Bordignon, Silvano (Via Garibaldi, 27 Rosà, Vicenza, I-36027, IT)
Bordignon, Romeo (Via M. Sanmicheli, 3/A Cassola, Vicenza, I-36022, IT)
Bordignon, Silvano (Via Garibaldi, 27 Rosà, Vicenza, I-36027, IT)
|1.||Gas spring, particularly of the type used in metal forming presses, comprising: a first, preferably cylindrical hollow casing (1) having two opposite parallel bases, in which a first one (18) of these bases is provided with an aperture (27), a piston (2) adapted to slidably move in a substantially airtight manner within said hollow casing, said first base (18) constituting an abutting member preventing said piston to slide out of said hollow casing, a rod (4) connected rigidly with an extremity thereof to a central portion of said piston and passing through said central aperture (27) in said base (18) so as to feature a portion (4a) thereof protruding on the outside of said hollow casing, a first sealed chamber (6) provided in the interior of said cylinder, and delimited by said piston and other inner walls of said hollow casing (1), on the opposite side of said rod (4), characterized in that it further comprises: a second sealed chamber (7), a first conduit (12) connecting the interior of said first sealed chamber (6) with the interior of said second chamber (7), first valve means (13) associated to said first conduit (12) and adapted to selectively open and close it, a third sealed chamber (8), a third conduit (16) connecting the interior of said third chamber (8) with said first conduit (12) at a position situated between said first valve means (13) and said first chamber (6), second valve means (17) provided on said third conduit (16).|
|2.||Gas spring according to claim 1, characterized in that there are provided: a second conduit (14) connecting the interior of said second chamber (7) with the interior of said third chamber (8), a pressure reducer (15) associated to said second conduit (14).|
|3.||Gas spring according to claim 1 or 2, characterized in that: a check valve (114) is provided in said third conduit (16), a conduit (16A) is provided in parallel with the section of said third conduit comprising said check valve (114), said parallel conduit (16A) includes said second valve means (17).|
|4.||Gas spring according to any of the preceding claims, characterized in that there are provided retaining means (20,22, 23; 30,31, 32) to selectively retain said rod (4) in its position when it lies in a predetermined position of its stroke.|
|5.||Gas spring according to claims 1 to 3, characterized in that: there is provided an outer conduit (40), which connects with said hollow casing (1) the inner chamber (41) that is arranged on the opposite side of said first chamber (6) with respect to said piston (2), said outer conduit (40) is connected to a source (42) of compressed gas via cutoff valve means (43), there is provided an aperture (44) that is capable of selectively opening into the outside ambient and is connected to said outer conduit (40) in the section thereof comprised between said cutoff valve means (43) and said inner chamber (41), there are provided vent valve means (45) adapted to open and/or close the access of said aperture (44) with respect to the outside ambient.|
|6.||Gas spring according to any of the preceding claims, characterized in that it further comprises: a plurality of further distinct and individual spring elements (41,42, 43) connected independently to said second chamber (7) via respective conduits (120,121, 122) which join with each other into a single common conduit (12) provided with said first valve means (13), in which the joining point thereof lies at a position between said spring elements (41,42, 43) and the position at which said first conduit (12) connects with said third conduit (16).|
|7.||Gas spring according to any of the preceding claims 1 to 4 and according to claim 6, characterized in that said first hollow casing (1) and said rod (4) are arranged relative to each other for a"singleacting" mode of operation, so as to eliminate any need for gastight sealing between said aperture (27) and said rod (4).|
|8.||Gas spring according to any of the preceding claims, characterized in that there are provided control means (100) adapted to selectively control the opening and closing of said first valve means (13) and said second valve means (17) as well as, where provided, said cutoff valve means (43), said vent valve means (45), to also actuate said selective retaining means (21,22, 23; 30,31, 32).|
|9.||Gas spring according to any of the preceding claims, characterized in that the portion of said first conduit (12) situated between said first chamber (6) and said first valve means (13) has an inner volume that is substantially nil.|
|10.||Gas spring according to any of the preceding claims, characterized in that the portion of said third conduit (16) situated between said first chamber (6) and said second valve means (17) has an inner volume that is substantially nil.|
|11.||Gas spring according to claim 9 or claim 10, characterized in that said first conduit (12) and said third conduit (16) connect with the interior of said first chamber (6) via two respective, mutually distinct apertures (7A, 8A).|
|12.||Method of operation of a gas spring according to any of the preceding claims, characterized in that said valve means (13,17) are actuated in the following orderly sequence: closing of said first valve means (13), opening of said second valve means (17), closing of said second valve means (17), opening of said first valve means (13), in which following said opening of said second valve means (17), and prior to the closing of said second valve means (17), said rod (4) undergoes a compression phase, and in which following said opening of the first valve means (13) said rod (4) undergoes a release phase which is the reverse of said compression phase. AMENDED CLAIMS [received by the International Bureau on 29 December 2003 (29.12. 