REGENERATIVE HYDRAULIC SHOCK-ABSORBER FOR VEHICLE SUSPENSION

Abstract

The shock-absorber comprises: a cylinder containing a hydraulic working fluid; a piston slidably arranged in the cylinder so as to split the cylinder into two variable-volume working chambers, namely a first working chamber, or extension chamber, and a second working chamber, or compression chamber; an auxiliary conduit in fluid communication on one side with the first working chamber and on the other with the second working chamber; a train of permanent magnets slidably arranged in the auxiliary conduit so as to reciprocally move along the auxiliary conduit, dragged by the working fluid flowing between the first and second working chambers through the auxiliary conduit as a result of the reciprocating motion of the piston in the cylinder; and electric energy generating device for generating electric energy by exploiting the movement of the train of permanent magnets along the auxiliary conduit.

Claims

1. A regenerative hydraulic shock-absorber for vehicle suspension, comprising: a cylinder containing a hydraulic working fluid; a piston slidably arranged in the cylinder so as to split the cylinder into two variable-volume working chambers, namely a first working chamber, or extension chamber, and a second working chamber, or compression chamber; an auxiliary conduit in fluid communication on the one hand with the first working chamber and on the other with the second working chamber; a plurality of permanent magnets slidably arranged in the auxiliary conduit to reciprocate along the auxiliary conduit, dragged by the working fluid flowing between the first and second working chambers through the auxiliary conduit as a result of the reciprocating motion of the piston in the cylinder; and an electric energy generating device for generating electric energy from the movement of the permanent magnets along the auxiliary conduit; wherein the auxiliary conduit is spirally wound around the cylinder, and wherein the permanent magnets are connected to each other so as to form a train of permanent magnets.

2. The shock-absorber as set forth in claim 1, wherein the permanent magnets are arranged one behind the other with opposed polarities and are connected to each other with a constant magnetic and mechanical pitch.

3. (canceled)

4. The shock-absorber as set forth in claim 1, further comprising a rod, which is rigidly connected to the piston and projects from the cylinder on one side of the latter only, and a reservoir, which is at least partially filled with a compressible fluid and acts to compensate for changes in the volume of the working fluid inside the cylinder occurring as a result of the movement of the assembly formed by the piston and the rod relative to the cylinder.

5. The shock-absorber as set forth in claim 4, wherein said reservoir is formed by a chamber located inside the cylinder between a bottom wall of the cylinder and a separating member which is freely slidable in the cylinder, the separating member separating the reservoir from the second working chamber of the cylinder.

6. The shock-absorber as set forth in claim 4, further comprising an outer tube inside which the cylinder is housed and from which the rod projects, wherein said reservoir is formed by a gap between the cylinder and the outer tube, which gap contains the working fluid in its lower part and the compressible fluid in its upper part, and wherein a first non-return valve, or compression valve, arranged to allow the working fluid to flow only in the direction from the second working chamber of the cylinder to the gap and a second non-return valve, or intake valve, arranged to allow the working fluid to flow only in the direction from the gap to the second working chamber of the cylinder are provided in the bottom wall of the cylinder.

7. The shock-absorber as set forth in claim 4, wherein said reservoir is formed by an external reservoir which is arranged outside the cylinder and contains in part the working fluid and in part the compressible fluid, the external reservoir being connected to the auxiliary conduit via a hydraulic circuit comprising a plurality of passive valves wherein the external reservoir is always connected to the low-pressure side of the auxiliary conduit.

8. The shock-absorber as set forth in claim 1, further comprising a rod which is rigidly connected to the piston and projects from the opposite sides of the cylinder.

9. The shock-absorber as set forth in claim 1, wherein said electric energy generating device comprises at least one electric winding arranged around a portion of the auxiliary conduit, whereby movement of the train of permanent magnets along the auxiliary conduit causes the magnetic flux concatenated with said at least one winding to change and thus an induced electromotive force to be generated in said at least one winding.

