US3787019A

US3787019A - Supporting element of adjustable length

Info

Publication number: US3787019A
Application number: US00240646A
Authority: US
Inventors: H Freitag
Original assignee: Stabilus Industrie und Handels GmbH
Current assignee: Stabilus Industrie und Handels GmbH
Priority date: 1971-04-06
Filing date: 1972-04-03
Publication date: 1974-01-22
Anticipated expiration: 1991-01-22
Also published as: FR2132491B1; GB1335323A; DE2116699A1; FR2132491A1; JPS5521209B1

Abstract

A normally upright, telescopically adjustable, supporting element, such as a leg for a stool, has a cylinder whose cavity is axially divided into two chambers by a partition. The lower chamber is liquid-filled, the upper chamber contains liquid under the pressure of a gas cushion, and the two chambers may be connected by a valve in the partition. The position of a plunger axially projecting from the lower chamber is generally determined by the amount of non-compressible liquid in the lower chamber, but limited axial movement is made possible by a gas cell partly bounded by the plunger and otherwise by a sealing member separating the gas in the cell from the liquid in the lower chamber.

Description

United States Patent 91 Freitag 1 SUPPORTING ELEMENT OF ADJUSTABLE LENGTH [75] Inventor: Herbert Freitag, Koblenz-Lutzel,

Germany [73] Assignee: Stabilus lndustrie und Handelsgesellschatt MBl-l, Koblenz-Neuendorf, Germany [22] Filed: Apr. 3, 1972 [21] Appl. No.: 240,646

[58] Field of Search 248/399, 400, 404, 188.2, 248/188.8, 188.3, 354 H; 297/347; 188/314, 322

[56] References Cited UNITED STATES PATENTS 2,042,443 5/1936 Buckstone 248/404 3,142,156 7/1964 Mills et a1 248/354 l-l 3,163,262 12/1964 Allinquant 188/314 3,388,883 6/1968 Axthamrner et a1. 248/l88.2

[11] 3,787,019 1451 Jan.22, 1974 3,656,593 4/1972 Bauer 248/354 H FORElGN PATENTS OR APPLlCATlONS Primary ExaminerMarion Parsons, J r.

[57] ABSTRACT A normally upright, telescopically adjustable, supporting element, such as a leg for a stool, has a cylinder whose cavity is axially divided into two chambers by a partition. The lower chamber is liquid-filled, the upper chamber contains liquid under the pressure of a gas cushion, and the two chambers may be connected by a valve in the partition. The position of a plunger axially projecting from the lower chamber is generally determined by the amount of non-compressible liquid in the lower chamber, but limited axial movement is made possible by a gas cell partly bounded by the plunger and otherwise by a sealing member separating the gas in the cell from the liquid in the lower chamber.

10 Claims, 3 Drawing Figures PATENTED JAN 2 2 I974 SHEET 2 0F 2 This invention relates to telescopically adjustable supporting elements, and particularly to improvements in a supporting element whose principal elements are a cylinder partly filled with liquid and a plunger axially projecting from the cylinder.

It is known to provide the cylinder of such an element with two chambers of which one is filled with liquid and receives an axially terminal portion of the plunger whereas the other contains a reserve of liquid. When it is desired to change the effective length of the supporting element, liquid is transferred between the chambers to expel or to retract the plunger. Because the liquid is practically incompressible, a supporting element of the type described is rigid in an axial direction unless a cushion of compressed gas is provided in pressure transmitting relationship with the liquid receiving the plunger. Such a known modification of the basic supporting element makes the construction of the element rather complex and costly, and makes it very difficult to set the element to a desired precise length.

A basic object of this invention is the provision of a supporting element of variable length which resiliently resists axial stress with a force independent of the effective length of the element, and thus permits the length of the element under a fixed load to be set with great precision prior to loading.

Another object is the provision of such a resilient support which is of simple and rugged construction and thus capable of long, reliable service while permitting manufacture at low cost.

With these and other objects in view, as will hereinafter become apparent, the invention provides a supporting element in which the cavity of a cylinder is axially divided into two chambers by a fixed partition. A valve operatively interposed between'the chambers may be moved between an open position and a closed position by an operating mechanism accessible outside the cylinder cavity.

A first one of the chambers contains an amount of gas under super-atmospheric pressure and a first body of liquid in pressure-transmitting relationship. A plunger is axially movable in the cylinder and has respective terminal portions in the second chamber and outside the cylinder. Yieldably resilient means bias the plunger outward of the cylinder. Although a second body of liquid fills the remainder of the second chamber and communicates with the first body only in the open position of the valve, the yieldably resilient means permit limited movement of the plunger inward of the second chamber when the valve is in its closed position.

