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Title:
ROLLING BEARING AND SEISMIC INSULATOR COMPRISING SAID ROLLING BEARING
Document Type and Number:
WIPO Patent Application WO/2008/126120
Kind Code:
A2
Abstract:
The present invention refers to a roller bearing (1) particularly suitable for use in seismic isolator, comprising a sliding plate (2) having a substantially circular bottom surface (3) intended for resting and rolling on a layer of balls (4), a boundary element (5) of the layer of balls substantially ring-shaped surrounding the bottom surface and having an internal knife-shaped edge and a f rustoconical ring-shaped interspace (7) for the accommodation and recirculation of the balls open towards the bottom surface.

Inventors:
VALENTINI Valentino (Via Municipio 26, Marano Marchesato Cosenza, I-87040, IT)
Application Number:
IT2008/000231
Publication Date:
October 23, 2008
Filing Date:
April 09, 2008
Export Citation:
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Assignee:
VALENTINI Valentino (Via Municipio 26, Marano Marchesato Cosenza, I-87040, IT)
International Classes:
F16C29/00; E04H9/02; F16C19/12; F16C21/00
Domestic Patent References:
WO1999039985A11999-08-12
Foreign References:
DD279047A11990-05-23
DE1803946A11969-05-29
EP0467670B11995-03-01
US5689919A1997-11-25
FR969627A1950-12-22
DE1294108B1969-04-30
Attorney, Agent or Firm:
FERRECCIO Rinaldo et al. (BOTTI & FERRARI S.r.l, Via Locatelli 5, Milano, 1-20124, IT)
Download PDF:
Claims:

CLAIMS

1. Roller bearing characterised in that it comprises a sliding plate having a substantially circular bottom surface intended for resting and rolling on a layer of balls, a boundary element of said layer of balls substantially ring-shaped surrounding said bottom surface and having an internal knife-shaped edge, a frustoconical ring-shaped interspace for the accommodation and recirculation of balls open towards said bottom surface.

2. Bearing according to claim 1, further comprising a preset number of passages arranged at a substantially opposite position with respect to said bottom surface, for the insertion of a preset number of balls into said interspace.

3. Bearing according to claim 1 or 2, wherein said sliding plate comprises a substantially frustoconical inclined side surface. 4. Bearing according to claim 3, further comprising a covering cap associated to said sliding plate, arranged at a preset spaced relation from said side surface in such a manner to define said interspace.

5. Bearing according to claim 4, wherein said boundary element is constrained in rotation to, and moveable axially with respect to, said cap.

6. Bearing according to any one of the preceding claims, further comprising an accommodation seat for engaging the bearing with a preset body, said accommodation seat being provided in said sliding plate at one end portion opposite to said bottom surface. 7. Bearing according to any one of claims 3-6, wherein between said side surface and said bottom surface is defined a bevelled edge.

8. Bearing according to any one of the preceding claims, wherein said interspace has an end delimited by an annular groove.

9. Bearing according to any one of the preceding claims, wherein said

bottom surface is flat or spherical cap shaped.

10. Transport assembly for controlled switching from sliding to rolling friction and vice versa, comprising an idle support with a high coefficient of adherence adapted to bear a preset load Fc, a rolling element accommodated inside said idle support and substantially free to slide vertically within it for a preset limited length section, a switching device adapted to transfer said load from said idle support to said rolling element and vice versa.

11. Transport assembly according to claim 10, wherein said switching device comprises thrust means which can be activated on said rolling element, propulsion means adapted to develop a force Fl substantially corresponding to said load Fc, said force acting on said thrust means for a preset period of time transferring said load from said idle support to said rolling element, and activating means for controlling said propulsion means.

12. Transport assembly according to claim 11, wherein said thrust means are mechanical means acting on said rolling element.

13. Transport assembly according to claim 11, wherein said thrust means are hydraulic means acting on said rolling element. 14. Transport assembly according to any one of claims 10 - 13, wherein said rolling element consists in a roller bearing comprising a sliding plate having a substantially circular bottom surface resting on a layer of balls, a boundary element of said layer of balls substantially ring- shaped surrounding said bottom surface and having an internal knife- shaped edge, a frustoconical ring-shaped interspace for the accommodation and recirculation of balls open towards said bottom surface.

15. Seismic isolator for isolating a superstructure from the movement of the ground on which said superstructure lies during a seismic event, comprising:

A sliding base integral to the ground,

An idle support with a high coefficient of friction arranged above said sliding base adapted to bear a preset load Fc dependent on said superstructure ,

A roller bearing comprising a sliding plate having a substantially circular bottom surface resting on a layer of balls arranged on said sliding base, a boundary element of said layer of balls substantially ring-shaped surrounding said bottom surface and having an internal knife-shaped edge, a frustoconical ring-shaped interspace for the accommodation and recirculation of balls open towards said bottom surface.

A switching device adapted to transfer said load from said idle support to said roller bearing and vice versa.

16. Isolator according to claim 15 further comprising a fixing header integral to said superstructure. 17. Isolator according to claim 15 or 16, wherein said sliding base is flat or spherical concave cap shaped.

18. Isolator according to any one of claims 15-17, further comprising a sheet of preset metal or metal alloy integral with, and covering, said sliding base. 19. Isolator according to any one of claims 16-18, further comprising a bridge element articulated beneath said fixing header through a ball joint.

20. Isolator according to any one of claims 15-19, wherein said switching device comprises thrust means which can be activated on said roller bearing, propulsion means adapted to develop a force Fl substantially corresponding to said load Fc, said force acting on said thrust means for a preset period of time transferring said load from said idle support to said roller bearing.

21. Isolator according to any one of claims 15-20, wherein said switching device comprises activation means for the control of said

propulsion means which can be activated in an inertial manner by said movement of the ground upon reaching a preset horizontal acceleration value of the ground.

22. Isolator according to claim 20 or 21, wherein said thrust means comprise a first chamber and a second chamber expandable under hydraulic oil pressure and in fluid communication with each other.

23. Isolator according to claim 22, wherein said first expandable chamber is defined inside said idle support and said expandable second chamber is comprised between said idle support and said roller bearing. 24. Isolator according to claim 23, wherein the increase of said hydraulic oil pressure in said first chamber occurs faster with respect to the increase of said hydraulic oil pressure in said second chamber.

25. Isolator according to any one of claims 15-21, wherein said switching device comprises enabling/ disabling means for controlling said propulsion means with autonomous energy.

26. Isolator according to claim 25, wherein said enabling/ disabling means comprise local and/ or remote sensors.

27. Isolator according to claim 25 or 26, wherein said thrust means are activated by the thrust of a preset gas or mixture of gases provided by the abovementioned propulsion means.

28. Isolator according to any one of claims 25-27, wherein said preset gas is carbon dioxide.

29. Isolator according to claim 28, wherein said carbon dioxide is liquid.

Description:

Title: Rolling bearing and seismic insulator comprising said rolling bearing

DESCRIPTION Field of application In its most general aspect, the present invention refers to the technical sector of elements of reduction and control of the friction between two bodies, in particular, to the sector of the so-called ball bearings and roller bearings.

