GB2131517A

GB2131517A - Adjustable bellows-type shock absorber

Info

Publication number: GB2131517A
Application number: GB08332065A
Authority: GB
Inventors: Kurt Stoll
Original assignee: Festo Maschinenfabrik Gottlieb Stoll Firma
Current assignee: Festo Maschinenfabrik Gottlieb Stoll Firma
Priority date: 1982-12-04
Filing date: 1983-12-01
Publication date: 1984-06-20
Also published as: JPH0424581B2; KR840007156A; IT1169481B; KR910000777B1; GB8332065D0; FR2537232A1; GB2131517B; JPS59110930A; SE8306649L; ES527743A0; SE8306649D0; ES8406671A1; IT8323993A0; DE3244997A1; DE3244997C2

Abstract

A shock absorber, more specially for use in office machines, is made up of a housing with two oppositely placed, rigid end plates (2, 3) joined together by a bellows-like casing 4, one of the end plates having a port 6 running into the space inside the casing and having a choke valve fitted therein. The choke is adjustable and preferably has a check valve function. The restoring force of the bellows casing is reinforced by spring elements 15, 16. The casing may be frusto-conical with the size of the folds therein decreasing towards the end with the smaller diameter. Alternatively (Fig. 4) it may be enclosed by telescoping guides. <IMAGE>

Description

SPECIFICATION A shock absorber The present invention is with respect to shock absorbers, and more specially although not exclusively to shock absorbers as used for damping compression forces coming into existence between moving machine parts.

Such shock absorbers are for example used in the form of buffers that are made of an elastic material. Such buffers are fitted in the way desired between the moving machine parts, whose motion in relation to each other is to be damped. If the parts are then moved towards each other, impacting the buffer, the impact energy will be absorbed by elastic deformation.

Buffers of this sort are highly simple in design, but they do have the shortcoming that their shock absorbing power is once at for all fixed by the selection of the material of which they are made and may then not be changed later. Furthermore, after a certain number of deformation cycles have been completed, there will be signs of fatigue so that the damping effect of such a buffer will become less. A further known design of shock absorber is the friction one with two lever arms that are pivoted together. For causing shock absorption by friction each of the lever arms is placed so that it is acted up by one of the two machine parts to be damped. Because of the pivot joint between them, the lever arms are rocked in relation to each other and the kinetic energy of the moving machine parts is taken up by the friction at the joint and turned into heat.

Dependent on the degree of stiffness of the pivot joint, such frictional shock absorbers may be used for absorbing larger or smaller amounts of energy.

The energy amount absorbed may be adjusted from one case to another by tightening plates on the joint. The shortcoming of such shock absorbers working by friction is their relatively complex design, the high price of manufacture and the large overall size. Lastly there is the design of shock absorber as used in car manufacture, in the form of hydraulic shock absorbers by which the vibration of a spring system coming from driving along an uneven road surface are turned into heat energy by the viscosity of a liquid. In this case a hydraulic oil is forced through a spring-loaded valve system by a piston. Such shock absorbers give a first rate damping effect, that in some designs may be changed by adjustment of the valve spring and/or of the cross section of the transfer ducts in and running through the piston. Hydraulic shock absorbers are however relatively complex in design.In order to make certain that the piston and cylinder mal < ing up the hydraulic system are in sealing contact with each other, very tight manufacturing tolerances have to be kept to, this in itself putting up the price of producing such shock absorbers. Because for operation there has to be an exchange of liquid between the cylinder of a hydraulic shock absorber and liquid reservoir, such shock absorbers may not be made very small in size and low in height; at any rate the price of producing a shock absorber with a very small size no longer has any reasonable relation to the its usefulness.

One purpose of the present invention is to take care of the short-comings of the known shock absorbers and to make possible a design thereof such that the damping properties may be quite simply adjusted over a wide range.

Another purpose of the invention is to make possible a design of shock absorber that may be manufactured in a large number of different models and sizes by a simple production process.