Additional features of this invention and many of the attendant advantages thereof will readily be appreciated as the same becomes better understood from the following detailed description of preferred embodiments when considered in connection with the appended drawing in which:

FlG. 1 shows an adjustable stool leg of the invention in fragmentary elevational section; and

FlGS. 2 and 3 show modifications of the device of FIG. 1 in respective corresponding views.

Referring now to the drawing in detail, and initially to FIG. 1, there is seen the single, adjustable leg of a stool, not otherwise shown. An upper portion of the leg is formed essentially by a tubular sheet-metal cylinder 12, and the lower portion by a plunger 1 coaxially projecting from the radial bottom wall 2 of the cylinder. The plunger 1 movably enters the cylinder through a central opening of the bottom wall 2 in which it is sealed by an annular packing 3 held in position by a cylindrical spacer 4. The spacer 4 is axially secured by an internal, annular shoulder on the cylinder 12 corresponding to a groove 4a rolled into the outer cylinder face.

The radial top wall of the cylinder 12 is formed by a fixed plug 114 projecting outward of the cylinder and externally threaded over much of its projecting length for assembly with the seat of thestool by means of a suitable connector, not shown. A rod 13 passes axially through a central bore in the plug 14 and carries a seal ing ring 23 in the bore. A transverse bar 13a permits the end portion of the rod 13,accessible outside the cavity of the cylinder 12, to be moved axially.

. The cylinder cavity is divided axially into an upper chamber and a lower chamber by a partition 10 held in a fixed axial position between two internal shoulders of the cylinder wall corresponding to rolled, circumferential grooves 18 on the outer cylinder face. The partition 10 is sealed to the cylinder 12 by a ring 19. A central bore in the partition 10 receives the lower end portion of the rod 13 with ample clearance, but a resilient ring 20 partly retained in a circumferential groove of the rod forms a valve which closes the conduit in the partition 10 when in the illustrated position and seals the two chambers of the cylinder cavity from each other.

Outward movement of the rod13 from the illustrated position in thecylinder 12 is prevented by a washer 21 on the free inner end of the rod which abuttingly engages the lower radial face of the partition 10. When the rod 13 is pushed inward of the cylinder cavity, the valve ring 20 enter the lower cylinder chamber and permits fluid to flow through the annular conduit around the rod 13 in the bore of the partition 10. The upper chamber holds a body of liquid 1 1 whose free, horizon tal surface is in direct pressure-transmitting contact with an amount of a gas 22 under a pressure higher than atmospheric pressure. The gas fills the remainder of the first chamber.

The lower cylinder chamber is provided with a piston 8 which is axially movable and divides the chamber into two

compartments

5, 9 communicating through throttling passages 15 in the piston 8 and as completely filled with another body of liquid as is possible. Any gas that may be present initially in the lower cylinder chamber ultimately makes its way to the gas 22 in the upper chamber.

The piston 8 is axially fastened on the tubular upper end of the plunger 11 between two integral shoulders of the latter. The cylindrical, blind bore of the plunger 1 is sealed from the liquid in the upper compartment 9 of the lower cylinder chamber by a cylindrical plug 7 carrying a resilient sealing ring 17 to retain a body of highly compressed gas in the cell 6 axially bounded in the plunger bore by the plug '7 and the closed end of the bore. The plug 7 is normally held by the gas in the cell 6 against a spring washer 16 which prevents ejection of the plug from the plunger 1.

As long as the resilient valve ring 20 is in the illustrated position, the length of the illustrated support element when free from an applied load is precisely determined by the combined amount of incompressible liquid in the

compartments

5,9. The plug 7 abuts against the washer l6, and the plunger 1 cannot be pulled outward of the cylinder by a force not capable of causing cavitation in the liquid below the partition 10..

When an axial load is applied to the support element, pressure is transmitted from the plunger 1 to the liquid in the compartments 5', 9, the plug 7, and the compressed gas in the cell 6. The plunger 1 can move inward of the cylinder 12 to the extent that the applied force can drive the plug 7 inward of the cell 6 and further stress the gas whose reaction to a load of known magnitude is precisely predictable, and may be chosen by selecting the dimensions of the apparatus and the pressure of the gas. The stress in the gas is partly relaxed during outward movement of the plunger 1, and such relaxation is limited by abutting engagement of the plug 7 by the washer 16. The resiliency of the support element is entirely independent of its effective length and the amount of liquid in the

compartments

5, 9. i

The latter amount controls the overall length of the element. if this length is to be changed, the valve ring 20 is moved to its open position by means of its operating rod 13, and liquid is permitted to flow downward through the partition 10 under the pressure of the gas 22, or is forced to flow upward through the partition under a compressive, external force applied to the cylinder 12 and the plunger 1. Too sudden a length change is prevented by the reduced flow section of the throttling passages 15. The piston 8 also guides the plunger 1 and the plug 7 on the plunger during their joint axial movement. The valve ring is returned manually to the illustrated, closed position as soon as the element has reached the desired increased or decreased length.