Still more in particular, the invention refers to a roller bearing in particular but not exclusively suitable to be used in a transport assembly for heavy loads with a controlled switch of friction, and in a seismic isolator of the kinematic type.

Therefore, for exemplifying and non-limiting purposes, the roller bearing according to the present invention shall be described hereinafter with reference to the seismic prevention sector, in particular to the seismic isolator sector.

Prior Art

As known, in the building and in the constructions sector in general, particularly felt is the need to provide structures extremely resistant and capable of overcoming even violent natural events such as earthquakes, especially undulatory earthquakes, without any damage.

In order to meet such need, the prior art has provided construction methods in which the so-called seismic isolators are used.

A seismic isolator is a special device capable of isolating a superstructure, for example a residential construction such as a building, a flat, a house and similar constructions, but also constructions of the type of industrial plants and various infrastructures, from the movement of the ground on which the superstructure lies, during a seismic event or an earthquake. Among the various types of seismic isolators, though advantageous, the ones most indicated specifically as elastoplastic dampers and the

structural energy loss systems, reveal some drawbacks.

As a matter of fact, though capable of preventing a building for example from collapsing upon the occurrence of an earthquake, the abovementioned isolators are not capable of ensuring suitable protection to people possibly present in the same building during the earthquake.

Another solution provided by the prior art consists in the use of the so- called kinematic isolators which are substantially characterised for the fact of, as isolating elements for isolating the superstructure from the ground, balls or ball bearings or roller bearings capable of moving on a surface referred to as sliding surface, also defined as rolling or slipping surface.

In practice, such isolators act as some kind of slides, interposed between the ground and the superstructure, which allow the same structure to move, with low friction, on the rolling surface integral with the ground.

Also such type of isolators, though advantageously providing high isolation capacity, , consisting mainly in reducing the horizontal components of the relative acceleration transmitted to the superstructure to values equivalent to the to the rolling coefficient of friction, reveal some drawbacks.

In particular, the isolators provided with isolation elements made up of balls with a rolling constraint between flat or spherical surfaces, in the simultaneous presence of Love waves and Reyleigh waves at the same frequency, that is in the presence of rototranslation motion, suffer from the drawback that, once the seismic event is over, the final relative position of the balls no longer corresponds to the initial position before the occurrence of the seism.

In this case, it is even possible that the balls be dislodged from their provided seat, with negative effects on the integrity of the superstructure .

The abovementioned drawback is referred to as kinematic inconsistency and it generally affects all the isolators provided by the prior art which employ balls rolling between the cap surfaces, where one surface corresponds to the aforementioned sliding surface integral with the ground, while the other corresponds to a rolling surface of the same bearing.

The composite linear sliding isolators, such as the composite one-way recirculation bearing or ball isolators, known in the art to prevent kinematic inconsistency, are not capable of isolating from the vertical torsion generated by the Love waves.

Still regarding the rolling surface, it should be observed that when such rolling surface is flat or spherical, the relative isolator is critically subject to the effect of the wind to the point that, in order to be stable in the presence of strong wind, such isolators require to be provided with auxiliary centring and damping elements which imply providing an additional transmission element thus inevitably leading to nullifying the advantage of the potential high isolation of the rolling on balls.

In particular, the centring elements, which can be provided with various degrees of elasticity, have resonance frequencies which inevitably lie within the intense spectrum of the seism.

Consequently, damping elements are required with characteristics such that while the superstructure is isolated from very high frequencies, it is also integrally subjected to substantial low frequency oscillations. Furthermore, in a system comprising a plurality of isolators of the abovementioned type, there are problems linked to the dynamics due to the fact that the centre of thrust of the interactions with the ground of such system is not always on the vertical axis of the centre of gravity of the superstructure, which means that the resultant of the transmitted forces has a vertical moment not null with respect to the centre of gravity of the superstructure itself.

It should be observed that isolators with a conical sliding surface would

not be subjected to the abovementioned drawbacks due to the wind, but, they would be subject to an even more serious drawback, related to the vertical impulse peak which would occur upon the passage, through the centre of the conical surface during the seism, of the ball or of the rolling element.

In this case a counter-impact (rebound) would be generated on the superstructure, with vertical and horizontal instantaneous accelerations even greater than the ones caused by the seismic event itself as well as consequently inevitable damages also on the rolling surface.

Consequently, in practice, a rolling surface of the abovementioned type is to be considered impracticable.

Furthermore, it should be observed that all the ball isolators provided by the prior art suffer from the further serious drawback of the so-called cold welding, due to a restricted contact surface area between the isolation elements and the sliding surface, which is also subjected to a high pressure, that is, to high load values, for long periods of time.

In other words, the resistance of a superstructure against the seismic waves as described above, to now represents a substantial unsolved problem in the construction sector to which the prior art still provides inadequate solutions.

Therefore, it would be desirable to provide a kinematic seismic isolator capable of overcoming the abovementioned drawbacks of the prior art, in particular a seismic isolator of the abovementioned type, provided with isolation elements capable of ensuring, concerning friction, an almost complete isolation of a superstructure from the ground in the event of an earthquake in particular of the undulatory type, and which is at the same time practically not affected by the wind in the absence of a seismic event. Summary of the invention

The present invention provides isolating means for reducing and

controlling friction between two bodies of the roller bearing type capable of overcoming the abovementioned drawbacks, and such to provide an almost complete isolation of a first body moving relatively to a second body. Therefore, within the scope of certain embodiments, the present invention refers to a roller bearing characterised in that it comprises a sliding plate having a substantially circular flat or spherical cap-shaped bottom surface intended for resting and rolling on a layer of balls, a boundary element of said layer of balls substantially ring-shaped surrounding said bottom surface and having an internal knife-shaped edge, and a frustoconical ring-shaped interspace for the accommodation and recirculation of balls open towards said bottom surface.

Within the scope of other embodiments, the present invention refers to a transport assembly for switching the friction from a sliding to a rolling friction and vice versa, particularly suitable for moving loads, even heavy ones, preferably comprising a roller bearing of the abovementioned type.

Still within the scope of other embodiments, the present invention refers to a seismic isolator of the kinematic type comprising a transport assembly for switching the friction from a sliding to a rolling friction and vice versa, including a roller bearing of the abovementioned type.

Further characteristics and advantages of this invention shall be clearer from the detailed description, provided hereinafter with reference to the attached drawings, given solely for indicative and non-limiting purposes.