For effecting these and other purposes, in the present invention a shock absorber comprises a housing made up of opposite rigid end plates and a bellows-like casing forming a connection between said end plates, one of said end plates having a port running into a space inside said housing, and an adjustable choke valve fitted in said port. The outcome is a shock absorber which to high degree may be made up of standard components as developed in the pneumatic systems industry and used on a wide scale regularly therein. To take an example, bellows are commercially supplied in different forms and sizes. Furthermore adjustable choke valves are very well known to those in the art so that no detailed account thereof is needed.In short, the shock absorber in keeping with the present invention may be produced very simply using components that have come into general use and have gone through a complete and painstaking process of development before becoming industry standard products. This being so, the invention is characterized by low production costs and very trouble-free operation. The shock absorbing fluid is the air in the casing, that is forced out through the choke valve as the machine parts that are to be damped take effect on the end plates causing compression of the bellows-like part of the casing. The shock absorbing effect of the shock absorber in keeping with the invention is dependent on the resistance to flow offered by the choke valve to the air.This flow resistance may be quite simply adjusted over a wide range so that the invention makes possible a shock absorber with adjustable damping properties. This shock absorber may on the other hand be made to be quite compact and as a small unit so that it may readily be used as a replacement for the widely used buffers of solid elastic material. A preferred field of use of the shock absorber is in small hand-worked apparatus such as office machines. The use of a shock absorber with an adjustable damping effect in such machines makes it possible for it to be matched to the weight and the tendency to produce vibrations and the like of the office machine, so that there will be less wear on the machine and it is more pleasing to use.The shock absorber in keeping with the invention may however be used in other fields, more specially when the amounts of energy to be absorbed are not very great.

Examples of different further developments of the invention are noted in the dependent claims.

As one such possible development, the bellows-like casing is in the form of a hollow frustum of a cone, this being a specially important further outgrowth of the basic idea of the invention, inasfar as a first rate damping effect is produced even if the shock absorber is low in height. This is because of the fact that the degree of compression of a bellows is dependent on the geometry of its folds.If the form of the bellows is cylindrical then the degree of compression is relatively limited because the folds are pushed together like the folds of a concertina in a cylindrical form, whereas if the bellows-like casing is made frusto-conical, the folds may be moved into positions in which one fold is at least partly inside the fold next to it on the one side and is partly inside the fold on the other side thereof concentrically, that is to say the folds are nested inside each other and for a given height of bellows the air displacement may be made greater with a purely cylindrical form. This is the reason why frusto-conical shock absorbers are characterized by a very compact form in comparison with their impact absorbing power.

Furthermore their outer form is the same as that of a normal rubber buffer so that such shock absorbers may in many fields be used in place thereof without any changes in the machine to which they are to be fitted having to be made.

For moving the shock absorber casing back into its starting position after being compressed by an impact and after the force acting on the end plates has become less, a return or restoring force is needed. In keeping with one basic notion of the invention this return force may be produced by the inner elasticity of the bellows-like material.

However the material then has to be high in quality and resiliently elastic. In the case of a specially low-price further development of the invention that takes little material for its manufacture and may more specially be manufactured in synthetic resin, the resilient elasticity of the bellows material is reinforced or has its place taken by spring elements and/or a compression spring placed between the end plates. Such a spring may be a helical one or in the form of a number of resilient rings placed in the said folds. If such a compression spring is used it may be positioned within the shock absorber casing, this giving a more specially compact design. The end plates may be guided for motion in relation to each other in the axial direction of the casing while stopping any twisting motion.This guiding effect may be produced by sleeves placed coaxially one inside the other and with a groove in the one sleeve to take up a guide head on the other sleeve. The two sleeves at the same time have the function of a guard so that the shock absorber is sturdy.

However the amount of space needed is then greater.

In additon to the choke valve there may be a check valve that is fixed in a port running into the inside of the casing. This important further development of the basic idea of the invention makes it possible for air to be let into the inside of the housing in a process of expansion after an impact so that the casing is quickly moved back into its position ready for full operation again. On the other hand the check valve is shut when the casing of the shock absorber is compressed again by an outside force so that the air present within the casing is only able to be let off through the choke valve. Because of this system the resistance to flow of air being let off from the casing is very much greater than the flow of air into the casing. Such a design has very useful properties and may in fact be necessary if a train of impacts taking place at a high rate is to be absorbed.The design of the shock absorber is not made markedly more complex by this further development seeing that the check valve may be united with the choke valve as a single choke valve with a check valve function in addition.

in keeping with a still further outgrowth of the main idea of the present invention the size or wavelength of the separate folds goes down in small, equal steps of continuously from the end of the casing with the larger diameter to the end with the smaller one. Furthermore, there may be a small stepwise or regular decrease in the radius of curvature or bending of the folds from the end of the casing with the greater diameter to the other, opposite end, that is to say the end with the lesser diameter. In this connection the stepwise change in form of the folds is such that the stress of the folds (given by the formula: bending moment/moment of resistance) is constant.

The inner and outer crest parts of the folds may be elliptically curved, all major axes of the ellipses having the same size, whereas the length of the minor axes becomes longer with an increase in their distances from the end of the casing at which the casing has its smaller diameter.

