Piston rod seal for adjustable pneumatic spring

Abstract

In a pneumatic spring of adjustable length, the piston rod is sealed to the cylinder by an annular sealing disc stressed in compression between the inner cylinder wall and a rigid, tubular projection on the radial end wall of the cylinder through which the piston rod extends outward of the cylinder cavity. The sealing disc is axially longer than the projection so that it extends inward of the cavity beyond the projection and carries an annular sealing lip engaging the piston rod only under the fluid pressure in the cylinder cavity, but practically fully relieved by the annular projection from the compressive stresses.

What is claimed is: 
     
       1. A pneumatic spring comprising: a. a cylinder having an axis and bounding a cavity therein;   b. a piston axially slidable in said cavity and separating two compartments of said cavity;   c. valve means operatively interposed between said compartments;   d. valve operating means accessible outside said cavity for moving said valve means toward and away from an open position in which said valve means connects said compartments;   e. a piston rod fixedly fastened to said piston and axially extending therefrom outward of said cavity, said cylinder including an end wall transverse to said axis and formed with an aperture for passage of said piston rod;   f. fluid filling said cavity; and   g. sealing means interposed between said end wall and said piston rod for preventing escape of fluid through said aperture, said sealing means including: 1. a rigid tubular member substantially coaxially enveloping said piston rod with sufficient clearance to permit free axial movement of said piston rod through said tubular member,   2. a sealing member of resilient material formed with an opening therethrough, said .[.tubular.]. .Iadd.sealing .Iaddend.member having a first axial portion enveloping said rigid tubular member and a second axial portion extending axially beyond said tubular member in a direction inward of said cavity,   3. said second portion having a radially outer, axially extending face radially spaced from said cylinder and exposed to said fluid,   4. the radially innermost part of said second portion constituting a lip portion, said lip portion being the only part of said sealing member frictionally engaging said piston rod.     
     
     
       2. A spring as set forth in claim 1, wherein said lip portion is axially shorter than said face of said second portion. 
     
     
       3. A spring as set forth in claim 1, wherein said tubular member is fixedly fastened to said cylinder. 
     
     
       4. A spring as set forth in claim 1, wherein said tubular member is fixedly fastened to said end wall. 
     
     
       5. A spring as set forth in claim 4, wherein said lip portion is axially spaced from said tubular member. 
     
     
       6. A spring as set forth in claim 4, wherein said cylinder member has an inner axial face extending about said axis in a closed loop, said sealing member having a circumferential portion engaging said inner face, and said first portion being held under compressive radial stress between said inner .[.wall.].  .Iadd.face .Iaddend.and said tubular member. 
     
     
       7. A spring as set forth in claim 6, wherein said sealing member, when in the relaxed condition, has an annular rib portion radially adjacent said circumferential portion and projecting from said circumferential portion in said direction. 
     
     
       8. A spring as set forth in claim 6, wherein said lip portion is axially offset from said circumferential portion in a direction inward of said cavity. 
     
     
       9. A spring as set forth in claim 8, further comprising an annular partition member fixedly fastened in said cavity and axially interposed between said piston and said end wall, said partition member separating a chamber in said cavity from one of said compartments, said fluid in said compartments essentially consisting of a gas, and the fluid in said chamber essentially consisting of a liquid. .Iadd. 
     
     
       10.  A pneumatic spring comprising: a. a cylinder having an axis and bounding a cavity therein; 1. said cylinder having an inner axial face extending about said axis in a closed loop;     b. a piston axially slidable in said cavity and separating two compartments of said cavity;   c. a piston rod fixedly fastened to said piston and axially extending therefrom outward of said cavity, said cylinder including an end wall transverse to said axis and formed with an aperture for passage of said piston rod;   d. fluid filling said cavity; and   e. sealing means interposed between said end wall and said piston rod for preventing escape of fluid through said aperture, said sealing means including:   
     
