US3638769A

US3638769A - Dashpot assembly

Info

Publication number: US3638769A
Application number: US857697A
Authority: US
Inventors: Arthur M Cohen
Original assignee: AIRPOT CORP
Current assignee: AIRPOT CORP
Priority date: 1969-09-15
Filing date: 1969-09-15
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01

Abstract

The cylinder of a dashpot is formed from an accurately dimensioned rigid tube which is received within a soft plastic sheath, the latter surrounding the sidewalls of the tube and also closing the end of that tube. The sheath is preferably provided with a downwardly extending part which facilitates the mounting of the assembly on an appropriate support.

Description

, 1, 21. 1 3, Elite States atem H 1 3,638,76

Cohen Feb. 1, 1972 [54] DASHPOT ASSEMBLY 3,005,523 10/1961 May ....188/100 X 3 343 833 9/1967 Fader 1 88/100 X l t M. h [72] Arthur westpm 3,368,650 2/1968 Wasdell ..188/322 [73] Assignee: Ail-pot Corporation, Norwalk, Conn. 2 Filed: Sept. 15, Primary Examiner-George E. A. Halvosa [21] A l N 857 697 Attorney-James and Franklin [57] ABSTRACT [52] US. Cl ..188/298, 188/322 The cylinder of a dashpot is formed from an accurately dimem [51] 1111.15]; "F161 9/54 Sioned rigid tube which is received within a soft plastic SheathI [58] he 0 Search ..188/100, 322, 298, 311 the latter surrounding the sidewalls of the tube and also clos ing the end of that tube. The sheath is preferably provided [56] References cued with a downwardly extending part which facilitates the mount- UNITED STATES PATENTS ing of the assembly on an appropriate support.

2,092,259 9/1937 Padgett ..188/100 UX 17 Claims, 3 Drawing Figures PATENTEU FE 1 2 INVENTOR ,Q M, C nt-N ATTORNEY DASHPOT ASSEMBLY The present invention relates to a dashpot assembly, and in particular to the construction of the cylinder portion thereof.

Dashpots generally comprise a cylinder within which is piston is slidable, the dashpot action being provided by the compression or expansion of the air in the chamber defined between the piston and cylinder. A valve is provided to control the flow of air either into or out of that chamber, thereby to vary the dashpot action, permit the piston to move more readily on one direction or the other, or both. In order for the dashpot action to be effective and to be accurately controllable it is essential that the piston fit into the cylinder in an airtight fashion while still being slidable therethrough. This presents great problems, particularly where the dashpot is to be subjected to varying temperatures. Both the piston and the cylinder can be made of the same substance, usually a metal, in which case they will both tend to expand and contract at the same rate with changes in temperature, but if this approach to the problem is taken the inner surface of the cylinder and the outer surface of the piston must both be machined with great accuracy, and this is quite expensive.

An inexpensive type of dashpot which nevertheless is exceptionally accurate is of the type shown in May U.S. Pat. No. 3,005,523 of Oct. 24, 1961 entitled Damping Dashpot." That dashpot comprises a cylinder which is formed of glass tubing within which a piston slides, the piston being formed of compressed powdered graphite. With this combination, it has been found, a very precise sealing yet sliding fit is achieved between the piston and the cylinder at exceptionally low cost, while the temperature coefficients of expansion of the piston and cylinder are sufiiciently close to one another so that the dashpot can be subjected to wide variations in temperature without deleterious effects.

In such a dashpot the piston rod extends from one end of the tube. The other end of the tube must be closed. To that end, and as shown in U.S. Pat. No. 3,005,523, the glass tube is mounted in a baseplate formed of some suitable structural material. A seal must be produced between the cylinder tube and that end plate, and that seal must be capable of withstanding wide variations in temperature. It therefore is necessary to use for the base plate a material which must be rather precisely dimensioned and which has closely the same temperature expansion characteristic as the glass tube. These criteria have in the past been met only approximately, and even then only through the use of comparatively expensive materials.

Two other problems are presented by the prior art dashpot structure exemplified by U.S. Pat. No. 3,005,523. In the first place, since the cylinder is formed of glass it is essentially fragile. Hence it must be protected in shipment and during assembly and must be used in an environment in which it is not liable to receive external blows or severe shocks. In the second place, mounting of the dashpot on an appropriate supporting structure, such as a panel, while not insuperable by any means, is nevertheless somewhat troublesome. Screws or the like must be employed to attach the end plate to the mounting structure. If those screws are located within the confines of an extension of the cylinder they will weaken the cylinder end wall; if they are disposed outside those confines they require more area for the mounting of the dashpot than the dashpot proper takes up. The fact that screws are used for attachment means that an appreciable time is involved in removing a defective dashpot from an installation and replacing it with a new one, particularly where the dashpot is located in a relatively inaccessible position where it is hard to get to and manipulate its mounting screws.