Brief description of the drawings In such drawings:

Figure 1 illustrates a perspective view with cut-away portions of a roller bearing according to the present invention; Figure 2 illustrates a view with separated parts of the bearing of figure

i;

Figure 3 illustrates a cross-sectional and smaller schematic view of the bearing of figure 1 ;

Figure 4 illustrates a smaller view of a plan diagram of a flow of balls in the bearing of figure 1 ;

Figure 5 schematically illustrates a sectional and elevated view of an isolator with a vertical axial symmetry according to the invention comprising a transport assembly for switching the load according to the present invention; Figures 6 and 7 schematically represent a set of a plurality of isolators according to the invention interposed between a superstructure and the ground;

Figures 8 and 9 represent a cutting force/ relative shifting diagram of an isolator according to the present invention and respectively a typical time diagram of the force Ft transmitted by the ground to a superstructure through the present isolator and of the force Fl operating vertically on the ball bearing according to the present invention;

Figures 11 and 10 represent a typical diagram of the seismic event and respectively the relative diagram of the acceleration and shifting transmitted by the seismic event to the superstructure through the isolator according to the present invention;

Figures 12-17 schematically represent an inertial self-activating seismic isolator according to the present invention at some stages of its operation;

Figures 18 and 19 schematically represent an external control activating seismic isolator according to the present invention at some stages of its operation;

Detailed description

According to a first aspect of the present invention and referring to figures 1-3, an element for the reduction and the control of friction between two bodies, herein and subsequently identified as a roller bearing or simply a bearing is indicated in its entirety with 1.

The bearing 1 , which is of the type to be used in association with balls, is intended to be interposed between two bodies to reduce or eliminate friction between them when a relative movement occurs between the bodies themselves, and according to the invention it is particularly suitableto be used in a seismic isolator as better explained in the description hereinafter.

According to the invention, the bearing 1 essentially comprises a sliding plate 2 having a substantially circular, flat or spherical cap-shaped, bottom surface 3, intended for resting and rolling on a compact or almost compact layer of balls 4 (rolling layer), a boundary element 5 of the layer of balls 4 substantially ring-shaped surrounding the bottom surface 3 which has an internal knife- shaped edge 6, and a frustoconical ring-shaped interspace 7 for the accommodation and recirculation of the balls open towards, and communicating with , the bottom surface 3.

In particular, the balls 4 of the abovementioned layer of balls are substantially of the same size and they are arranged on a sliding surface of one of the two bodies between which friction is meant to be reduced, identified as the first body, not shown in the abovementioned figures, or on a sliding surface integral to such first body, as better explained hereinafter.

Such sliding surface can be flat or spherical cap-shaped, in the latter case concentric with respect to the spherical cap- shaped bottom surface 3 of the sliding plate 2 of the bearing 1. Furthermore, the bearing 1 is provided with a preset number of passages 9c of an appropriate preset dimension, substantially extended axially with respect to the frustoconical ring-shaped interspace 7, and

substantially arranged at an opposite position with respect to the bottom surface 3 of the bearing 1, for the insertion of balls 4 into the same interspace as better explained hereinafter.

As shown in the abovementioned figures and with particular reference to the example of figure 2, according to an embodiment of the present invention, the abovementioned sliding plate 2 is an essentially frustoconical body provided with a inclined and substantially frustoconical side surface 8.

The side surface 8 extends between the abovementioned bottom surface 3 and an opposite cylindrical ring-shaped portion 9, while between the side surface 8 and the bottom surface 3, there is advantageously formed a bevelled edge 9b.

Furthermore, the bearing 1 comprises a covering cap 10 of the sliding plate 2, arranged at a preset spaced relation from the side surface 8 in such a manner to define the abovementioned interspace.

It should be observed that the cap 10 is associated to the sliding plate 2 at the abovementioned cylindrical ring-shaped portion 9 through fixing means of the known type, for example screws 9d, in such a manner to form together a substantially rigid system. Advantageously, at the circular ring-shaped portion 9, that is, in proximity to a relative end portion of the abovementioned side surface 8, the sliding plate 2 and the cap 10 define an annular groove 9a, which delimits the upper part of the interspace 7, which however communicates with the external space through the abovementioned passages 9c, in the example of the figures represented by two through holes provided on the cap 10.

On the contrary, as described above, the other end portion of the interspace 7 is entirely open and communicating with the bottom surface 3 of the sliding plate 2, hence with the abovementioned rolling layer made up of the balls 4.

Regarding the abovementioned boundary element 5 of the layer of balls

4, it should be observed that, preferably, it is constrained in rotation and axially shiftable with respect to the cap 10.

Therefore, in the above-described embodiment of the bearing according to the present invention, the abovementioned fmstoconical ring-shaped interspace 7 is transversely delimited and comprised between the side surface 8 of the sliding plate 2 and the cap 10 and it forms an actual chamber for the accommodation and recirculation of the balls 4 as better described hereinafter.

Preferably, the bearing 1 is provided, at one end portion opposite to the bottom surface 3 of the sliding plate 2, with an accommodation seat 11, intended to be engaged with the other of the two bodies between which friction is meant to be reduced during the abovementioned relative movement, referred to as the second body, not represented in the figures, or to be engaged with a different body integral to such second body, or furthermore for the accommodation of preset thrust means for the substantially vertical movement of the bearing, as better described in the description hereinafter.

As shown in the examples of the figures, in the case that the present bearing is provided with the abovementioned accommodation seat 11 provided for in the sliding plate 2, the cap 10 is provided with a relative passage 9e substantially of an analogous width for access into such accommodation seat.

In practice, the bearing according to the present invention, when operating, is placed resting on the abovementioned layer of balls which is closed circumferentially by the boundary element which substantially lies in contact with the sliding surface of the first body, while a suitable number of other balls are accommodated in the abovementioned interspace.

It should be observed that the rolling layer of balls 4, always represented as compact in the figures, actually forms itself during the use of the present bearing, this because the boundary element is a substantially ring-shaped element which hence leaves the bottom of the

bearing "open".

Upon occurrence of a relative movement between the abovementioned first and second body, or in the event of a relative movement between other bodies integral to them, in the bearing according to the present invention, which in practice is made integral to the second body, there occurs a substantially recirculation and a closed flow movement of the balls with the possibility of an omni-directional sliding, as better described hereinafter.

For example, in the case of a translation movement of the second body with respect to the first at velocity Uc, there corresponds a relative translation of the balls in the abovementioned layer of balls (rolling layer) with velocity UsI = 1/2Uc.

In detail, the balls move between the rolling surface of the first body and the bottom surface of the sliding plate of the bearing until they reach the boundary element.

The boundary element, through the abovementioned knife- shaped internal edge, conveys the balls exiting from the rolling surface of the first body (that is the rolling layer) in the interspace and thus in the opposite direction with respect to the movement of the second body (the bearing).

Furthermore, the knife-shaped edge of the boundary element also acts as an aid to access, on the rolling surface of the first body and hence on the rolling layer, of other balls coming from the interspace (recirculation chamber), which replace the ones conveyed into the interspace as described above, substantially in the opposite part of the moving layer of balls, therefore forming the abovementioned closed flow recirculation.