03); original claim 1 replaced by new claim 1 ; remaining claims 212 unchanged New amended claim 1 1. Gas spring, particularly of the type used in metal forming presses, comprising: a first, preferably cylindrical hollow casing (1) having two opposite parallel bases, in which a first one (18) of these bases is provided with an aperture (27), a piston (2) adapted to slidably move in a substantially airtight manner within said hollow casing, said first base (18) constituting an abutting member preventing said piston to slide out of said hollow casing, a rod (4) connected rigidly with an extremity thereof to a central portion of said piston and passing through said central aperture (27) in said base (18) so as to feature a portion (4a) thereof protruding on the outside of said hollow casing, a first sealed chamber (6) provided in the interior of said cylinder, and delimited by said piston and other inner walls of said hollow casing (1), on the opposite side of said rod (4), characterized in that it further comprises: a second sealed chamber (7), having fixed and constant volume, a first conduit (12) connecting the interior of said first sealed chamber (6) with the interior of said second chamber (7), first valve means (13) associated to said first conduit (12) and adapted to selectively open and close it, a third sealed chamber (8), having fixed and constant volume, a third conduit (16) connecting the interior of said third chamber (8) with said first conduit (12) at a position situated between said first valve means (13) and said first chamber (6), second valve means (17) provided on said third conduit (16). a third conduit (16) connecting the interior of said third chamber (8) with said first conduit (12) at a position situated between said first valve means (13) and said first chamber (6), second valve means (17) provided on said third conduit (16).|
|13.||2 Gas spring according to claim 1, characterized in that there are provided: a second conduit (14) connecting the interior of said second chamber (7) with the interior of said third chamber (8), a pressure reducer (15) associated to said second conduit (14).|
|14.||3 Gas spring according to claim 1 or 2, characterized in that: a check valve (114) is provided in said third conduit (16), a conduit (16A) is provided in parallel with the section of said third conduit comprising said check valve (114), said parallel conduit (16A) includes said second valve means (17).|
|15.||4 Gas spring according to any of the preceding claims, characterized in that there are provided retaining means (20,22, 23; 30,31, 32) to selectively retain said rod (4) in its position when it lies in a predetermined position of its stroke.|
|16.||5 Gas spring according to claims 1 to 3, characterized in that: there is provided an outer conduit (40), which connects with said hollow casing (1) the inner chamber (41) that is arranged on the opposite side of said first chamber (6) with respect to said piston (2), said outer conduit (40) is connected to a source (42) of compressed gas via cutoff valve means (43), there is provided an aperture (44) that is capable of selectively opening into the outside ambient and is connected to said outer conduit (40) in the section thereof comprised between said cutoff valve means (43) and said inner chamber (41), there are provided vent valve means (45) adapted to open and/or.|
In view of ensuring a better understanding of the actual scope of the present invention, it appears adequate at this point to make it clear that, when the return stroke of the piston is defined as a"controlled"one, this is intended to mean that both the moment at which the return stroke of the piston begins at the end of the impact or compressive stress, and the speed at which said return stroke takes place are not free and dependent on the sole elastic reaction of the elastic means used, but are somehow controlled both as far as said initial moment and said return stroke rate are concerned.
The state of art concerning a spring provided with at least a piston, which is adapted to act as a dampening member under abrupt loads
being imposed thereupon, and capable of recovering into its initial working position in a substantially smooth manner, i. e. regaining such an initial position not only without any violent return movement, but also without any delay or braking effect, is generally known and has already been discussed exhaustively in the past, along with the state of the prior art, e. g. in the publication EP 1 186 795 A2 (claiming a priority date of August 29,2000), filed by these same Applicants. A further description thereof shall therefore be omitted here for reasons of brevity.
The solution disclosed in the above-mentioned patent publication turns out to be fully functional, reliable and advantageous, actually.
However, it still has a drawback. As a matter of fact, although a gas spring of this kind makes it possible to very effectively control and adjust the return speed of the piston, the piston return stroke itself is not fully "controllable"in the real sense, since the beginning of the return phase of the piston occurs immediately upon cessation of the working pressure exerted on the piston rod, without any time interval of a controllable length being allowed to occur therebetween.
As all those skilled in the art are largely aware of, such a fact gives rise to some drawbacks that may be fully unacceptable, especially in some technological applications such as-as already hinted above-in sheet- metal forming and, more generally, metal-working presses.
Disclosed, e. g. in WO 96/39588, WO 92/19886 and even in US 5,076, 404, are also a number of innovatory technical solutions, which enable the moment, at which the piston return stroke begins, to be controlled with a great accuracy. These solutions, therefore, actually represent gas springs that are"controllable"from the above-mentioned point of view. On the other hand, however, all these solutions imply a rather complicated mode of operation, since they in all cases require the provision of two cylinders and related pistons and actuating rods, while in the preferred application, i. e. in sheet-metal forming presses, use is made
on the contrary of a single rod, even if associated to several members or organs.
A number of other solutions are also known, which make use of springs for the above-described application purposes, and which are based on the use of both gas and hydraulic medium, i. e. oil, at the same time for operation. Unfortunately, these solutions, as disclosed for instance in WO 81/02044 and in US 5,161, 449, are expensive and complicated, since the presence of two technologies is obviously more severe than the use of the sole gas technology, not to mention the fact that the hydraulic technology is certainly most delicate and burdensome.