10. The shock-absorber as set forth in claim 9, wherein said at least one electric winding is connected to a conversion device arranged to recover electric energy, the conversion device including a controllable equivalent input resistance the value of said equivalent input resistance determining the intensity of the reaction force with which the train of permanent magnets opposes the motion of the piston, in such a way that desired damping curves of the shock-absorber are obtainable by adjusting the value of said equivalent input resistance.

11. The shock-absorber as set forth in claim 9, wherein the train of permanent magnets has a length greater than that of the portion of auxiliary conduit around which said at least one electric winding is wound.

12. The shock-absorber as set forth in claim 1, wherein said electric energy generating device comprises a wheel that is magnetically coupled to the train of permanent magnets so as to rotate in one direction or the other as a result of the movement of the train of permanent magnets along the auxiliary conduit in one direction or the other, and an electric machine mechanically coupled to said wheel so as to be rotated by the latter.

13. The shock-absorber as set forth in claim 1, wherein the ratio of the flow cross-section area of the auxiliary conduit to the internal working cross-section area of the cylinder is equal to a given value less than 1 and wherein the ratio of the length of the auxiliary conduit to the length of the stroke of the piston is greater than the reciprocal of said value.

14. (canceled)

15. A regenerative hydraulic shock-absorber for vehicle suspension, comprising: a cylinder containing a hydraulic working fluid; a piston slidably arranged in the cylinder so as to split the cylinder into two variable-volume working chambers, namely a first working chamber, or extension chamber, and a second working chamber, or compression chamber; an auxiliary conduit in fluid communication on the one hand with the first working chamber and on the other with the second working chamber; a plurality of permanent magnets slidably arranged in the auxiliary conduit to reciprocate along the auxiliary conduit, dragged by the working fluid that flows between the first and second working chambers through the auxiliary conduit as a result of the reciprocating motion of the piston in the cylinder; and an electric energy generating device for generating electric energy from the movement of the permanent magnets along the auxiliary conduit, said electric energy generating device comprising at least one electric winding wound around a portion of the auxiliary conduit, in such a way that the movement of the permanent magnets along the auxiliary conduit causes the magnetic flux concatenated with said at least one winding to change, thus generating an induced electromotive force in said at least one winding; wherein the ratio of the flow cross-section of the auxiliary conduit to the internal working cross-section area of the cylinder is equal to a given value less than 1; wherein the ratio of the length of the auxiliary conduit to the length of the stroke of the piston is greater than the reciprocal of said value, the permanent magnets are connected to each other so as to form a train of permanent magnets, and the length of the train of permanent magnets is greater than the length of the portion of auxiliary conduit around which said at least one electric winding is wound.

16. The shock-absorber as set forth in claim 15, wherein the auxiliary conduit is spirally wound around the cylinder.

17. The shock-absorber as set forth in claim 15, wherein the permanent magnets are arranged one behind the other with opposed polarities and are connected to each other with a constant magnetic and mechanical pitch.

18. (canceled)

19. The shock-absorber as set forth in claim 15, further comprising a rod, which is rigidly connected to the piston and projects from one side only of the cylinder, and a reservoir, which is at least partially filled with a compressible fluid and acts to compensate for changes in the volume of the working fluid inside the cylinder occurring as a result of the movement of the assembly formed by the piston and the rod relative to the cylinder.

20. The shock-absorber as set forth in claim 19, wherein said reservoir is formed by a chamber located inside the cylinder between a bottom wall of the cylinder and a separating member mounted freely slidable in the cylinder, the separating member separating the reservoir from the second working chamber of the cylinder.

21. The shock-absorber as set forth in claim 19, further comprising an outer tube inside which the cylinder is received and from which the rod projects, wherein said reservoir is formed by a gap between the cylinder and the outer tube, which gap contains the working fluid in its lower part and the compressible fluid in its upper part, and wherein a first non-return valve, or compression valve, arranged to allow the working fluid to flow only in the direction from the second working chamber of the cylinder to the gap and a second non-return valve, or intake valve, arranged to allow the working fluid to flow only in the direction from the gap to the second working chamber of the cylinder are provided in the bottom wall of the cylinder.