It is the prime object of the present invention to devise a dashpot assembly which will be as accurate and reliable as the prior art glass tube-graphite piston dashpot but which will be considerably less expensive to manufacture, both as regards cost of parts and assembly.

lt is another object of the present invention to devise such a dashpot which is even more reliable than said prior art dashpots, particularly insofar as resistance to shock, liability to breakage and reliability of seal between the end wall and the corresponding cylinder end are concerned.

It is a further object of the present invention to devise such dashpot which can readily be mounted and dismounted in an installation.

It is yet another object of the present invention to devise such a dashpot which is exceedingly insensitive to temperature variations.

In accordance with the present invention the dashpot here, like that of the prior art, has its cylinder wall defined by a tubular member formed of an appropriate material such as glass and has a piston slidable therein which may be fonned of compressed powdered graphite. It departs from the prior art in that the wall closing the end of the cylinder opposite that through which the piston rod extends is formed of a soft plastic body having a first part which extends across and closes the tube end and having a second part which extends around and snugly grips the outer surface of the glass tube, thus sheathing that portion of the glass tube which it surrounds. The material of which this sheath is formed is preferably elastomeric, so that it resiliently grips the tube. Hence as the tube contracts or expands upon temperature change the sheath will expand or contract with it, thus maintaining the seal inviolate at the end of the tube. The sheathing part, which may well extend the full length of the glass tube, provides protection to the tube, insulating it from and supporting it against external shock. To assemble the tube with the sheath all that need be done is to insert the former into the latter, the latter preferably being provided with a seat on which the tube is adapted to rest when in proper position.

The end wall formed by the soft plastic material may have a portion extending down therefrom which is externally shaped so as to cooperate with the mounting member which is provided for the dashpot. The downwardly extending portion may thus serve to mount or dismount the dashpot on the mounting member by being inserted or removed from a recess in the mounting member. The compressibility of the downwardly extending end wall portion facilitates the ready mounting and dismounting of the dashpot; to render that downward extending portion more compressible, thereby to make the mounting and dismounting of the dashpot even easier, a recess may be provided in the end wall which extends down into the mounting portion and opens into the chamber defined between the cylinder and the piston.

To the accomplishment of the above, and to such other objects as may hereinafter appear, the present invention relates to the construction of a dashpot assembly, as described in this specification, and as disclosed in the accompanying drawings in which:

FIG. 1 is a side elevational exploded view of the parts of the dashpot assembly, the outer part of the cylinder being shown mounted on a mounting member;

FIG. 2 is a cross-sectional view, on an enlarged scale, of the dashpot assembly of FIG. 1 but with the parts in assembled condition; and

FIG. 3 is a cross-sectional view taken along the line 33 of FIG. 2.

The dashpot, as is conventional, comprises a cylinder generally designated 2 within which a piston generally designated 4 is sealingly slidable, the piston being connected to a piston rod generally designated 6 which extends out through the open upper end 8 of the cylinder 2. As here specifically disclosed the connection 10 between the piston 4 and the piston rod 6 may be of the one way valve type disclosed in Wilcox U.S. Pat. No. 3,175,646 of Mar. 30, 1965, entitled Joint for Piston-Piston Rod Combination, and Valve Function Thereof," the connection 10 in one embodiment providing for valve opening when the piston rod 6 is pushed down and for valve closing when the piston rod 6 is pulled up, thus providing for free movement of the piston 4 into the cylinder 6 and retarded movement of the piston in the other direction. The upper end of the piston rod 6 may be connected by a ball and socket joint 12 to any appropriate actuating member 14. The piston 4 may be formed of any appropriate material; compressed powdered graphite is preferred.

The cylinder 2 is formed of two parts, a cylinder tube 16 and an outer part generally designated 18. The cylinder tube 16 is preferably formed of glass the inner surface 20 of which is very accurately dimensioned to fit the outer dimension of the piston 4, thereby to render the latter sealingly slidable in the former. For the same reason, the inner surface 20 of the tube 16 is smoothly polished. The surface characteristics and accuracy of dimension of the outer surface 22 of the tube 16 are not critical.