Known in the art is also a gas spring representing a variant of the gas spring embodiments indicated above, and disclosed in the afore cited patent publication EP 1 186 795 A2 (priority date: 29th August 2000), which provides a solution, based again on a combined gas and hydraulic oil spring that is effective in totally doing away with the above mentioned drawback. However, such a solution, although effective functionally and ensuring full"controllability"in the afore indicated sense and to the afore cited purposes, calls for a section using a hydraulic circuit to be specially provided and used. In other words, a solution of such a kind, like all other kinds of spring arrangements that are based on the use of combined gas and oil springs, while proving fully capable of not only complying with a wide variety of requirements in an effective manner, but also being manufactured using largely available and well-known techniques, are however associated with a couple of major drawbacks that make the use thereof critical in particularly demanding situations, i. e.: - higher manufacturing and operating costs, owing to the utilization of a hydraulic medium, i. e. the oil, and the resulting need to provide the related circuits, - a very intensive dissipation of heat, which must of course be
adequately disposed of, but anyway limits both the speed and the performance capabilities of such kinds of combined springs, and which by the way is the equally heavily weighing cause of an incremental energy usage, - and, furthermore, the resulting temperature increase that unavoidably takes place, consequently causes the oil to undergo a thermal expansion, thereby causing the spring itself to quickly deviate from the rated operating range thereof.
It would therefore be desirable, and it is actually a main purpose of the present invention, to provide a solution for the implementation of gas springs, in particular such springs that do not make any use of hydraulic oil, intended for use in heavy-duty metal forming equipment, in which such springs comprise a working piston and a cylinder adapted to slidably hold said working piston, the return stroke of which is selectively controllable as far as both the return stroke speed and, at least partially and under determined external conditions, the moment at which said return stroke starts are concerned, these springs being further capable of being easily and economically made and operated, using simple, readily available techniques and materials.
These aims, along with other features of the present invention, are reached in a gas spring made and operating as recited in the appended claims.
Features and advantages of the present invention will anyway be more readily and clearly understood from the description that is given below by way of non-limiting example with reference to the accompanying drawings, in which: - Figures 1 to 5 are schematical, symbolical views of the relative arrangement of the various component parts of a gas spring according to
the present invention, in five successive phases of an operating cycle thereof, respectively: - Figure 6 is diagrammatical illustrating the corresponding course of the pressure taking simultaneously place inside three respective chambers making up said spring; - Figure 7 is a partially enlarged view of an improvement variant of the spring illustrated in the preceding Figures; - Figures 8 and 9 are symbolical views of respective examples of embodiment of a device provided to hold and control the starting moment of the return stroke of the piston of a spring according to the present invention; - Figure 10 is a symbolical view of a further example of an improved embodiment of a gas spring according to the present invention; - Figure 10A is a view of the spring shown in Figure 10, in an improved operating configuration thereof; - Figure 11 is a view of an advantageous operating configuration of use of a plurality of springs according to the present invention; - Figure 12 is a schematical, symbolical view of the relative arrangement of the various component parts of a gas spring according to an improved variant of the present invention; - Figure 13 is a diagrammatical view of the course of the pressure inside one of the chambers of a spring according to the illustration in Figure 12, as measured at a definite given moment of the working cycle, during successive working cycles;
- Figure 14 is an enlarged view of a detail of Figure 12; - Figures 15A and 15B are respective views of two embodiment variants of a spring according to the present invention.
With reference to Figures 1 to 5, a gas spring according to the present invention can be noticed to essentially comprise: - a hollow cylindrical casing 1, - a piston 2, housed inside said hollow cylindrical casing 1 and adapted to tightly slide against the inner cylindrical walls of said casing, - a rod 4, which is rigidly applied on a side of said piston and is adapted to be alternatingly displaced inwardly and outwardly with respect to said cylinder 1, consistently with the motion of said piston, - a first sealed chamber 6 provided inside said cylinder and delimited by said piston and other inner walls of said hollow cylinder, and arranged on the opposite side of said rod 4 with respect to said piston, - a second sealed chamber 7, - a first conduit 12 connecting the interior of said first sealed chamber 6 with the interior of said second chamber 7, - first valve means 13 associated to said first conduit 12 and adapted to selectively open and close it, - a third sealed chamber 8, - a second conduit 14 connecting the interior of said second chamber 7 with the interior of said third chamber 8, - a pressure reducer 15 associated to said second conduit 14 and adapted to control and adjust a pre-determinable pressure reduction from said third chamber 8 to said second chamber 7, - a third conduit 16 connecting the interior of said third chamber 8 with said first conduit 12 at a position situated in the section thereof located upstream of said first valve means 13, second valve means 17 associated to said third conduit 16 and adapted to selectively open and close it.
According to the present invention, there are provided-as duly illustrated in the Figures, albeit just symbolically-suitable control means 100 adapted to actuate said firs and second valve means 13 and 17.
In an advantageous manner, said casing 1 and the related piston 2 and rod 4 are not double-acting, but simply single-acting, wherein this means that there exists a fully effective and operative sealing between said piston 2 and the inner wall of said casing 1, while said rod 4 itself, which is connected at an end portion thereof to the piston and forms the actuating member of the same piston, is adapted to slide in a non-tightly sealing manner in an aperture 27 provided in the middle of the upper base 18 of said first cylinder 1; the guide of the rod and piston assembly is ensured by the matching of shapes between the cylindrical wall of the piston and the inner cylindrical surface 19 of the casing 1 (see Figure 3).