22. The shock-absorber as set forth in claim 19, wherein said reservoir is formed by an external reservoir which is arranged outside the cylinder and contains in part the working fluid and in part the compressible fluid, the external reservoir being connected to the auxiliary conduit via a hydraulic circuit comprising a plurality of passive valves wherein the external reservoir is always connected to the low-pressure side of the auxiliary conduit.

23. The shock-absorber as set forth in claim 15, further comprising a rod which is rigidly connected to the piston and projects from the opposite sides of the cylinder.

24. The shock-absorber as set forth in claim 15, wherein said at least one electric winding is connected to a conversion device arranged to recover electric energy, said conversion device including a controllable equivalent input resistance, the value of said controllable equivalent input resistance determining the intensity of the reaction force with which the train of permanent magnets opposes the motion of the piston, in such a way that desired damping curves of the shock-absorber are obtainable by adjusting the value of said equivalent input resistance.

25. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Further characteristics and advantages of the present invention will become more apparent from the following detailed description, given purely by way of non-limiting example with reference to the attached drawings, in which:

[0020] FIG. 1 is a view in axial section of a regenerative shock-absorber for vehicle suspension according to a first embodiment of the present invention;

[0021] FIG. 2 is a front view of the shock-absorber of FIG. 1;

[0022] FIG. 3 is a schematic illustration of the shock-absorber of FIG. 1;

[0023] FIG. 4 is a schematic illustration of an intermediate portion of the auxiliary conduit of a shock-absorber according to the present invention;

[0024] FIG. 5a is a schematic illustration of an end portion of the auxiliary conduit of a shock-absorber according to the present invention;

[0025] FIG. 5b is another schematic illustration of an end portion of the auxiliary conduit of a shock-absorber according to the present invention;

[0026] FIG. 6 shows an alternative form of permanent magnet that may be used in a shock-absorber according to the present invention;

[0027] FIG. 7 is a schematic illustration of a second embodiment of a regenerative shock-absorber for vehicle suspension according to the invention;

[0028] FIG. 8 is a schematic illustration of a third embodiment of a regenerative shock-absorber for vehicle suspension according to the invention;

[0029] FIG. 9 is a schematic illustration of a fourth embodiment of a regenerative shock-absorber for vehicle suspension according to the invention;

[0030] FIG. 10 shows an equivalent electric circuit with which a regenerative shock-absorber according to the present invention can be modelled;

[0031] FIG. 11 is a schematic illustration of an intermediate portion of the auxiliary conduit of a shock-absorber according to the present invention, with two windings arranged around the auxiliary conduit so as to create a two-phase electric circuit;

[0032] FIG. 12 is a schematic illustration of an intermediate portion of the auxiliary conduit of a shock-absorber according to the present invention, with three windings arranged around the auxiliary conduit so as to create a three-phase electric circuit;

[0033] FIG. 13 shows schematically an example of electric energy generating device suitable for generating electric energy using the movement of the train of permanent magnets along the auxiliary conduit of a shock-absorber according to the present invention;

[0034] FIG. 14 shows schematically an alternative example of electric energy generating device suitable for generating electric energy using the movement of the train of permanent magnets along the auxiliary conduit of a shock-absorber according to the present invention; and

[0035] FIG. 15 is a schematic illustration of a regenerative shock-absorber for vehicle suspension according to a further embodiment of the present invention.

[0036] In the description and the claims that follow, terms such as “upper” and “lower” etc. are to be understood as referring to the normal mounting condition of the shock-absorber on a vehicle, in which the cylinder of the shock-absorber is connected to a wheel mount or a suspension arm and in which the piston rod of the shock-absorber projects upwards from the cylinder and is connected to the vehicle body.