The outer part 18 is formed of a suitable soft plastic material, preferably stretchable and elastomeric in nature. Rubber, natural or artificial, is excellently suited for use in that connection. That outer member comprises an end wall portion 24 from which a cylindrical portion 26 extends upwardly, the normal inner diameter of the upwardly extending cylinder portion 26 preferably being slightly less than the diameter of the outer surface 22 of the tube 16. The tube 16 is slid into the open upper end of the cylinder portion 26 so that the latter stretches and grips the outer surface of the former, thereby forming a seal between the two. When this has been done the end wall portion 24 effectively closes the bottom end 8' of the tube 16, thereby defining a chamber 28 between the piston 4 and the inside of the cylinder 2, the volume of that chamber varying with the position of the piston 4 along the tube 16.

Because of the deforrnability, and preferably the resilient deformability, of the outer member 18, and because of the close grip between that outer member 18 and the tube 16, an effective seal is produced between the parts 16 and I8 merely by inserting the former into the latter, and that seal will remain inviolate even though the assembly is subjected to wide variations in temperature, the outer member 18 accommodating itself to any changes in dimension of the tube 16.

in order to facilitate properly locating the tube 16 within the outer member 18 the latter may be interiorly provided with a shoulder 30 located near, and preferably spaced somewhat above, the end wall portion 24, the lower end 8' of the cylinder 16 being adapted to rest on that shoulder 30 when the parts are assembled. it is further preferred that the axial length of the cylinder portion 26 above the shoulder 30 be at least equal to the axial length of the tube 16 so that all of the exterior of the tube 16 is covered by the sofi cylinder portion 26. In this way the cylinder portion 26 constitutes a protective sheath along the entire length of the glass tube 16. As a result, even if the dashpot be dropped or struck by some external object the possibility of damage or breakage is greatly minimized.

In order to provide means for facilitating the mounting of the dashpot on an external supporting member, such as the panelboard 32 fragmentarily shown in the drawings, the end wall portion 24 of the outer member 18 may be provided with a downwardly extending portion 34 of a size and shape such as to be received within w opening 36 in the panelboard 32. The downwardly projecting portion 34 may be provided with a radially outwardly extending part 38 axially spaced from the lower surface of the end wall portion proper 24, thereby to define an outwardly opening groove 40 within which the opening-exposed surfaces of the panelboard 32 are adapted to be received, as shown in FIG. 2. Because of the soft, and preferably elastomeric nature, of the portion 34, aided by the fact that the surface 42 from the lower end thereof to the radially outwardly projecting part 38 is upwardly and outwardly tapered, the dashpot assembly may be mounted on the panelboard 32 merely by forcing the portion 34 down into the panelboard opening 36 until the part 38, which has been compressed as it passes through the opening 36, snaps out after it has escapedfrorn that opening. To remove the dashpot assembly it need merely be pulled up, disengagement of the part 38 from the underside of the panelboard 32 being facilitated as the dashpot is turned at the same time that it is pulled.

in order to make it easier for the part 34 to compress as it passes through the opening 36, a recess 44 may be formed in the end wall portion 24 which extends down into the portion 34.

in the simplified version of the dashpot assembly here disclosed the end wall portion 24 completely closes and seals the lower end of the chamber 28. If desired, an adjusting valve could be assembled into the end wall portion 24, in a manner similar to the adjusting valve shown in Wilcox U.S. Pat. No. 3,175,646, but in many instances it is not necessary that this be done. The dashpot could either be operated as a nonadjustable dashpot, or its adjustment could be accomplished in some other fashion, as by adjusting the tension of external springs operatively connected to the piston rod 6.

It will be appreciated from the above that the construction here disclosed is exceedingly simple and inexpensive. The tube 16 may be cut to appropriate length from a long tube of precision-formed glass of a type which is commercially available. The outer member 18 is well suited to be manufactured in large quantities by being molded, and hence it too can be manufactured at low cost. it is particularly noteworthy that it need not be manufactured to a high degree of precision, since its elastomeric character permits it to adapt itself to rather wide variations in dimensions. Assembly of the cylinder 2 is simple in the extreme the tube 16 is merely slid into the outer member 18. Thus material costs and assembly costs are both greatly minimized, and all without detracting from the high degree of accuracy attendant upon the use of a glass tube 16 and a graphite piston .4. The glass tube 16 is fragile, but because it is surrounded by the sheathing cylinder portion 26 it is protected. As the tube 16 changes dimension because of temperatures variations the outer member 18 accommodates itself to those changes, so that the seal between the two remains unbroken. Thus an exceptionally high degree of sturdiness and reliability is achieved with an appreciable saving in cost even as compared with the relatively inexpensive devices of the prior art.