The afore mentioned"single-acting"effect is called like this exactly owing to the above described nature of the couplings involved, that is the manner in which the various parts match with each other, i. e. a tightly sealing matching of parts in the first case and a non-tightly sealing matching of parts in the second case, whereby an elastic reaction of the compressed gas is caused to take place only in the chamber 6, the volume of which does not contain the rod, whereas the chamber 5, which is comprised between said hollow casing 1, said piston 2 and said rod 4, is by no means and in no way functional to and does by no means and in no way take part in the occurring operations, since the inner volume thereof is constantly at ambient pressure.
Those skilled in the art will of course be fully capable of readily noticing that a"single-acting"gas cylinder like the one that has been described above can be implemented by also interchanging the above- cited tightly and non-tightly sealing characteristics of the sealing means, i. e. gaskets provided between:
- said piston 2 and the inner wall of said hollow casing 1, and - the side wall of said rod 4 and the corresponding through-aperture 17A.
Those skilled in the art will also be fully capable of identifying the advantages (which shall therefore not be repeated here) of a single-acting cylinder over a double-acting one.
It will anyway be readily appreciated that the present invention applies, with no limitation or drawback whatsoever, also to gas cylinders of the illustrated kind, but of the cited"double-acting"type.
In addition, according to the present invention said third chamber 8 is only filled with gas to a normally very high pressure pre-loading value of up to 200 bar, or even higher, in accordance with the magnitude of the stress that must be sustained.
The operation of the spring according to the present invention is as follows (see Figure 6): - In the initial phase (Figure 1), said first chamber 6 and said third chamber 8 are in a state in which they are pre-loaded to a high working pressure, e. g. 100 bar, whereas-owing to the action of the pressure reducer 15-said second chamber 7 lies at a far lower pressure value, e. g. 10 bar. It should be pointed out here, although all those skilled in the art should be largely aware of this, that a pressure reducer is a device that is generally provided with an inlet and an outlet in two respective distinct volumes that are filled with gas at different pressure values, and is adapted to ensure, in the volume into which said outlet leads, a substantially constant, pre-settable pressure, which is sensibly independent of the pressure in the volume in which the inlet is situated, in the case that the pressure in said inlet volume (upstream pressure) is greater than the pre-set pressure value of said pressure reducer; when the
downstream pressure is on the contrary greater than the upstream pressure, then the pressure reducer is generally known to behave in the same manner as a closed valve, or check valve, and does not enable any gas to flow from the downstream volume into the upstream volume.
The valve 13 is closed and, as a result, there is no gas being transferred and, as a consequence, there is no levelling off of the gas pressure between the two chambers 6 and 8, which are connected with each other owing to the valve 17 being open, on the one side, and the chamber 7 on the other side.
The pushing means 20, which is illustrated in a conventional manner in the Figures so as to even include in the representation a rigid element of any kind that may be used to support a side of the workpiece being processed, moves into contact with the protruding upper stem portion 4a of said rod 4, which is in its top dead-centre position due to the pushing action exerted by the pressure of the pre-pressurized, levelled-off gas existing both in said first chamber 6 and in said third chamber 8; since said rod 4 is not yet undergoing any stress imposed upon it, the gas existing in the first chamber 6 keeps the piston 2 pressed against that base wall 18 of the hollow casing 1, in which said rod 4 is able to slide.
- In the subsequent phase 2 (Figure 2), the pushing means 20 presses against the upper stem portion 4a of said rod 4, thereby causing it to move downwards, thereby-owing to a cascade effect brought about as an immediate consequence-causes said first piston 2 to sink, i. e. to move downwards, too, thereby compressing the gas in both chambers 6 and 8, which communicate with each other via the conduit 16; at the end of this downstroke of the piston 2, said chambers 6 and 8 are at a pressure which is sensibly greater than the starting one, e. g. 200 bar, whereas the pressure in the second chamber 7 clearly remains unchanged, since the valve 13 is kept closed throughout this process.
In the process, the pressure reducer 15 ensures that no pressure and, therefore, no gas is transferred from the chamber 8 into the chamber 7 to any perceptible extent.
- In the subsequent phase 3 (Figure 3), the valve 17 is closed and, immediately thereupon, said valve 13 is opened; as a result, part of the gas at a pressure of, say, 200 bar existing in said first chamber 6 is able to flow into said second chamber 7 via said conduit 12 and the related valve 13, which has been just opened. The pressures in these two chambers level off at an intermediate value, which will anyway depend on the volume ratio existing between said chambers. However, owing to the volume of the chamber 7 being actually much larger than the residual volume of the chamber 6, the resulting pressure will of course be situated at a value that is much closer to the initial pressure value (10 bar) in the chamber 7, e. g. at a value of 18 bar.
- In the subsequent phase 4 (Figure 4), if the pushing means 20 is relieved of the pressure that was keeping it pressed against the rod 4 in the preceding phases, the rather low pressure of approx. 18 bar existing in the chambers 6 and 7 will prove sufficient in view of causing said pushing means 20 to raise, while anyway exerting a correspondingly weak and, furthermore, decreasing force, so that the return stroke of the rod is of course slowed down.