     
       1.  a rigid tubular member substantially coaxially enveloping said piston rod with sufficient clearance to permit free axial movement of said piston rod through said tubular member, 2. a sealing member of resilient material formed with an opening therethrough, said sealing member having a circumferential portion engaging said inner axial face and a first axial portion enveloping said rigid tubular member and held under compressive radial stress between said inner axial face and said tubular member, said sealing member having a second axial portion extending axially beyond said tubular member in a direction inward of said cavity,   3. said second portion having a radially outer, axially extending face radially spaced from said cylinder and exposed to said fluid,   4. the radially innermost part of said second portion constituting a lip portion, said lip portion being the only part of said sealing member frictionally engaging said piston rod and being axially spaced from said tubular member,   5. said sealing member, when in the relaxed condition having an annular rib portion radially adjacent said circumferential portion and projecting from said circumferential portion in said direction. .Iaddend..Iadd. 11. A pneumatic spring comprising:   a. a cylinder having an axis and bounding a cavity therein; 1. said cylinder having an inner axial face extending about said axis in a closed loop;     b. a piston axially slidable in said cavity and separating two compartments of said cavity;   c. a piston rod fixedly fastened to said piston and axially extending therefrom outward of said cavity, said cylinder including an end wall transverse to said axis and formed with an aperture for passage of said piston rod;   d. fluid filling said cavity;   e. sealing means interposed between said end wall and said piston rod for preventing escape of fluid through said aperture, said sealing means including: 1. a rigid tubular member substantially coaxially enveloping said piston rod with sufficient clearance to permit free axial movement of said piston rod through said tubular member,   2. a sealing member of resilient material formed with an opening therethrough, said sealing member having a circumferential portion engaging said inner axial face and a first axial portion enveloping said rigid tubular member and held under compressive radial stress between said inner axial face and said tubular member, said sealing member having a second axial portion extending axially beyond said tubular member in a direction inward of said cavity,   3. said second portion having a radially outer, axially extending face radially spaced from said cylinder and exposed to said fluid,   4. the radially innermost part of said second portion constituting a lip portion axially offset from said circumferential portion in a direction inward of said cavity, said lip portion being the only part of said sealing member frictionally engaging said piston rod and being axially spaced from said tubular member; and     f. an annular partition member fixedly fastened in said cavity and axially interposed between said piston and said end wall, 1. said partition member separating a chamber in said cavity from one of said compartments,   2. said fluid in said compartments essentially consisting of a gas, and the fluid in said chamber essentially consisting of a liquid. .Iaddend..Iadd. 12. A pneumatic spring comprising:     a. a cylinder having an axis and bounding a cavity therein;   b. a piston axially slidable in said cavity and separating two compartments of said cavity;   c. a piston rod fixedly fastened to said piston and axially extending therefrom outward of said cavity, said cylinder including an end wall transverse to said axis and formed with an aperture for passage of said piston rod;   d. fluid filling said cavity; and   e. sealing means interposed between said end wall and said piston rod for preventing escape of fluid through said aperture, said sealing means including:   
     
     
       1.  a rigid tubular member substantially coaxially enveloping said piston rod with sufficent clearance to permit free axial movement of said piston rod through said tubular member, 2. a sealing member of resilient material formed with an opening therethrough, said sealing member having a first axial portion enveloping said rigid tubular member and a second axial portion extending axially beyond said tubular member in a direction inward of said cavity,   3. said first axial portion having an outer circumferential face engaging the inner wall of the cylinder and, when in the relaxed condition, an annular rib radially adjacent said outer circumferential face and projecting in said axially inward direction,   4. means coacting between the cylinder and said annular rib to hold said first axial portion in compressive radial stress between said cylinder inner wall and said tubular member,   5. said second axial portion having a radially outer, axially extending face radially spaced from said cylinder inner wall and exposed to said fluid, and   
     
     
       6.  the radially innermost part of said second portion constituting a lip portion, said lip portion being the only part of said sealing member frictionally engaging said piston rod. .Iaddend..Iadd. 13. A pneumatic spring including a cylinder having a closed end and an open end, a piston slidingly received within the cylinder, a piston rod connected to the piston and extending through the open end of the cylinder, a working fluid under pressure in the cylinder for coacting with the piston, and means interposed between the cylinder and the piston rod at said open end for sealing against loss of said working fluid, wherein the improvement in said sealing means comprises: a. a rigid tubular member substantially coaxially enveloping said piston rod with sufficient clearance to permit free axial movement of said piston rod through said tubular member;   b. a sealing member of resilient material formed with an axial opening therethrough, said sealing member having a first annular portion enveloping said rigid tubular member and a second annular portion of reduced outer diameter extending axially inwardly from said first annular portion, said second annular portion having a radially outer, axially extending face radially spaced from the inner wall of the cylinder and exposed to the pressure of said working fluid, said second annular portion terminating at the axially innermost end thereof in a lip portion which extends radially inwardly towards and engages said piston rod, said lip portion being the only part of said sealing member frictionally engaging said piston rod;   c. means for compressing said first annular portion of said sealing member between the inner wall of the cylinder and said tubular member; and   d. means defining a lubricating chamber axially inwardly of said sealing member, said chamber being open to said sealing member and to said piston rod and containing a lubricating fluid for lubricating said piston rod and for transmitting the pressure of said working fluid to said second annular portion of the sealing member. .Iaddend..Iadd. 14. A spring as set forth in claim 13, wherein said lubricating fluid comprises a liquid and said working fluid comprises a gas, whereby said sealing member seals against the leakage through said open cylinder end of a liquid notwithstanding that the working fluid is a gas. .Iaddend..Iadd. 15. A spring as set forth in claim 15, wherein the radially inner end of said lip portion tapers axially towards the piston rod so as to frictionally engage the piston rod along only an axially narrow interface..Iaddend.