The description outlined above is illustrated in the example of figure 4, in which schematically shown in plan view are flow lines indicated by A of balls subjected to the load of the second body (rolling layer balls), and flow lines indicated by B of balls in the interspace with velocity Us2 = 3/2Uc.

Basically, when the bearing is in use, the interspace of the bearing according to the invention is already partially occupied by a set suitable number of balls even in the absence of movement (rolling), and given that the interspace is suitably dimensioned with respect to the dimension of the balls, the layer of balls between the rolling surface of the first body and the sliding bottom of the bearing (rolling layer) practically remains compact also during the abovementioned movement.

It should be observed that, in practice, the elastic impacts between the balls due to the free rolling in the interspace under the thrust of the balls exiting the rolling surface of the first body, make it unlikely that the balls come into contact before and hence it is unlikely that any sliding friction between two adjacent balls will occur.

The geometry of the bearing must be such that no ball can come into contact simultaneously with the bottom surface of the sliding plate and one between the boundary element and the bearing cap.

The static and dynamic rolling friction coefficient values of the bearing are overall due both to the balls on the rolling surface of the first body (rolling layer) and to the free balls in the interspace. The contribution to friction of the balls in the interspace is due to the flow of transport energy upon the lifting of the balls in the interspace which is converted into heat due to collision.

Without limiting the scope of protection of the present invention to any theory, it should be observed that, in practice, the operation of the present bearing exploits the properties of the sets of identical balls (or almost identical) constrained in rotation between two surfaces in relative movement, summarised below.

The load capacity of the layer of balls and the relative contraction under the load does not depend on the radius of the balls but on the total section at the centres. Also the static and dynamic rolling friction coefficients are substantially independent from the radius of the balls, therefore the present bearing basically has a great load capacity and

ensures a very low rolling friction coefficient.

The distance between the centres of the balls is constant and it does not change due to translation and rotation, thus the assembly of the centres of the balls moves in a compact manner. It should be observed that, advantageously, the lower limit of the radius of the balls is essentially determined by the degree of tolerance in the reproducibility of the balls themselves.

Still advantageously, it should be observed that the present bearing does not suffer from drawback described above as kinematic inconsistency, which negatively affects the double rolling surface ball bearings provided by the prior art.

As observed beforehand, in such bearings, the balls roll between flat or spherical surfaces, and in the case of overlapping of the relative translational and rotational elliptic motion (rototranslational motion), the final relative position of the balls does not correspond to the initial one, leading to unwanted effects regarding the preservation of a superstructure. This does not occur in the case that the present bearing is employed in a kinematic seismic isolator as described previously.

According to a second aspect of the present invention, there is provided a friction switching transport assembly for the movement of loads, as schematically shown in the example of figure 5, in which such transport assembly is employed in a seismic isolator used for isolating a superstructure from the relative movement of the ground on which it lies. In practice, there is provided a transport assembly having controlled switching from sliding to rolling friction and vice versa, indicated in its entirety by 100, particularly suitable for the transportation or movement of loads, even heavy ones, just like it occurs in the case that the abovementioned ground/ superstructure isolation is required. According to the invention, the abovementioned controlled friction switching transport assembly 100 comprises an idle support 101 with a

high adherence coefficient (sliding friction) capable of bearing a preset load (Fc) including heavy loads at idle conditions (static condition), and a rolling element 102 accommodated inside the idle support (101) on which the abovementioned load is discharged through a device or a mechanism capable of developing a relative thrust (Fl=FC) between the idle support 101 and the rolling element 102, switching to the rolling friction.

Therefore, the rolling element 102 must be allowed to move freely in a substantially vertical manner inside the idle support 101 for a section of limited preset length, about 1 mm.

According to the invention, the friction switching transport assembly 100 is completed by a load switching device 100a (or friction switching device) essentially comprising a bridge element 103 which lies on the idle support 101 and which acts as an actual support for the load Fc, thrust means 105 operating on the rolling element 102, and propulsion means 106 capable of developing a force Fl = Fc on the abovementioned thrust means for a preset period of time.

The switching device is advantageously controlled by dedicated enabling/ disabling means 107. In practice, it is the bridge element 103 which acts as a support for the abovementioned load Fc and which in turn transfers the load itself onto the idle support 101 on which it substantially lies.

On the contrary, the abovementioned force developed by the propulsion means 106 is transmitted to the rolling element 102 through the abovementioned thrust means 105.

It should be observed that the abovementioned exchange, thus the thrust (Fl) on the rolling element which corresponds to the load Fc, can be obtained through mechanical or hydraulic means and it is preferably obtained by means of hydraulic oil pressure. Preferably, the abovementioned rolling element 102 is a roller bearing according to the description outlined previously, that is a balls

recirculation omni-directional bearing laying on a layer of rolling balls, but without excluding the possibility of providing the bearings of the known type.

In practice, what matters is that the load switch, and thus the switching of the friction from sliding to rolling and vice versa, between the idle support and the rolling element (and vice versa), occurs quickly.

Further characteristics of the friction switching transport assembly 100 illustrated above are described hereinafter with special reference to its use in a kinematic seismic isolator which represents a further aspect of the present invention, and which in the examples of figures 6 and 7 is indicated in its entirely by 200.

The term "seismic isolator" is herein used to indicate a special device as previously described, capable of isolating a superstructure 500 from the movement of the ground 600 on which the superstructure lies during a seismic event or earthquake.

In the abovementioned figures 6 and 7 there is represented a method of installation of a plurality of isolators arranged at pillars under respective plinths of suitable height to allow their maintenance.

In particular, in the example of figure 6, a plurality of isolators are arranged on sliding bases 201a parallel to the ground, and the arrows indicate the only forms of deformation the superstructure is subjected to due to the height difference between the positions of the isolators in the presence of possible rotations of the ground.

The illustrated arrangement allows to block the transmission of the horizontal acceleration and the vertical angular acceleration letting the horizontal angular acceleration and the vertical acceleration components through.

On the contrary, in the example of figure 7 a plurality of isolators are arranged on concentric sliding bases 900 which allow reducing all the three angular acceleration components, letting only the vertical linear acceleration through.

In any case, Hie centre of rotation C (centre of the concentric bases) can also be positioned much higher and in any case above the centre of gravity of the superstructure 500, hence the cap-shaped sliding bases can actually be replaced by flat surfaces, and possibly slightly oval- shaped to provide vertical axial rotation stability to the superstructure.

The seismic isolator 200 essentially comprises a sliding base 201 of the abovementioned type, the load switching transport assembly 100 described above in turn comprising the idle support 101 with a high coefficient of friction with the sliding base 201 and adhering thereto, the omni-directional roller bearing 102 accommodated inside the idle support 101, vertically shiftable therein, laying on a layer of balls 4, and the load switching device described above and indicated in its entirety by 100a which transfers the load of the superstructure 500 from the idle support 101 to the bearing 102 and vice versa. Furthermore, the isolator 200 also comprises a fixing header 206 to the superstructure 500, as illustrated in the examples of figures 5-7.