At the end of the upstroke of the rod and, therefore, the piston, owing to the increase in the volume of the chamber 6, the pressure in the two mutually communicating chambers 6 and 7 will decrease to a rather low value of minimum final pressure, e. g. 8 bar. It should be noticed that this final pressure will in all cases depend on the volume ratio existing between the two chambers 7 and 6; if such a ratio of the respective volumes of the chambers to each other is adequately large, then the final pressure will also be lower than the initial pressure of 10 bar, since in this last phase of the process part of the gas that was initially present in
the chamber 6 at a pressure of 100 bar has been transferred into the chamber 8 which now lies at the maximum pressure of 200 bar.
What in any case really matters is not so much the absolute value of the final pressure in the chamber 7 with respect to the previously existing value, but rather the controllability of the pressure reduction in the chambers 6 and 7, and this feature is can be obtained through a proper selection of the volume ratios of the chambers involved to each other.
Although not an ideal one, this situation, involving a rod 4 which presses quite lightly against the pushing means 20 during the upstroke, i. e. raising phase, without any delay in the starting moment of the return stroke taking place yet, may anyway prove acceptable in all those circumstances and processing conditions in which the low re-ascending force of said rod does by no way alter the surface appearance of the pushing means 20 and, furthermore, the moment at which the re- ascending movement starts may not be delayed.
- In the subsequent and last phase 5 (Figure 5) the valve 13 is first closed and, immediately thereupon, the valve 17 in the conduit 16 is opened; the initial pressure is therefore re-established in the chamber 7, owing to the valve 13 having been previously closed to prevent gas from flowing into the chamber 7 and, as a result, to prevent the pressure in this chamber from levelling off to the value of the pressure existing in the other chambers. Upon opening the valve 17, the high-pressure gas existing in the chamber 8 expands violently into the first chamber 6, but, owing to the fact that the piston 2 has already moved into the outer end of its stroke at the top dead-centre position, and therefore in contact with said base 18, the piston itself does not move any further. As a result, part of the gas in the chamber 8 is transferred, i. e. flows into said chamber 6, however without any further movement of the piston.
The working cycle of the spring in this way concluded and a new
working cycle can therefore be started.
The operation of the above described spring can be more readily understood by taking a look at Figure 6; the course of the instant pressure values in the above-described successive phases of the working cycle is indicated in this Figure, in which the three diagrams, as indicated at P6, P7 and Ps from top to bottom, refer to the inner pressure in the first chamber 6, the inner pressure in the second chamber 7 and the inner pressure in the third chamber 8, respectively.
In particular, following should be noticed in this connection: a) the pressures P6, Ps, follow an identical course during the phase 2 of the working cycle; this can be explained by the fact that, during said phase 2, the valve 17 is open and, as a result, the pressure tends of course to level off; b) there is always a pressure difference existing between P7 and Ps, owing to the provision of the pressure reducer 15 which does in no case allow for the pressures in said two chambers to be able to level off, not even during transients (as a matter of fact, the pressures in said two chambers might well equalize, but solely in the case that both valves 13 and 17 are opened at the same time: an occurrence that is anyway ruled out by the afore illustrated control sequence of the valves).
A useful advantageous improvement can be obtained with the set-up illustrated in Figure 7. In fact, if during the afore described phase 2 of the working cycle, in which the spring is being compressed (and, as a result, gas is caused to flow under pressure from the chamber 6 into the chamber 8), said valve 17 fails to open, i. e. remains closed for any reason whatsoever, i. e. even one that is not ascribable to the valve itself, but rather to said control means 100, for example, the pressure of the gas in said chamber 6 would then increase up to values that may sometimes be
even intolerable, since the gas contained in said chamber would be unable to escape into the chamber 8 through said valve 17, not to mention the outright enormous stresses and loads, which other parts of the set-up, such as the conduit 12, the valve 13 and even the casing 1, would unavoidably be exposed to.
In order to do away with such a drawback, said third conduit 16 is provided with a suitable automatic check valve 114, which is able to anyway and always ensure an unhindered passage of the gas compressed by the piston 2 from the chamber 6 to the chamber 8 during said phase 2 of the working cycle of the spring.
The stop valve 17, usually associated to the conduit 16, must therefore be inserted in a parallel conduit 16A, which must branch with its connection openings 16B and 16C into said conduit 16 upstream and downstream of said automatic check valve 114, respectively. It can further be readily appreciated that the provision of said check valve 114 does in no way and by no means affect or alter the operation of the spring in the other phases of the working cycle thereof, as described above.
In this way, as illustrated schematically in Figure 7, a circuit arrangement is provided, which enables all of the pursued aims to be reached and, in addition, allows for an easy installation in the most favourable positions, as well as a simple maintenance and disassembly of the various component parts, with obvious favourable effects on the actual possibility for the requirements connected with the need of setting, adjusting, repairing and replacing the individual parts and devices to be conveniently coped with.
As this has already been explained hereinbefore, the gas spring that has been just described above has a return or recovery stroke that may be considered as acceptable in all those cases in which it is the return or recovery speed of the same spring, and not the moment at which the
return stroke actually begins, that must be perfectly controllable. In those cases in which it is on the contrary required that also the starting moment of such a return stroke be controllable, an advantageous improvement can be introduced, wherein this improvement may be embodied in a number of different ways, such as illustrated in Figures 8 and 9 by way of mere example. This improvement consists in providing said rod 4 with an appropriate, selectively actuatable retaining device, which is adapted to restrain, i. e. stop the upstroke of the piston up to a desired instant.