DETAILED DESCRIPTION OF THE INVENTION

[0037] With reference first to FIGS. 1 to 3, a regenerative shock-absorber (hereinafter simply referred to as “shock-absorber”) according to a first embodiment of the present invention is generally indicated 10. The shock-absorber 10 comprises first of all, in a per-se-known manner, a cylinder 12 having a longitudinal axis z (typically oriented vertically or slightly inclined with respect to the vertical) and a piston 14 mounted slidably inside the cylinder 12 along the axis z. The cylinder 12 is filled with a hydraulic working fluid (typically oil, which proves to be an almost incompressible fluid). The cylinder 12 comprises a cylindrical lateral wall 16, a lower wall (or bottom wall) 18 and an upper closure assembly (or cap) 20. The piston 14 splits the internal volume of the cylinder 12 into two variable-volume working chambers, namely an upper working chamber, or extension chamber, 22 and a lower working chamber, or compression chamber, 24. A rod 26 is rigidly connected to the piston 14 and projects from the cylinder 12 through a hole 28 provided in the upper closure assembly 20. Suitable sealing elements (gaskets), not shown, are provided in the hole 28 to make a seal with the rod 26. The piston 14, and the rod 26 therewith, reciprocally moves along the axis z of the cylinder 12 as a result of the relative movement between the wheel of the vehicle (not shown), which is connected to the cylinder 12, and the vehicle body (also not shown), which is connected to the rod 26.

[0038] The shock-absorber 10 further comprises an auxiliary conduit 30 which is in fluid communication on the one hand with the upper working chamber 22 and on the other with the lower working chamber 24. The upwards movement of the piston 14 (the so-called extension movement of the shock-absorber) with respect to the cylinder 12 causes the working fluid to flow through the auxiliary conduit 30 from the upper working chamber 22 to the lower working chamber 24. Vice versa, the downwards movement of the piston (the so-called compression movement of the shock-absorber) with respect to the cylinder 12 causes the working fluid to flow through the auxiliary conduit 30 from the lower working chamber 24 to the upper working chamber 22.

[0039] Preferably, as shown in FIGS. 1 and 2, the auxiliary conduit 30 is spirally wound around the lateral wall 16 of the cylinder 12. Such a shape, in fact, makes it possible to have an auxiliary conduit of great length, without this leading to an excessive increase in the radial size of the shock-absorber. The auxiliary conduit 30 preferably has a transverse cross-section (fluid flow cross-section) of circular shape. Furthermore, the flow cross-section area of the auxiliary conduit 30 is less than the internal working cross-section area of the cylinder 12 (equal to the difference between the internal cross-section area of the cylinder and the cross-section area of the rod), for example comprised between 5% and 25% of the internal working cross-section area of the cylinder 12. This makes it possible to have in the auxiliary conduit 30 a flow with a speed significantly greater than the speed with which the piston 14 slides in the cylinder 12, as the speed is inversely proportional to the cross-section area. In the case for example of an auxiliary conduit 30 having a cross-section area equal to 1/20 of the internal working cross-section area of the cylinder 12, the fluid flow inside the auxiliary conduit 30 will have a speed equal to 20 times the relative speed of the piston 14 with respect to the cylinder 12.

[0040] The shock-absorber 10 further comprises a train of permanent magnets 32 received in the auxiliary conduit 30 so as to slide along this conduit, dragged by the working fluid flowing between the upper working chamber 22 and the lower working chamber 24 as a result of the movement of the piston 14 in the cylinder 12. With reference in particular to FIG. 4, which shows in section a portion (straightened) of the auxiliary conduit 30, the permanent magnets 32 are arranged one behind the other with opposed polarities. The permanent magnets 32 are connected to each other, for example by a flexible mesh 34 (shown only schematically in FIG. 4) of polymer material which encloses the permanent magnets 32. In this way, the pitch between the permanent magnets 32, i.e. the distance between two adjacent magnets, is kept constant. To this end, spacers may also be provided between each pair of adjacent magnets. Preferably, as shown in FIG. 4, the permanent magnets 32 have the shape of a straight cylinder with a diameter substantially equal (apart from the minimal play necessary to allow the permanent magnets in the auxiliary conduit to move) to the internal diameter of the auxiliary conduit 30. Alternatively, as shown in FIG. 6, the permanent magnets 32 may have a barrel shape, with a maximum diameter substantially equal to the internal diameter of the auxiliary conduit 30. The permanent magnets 32 are preferably made as hollow elements so that they have reduced inertia.