It should be observed that by switching from the sliding friction to the rolling friction the problem concerning the wind is virtually eliminated and hence the need to use in the isolator centring elements with a suitable preset force.

Regarding the abovementioned sliding base, it should be pointed out that it is generally made of reinforced concrete and preferably cap- shaped with a wide radius of curvature.

Advantageously, in the case of a wide radius of curvature (Rc), very long resonance periods shall be involved for the present isolator.

The sliding base 201 is made integral to the ground 600 and advantageously covered with a steel sheet or other suitable metal or metal alloy whose thickness shall preferably be of the dimension of the balls 4 used in the bearing 102, which is indicated by 205 in the examples of the figures. Such solution is preferably adopted with the aim of avoiding the disintegration of the concrete which would be caused by the strong point pressure upon contact between the balls and

the concrete itself.

It should be observed that the use of relatively small balls allows to reduce the thickness of the sheet 205 which becomes the actual sliding surface in the case it is provided for covering the sliding base 201, hence reducing the weight and the costs of the entire seismic isolator.

The bearing 102 which is of the omni-directional type as described previously and which slides in a vertical direction within the low friction idle support 101, is not subject to kinematic inconsistency as described above. As a matter of fact, the balls which at the end of the seismic event can be found between the rolling surfaces (steel sheet covering the sliding base and the bottom surface of the bearing) can be partially or entirely the ones that are accommodated in the abovementioned interspace (which is the recirculation chamber of the bearing) before the seism. Regarding the load switching device 100a which transfers the load from the idle support 101 to the bearing 102 and vice versa, and thus converts the coefficient of friction from the one of adherence of the idle support 101 on the sliding base 201 (meant with or without the metal sheet ) to the rolling friction of the bearing 102 on the sliding base 201 it should be observed that, according to the invention, it can be of the so called inertial self-activating type capable of obtaining operation energy from the seismic event itself, or of the external control activating type with an autonomous source of energy.

In the case of an inertial self- activating isolator (IA), it is necessary to set in advance a coefficient called the coefficient of first detachment, almost identical for all the isolators of a composite system comprising a plurality of isolators of this type, in such a manner to eliminate all the effects of non- seismic thrusts, with a synchronous avalanche activation of all the isolators. The way this can be obtained shall be illustrated hereinafter.

Furthermore, a distinctive and advantageous characteristic of the inertial self-activating isolator lies in the fact that, activating the isolator

while the superstructure is still, there is a degree of freedom for vertical axis rotation which is particularly useful during the maintenance stage to avoid cold welding due to prolonged pressure and plastic deformation of the internal laying and rolling surfaces. On the contrary, the external control activating isolator embodiment does not require setting of a coefficient of first detachment and it does not have internal rolling surfaces and comprises, alongside the abovementioned autonomous source of energy, also local or remote accelerometer sensors, in such a manner that the activation can be allowed before the arrival of a seismic wave.

A combined activation of the switching device, obtained from the combination of the abovementioned two types of activation , is also possible.

The main condition is that, in the case of self-activation, the abovementioned specific threshold characteristics almost identical for all the isolators of a system comprising a plurality of isolators occur, according to the invention, both in terms of the switching and time hysteresis operation and of the switching times.

In any case, alongside the abovementioned fixing header 206 to the superstructure 500, the isolator according to the present invention also comprises a sub-header with a ball joint 207 on which the header 206 lies and which in practice coincides with the upper portion of the abovementioned bridge element 103.

The abovementioned configuration, that is the "disarticulation" of the header 206 obtained due to the joint or ball joint 207 of the sub-header (bridge element 103), compensates for the variations of inclination during the motion which occur in case of sphericity of the rolling base and, hence, avoids torsional moments on the same bridge element 103 and on the bearing 102. Therefore, the support surfaces between the header 206 and the subheader with a ball joint 207 are preferably made in a spherical cap shape with a slightly different radius and being the largest possible in

order to increase the same contact surface.

As illustrated previously, the abovementioned load switching device 100a essentially comprises the bridge element 103, the thrust means 105 acting on the bearing 102, and the propulsion means 106 capable of developing the force Fl equal to the load Fc for a suitable period of time, and shall be described better hereinafter with reference to the examples of figures 12-17 and 18-19 in which respectively illustrated are an isolator according to the invention comprising an inertial self- activating friction switching device and an isolator according to the invention comprising an external control activating friction switching device, as described above.

In the case of self-activation, the present isolator comprises a load switching device of the hydraulic oil-pressure type provided with pistons arranged to form a ring, in other words inertial activating pistons 301, preferably more than three, are arranged to form a ring in the idle support 101 which in this specific case comprises a bell 302 adhering against the covering metal sheet 205 of the base 201 and an element identified in a cylindrical symmetry casing 303 having vertical axis positioned above and laying through a perimeter annular surface, on the bell 302 which in practice is inserted into the casing element 303.

Defined between the casing 303 and the bell 302 are a central interspace 303a with a thickness suitable to avoid contact in the central portion between the same casing and bell and hence concentrate the load Fc in an annular manner on the same bell 302 (thus absorbing also the elastic deformation of the upper portion of the casing under the load with a uniform distribution of the load itself on an element beneath it, in particular a layer of small balls 308) and a perimeter annular interspace, here also referred to as the first chamber 304, which is in communication through a relative first pipe 306 with the abovementioned pistons 301, as better described hereinafter.

It should be observed that in this specific case the bearing 102 us accommodated inside the bell 302 of the idle support 101.

In detail, the bearing 102 inside the bell 302 lies on a layer of balls 4 (rolling layer), as described previously, arranged on the sliding base 201, in particular on the sheet 205, while one accommodation seat 11 thereof (of the type described above) is engaged by a piston portion 302a of the bell 302, defined between the accommodation seat 11 and the piston portion 302a of a relative interspace referred to as a second chamber 305.

The second chamber 305 is in communication through a relative second pipe 307 with the first chamber 304, as illustrated in the examples of figures 12-17.

Concerning the abovementioned pistons, it should be pointed out that they are accommodated in an annular manner in the bell portion 302 of the idle support 101, while the casing 303 is accommodated beneath the abovementioned bridge element 103 which is in turn in contact with the abovementioned pistons 301 through corresponding dedicated bracket elements 103a integral to the bridge element itself, such elements acting as piston actuation elements.

Arranged between the casing 303 and the bridge element 103 (subheader) is the abovementioned layer of small balls 308, that is, balls with a small diameter, in such a manner that the bridge element 103 is allowed to slide freely on the casing 303 in all directions, through a significant frictionless movement, for a maximum width δ section, which depends on the acceleration of first detachment (coefficient of first detachment) and on the time hysteresis provided for when designing the isolator.