This retaining device may for instance be comprised of a mechanism of the so-called"freewheel"type comprising an annular chamber 20 extending all around the rod, whose walls 21 are so inclined as shown in Figure 8, rotating members 23, or functionally equivalent means, being so provided in said chamber as to be capable of being engaged between said walls 21 and the outer surface of said rod, so that an upstroke movement of said rod will cause said rotating members to be automatically carried along against said inclined walls and this in turn causes the rod itself to undergo a corresponding reaction, until it is effectively stopped. When the piston and, therefore, the rod must then resume their upstroke movement, i. e. when it is desired that said upstroke be started, all it takes is to provide a minor release action, which would set said rotating members 23-which by the way can also be non-rotating-free from restraint, with the help of simple mechanical or air-operated means (not shown).
Another example of embodiment of a controllable retaining device for the rod 4 is illustrated in Figure 9, in which it can be noticed that the rod 4 is provided with a recess 30, a cotter pin 31 that is capable of selectively engaging into said recess being suitably provided slidably in a support 32 forming an integral part of the body of said casing 1. It can be readily appreciated that, if said cotter 31 is acted upon when the rod is fully lowered, as this is illustrated in the Figure, it will prevent the piston from
being able to raise, until the same cotter 31 is suitably actuated so as to move back out of said recess, thereby automatically releasing the rod and, as a result, enabling the return stroke of the piston to start at the desired moment.
It can also be noticed that a possible action on the rod, in view of preventing it from accomplishing its return stroke, is taken, i. e. occurs at an instant during the intermediate period situated between the phases 3 and 4 described above. In this period, the pressure in the chamber 6 will have already undergone a radical decrease from its maximum value due to the effect of the gas expanding from the same chamber 6 towards and into the chamber 7 (opening of the valve 13), so that the workload imposed on the rod retaining device is correspondingly modest. Even for this reason, said rod retaining device, as generally described with reference to Figures 8 and 9, is not a part of the present invention and is fully capable of being implemented by all those skilled in the art in the form that will most adequately suit any particular requirement, design or application constraint that may possibly be coped with.
However, in certain kinds of uses and applications it might be required and/or desirable that-upon conclusion of the compression phase and before the return stroke of the piston 2 is started, and therefore in the intermediate period between the afore-described phases 3 and 4, during which the pressure in the chamber 6 has already undergone a radical decrease from its maximum value, e. g. 200 bar, to a value of approx. 18 bar, due to the effect of the gas expanding from the same chamber 6 towards and into the chamber 7 following the opening of the valve 13- the rod 4 itself be not only blocked in its bottom dead-centre position by the force exerted on it by the pushing means 20, but be capable of performing a further residual downstroke movement (or, with reference to Figure 10, a limited extent of additional lowering movement) so as to enable the protruding upper stem portion 4a thereof to physically separate from said pushing means 20 in a distinct manner.
There may be various reasons behind the actual advantage of such an additional phase; anyway, all of them are certainly well-known to those skilled in the art, so that no need arises here for them to be explained any further.
In order to allow for such an additional step to be performed, the spring according to the present invention is provided with an outer conduit 40, which connects a variable-volume chamber 41, as delimited by: - the side surface of the stem of the rod 4, - the upper portion of the piston 2 adjacent to said rod, - the inner surface of said hollow casing 1, - the inner surface of said upper base portion 18, with a source 42 of pressurized gas, preferably compressed air, wherein the inflow of said pressurized gas into said conduit 40 is controllable with the help of usual, selectively controllable cut-off means 43, as this is best shown in Figure 10.
At a point located downstream of said cut-off means 43 with respect to said compressed-air source 42, and in said outer conduit 40, there is provided an aperture 44 that is capable of opening into the outside ambient through a further vent valve 45.
Furthermore, said chamber 41 is sealed in an air-tight manner, and this obviously means that the piston 2 and the casing 1 are not of a single-acting type any longer (as this has been defined and explained hereinbefore) and that, therefore, the need arises for an air-tight sealing to be positively ensured between said rod 4 and said opening 17 in which the rod itself slides.
The operation of a gas spring embodying such a kind of improvement is as follows: the spring itself keeps operating exactly according the five afore-described phases, with the difference, however, that two additional steps, to be defined as phase 3A and phase 3B hereinafter, are introduced between the phase 3 and the phase 4. Immediately upon the conclusion of the phase 3, the phase 3A is therefore started, in which the cut-off means 43 in the conduit 40 are opened, thereby allowing a flow of compressed- air to flow from the supply source 42 into the chamber 41 and, thus, putting the chamber 41 under pressure, i. e. raising the pressure in said chamber 41. However, owing to the contrasting pressure in the chamber 6 is rather low, the ultimate result of all this is that the differential pressure existing between the opposite faces of the piston 2 tends to cause the same piston to be pushed against the bottom 5 of the hollow casing 1, thereby causing it to additionally perform a residual final downstroke movement Cr, as this is illustrated schematically in Figure 10A as compared with Figure 10, said Figure 10A showing the spring at an instant immediately following said additional phase 3A.