These further developments in connection with the geometry of the folds are representative of preferred forms of the invention using a frustconical, bellows-like casing or housing. On the one hand such further developments make it possible for the casing to be compressed to an even greater degree so that for a given overall height of the bellows element there is a greater acting damping stroke. A still further point in this connection is that the stresses in the folds are generally equal so that troubles caused by fatigue and cracking are not to be feared in the early working life of the bellows.

A more detailed account of the invention as based on working examples to be seen in the accompanying figures herein will now be given.

Figure 1 is an axial section through a first design in keeping with the present invention in the form of a frusto-conical bellows shock absorber.

Figure 2 is a further axial section taken through a further working example of a bellows shock absorber.

Figure 3 is a radial section through the wall of the bellows casing in connection with the bending of the folds thereof.

Figure 4 is an axial section of a still further possible working example of the invention.

Turning now to these figures, in which like part numbers are used for like parts, it will be seen firstly from figure 1 that a shock absorber generally numbered 1 has as its main parts two stiff end plates 2 and 3 that are joined together by a casing 4 in the form of a bellows, the end plates 2 and 3 forming with the casing 4 a housing that may be compressed by pushing together the folds 5 in the axial direction. When this takes place the end plates 2 and 3 are moved nearer together.

The compression of the housing is caused by an impact that is to be damped or absorbed, such impacts or vibrations acting in the main in the axial direction with respect to the end plates 2 and 3. The impact energy then coming into existence is changed into the work needed for forcing the air in the casing out of it through a choke valve. The choke may be placed in a port 6 in one of the end plates 2 and 3 and forming a connection between the inside of the casing with the outside atmosphere. Such choke valve, that is not marked in the figure, may be of known design and adjustable so that the resistance to the flow of the air let off from the bellows may be changed as desired. This in turn is responsible for a change in the damping or shock absorbing properties of the shock absorber in keeping with the invention so that they may be matched to any desired conditions of operation.More specially the choke will be screwed into the port 6, same having a female thread for this very purpose.

The effect of an impact acting on the two end plates 2 and 3 is that of moving the housing of the shock absorber 1 into a partly compressed position, air being let off by way of the choke valve that is screwed into the port 6 from the housing. On a decrease in the force acting on the end plates 2 and 3, the housing will be elastically moved back into its starting position, the inner elasticity of the bellows casing 4 being responsible for such motion. In figure 2 the reader will furthermore be able to see the preferred frusto-conical form of the bellows-like casing 4.

This geometry gives the casing 4 a high degree of radial stiffness and a high level of guiding effect in the axial direction. Furthermore when the casing 4 is compressed it folds 5 in part take up position inside each other concentrically so that a relatively long compression stroke is made possible and the end plates 2 and 3 are moved quite a long way towards each other. This design furthermore makes possible a low overall height of the shock absorber 1 while at the same time increasing the volume of air that may be forced out of the casing. That is to say, on the one hand the shock absorber 1 makes possible a high level of energy absorption and on the other a wide dynamic range of operation.If in keeping with the invention the bellows-like casing 4 is made frusto-conical, it is best for the end plate 3 at its end 7 with the greater diameter to be made so large that its edge is sticking out radially past the limit of the casing 4. The edge parts 9 of the end plate 3 running out past the outer limit of the casing 4 may be used for fastening elements (not figured), by way of which the shock absorber 1 may be fixed to a piece of apparatus whose parts are to be shock absorbed, such appparatus being more specially in the form of an office machine.

The end plate 3, that at the same time has the function of a mounting plate, will as a rule have the port 6 therein, in which the choke valve is seated. On the other hand the other end plate 2 opposite thereto is best made without any holes or the like as buffer plate running outwards from the machine base towards the moving part thereof whose motion is to be damped.

The shock absorber 1 as in figure 1 has a bellows-like body that, without the end plates 2 and 3, would be open at one end and shut off at the other. To put it differently, the end of the bellows casing 4 at the end 8 with the smaller diameter is molded in the form of a flat end wall 10. The end plate 2 is of generally the same size as the end wall 1 0 and is strongly joined thereto, as for example by welding or bonding. On the other hand at the end 7 with the greater diameter the casing 4 is open towards the end plate 3.

At the line at which it is touching the end plate 3, the casings flared outwards to take the form of an edge lip 11 , that is air-tightly joined to the end plate 3. This connection as well may be produced by bonding or welding, but this does not have to be so in all cases: in fact it may be seen further from figure 2 that the bellows structure may be walled off on its side next to the end plate 3 by an end wall 12 as well. This end wall 12 then has a port 13 to give a connection between the choke valve (not figured) and the space 14 inside the shock absorber 1.