Therefore, provided in the abovementioned switching device is a hydraulic oil-pressure "circuit" which through the abovementioned oil pistons 301 supplied by a common tank 320 (the abovementioned propulsion means as a whole), allows the switching of the friction and which in detail is defined by the abovementioned first chamber 304, expandable and in communication through the first pipe 306 with the pistons 301, and by the abovementioned second chamber 305, also expandable and in communication through the second pipe 307 with

the first chamber 304.

The abovementioned hydraulic oil-pressure circuit is filled with oil, without air bubbles and free of leakages, in other words watertight and, therefore special gaskets can be provided for where required according to the experience of the man skilled in the art of hydraulic oil systems and circuits.

Arranged upstream of the first chamber, that is between the pistons 301 and the first chamber 304, is a valve 310 which allows a quick flow of oil pumped by the pistons 301 towards the first chamber and a very slow outflow which as explained better hereinafter determines the return time, for the present isolator, in the sliding friction state.

The abovementioned second pipe 307 which connects the first and the second chamber comprises, substantially at its inlet into the first chamber, a bifurcation which determines a first channel 311 and a second channel 312 positioned at slightly different heights.

The first channel 311 positioned lower with respect to the second channel 312 and of a limited section ensures constant fluid communication between the first and the second chamber, while the second channel, of a much larger section, positioned higher is not always in communication with the first chamber 304, as observable in the enlarged details of the examples of figures 12-17.

In practice at idle or static (absence of seismic activity) conditions the load (Fc) of the superstructure 500 bears on the idle support 101, more in particular it bears on lies on the casing 303 which discharges the load onto the bell 302, and then onto the sliding base 201 possibly covered by the steel sheet.

Under such maximum load conditions (sliding friction) the thickness of the abovementioned first annular chamber 304 is minimum or even non-existent in that there might only be lubrication oil between the walls of the first chamber defined by respective portions of the bell 302 and of the casing 303 substantially in contact against each other.

The base area of the first chamber is indicated by S 1.

On the contrary, the thickness of the second chamber 305 is such that the walls of the casing 303 and of the bell 302 are not in direct contact with each other, a certain amount of oil being provided to fill the same second chamber, with a base area indicated by S2.

In any case, it should also be observed that the entire hydraulic oil- pressure circuit as described above is filled with oil without air bubbles and is practically free of pressure.

In such condition, there is a position defined as centred of the switching device in which each activation piston 301 has an amount of oil equivalent to the filling of a thickness indicated by crp>δ and it is, through a relative drive pin 103b, in contact with a respective bracket element 103a and thus the bridge element 103, as illustrated in the example of figure 12. It should be observed that if the number of pistons 301 is N, the number of pistons moving due to the thrust of the relative bracket elements 103a is N/ 2 and each of these pistons shifts proportionally to cos(α) where α is the angle between the acceleration direction of the ground as and the direction of its own axis. Hence, the entire number of pistons moving is equivalent to a single piston of stroke crp and section Sp= (N/4)*sp, sp standing for the section of each one of them.

When the abovementioned acceleration of the ground as starts, that is upon a seismic event and propagation of seismic waves, a relative force Fs acts on the corresponding movement piston 301 with thickness crp=δ and section Sp and when Fs≥(Fc/Sl)Sp the compression of the oil in the movement pistons starts with the oil passing into the first chamber (which is the only expandable one at that moment) through the valve 310 of the first pipe and thus also the consequent lifting of the casing 303. It occurs that at this step the bell 302 still bears the load Fc through the oil under pressure in the second chamber and thus the friction is still of the sliding type.

The narrowness of the abovementioned first connection channel 311 between the two chambers prevents direct and quick flow of the oil from the first into the second chamber thus the oil pressure in the second chamber increases very slowly with respect to the increase of pressure in the first chamber which hence expands until the upper surface of the same reaches the height of the second channel 312 which has a considerably larger section with respect to the first channel 311, when the value of first detachment (figure 13) has not been reached yet.

At this stage, the thickness of the second chamber remains substantially unvaried and the oil flows freely into the second channel 312 of suitable section towards the second chamber 305.

In practice, what occurs is that before the value of first detachment has been reached, the first chamber expands until it reaches the opening of the second channel 312 at a higher height with respect to the first channel, from where the oil can then flow at a higher rate into the second chamber.

As soon as the volume of oil in the second chamber 305 reaches the value required for switching the load, the abovementioned detachment and rolling start. It should be taken into account that due to the elasticity characteristics of the materials subjected to high pressures, finite and not infinitesimal volumes of oil are required to reach determined pressure difference values.

The number of pistons 301 , their diameter and the stroke of the bracket element determine the maximum volume of oil supplied into the first pipe and thus in the first and second chamber.

It should be added that the movement pistons 301, are hydraulically parallel through an annular pipe 310b in turn connected to the abovementioned common tank 320, arranged in a suitable position, with a useful volume equivalent to the overall volume Vc of the oil shifted by the movement pistons during inertial compression (Vc=Sp*crp).

The tank 320 is provided with a moveable septum 320b which separates the oil from a suitable means, for example liquid propane under saturated vapour pressure, allowing to keep the oil under enough pressure to return the pistons to the initial position and hence the bridge element 103 at a central position during the rolling to avoid the kinematic inconsistency phenomenon of the layer of small balls 308.

In particular, the abovementioned moveable septum should be positioned as close as possible to the end stroke of the common tank in such a manner to prevent further increase of oil in the tank itself during the beginning of the switching stage.

The example of figure 14 instead illustrates the maximum shifting condition of the bracket element corresponding to which is the first detachment at maximum load condition Fc.

If Mc indicates the mass laying on the casing 303 and g is the gravity acceleration, then:

Fc=Mc*g; and Fs=Mc*as

Then the condition of first detachment occurs when Fs reaches and exceeds the value of the overall friction force due to the sliding contribution of the bell and the rolling contribution of the bearing, the two being respectively provided by:

Fca=Crad*(Fc-P2*S2) and Fcu=Cvol*P2*S2

Wherein Crad and Cvol are respectively the coefficients of the sliding and the rolling frictions and P2 corresponds to the oil pressure in the second chamber. Therefore, the acceleration of first detachment (as)pd, being Fs≥Fca+Fcu; P2=Fs/Sp is obtained from: (as)pd/g=l/((l/Crad)+(l-Cvol/Crad) *S2/Sp)«Sp/S2 According to the invention, it is observed that, given the respective

orders of magnitude, (as)pd»Sp/S2 which thus does not depend neither on the coefficients of friction, quite uncertain, nor on the load mass Mc and thus on Fc, but only on the construction features of the isolator, that is on its specific internal geometry. In this manner complete stability of the superstructure laying on the isolators with the same geometry is ensured during a seismic event also from a dynamic point of view.

Once beyond the acceleration of first detachment rolling starts on the rolling layer; the pressure on the movement pistons 301 is annulled , the force Fc is practically nullified, the abovementioned valve 310 prevents quick return of the oil into the pistons 301, thus, once the detachment has occurred, Fc remains loaded and it is supported by the oil present in the first and the second chamber.