The pressures of the gas 22 in the first cylinder chamher and of the gas in the cell 6 are chosen so that the plug 7 remains in the illustrated position of abutment against the spring washer 16 when the valve ring 20 is in its open position, that is, the force exerted by the gas in the cell 6 on the plunger 1 and tending to shift the plunger outward of the cylinder 12 must always be greater than the corresponding force of the gas 22 transmitted to the plunger by-the liqud ll. Under these conditions, the volume of the cell 6 remains constant at its maximum value while the valve in the partition 10 is open during adjustment of element length, and the adjusted length is not changed after closing of the valve by volume changes of the cell 6.

The modified stool leg shown in H6. 2 is identical with that described above in detail with reference to FIG. 1 except as specifically stated hereinbelow.

The plunger 1 is a solid piece of metal of circular cross section. it passes through an annular bottom wall 2 provided with inner and outer sealing rings 3a, 3b. The piston 8' slidably engages the wall of the cylinder 12 and also the plunger 1' and is provided with inner and

outer sealing rings

25, 26, and with throttling passages 15. A container 24 having-the shape of an inverted cup is fixedly fastened to the piston 8' in a manner not explicitly shown, and its rim is in fluid-tight engagement with the radial top face of the piston. The upper terminal portion of the plunger 1 passes movably through the central opening of the piston 8' into a cell 6 within the container 24, filled with a gas under high pressure as described above. A coaxial split ring 29 partly received in a groove of the plunger 1' abuts against a shock absorbing ring 27 on the piston 8' in the illustrated relative position of piston and plunger, and a shock absorbing pad 28 on the bottom of the cupshaped container 24 in the cell 6' reduces noise when the plunger 1' moves to the non-illustrated terminal position of its stroke relative to the container 24.

The valve operating rod 13 differs from the aforedescribed rod 13 by beng provided with an annular abutment 35 limiting movement of the rod inward of the cylinder 12, and by being sealed to the fixed, threaded plug 14' constituting the radial top wall of the cylinder by a packing 23a recessed in the plug 14' and movably engaging the smooth cylindrical surface of the rod 13'. r

Under normal operating conditions, when the conduit in the partition 10 is blocked, a load axially applied to the supporting element and sufficient to overcome the resistance of the compressed gas in the cell 6 can shift the plunger 1' inward of the cylinder 12, and the plunger moves outward again when the load is reduced or removed. The illustrated element thus permits an attached seat to yield resiliently when the weight of an occupant is shifted as is conventional in spring mounted seats. The cell 6' provides a pneumatic spring whose characteristics are entirely independent of the amount of liquid in the lower cylinder compartment and of the effective length of the supporting element.

When the valve ring 20 is moved into its open position in the compartment 9 by means of the rod 13, and no load is applied to the supporting element, the plunger 1' is moved outward of the cylinder 12 through the bottom wall 2', and shifts the piston 3' and container 24 downward. The rate of this movement is slowed by the flow resistanceencountered by the liquid passing upward from the compartment 5 to the compartment 9 through the throttling passages 15 in the piston 8. The pressure of' the gas in the cell 6' exerts a sufficiently greater axial force on the plunger 1 than the gas 22 that the relative position of the plunger and the piston 8' is not changed while the valve ring 20 is in its open position. When the ring is returned to the illustrated closed position, the length of the supporting element does not change further unless a load is applied. I

When it is desired to shorten the element, the conduit in the partition 10 is opened, and the plunger 1' is pushed inward of the cylinder 12 at a rate controlled by the resistance of the passages 15 to downward flow of liquid. The gas 22 is compressed to admit additional liquid to the upper chamber Of the cylinder 12, but no significant displacement of the plunger 1' relative to the container 24 can occur, and the unloaded length of the element after the closing of the valve in the partition 16 is the same as the length was at the moment of valve closing under an applied load.

The supporting element illustrated in H6. 3 is identical with that described with reference to FIG. 2 except for the devices in the upper end of the cylinder 12. The partition 10' and the externally threaded plug 14", not significantly different from the partition it) and the plug 14, are integrally connected by a coaxial tube 30. Several radial bores 31 in the tube 30 adjacent the partition 10' connect the portion of the upper cylinder chamber filled with liquid ill to an annular chamber 33 about a reduced portion 34 of the valve operating rod 13". in the illustrated position of the rod, the chamber is axially bounded by conically flaring parts 32, 32a of the rod and sealed by resilient rings 23, 2% closely adjacent the conical parts, the ring acting as a valve which, in the illustrated position, blocks the flow of liquid between the two cylinder chambers through the bores 31, only one being seen in the drawing, and the annular chamber 33.

