially outer position;
• (e) a fluid within said cavity;
• (f) means for permitting fluid flow from one side of said first piston means to the other when said first piston means moves axially in said cavity;
• (g) first flow control means for controlling fluid flow from one side of said second piston means to the other when said second piston means is located within said axially outer cavity portion, said first flow control means being responsive, when said second piston means is in said axially outer cavity portion, to (1) axially inward movement of said second piston means for restricting fluid flow from the axially inner side to the axially outer side of said second piston means and to (2) axially outward movement of said second piston means for permitting fluid flow from the axially outer side to the axially inner side of said second piston means;
• and
• (h) second flow control means for controlling fluid flow from the axially inner side to the axially outer side of said second piston means when said second piston means is located in said axially outer cavity portion, said second flow control means including (1) one or more passages in the external wall of said annular member by-passing said second piston means and connecting that part of the cavity inward of said annular member to that part of the cavity outward of said annular member and (2) valve means normally biased to a closed position, at which fluid flow through said one or more passages is prevented, said valve means being responsive, when said second piston means is in said axially outer cavity portion, to the application of sufficient axially inward force to the piston rod member to overcome the biasing force of said valve means to move said valve means to an open position, at which fluid flow through said one or more passages from the axially inner side to the axially outer side of said second piston means is permitted;
• (i) whereby when moved to said axially outer position said piston rod member will remain in said axially outer position until an external force sufficient to overcome the biasing force of said valve means is applied to the piston rod member to move it inwardly of said axially outer position.