[0041] The train of permanent magnets 32 moves therefore as a single body along the auxiliary conduit 30 substantially at the same speed as that of the working fluid flowing along this conduit, which speed is a multiple of the speed of the piston 14 relative to the cylinder 12, as already mentioned above. In order to ensure that the train of permanent magnets 32 remains confined inside the auxiliary conduit 30 during its movement, the ratio of the length of the auxiliary conduit 30 to the length of the stroke of the piston 14 must be greater than the reciprocal of the ratio of the flow cross-section area of the auxiliary conduit 30 to the internal working cross-section area of the cylinder 12. This condition may be achieved even in the case of a small ratio of the flow cross-section area of the auxiliary conduit 30 to the internal working cross-section area of the cylinder 12, for example by winding the auxiliary conduit 30 spirally around the cylinder 12.

[0042] With reference to FIGS. 5a and 5b, the end portions of the auxiliary conduit 30 (only one of which is shown in FIGS. 5a and 5b, where it is indicated 30a) have a larger diameter than the remaining part of the auxiliary conduit 30, so as to allow the working fluid to flow through the auxiliary conduit 30 in the event that the train of permanent magnets 32 is stationary, because it has reached an end-of-stroke position, adjacent to an end portion of this conduit.

[0043] As is shown schematically in FIGS. 3, 4, 5a and 5b, an electrical winding 36 (coil) is arranged around the auxiliary conduit 30. The movement of the train of permanent magnets 32 along the auxiliary conduit 30 causes variations in the magnetic flux of the permanent magnets 32 concatenated with the winding 36, and therefore generates in this winding an induced electromotive force whose intensity is proportional to the speed of the train of permanent magnets 32. As already stated above, the speed of the train of permanent magnets 32 corresponds to the speed of the fluid along the auxiliary conduit 30, a speed which is equal to the speed of the piston 14 multiplied by the reciprocal of the ratio of the flow cross-section area of the auxiliary conduit 30 to the internal working cross-section area of the cylinder 12. Setting a ratio between these areas less than 1 allows to obtain a multiplication effect on the speed of the train of permanent magnets 32 in the auxiliary conduit 30 with respect to the speed of the piston 14, and therefore an increase in the electromotive force generated in the winding 36. According to this embodiment, the winding 36 arranged around the auxiliary conduit 30 acts as an electrical energy generating device which generates electrical energy by exploiting the movement of the train of permanent magnets 32 along the auxiliary conduit 30 resulting from the movement of the piston 14 relative to the cylinder 12.

[0044] According to one embodiment of the invention (as shown in FIG. 15), the length of the train of permanent magnets 32 is greater than the length of the portion of auxiliary conduit 30 around which the winding 36 is arranged. This makes it possible to maximize the electromotive force generated and, at the same time, the electrical efficiency of the system. On the one hand, it ensures that all the turns of the winding 36 are always affected by the magnetic flux, irrespective of the position of the train of permanent magnets 32 inside the auxiliary conduit 30, thus maximizing the electromotive force generated. On the other, it limits the length, and therefore the electrical resistance, of the winding, thus maximizing the electrical efficiency.

[0045] In all cases where the rod 26 of the piston 14 projects on one side only (typically the upper side) of the cylinder 12, it is necessary to provide a reservoir filled with compressible fluid (gas) to compensate for the variation in the volume of oil in the cylinder which occurs when the piston moves inside the cylinder, due to the fact that, on each occasion, a certain volume of the rod, equal to the product of the cross-section area of the rod multiplied by the stroke travelled by the piston and rod assembly, enters the inside of the cylinder (compression movement) or leaves the cylinder (extension movement).