It should be observed that the bell 302 receives a downward thrust due to the oil pressure in the first chamber and an upward thrust due to the oil in the second chamber.

Dimensioning the horizontal section of the first chamber 304, slightly smaller than the horizontal section of the second chamber 305, the load being practically the same (without the specific weight of the bell), the pressure Pl in the first chamber 304 is greater than the one P2 in the second chamber 305, thus the flow of oil from the first to the second chamber, through the second pipe 311 during the rolling, continues even after the thrust of the pistons has ceased hence ensuring that the coefficient of friction passes from the value of first detachment, equivalent to 0.1-0.2 approximately to the value equivalent to 0.002- 0.005 of pure rolling.

This provides the hysteresis necessary to ensure that the switching occurs in a complete manner.

In practice, if the difference between the sections of the two chambers δS is very small the weight of the bell itself acts as a flow regulator in that the bell slides on the sliding base determining a friction force equivalent to:

(Fa)ca=Crad*(Mca*g-((δS) / S2)*Fc)

It should be observed that the lifting of the bell occurs if the second member of the relation described above is negative, that is if the weight of the bell is negligible. However any sliding, considering the order of magnitude(weight of the bell) /Fc, generates a friction force in the order of the rolling friction of the bearing and thus of no influence.

Furthermore, it should be observed that the closure of the valve 310 during the rolling stage leaves the bridge element 103 free to move with respect to the casing 303 lacking the centring force of the movement pistons 301.

The kinematic inconsistency which might result therefrom due to the layer of small balls is prevented by the presence of the abovementioned tank which due to the pressure of the saturated propane is capable or re-centring the movement pistons 301 with enough force to resist against the residual rolling friction force.

In addition, during the pure rolling stage, under strong pressure, the oil outflows slowly through the abovementioned valve located in the first pipe, which is not perfectly watertight, allowing to return the isolator to the initial configuration restoring the volume of oil in the tank which in practice acts as a compensation chamber.

Therefore, according to the invention, it can be understood that it is the combination of the abovementioned two chambers that allows the above, given that the direct delivery of oil into the second chamber would lead, upon reaching the acceleration of first detachment, to the isolator being constantly braked by the sliding of the bell on the sliding base, with a coefficient of friction constantly equivalent to the coefficient of first detachment.

On the contrary, according to the invention the combination of the two chambers of the load switching device 100a as described above allows complete passage of the load Fc from the bell 302 to the omnidirectional bearing 102. Still, it should be added that, in case of a seismic event with a period interval exceeding the period interval

required by the isolator to relax, a further cycle like the one described above is triggered as soon as the load Fc starts being discharged partially onto the bell.

In brief, the load switching device described above allows the conversion of a horizontal relative movement of the bridge element with respect to the idle support, into a downwards vertical movement of the thrust means, performed thanks to the propulsion means, with the consequent shifting of the load from the idle support to the bearing, thus carrying out a conversion of friction from sliding to rolling. For example, illustrated in figure 8 is a diagram F-x of the self- activating isolator according to the present invention, wherein F is the force transmitted by the isolator in relative motion towards a direction X, and x is the relative ground/ substructure shifting for the maximum excursion possible. The inclination angle α is determined by the radius of curvature Rc of the sliding base and it is proportional to Fc.

It should be observed that due to the freedom of choice of the size of the diameter D of the rolling base, the maximum excursion D-d, wherein d is the diameter of the bearing, is practically arbitrary. In any case, in the isolator IA, D must be consistent with the radius of curvature Rc to obtain a height difference between the centre and the edge of the sliding base suitable to block the drifting resulting from the impulse of first detachment.

In the case of a seismic event, it occurs that the force F of the seismic event rises from zero to a preset first detachment value (Fpd) upon the abovementioned relative shifting δ, before suddenly dropping to a value determined by the switching of the load.

The example of figure 9 illustrates a time diagram showing the general dynamic trend of the self-activating isolator according to the present invention.

Upon the occurrence of a seismic event with acceleration as, the cutting force Ft remains proportional to the acceleration as until the moment tl when Ft reaches the first detachment value Fpd.

Between moment tl and t2 the entire load Fc shifts onto the bearing, according to diagram Fl, and it remains there for a period of time tr after which the load returns to the idle support and Fl is nullified.

In case of persistence of the relative motion between the ground and the superstructure the process is triggered again after a period of time to.

The example of figure 10 shows a shifting/ acceleration diagram during a seismic event, whose relative response of a superstructure with a self activating isolator is illustrated in the example of figure 11 with a coefficient of sliding friction equivalent to 0.2 and coefficient of rolling friction equivalent to 0.003.

The peak acceleration of the ground is 2.7g with an oscillation of 40 cm and a space drift of 2m.

The superstructure receives a peak acceleration in the first detachment equivalent to about 0.3m/ s2, with a total relative space drift of about 1 cm.

The example of figures 18-19 instead shows the structure and the functioning an external control activating isolator (ECA) according to the present invention.

Not being provided with the self-activating mechanism described above, such isolator does not require neither the abovementioned casing nor that the bridge element act directly on the activation of the activating pistons, hence it does not require bracket elements associated to the same bridge element for the self-activating of the propulsion means, as illustrated previously for the isolator IA.

Therefore, isolator ECA differs from IA essentially due to the relative load switching device which in this case is structurally much simpler with respect to self- activating device described above.

However, isolator ECA maintains the general characteristics of the invention described above to which it is referred through the same reference numbers used previously for isolator IA.

In particular, in such case, the load switching device essentially comprises a bridge element 103c without brackets which forms the upper portion of an idle support 101a , a pair of movement pistons indicated by 700 and 701 (the abovementioned thrust means), the first sliding in a respective first seat which forms a first chamber 304a, the second sliding in a respective second seat communicating in a hydraulic oil manner with a second chamber 305a, propulsion means for supplying into the switching device a preset gas acting on an upper surface of the first movement piston 700, and externally controlled enabling/ disabling means advantageously comprising an accelerometer capable of triggering the switching and a tachymeter, preferably optical, which restores the sliding friction when the relative velocity between the ground and the superstructure has been stably nullified at the end of the seismic event.

The abovementioned first and second pistons are connected to each other and made integral in the sliding movement by means of a connection element 702 sliding in an accommodation seat provided on a piston portion 302a of the idle support 101a which is in turn inserted into an accommodation seat 11 of a bearing 102.

Regarding the propulsion means, it should be added that isolator ECA is preferably provided with a tank 800 in which is a suitable volume of a preset saturated gas, advantageously liquid carbon dioxide, connected through a first pipe 306a to the abovementioned first chamber 304a in which the first movement piston 700, in the absence of seismic events, is located at the head.