It can therefore be readily appreciated that, by covering said additional final length of downstroke displacement, the rod 4 separates physically from the pushing means 20, thereby attaining the desired result.
The actions that are taken in the subsequent phase 3B are practically the opposite of those described in the preceding phase 3A, i. e. said cut-off means 43 are closed and the vent valve 45 is opened, thereby bringing the chamber 41 immediately back to its initial pressure value. The overall effect of these operations is obviously a restoration, in the chamber 6, of the same conditions as the ones existing at the end of the phase 3, so that even the piston 2 is able to raise back along said downstroke length Cr, thereby regaining the position illustrated in the preceding Figure 3.
From this point on, the working cycle of the spring goes on exactly according to the afore described phases 4 and 5.
It stands as a matter of fact that, in order to enable the various component parts of the described types of springs to work in a correctly synchronized manner, even the retaining/releasing means 21,22, 23 provided to stop and release the movement of the rod 4, and the functionally equivalent means 30,31 and 32, as well as the valve means 43 and 45, must be suitably connected to said control means 100, which must in turn be so provided as to be able to send, at a pre-determinable rate, a definite sequence of signals/commands to the various valve means described above, as this is illustrated symbolically in Figures 1,7, 8,9 and 10.
The above-described spring allows for an advantageous possibility of extending the application scope thereof : with reference to Figure 11, it is considered appropriate to point specially out that a spring according to the present invention cannot be solely limited to a single elastic-resistance and pushing element, and related gas-pressure chambers, but can actually comprise in an advantageous manner a plurality of distinct and individual elastic-resistance elements 41,42, 43..., which may even be different from each other, but in all cases connected to the same common chamber 7 (which keeps connected via the conduit 16 with the chamber 8, which therefore acts as common element, exactly as the chamber 7).
The respective conduits 120,121, 122 for connection to the common chamber 7 join with each other, as well as with the conduit 12, at a point located upstream of the common chamber 7; the other elements illustrated in Figure 11 have construction and functional characteristics that are fully recognizable on a basis of close analogy, so that they are not identified specifically.
The operation of the devices that have been described above with reference to Figure 11 does not involve any particular difficulty or problem, since said spring element 41,42, 43, in the typical and preferred
use thereof, can be pressed and released in a perfectly synchronized manner, owing to them being related to, i. e. involved by the same metal- forming cycle.
In substance, each spring element is actuated at the same time, so that a kind of"diffuse spring"is practically obtained, in which a plurality of distinct elements of elastic resistance, provided that they are operating synchronically, are associated to and linked up with a single assembly of other common elements (i. e. the chambers 7,8 and the valves 13 and 17).
The advantage that is brought about by this improvement is readily appreciable and is of a both economic and functional nature: it in fact enables a plurality of individual chambers, which have to be filled with gas and are linked up with respective distinct elastically resisting elements, to be eliminated and be replaced by a single chamber 7 and 8, a single conduit 12 and related valve 13, a single conduit 16 and related valve 12, in which each one of these single elements will of course be suitably sized.
This solution, therefore, enables even further clear advantages of a manufacturing-related and functional nature to be obtained, since also said control means 100 are consistently downsized and simplified.
However, in the course of an extensive use thereof in practical industrial applications, it has been found that these gas springs, although very effective, turn out to be rather expensive owing to the various component parts used therein and, in particular, to the cost of the pressure reducer 15 installed between the first low-pressure chamber 7 and the second high-pressure chamber 8.
It has therefore been found very desirable, and it is actually the main purpose of the following advantageous variant of embodiment, to provide a kind of gas spring which, while preserving the ability of the return or
recovery stroke to be fully controllable, and therefore keeping the main advantageous features of the afore-described springs, is capable of being produced in a more cost-effective manner and ensures an at least equal level of simplicity and reliability as far as its installation and operation are concerned.
A spring made according to the above-indicated principles has been allowed to undergo extensive runs of functional tests in view of verifying the performance capabilities and the durability thereof. In the course of these test runs, which have been carried out with the pressure reducer 15 adjusted at different settings, it has been most surprisingly found that, the more the pressure reducer was being set at increasingly lower pressure values (i. e. the more the second sealed chamber 7 was being brought to work at an increasingly lower pressure), the more the overall operation of the spring tended to become substantially independent of the actual setting of said pressure reducer.
In view of thoroughly investigating and being able to go to the bottom of the so observed phenomenon, a closer look has been taken at the diagram appearing in Figure 6.
It has in this way been possible to actually notice that each curve P7 and Ps relating to the course of the pressure in the two respective pressure reservoirs or chambers 7 and 8, although varying in an even substantial manner relative to the extreme values thereof, keeps in all cases itself within an operating range that is markedly distant from that of the other curve.
In fact, the curve P7 varies from a minimum of 8 bar to a maximum of 18 bar, whereas the curve Ps varies from a minimum of 100 bar to a maximum of 200 bar. As a result, it can be stated without any hesitation that each curve varies by 100% with respect to the minimum values thereof, whereas the curve P7 stays on average at a pressure level which is
equal to only 10% of the average pressure value of the curve Ps.
Conclusively, the pressure separation effect brought about by the pressure reducer, in combination with the operation of the valves, generates a difference in the level of the pressure between the two reservoirs 7 and 8, which remains substantially stable at a high level throughout all phases of the working cycle.