[0046] In the embodiment of FIGS. 1-3, the gas reservoir is indicated 38 and is provided in the lower part of the cylinder 12. More specifically, the gas reservoir 38 is delimited laterally by the lateral wall 16 of cylinder 12, at its bottom by the bottom wall 18 of the cylinder 12 and at its top by a separating member 40 which is freely slidably mounted along the lateral wall 16 of the cylinder 12 and which separates the gas (at high pressure, for example at 15-20 bar) contained in the reservoir 38 from the oil contained in the lower working chamber 24. According to this embodiment, therefore, the shock-absorber 10 has an architecture similar to that of a traditional single-tube shock-absorber. However, unlike the case of a traditional single-tube shock-absorber, in which the piston is provided with a pair of one-way valves, namely a compression valve and a rebound (or extension) valve, arranged so as to put into communication with each other the upper working chamber and the lower working chamber of the cylinder during the movement of the piston along the cylinder, in the embodiment of FIGS. 1-3 there is no need for one-way valves fitted to the piston, since the function of communication between the upper working chamber 22 and the lower working chamber 24 is already performed by the auxiliary conduit 30, and the piston 14 is therefore a blind one. This embodiment is thus constructionally simple and furthermore is able to operate in any orientation, in particular even when it is oriented horizontally or 180° upside down, since the oil and the gas are physically separated from each other by the separating member 40.

[0047] According to the embodiment of FIG. 7, in which parts and elements identical or corresponding to those of the embodiment of FIGS. 1-3 have been indicated with the same reference numbers, the shock-absorber 10 has an architecture similar to that of a traditional double-tube shock-absorber, in that the cylinder 12 (operating as an inner tube) is housed inside an outer tube 42. In this case, the gas reservoir is constituted by the gap, indicated 44, between the cylinder 12 and the outer tube 42. The gap 44 contains oil in its lower part, while in its upper part it contains gas at low pressure, for example at 3-4 bar. The oil and gas contained in the gap 44 are in direct contact with each other. The outer tube 42 comprises a cylindrical lateral wall 46, an upper closure assembly (or cap) 48 and a lower wall, or bottom wall, 50. The cylindrical lateral wall 46 of the outer tube 42 has holes 52 through which the auxiliary conduit 30, which is preferably spirally wound around the outer tube 42, passes. The upper closure assembly 48 has a hole 28 through which the rod 26 extends. The lower wall 50 of the outer tube 42 is spaced apart from the lower wall 18 of the cylinder 12. Between these two parts there is always the oil contained in the lower part of the gap 44. The lower wall 18 of the cylinder 12, like in a traditional double-tube architecture, is provided with a compression valve 56 and an intake valve 58. As may be seen, the invention is easily applicable to a double-tube architecture, which is the most widespread architecture for mass-produced car applications indeed.

[0048] According to the embodiment shown in FIG. 8, where parts and elements identical or corresponding to those of the embodiment of FIGS. 1-3 have been given the same reference numbers, a reservoir 60 is provided which is located outside the cylinder 12 and contains gas at low pressure (3-4 bar) in its upper part and oil in its lower part. The reservoir 60 is connected to the auxiliary conduit 30 via a hydraulic circuit containing a plurality of passive valves such that the reservoir 60 is always connected to the low pressure side of the auxiliary conduit 30, irrespective of whether the piston 14 and rod 26 assembly is moving in extension or in compression. This plurality of passive valves comprises at least a non-return valve 62 and a two-way flow control valve 64. The non-return valve 62 is arranged along a line 66 which connects the reservoir 60 to the side of the auxiliary conduit 30 which leads to the lower working chamber 24 and enables the oil to flow only in the direction from the reservoir 60 to the auxiliary conduit 30. The flow control valve 64 is arranged along a line 68 which connects the reservoir 60 to the side of the auxiliary conduit 30 which leads to the upper working chamber 22. The flow control valve 64 is piloted by the difference between the pressures in the two working chambers 22 and 24 of the cylinder 12. In the extension phase, the flow control valve 64 is in the closed position, as a result of the difference in pressure between the two working chambers 22 and 24 of the cylinder 12, and the oil flows from the reservoir 60 to the lower working chamber 24 along the line 66, passing through the non-return valve 62. In the extension phase, the flow control valve 64 is in the closed position, as a result of the difference in pressure between the two working chambers 22 and 24 of the cylinder 12, and the oil flows from the auxiliary conduit 30 to the reservoir 60 along the line 68, passing through the non-return valve 64.