The apparatus shown in FIG. 3 operates in the same manner as described above with reference to FIG. 2.

It should be understood, of course, that the foregoing disclosure relates only to preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A supporting element of adjustable length comprising, in combination:

a. a cylinder member having an axis and defining a sealed cavity therein;

b. a partition fixed to said cylinder member in said cavity and axially dividing the cavity into a first chamber and a second chamber;

0. valve means operatively interposed between said chambers and movable between respective open and closed positions in which said valve means connects said chambers and seals said chambers from each other;

d. valve operating means accessible outside said cavity for moving said valve means between said positions thereof;

. a first body of liquid in said first chamber;

f. an amount of a gas under a pressure higher than atmospheric pressure in pressure-transmitting relationship to said body of liquid;

g. a plunger member axially movable in said cylinder member,

1. said plunger member having respective axially terminal portions in said second chamber and outside said cylinder;

h. a second body of liquid substantially completely filling the remainder of said second chamber and communicating with said first body in said open position of the valve means,

1. whereby said gas in the open position of the valve means exerts a first axial force on said plunger member in a direction outward of said cavity when said valve means is in the open position thereof; and

. yieldably resilient means in said second chamber opposing movement of said plunger member inward of said second chamber with a second force substantially greater than said first force when said valve means is in the closed position thereof.

2. An element as set forth in claim 1, wherein said yieldably resilient means are stressed during said inward movement of said plunger member and partly relaxed during movement of said plunger member outward of said second chamber when said valve means is in the closed position, said supporting element further comprising limiting means for limiting relaxation of said yieldably resilient means during said outward movement.

3. An element as set forth in claim 1, wherein said yieldably resilient means include a sealing member movable relative to said plunger member and defining therewith a cell, and a body of gas sealed from said second body of liquid in said cell by said sealing member.

4. An element as set forth in claim 3, wherein the axially terminal portion of said plunger member in said second chamber is formed with a recess therein, said sealing member being received in said recess for movement inward and outward of said recess, a portion of said recess constituting said cell and receiving said body of gas.

5. An element as set forth in claim 3, further comprising guide means axially guiding said sealing member in said second chamber.

6. An element as set forth in claim 5, wherein said sealing member is formed with a recess therein, the axi-. ally terminal portion of said plunger member being received in said recess for movement inward and outward of said recess, a portion of said recess constituting said cell.

7. An element as set forth in claim 5, wherein said guide means include a piston member axially movable in said second chamber and dividing the same into two compartments, said piston member being formed with a throttling passage connecting said compartments,said plunger member engaging said piston member.

8. An element as set forth in claim 7, wherein said sealing member is fixedly mounted on said piston member and formed with a recess therein, the axially terminal portion of said plunger member being received in said recess for movement inward and outward of said recess, a portion of said recess constituting said cell.

9. An element as set forth in claim 3, wherein said partition is formed with a conduit axially extending thereto, said valve operating means include a rod member elongated in the direction of said axis and having respective longitudinal portions outside said cavity, in said first chamber, and in said conduit, sealing means interposed between said rod member and said cylinder member permitting axial movement of said rod member inward and outward of said cavity, said valve means including a valve member mounted on said rod member for movement therewith and sealing said conduit in the closed position of said valve means.

10. An element as set forth in claim 3, wherein said first body of liquid has a free horizontal surface in said first chamber, said amount of gas making direct contact with said surface.

Claims

1. A supporting element of adjustable length comprising, in combination: a. a cylinder member having an axis and defining a sealed cavity therein; b. a partition fixed to said cylinder member in said cavity and axially dividing the cavity into a first chamber and a second chamber; c. valve means operatively interposed between said chambers and movable between respective open and closed positions in which said valve means connects said chambers and seals said chambers from each other; d. valve operating means accessible outside said cavity for moving said valve means between said positions thereof; e. a first body of liquid in said first chamber; f. an amount of a gas under a pressure higher than atmospheric pressure in pressure-transmitting relationship to said body of liquid; g. a plunger member axially movable in said cylinder member, 1. said plunger member having respective axially terminal portions in said second chamber and outside said cylinder; h. a second body of liquid substantially completely filling the remainder of said second chamber and communicating with said first body in said open position of the valve means, 1. whereby said gas in the open position of the valve means exerts a first axial force on said plunger member in a direction outward of said cavity when said valve means is in the open position thereof; and i. yieldably resilient means in said second chamber opposing movement of said plunger member inward of said second chamber with a second force substantially greater than said first force when said valve means is in the closed position thereof.

6. An element as set forth in claim 5, wherein said sealing member is formed with a recess therein, the axially terminal portion of said plunger member being received in said recess for movement inward and outward of said recess, a portion of said recess constituting said cell.