It logically ensues that such a situation can but be consolidated if the element connecting said two reservoirs 7 and 8, i. e. the pressure reducer 15, boosts its pressure separation effect; however, considering that the most effective pressure separator between two such reservoirs is the full fluid-tightness thereof with respect to each other, it can be concluded that such a result can be obtained by simply removing both the pressure reducer 15 and the related conduit 14 from the afore described circuit set- up according to the present invention, as this is illustrated schematically in Figure 12.
And, as this has already been set forth above, experimental data have fully confirmed this theoretical inference.
Going on with the experimental work, if the spring is started to work and the course of the pressure in the reservoir 7 is observed, it can be noticed that, during the initial cycles C1, C2, C3,... C5, and so on, at the instant immediately following the opening of the valve 13 (upon the closing of the valve 17, which in turn follows the compression of the piston) the pressure P7, follows a course that tends to generally rise in an asymptotical manner, as symbolically illustrated by the graph in Figure 13, in which the number of the successive initial cycles C1, C2, C3,... C5, etc. of operation of the spring is represented on the abscissa, while the pressure P7, as measured in each cycle at the exact instant immediately following the opening of the valve 13, is represented on the ordinate.
As it can be noticed, the pressure P7 tends to rise, but also to
eventually level out at a definite value Pi, which is then maintained indefinitely throughout the subsequent operation of the spring.
This phenomenon may be explained as follows: upon the opening of the valve 13, during the first cycle, the amount of gas transferring into the chamber 7 will on the one side depend directly on the pressure difference existing between said chamber 7 and the remaining chamber 6 and, on the other side it will depend inversely on the ratio of the volume of the chamber 7 to the volume existing upstream of the valve 13; this volume Vm includes both the volume of the chamber 6 and the volume of the three-arm conduit delimited by the chamber 6, the valve 17 and the valve 13; this volume Vm is schematically identified in Figure 14 by the visibly dotted portions of said conduit, further of course to the remaining chamber 6.
In the course of the next phase, when the piston moves slowly back into its resting (i. e. raised) position, part of the gas in the chamber 7 flows back into the chamber 6, the volume of which therefore increases gradually, so that the pressure in said chamber 7 decreases.
In the chamber 7, therefore, there occurs a sequence of inflows and outflows of gas, which brings about the afore-explained pressure fluctuation effect. However, setting aside actual technical explanations that would prove much too ponderous to be discussed here in an analytical manner, it is sufficient to consider the fact that a stabilisation of the pressures at corresponding instants of successive cycles must necessarily take place, the opposite case being simply impossible. If the occurrence of the opposite case is in fact supposed, the pressure should increase continuously (if the amount of inflowing gas prevails) or decrease continuously (if the amount of outflowing gas prevails), i. e. an occurrence that is clearly impossible considering the initial conditions and the mode of operation and, in particular, given the fact that the upper limit set to the pressure P7 is determined by the maximum pressure of the chamber
8, while the minimum pressure cannot of course be lower than zero.
The stabilisation of the pressure at corresponding instants of successive cycle, as specified in a more detailed manner above, has therefore been demonstrated by the logical way.
However, the stabilisation of the operation of the gas spring is rather dependent on the volume Vm and, if such a volume is too great, the resulting stabilisation effect becomes more uncertain and slower (i. e. requires a higher number of cycles).
In order to let the stabilisation of the pressures in the successive cycles be more effectively and certainly controllable, it has been found of advantage to minimize said volume Vm, and this object is quite easily reached in a gas spring embodied according to the illustration appearing in Figure 15A or Figure 15B, which show respective embodiments, in which the conduits between the three chambers 6,7 and 8 are practically reduced to nil, or to the minimum technically possible value, apart of course from the inner volumes of the valves 13 and 17, which cannot be reduced beyond certain limits imposed by constraints set by the functionality of the valves themselves.
In particular, according to the illustration in Figure 15A, the two chambers 7 and 8 are arranged on opposite sides of the chamber 6, from which two respective apertures 7A and 8A open directly, i. e. practically without any connecting conduit therebetween, into the respective valves 13 and 17; this solution practically enables the volumes of those conduits to be nullified, which do not anyway take inherently part in the actual functionality of the spring, since they are constantly connected with the chamber 6 and can therefore be considered as being a part thereof, however with a non-compressible volume that cannot therefore be used in the cycle.
Such a solution may however present some difficulties and imply
sensibly higher manufacturing costs, owing to the need for said apertures to be duplicated. In order to do away with such a drawback, the embodiment illustrated in Figure 15B may therefore be advantageously used, in which the two chambers are practically in contact with the outer casing of the chamber 6, so as to nullify the volume Vm of said three-arm conduit, except for the minimum length thereof required to accommodate the two valves 13 and 17.
It can furthermore be readily appreciated that the preferred embodiments and/or the variants thereof illustrated in Figures 7 to 11, as well as the modes of operation referring to such embodiments and related variants, equally apply to this variant, since they relate to parts and functions that are external to the conduit 14 and the pressure reducer 15 associated thereto, which are eliminated in this case. Therefore, for reasons of greater clarity and brevity, they shall not be repeated here and are considered as being included in this description.