Furthermore it will be seen from figure 2 that there are means for supplementing the elasticity of the bellows casing 4 so that when the bellows has been compressed the return stroke is not only dependent on such elasticity. To this end the casing may have spring rings 1 5 or a helical spring placed between its folds, such spring means being made for example of steel. The casing 4 itself is made of a much softer elastic material such as rubber or a synthetic resin. The spring rings 1 5 have the effect of stiffening the material and reinforcing its elastic restoring force.

Furthermore there is a compression spring 16 between and resting against the end plates 2 and 3, such spring 1 6 being able to be used jointly with the spring rings 1 5 or without them and to give birth to a further force stretching or restoring the casing. In keeping with a preferred form of the invention the compression spring 1 6 is placed in the space 14 within the shock absorber 1.

Lastly the reader will be able to see from figure 2 the form of a shock absorber 1 of the invention, in the case of which the size of the separate folds 5 of the bellows-like casing 4 goes down in small equal steps or continuously from the end 7 of the casing 4 with the larger diameter to the other end 8. This decrease in the size of the folds or corrugations is the outcome of the radiuses of curvature of the folds 5 decreasing representatively. The geometry is such that the thickness of the material hardly gets in the way of the compression of the shock absorber 1 at all inasfar as the folds 5 on cmpression take up generally concentric positions inside each other with a sort of nested system.The gradation of the fold or corrugation size in this respect is best made such that the strain in the folds, that is to say the ratio of the bending moment M and the moment of resistance W of the fold material is constant, that is to say =M/W=consta nt, all the way along the axial length of the casing 4.

When this is so there is an even distribution of the load on the shock absorber over all the folds 5 of the casing, this putting off or stopping completely fatigue of the material and making certain of a long working life for the shock absorber 1 of the present invention. The folds 5 in the working example of the invention to be seen in figure 2 are in this case bent into a more or less circular form.

The same stress pattern may furthermore be produced in the working example to be seen in figure 3 if the inner and outer crest parts 17 and 1 8 of the frusto-conical casing 4 are elliptically curved, the major axes 19 of all the ellipses being of equal size, whereas the length of the minor axes 20 goes up the further the folds are from the end 8 of the casing 4 with the smaller diameter.

The elliptical form of the folds 5 is made clear in figure 3 by a further, broken line 21. In this figure the reader will see a form of the 1 shock absorber 1 of the invention in which the two end plates 2 and 3 are made with outer edge parts running out past the limits of the ends of the bellows-like casing radially. Between these overhanging edge parts 9 and 22 of the end plates 3 and 2 there is a compression spring 1 6 forcing the plates away from each other as a restoring spring for the shock absorber 1, the spring being placed outside the casing 4 of the housing.

A further form of the invention is to be seen in figure 4, in which the end plates 2 and 3 are so guided that it is possible for their bellows-like casing 4 to be moved in the axial direction without there being any chance of the end plates being moved into a sloping position or being twisted. Such a guiding system is more specially to be used with the shock absorber 1 is likely to be acted on by uncontrolled impacts from different directions. It is more specially possible for the guiding effect to be produced by two telescoping and coaxially sliding sleeves 23 and 24, that are fixed to the separate end plates 2 and 3. These sleeves 23 and 24 are moved telescopingly in relation to each other, that is to say in and out of each other, while relative axial motion of the end plates 2 and 3 is taking place.

In this connection the telescoping sliding of the two sleeves into and out of each other gives a guiding effect cutting out any chance of an uncontrolled or irregular deformation of the bellows-like casing 4 when the impacts acting thereon are not more or less axial in their direction. In order, as noted, that there be no relative twisting of the end plates 2 and 3, an axial groove 25 may be machined into the one sleeve 24 with a head 16 on the other sleeve 23 running in it. The guiding system as in figure 4 may be used with the cylindrical bellows-like casing 4 and for the frusto-conical form 4.

Furthermore other details of design to be seen in the different figures of the shock absorber in keeping with the invention are not limited to such figures and may be used in the other forms of shock absorber as in the other figures. Any such changes and combinations are to be looked upon as parts of the present invention.