Provided upstream of the first pipe 306a, between the tank 800 and the first pipe is a diverter solenoid valve 310a which can substantially take two positions:

An activation position which connects the tank 800 to the first pipe

306a, thus also with the first piston 700; and a non-operating or idle position in which the first pipe is in communication with a vent 801 communicating with the external environment, positioned upstream of the first chamber at the mentioned valve. To control the solenoid valve, the isolator ECA according to the invention also comprises a control unit 802, which in response to a significant seismic signal delivered by the dedicated sensors commands the solenoid valve to the activating position allowing the carbon dioxide gas in the tank 800 to reach the abovementioned first chamber 304a and push the first piston to exert the switching pressure.

It should be observed that in the absence of seismic events also the second piston is positioned at the head in the respective seat being integrally joined to the first piston.

The sliding seat of the second piston is filled with oil and it is communication, as previously mentioned, with a second chamber with a minimum thickness configuration given that in the absence of seismic events there is no pressure on the abovementioned two pistons and the load of a superstructure 500 lies entirely on the idle support 101a.

Therefore, there is no load on the bearing 102, which represents the sliding friction condition, as shown in the example of figure 18.

It should also be observed that in this case the "circuit" considered strictly of the hydraulic oil-pressure type is given by the sliding seat of the second piston and by second chamber, while in the first chamber and in the first pipe instead of oil, when the isolator is activated, there is the abovementioned propulsion gas.

When the abovementioned sensors (not shown in the figures) detect seismic waves, the solenoid valve is commanded from the non-act position to the act one, the abovementioned vent is bypassed and the tanks are in communication, through the first pipe, with the first chamber allowing the carbon dioxide to exert pressure onto the first piston.

The first piston pushed downwards, through the abovementioned connection element, also moves the second piston which in turn pushes the oil from its sliding seat into the second chamber.

Therefore the piston portion of the idle support is lifted and hence the same idle support (of a section e) and the load of the superstructure is transferred to the bearing passing to the rolling friction.

The pressure exerted on the oil is equivalent to the pressure of the carbon dioxide gas multiplied by (Diameter of the first chamber/ Diameter of the second chamber) 2 . The return of the solenoid valve 310a to the non-operating position causes discharge into the external environment, through the abovementioned vent 801, of the carbon dioxide gas which thus leaves the first chamber depressurising also the second chamber with the consequent lifting of the first and the second piston and return to the to the sliding friction position.

It should be observed that the amount of heat required to obtain the expansion and the evaporation of liquid carbon dioxide is low enough to be provided by the same tank of carbon dioxide without any significant temperature drop of the same. As a matter of fact, for instance, considering a load Fc=IOO tons for a lifting by 0.5 mm, the switching energy Ec required amounts to about 500J.

Assuming a condition of -20 0 C to be the worst condition it is observed, through carbon dioxide thermodynamics tables which provide a relative vapour pressure Pv=2Mpa, and an evaporation enthalpy variation δH=280kJ/kg, that the mass of carbon dioxide required is equivalent

The specific entropy variation in the conversion is δS=1.2kJ/Kg*K, thus the heat required is Q=δS(273-20)KMco2= 127 cal. Therefore, 150 cm 3 of steel volume is capable of providing the heat

required with a temperature drop lower than one degree centigrade.

Inserting an aluminium structure with a large wet surface into the tank is useful to speed up the process.

Assuming the maximum oil pressure to be pol=30Mpa, the ratio of diameters of the first and the second pistons (or of the relative sliding seats) must be at least

Dfirst piston/ Dsecond piston= \(pθl/pv)=4

Where pol and pv are respectively the maximum pressure required for the oil and the saturated vapour pressure at minimum temperature conditions provided for in situ.

The stroke of the abovementioned two pistons is consequent to the overall elasticity of the isolator and it is defined by the stroke given by the first piston.

Advantageously, between the tank 800 and the solenoid valve 310a can be added a pressure reducer which keeps the propulsion gas flowing into the solenoid valve at the minimum environmental temperature pressure to avoid unwanted overpressure on the thrust means and on the end of stroke parts.

In brief, the isolator according to the present invention, during an earthquake, prevents the transmission of vertical axis rotational and horizontal tensions from the ground to the superstructure, reducing the effects to less than the ones caused by an artificial quake.

Furthermore, according to particularly advantageous embodiments of the present isolator, also the transmission of the remaining two horizontal axis moments is avoided and thus only the vertical stresses at the sliding base are transmitted to the superstructure.

The advantages of the present invention, already clearly observed over the description outlined above, mainly consist in the fact that there is provided a bearing with an omni-directional flow and recirculation of balls, capable of ensuring, in terms of friction between two bodies, an

almost total isolation upon the occurrence of a relative horizontal motion condition between the same two bodies, which is particularly advantageous for use in a friction switching transport assembly for moving loads, including heavy loads, and in a seismic isolator of the kinematic type.

In particular, in the isolator subject of the invention comprising such friction switching transport assembly, use of centring and damping elements to eliminate the unwanted wind effects is not required.

Furthermore, the drifting velocity on the sliding base is particularly low in case of the inertial self-activated isolator and practically nullified in case of a control activated isolator.

Advantageously, the present isolator is provided with a very long resonance period defined by the curvature of the sliding base.

Advantageously, the admissible maximum excursion of the ground is particularly high, and defined by the size chosen for the diameter of the sliding base.

Advantageously, the acceleration of first detachment is substantially independent from the coefficient of adherence between the sliding base and the idle support and, for the self-activated isolator, in practice it depends only on the geometric configuration of the isolator itself as well as its construction characteristics.

Regarding isolator ECA, it is possible to set arbitrary activation acceleration depending on the sensors, with a wide flexibility in use.

Advantageously, there is also the reduction of the relative acceleration transmitted to the superstructure to the coefficient of rolling friction value of the bearing on the rolling base during the activation stage, obtained for any acceleration value which has an absolute value that is higher than the one of the first detachment in the case of isolator IA, and which has an absolute value that is higher than the set threshold in the case of isolator ECA.

Advantageously, the centre of thrust of the interactions with the ground of a system comprising a plurality of isolators according to the invention is always on the vertical of the centre of gravity of the superstructure and thus the superstructure shall be particularly stable during an earthquake.

Advantageously, there is no kinematic inconsistency as described above while a vertical axis translational and rotational isolation of the superstructure is ensured.

Advantageously, the problem concerning cold welding is eliminated due to the fact that the balls of the rolling layer bear the weight of the superstructure only during an earthquake.

Furthermore an accurate and easy post-seismic event centring can be obtained.

Additionally, the isolator according to the invention can be made using less mass of heavy material (steel) employed for making the sliding surfaces, entails lower costs of production and it is easier to install and maintain with respect to the known isolators.

The ball bearing, the friction switching transport assembly and the seismic isolator according to the embodiments illustrated and described, shall be subjected, by a man skilled in the art with the aim of meeting the required and specific needs, to various modifications, all of which falling within the scope of protection of the invention, as defined by the claims provided hereinafter.