While but a single embodiment of the present invention has been here specifically disclosed, it will be apparent that many variations may be made therein, all within the scope of the instant invention.

lclaim:

l. A dashpot assembly comprising an open-ended cylindrical tube defining the dashpot cylinder, and an integral soft stretchable sheath for said tube comprising a cylindrical portion fitting snugly around said tube and an end wall covering and sealing an end of said tube, and a piston slidably mounted within said tube and adapted to be moved within said tube towards and away from said end wall, a single working dashpot chamber being defined within said cylinder at one end by said piston and at the other end by said end wall.

2. The assembly of claim 1 in which the inner surface of said cylindrical portion of said sheath has a shoulder spaced above said end wall, said tube resting on said shoulder.

3. The assembly of claim 1, in which the inner surface of said cylindrical portion of said sheath has a shoulder spaced above said end wall, said tube resting on said shoulder.

4. The assembly of claim 1, in which said end wall has a portion extending down therefrom and provided with a radially outwardly projecting part axially spaced from the lower surface of said end wall, said portion being adapted to be received in a hole in a mounting member, thereby to mount said assembly on said mounting member.

5. The assembly of claim 4, in which said end wall has a recess extending down into said downwardly extending portion.

6. A dashpot assembly comprising an open-ended cylindri cal tube defining the dashpot cylinder, and an integral soft stretchable sheath for said tube comprising a cylindrical portion fitting snugly around said tube and an end wall covering and sealing an end of said tube, said end wall being provided with means extending therefrom and adapted to be holdingly received-in an aperture in a mounting member, thereby to mount said assembly on a mounting structure.

7. The assembly of claim 6, in which the inner surface of said cylindrical portion of said sheath has a shoulder spaced above said end wall, said tube resting on said shoulder.

8. The assembly of claim 6, in which said tube is made of glass.

9. The assembly of claim 8, in which said sheath is elastomeric and resiliently grips said tube.

10. The assembly of claim 8, in which said means on said end wall comprises a portion extending down therefrom and provided with a radially outwardly projecting part axially spaced from the lower surface of said end wall, said portion being adapted to be received in said aperture in said mounting member, thereby to mount said assembly on said mounting member.

11. The assembly of claim 10, in which said end wall has a recess extending down into said downwardly extending por- U011.

12. The assembly of claim 6, in which said means extending from said end wall is provided with a radially outwardly projecting part axially spaced from the lower surface of said end wall, said portion being adapted to be received in said aperture in said mounting member, thereby to mount said assembly on said mounting member.

13. The assembly of claim 12, in which the end of said sheath remote from said end wall extends beyond the corresponding end of said tube.

14. The assembly of claim 12, in which the inner surface of said cylindrical portion of said sheath has a shoulder spaced above said end wall, said tube resting on said shoulder.

15. The assembly of claim 12, in which said end wall has a recess extending down into said downwardly extending portion.

16. The assembly of claim 15, in which the end of said sheath remote from said end wall extends beyond the corresponding end of said tube.

17. The assembly of claim 15, in which the inner surface of said cylindrical portion of said sheath has a shoulder spaced above said end wall, said tube resting on said shoulder.

Claims

1. A dashpot assembly comprising an open-ended cylindrical tube defining the dashpot cylinder, and an integral soft stretchable sheath for said tube comprising a cylindrical portion fitting snugly around said tube and an end wall covering and sealing an end of said tube, and a piston slidably mounted within said tube and adapted to be moved within said tube towards and away from said end wall, a single working dashpot chamber being defined within said cylinder at one end by said piston and at the other end by said end wall.

6. A dashpot assembly comprising an open-ended cylindrical tube defining the dashpot cylinder, and an integral soft stretchable sheath for said tube comprising a cylindrical portion fitting snugly around said tube and an end wall covering and sealing an end of said tube, said end wall being provided with means extending therefrom and adapted to be holdingly received in an aperture in a mounting member, thereby to mount said assembly on a mounting structure.

8. The assembly of claim 6, in which said tube is made of glass.

11. The assembly of claim 10, in which said end wall has a recess extending down into said downwardly extending portion.