[0049] According to the embodiment shown in FIG. 9, where parts and elements identical or corresponding to those of the embodiment of FIGS. 1-3 have been given the same reference numbers, the rod 26 is a through rod, in that it extends both through the upper closure assembly 20 of the cylinder 12, passing through the hole 28 provided therein, and through the lower wall 18, passing through a hole 70 provided therein. In this case, a gas reservoir is not necessary.

[0050] All the embodiments described above enable therefore to generate electric energy by inducing an electric current in a winding surrounding an auxiliary conduit which is in fluid communication with the two working chambers of the cylinder and along which a train of permanent magnets moves with reciprocating motion, dragged by the working fluid which flows from one working chamber to the other as a result of the reciprocating movement of the piston relative to the cylinder.

[0051] As is shown in FIG. 10, the shock-absorber 10 described above can be modelled with an equivalent electric circuit, in which the assembly formed by the cylinder 12 and the piston 14 is represented by a counter-electromotive force F.sub.CEM, while the winding 36 arranged around the auxiliary conduit 30 is represented by a resistance R and an inductance L. This circuit is interfaced with a diode bridge or a controlled synchronous rectifier D, capable of rectifying the voltage signal, and with a variable resistance R.sub.V, which in turn models a conversion device capable of recovering the electric energy. This conversion device includes a controllable equivalent input resistance equal to R.sub.V, whose value determines the intensity of the reaction force with which the train of permanent magnets 32 opposes the movement of the piston 14, and thus determines the damping characteristics of the shock-absorber. By adjusting the value of the resistance R.sub.V using suitable power electronics, it is therefore possible to obtain the desired damping curves (force-speed curves) for control of the vehicle dynamics (comfort and road-holding).

[0052] The configuration shown for example in FIG. 4, with a single winding 36 arranged around the auxiliary conduit 30, is a single phase configuration. It is, however, possible to obtain a two-, three- or more phase system, by arranging more windings around the auxiliary conduit 30 with suitable spatial relocation of the permanent magnets in order to minimize the torque and current ripple. FIG. 11 shows, for example, a two-phase configuration, with a first winding 36 (first phase) and a second winding 36a (second phase), wound alternately around the auxiliary conduit 30. FIG. 12, on the other hand, shows a three-phase configuration, with a first winding 36 (first phase), a second winding 36a (second phase) and a third winding 36b (third phase), wound alternately around the auxiliary conduit 30.

[0053] The windings coming from the shock-absorber may be connected in various ways, all of which are known. The windings may, for example, all be connected in series, or all in parallel, according to a fixed configuration of connections in series and in parallel, or again according to a variable configuration of connections in series and in parallel.

[0054] With reference, finally, to FIGS. 13 and 14, according to a variant of the present invention the electric energy is generated not by arranging one or more windings around the auxiliary conduit along which the train of permanent magnets 32 moves, as in the embodiments described above, but by driving in rotation, by the train of permanent magnets 32, a wheel 72 which is provided with permanent magnets 74 and is mechanically coupled, for example by a shaft 76, to an electric machine 78. In this way a contactless motion transmission mechanism is obtained, similar to a rack-and-pinion mechanism, in which the train of permanent magnets 32 acts as the rack and the wheel 72 with the permanent magnets 74 acts as the pinion. The reciprocating motion of the train of permanent magnets 32 along the auxiliary conduit 30 in this case produces reciprocating rotation of the wheel 72 around its axis (indicated x in FIG. 13) and thus electric energy generation by the electric machine 78 operating as a generator.

[0055] The regenerative hydraulic shock-absorber of the present invention may also be used actively by supplying electric power to the coils, and therefore transmitting force and mechanical work to the train of permanent magnets.

[0056] Naturally, the principle of the invention remaining unchanged, the embodiments and the constructional details may vary widely from those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the appended claims.