The designs of the shock absorber in keeping with the invention may all be fitted with a normal form of choke valve in the port 6. In this respect it is a question, as we have seen, of an adjustable valve, with which the resistance to flow of the air forced from the shock absorber 1 may be changed. This will make it possible for the damping properties or curve of the shock absorber to be changed at will and to be adjusted to be in harmony with the machine conditions where the shock absorber is to be used. If the frequency of the impacts to be damped is thought to be likely to low, the shock absorber of the invention may be used simply with the choke valve by itself and without any other valve fitting so that the air is let in and let off therethrough into and from the inside of the shock absorber 1.The only point to be given attention with such a form of shock absorber 1 is that the time needed by the shock absorber 1 for moving back into its starting position and taking in air after the impact has ended is much shorter than the time between one impact and the next one. If the conditions of operation are not like this, then it is possible, in keeping with a further part of the invention, for the shock absorber 1 to be fitted with a check valve in addition, that is as well fitted in a port running into the inside of the casing. This port may be the same as the port 6, in which the choke valve is placed, if the valve used is a choke valve with a check valve function as well.

However it is furthermore possible for there to be a separate port for a check valve in one of the end plates 2 and 3 (although this is not figured in the present case). The check valve is to be so fitted in the shock absorber 1 that when the housing is acted upon by the impact of some outside force, the valve automatically goes into its shut position and when the shock absorber is no longer acted upon by the impact it goes over into its open position. This makes it possible for the air shut up within the space 14 in the shock absorber to be let off only through the choke valve only when the shock absorber is acted upon by the impact, whereas the check valve is kept for letting in air when the shock absorber is freed of its load and is moving back into its starting position. In this respect the size of the check valve is naturally to be such that the resistance to the incoming air is very much less than the resistance offered by the choke when functioning. This makes certain that the expansion cycles of the shock absorber 1 are kept short so that it may be used for damping high frequency impacts.

Claims

1. A shock absorber comprising a housing made up of opposite rigid end plates and a bellows-like casing forming a connection between said end plates, one of said end plates having a port running into a space inside said housing, and an adjustable choke valve fitted in said port.

2. A shock absorber as claimed in claim 1 wherein said bellows-like casing has a frustoconical form.

3. A shock absorber as claimed in claim 1 or 2 comprising resilient wire means at folds of said casing.

4. A shock absorber as claimed in claim 3 wherein said wire means is made up of separate wire rings.

5. A shock absorber as claimed in claim 3 wherein said wire means is made up of at least one helical spring.

6. A shock absorber as claimed in claim 1 or claim 2 comprising at least one compression spring means placed between the said end plates, said spring means acting with a spring force on said end plates.

7. A shock absorber as claimed in claim 6 wherein said spring means is in the form of a single compression spring placed within said housing.

8. A shock absorber as claimed in any one of claims 1 to 7 comprising guide means for twistfree guiding of the end plates towards and away from each other in the axial direction of the bellows-like casing.

9. A shock absorber as claimed in claim 8 wherein said guide means comprises a first sleeve seated on one said end plate and a second sleeve seated on said other end plate, said two sleeves telescoping into each other with one thereof placed coaxially round the other, one such sleeve having a groove machined therein and the other said sleeve having a head thereon running in said groove in the axial direction of said casing.

10. A shock absorber as claimed in any one of claims 1 to 9 comprising a check valve in addition to the choke valve and a port to take up said check valve for letting air into said casing through said check valve.

11. A shock absorber as claimed in claim 1 wherein said choke valve is designed to give a check valve function in addition to the choke function thereof.

12. A shock absorber as claimed in claim 2 wherein the wavelength of the said folds becomes less from the end of the casing with the larger diameter to the end with the smaller diameter, such decrease in wavelength being at a low rate and continuous.

13. A shock absorber as claimed in claim 12 wherein the folds have radiuses of curvature decreasing at a low rate from the end of the casing with the greater diameter to the other end.

14. A shock absorber as claimed in claim 12 or claim 13 wherein the folds have such a gradation in size that the stress () of the folds is given by the equation =M/W=constant wherein M is the bending moment and W is the moment of resistance.

1 5. A shock absorber as claimed in any one of claims 12 to 14 wherein the folds have inner and outer crest parts with elliptical curvature, the major axes of all ellipses being of equal size and the minor axes of the folds increasing in length with the distance from the end of the casing with the smaller diameter.

1 6. A shock absorber as claimed in any one of the clalims hereinbefore designed for use in office machines.

17. A shock absorber as claimed in claim 1 substantially as described hereinbefore with reference to and as illustrated in figure 1 of the drawings herein.

18. A shock absorber as claimed in claim 1 substantially as described hereinbefore with reference to and as illustrated in figure 2 of the drawings herein.

19. A shock absorber as claimed in claim 1 substantially as described hereinbefore with reference to and as illustrated in figure 3 of the drawings herein.

20. A shock absorber as claimed in claim 1 substantially as described hereinbefore with reference to and as illustrated in figure 4 of the drawings herein.