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Title:
HYDRAULIC SHOCK-ABSORBER FOR A VEHICLE SUSPENSION PROVIDED WITH A HYDRAULIC STOP MEMBER OPERATING DURING THE COMPRESSION STROKE OF THE SHOCK-ABSORBER
Document Type and Number:
WIPO Patent Application WO/2018/224961
Kind Code:
A1
Abstract:
The shock absorber (10) comprises: a first cylindrical tube (14), a piston rod (18), a main piston (20) fixed to the piston rod (18) and slidably mounted in the first cylindrical tube (14) so as to separate the internal volume of this tube into an extension chamber (22) and a compression chamber (24), and a hydraulic stop member (30) arranged to operate during the compression stroke of the shock absorber (10). The hydraulic stop member (30) comprises a cup-shaped body (32) mounted in the compression chamber (24) and an auxiliary piston (34) mounted at the lower end of the piston rod (18). The cup-shaped body (32) comprises a lateral wall (44) and a bottom wall (46) which define, together with the auxiliary piston (34), a working chamber (52) in which the damping fluid of the shock absorber (10) is compressed by the auxiliary piston (34) during the compression stroke of the shock absorber (10). The auxiliary piston (34) comprises two piston elements (36, 38) which are telescopically coupled to one another, i.e. a first piston element (36) fixed to the piston rod (18) and a second piston element (38) mounted axially slidably on the first piston element (36), and at least one spring (64), which is axially interposed between the first piston element (36) and the second piston element (38) and is configured to apply on the second piston element (38) an elastic force directed towards the bottom wall (46) of the cup-shaped body (32), i.e. an elastic force tending to move the second piston element (38) away from the first piston element (36), and thus from the piston rod (18).

Inventors:
BRUNO, Walter (Via Cendola 2, Asti, I-14100, IT)
CONTI, Piero Antonio (Loc. Viatosto 53/C, Asti, I-14100, IT)
GRECO, Giordano (Via Paolo Gaidano 109/13, Torino, I-10137, IT)
Application Number:
IB2018/054018
Publication Date:
December 13, 2018
Filing Date:
June 05, 2018
Export Citation:
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Assignee:
SISTEMI SOSPENSIONI S.P.A. (Viale Aldo Borletti 61/63, Corbetta, I-20011, IT)
International Classes:
F16F9/49; F16F9/16
Domestic Patent References:
WO2016146660A12016-09-22
WO2017001675A12017-01-05
Foreign References:
FR1292739A1962-05-04
FR2991016A12013-11-29
US20160025174A12016-01-28
Attorney, Agent or Firm:
RONDANO, Davide et al. (Corso Emilia 8, Torino, I-10152, IT)
Download PDF:
Claims:
CLAIMS

1. Hydraulic shock absorber (10) comprising

a first cylindrical tube (14),

a piston rod (18) which is arranged coaxially with the first cylindrical tube (14) and partially protrudes therefrom,

a main piston (20) which is fixed to a first end of the piston rod (18) and is slidably mounted in the first cylindrical tube (14) so as to separate the internal volume of the first cylindrical tube (14) into an extension chamber (22) and a compression chamber (24), and a hydraulic stop member (30) which is arranged in the compression chamber (24) and is arranged to operate during the compression stroke of the shock absorber (10) to hydraulically dissipate kinetic energy when the shock absorber (10) approaches an end-of- travel position during the compression stroke,

wherein the hydraulic stop member (30) comprises a cup-shaped body (32) mounted in the compression chamber (24) of the shock absorber (10), coaxially therewith, and an auxiliary piston (34) mounted on said first end of the piston rod (18) of the shock absorber (10), coaxially therewith, and

wherein the cup-shaped body (32) comprises a lateral wall (44) and a bottom wall (46) which define, together with the auxiliary piston (34), a working chamber (52) in which a damping fluid of the shock absorber (10) is compressed by the auxiliary piston (34) during the compression stroke of the shock absorber (10),

characterized in that the auxiliary piston (34) comprises

two piston elements (36, 38) telescopically coupled to each other, that is to say, a first piston element (36), which is fixed to the piston rod (18), and a second piston element (38), which is arranged coaxially with the first piston element (36), is provided with sealing means (42) configured to seal against an internal surface of the lateral wall (44) of the cup-shaped body (32), and is axially slidable with respect to the first piston element

(36), and

elastic means (64) which are axially interposed between the first piston element (36) and the second piston element (38) and are arranged to apply on the second piston element (38) an elastic force directed towards the bottom wall (46) of the cup-shaped body (32), i.e. an elastic force tending to move the second piston element (38) away from the first piston element (36), and thus from the piston rod (18).

2. Hydraulic shock absorber according to claim 1, wherein said elastic means (64) comprise at least one spring.

3. Hydraulic shock absorber according to claim 2, wherein said at least one spring is a cylindrical coil spring or a Belleville spring.

4. Hydraulic shock absorber according to any one of the preceding claims, wherein the second piston element (38) is of tubular shape.

5. Hydraulic shock absorber according to claim 4, wherein the second piston element (38) is provided at its bottom with a cap (70) which separates an internal chamber (86) of the second piston element (38) from the working chamber (52) of the cup-shaped body (32).

6. Hydraulic shock absorber according to claim 5, wherein said cap (70) is provided with at least one hole (88) arranged to put the internal chamber (86) of the second piston element (38) into fluid communication with the working chamber (52) of the cup-shaped body (32).

7. Hydraulic shock absorber according to claim 4, wherein the second piston element (38) is open at its bottom. 8. Hydraulic shock absorber according to any one of the preceding claims, wherein the auxiliary piston (34) is provided with a pressure relief valve (90, 92, 94) arranged to limit the pressure in the working chamber (52) of the cup-shaped body (32) up to a predetermined threshold value. 9. Hydraulic shock absorber according to any one of the preceding claims, further comprising a second cylindrical tube (12) arranged externally of and coaxially with the first cylindrical tube (14) so as to define with the first cylindrical tube (14) an annular chamber (16).

10. Vehicle suspension comprising a hydraulic shock absorber according to any one the preceding claims.

Description:
Hydraulic shock absorber for a vehicle suspension provided with a hydraulic stop member operating during the compression stroke of the shock-absorber

The present invention relates in general to a hydraulic shock absorber for a vehicle suspension provided with a hydraulic stop member. More specifically, the present invention relates to a hydraulic shock absorber of the type identified above, wherein the hydraulic stop member is arranged to operate during the compression movement of the shock absorber. The invention will be described herein with particular reference to a hydraulic shock absorber for a vehicle suspension of the so-called double-tube type, but is intended to be applicable to any other type of hydraulic shock absorbers for vehicle suspensions.

As is known, a double-tube hydraulic shock absorber for vehicle suspensions typically comprises an external cylindrical tube, an internal cylindrical tube coaxial with the external cylindrical tube and defining therewith an annular chamber, a piston rod arranged coaxially with the two cylindrical tubes and partially protruding therefrom, and a piston which is slidably mounted in the internal cylindrical tube and is fixed to the lower end of the piston rod. The piston separates the internal volume of the internal cylindrical tube into an extension chamber and a compression chamber, in which chambers a damping fluid, typically oil, is contained. The piston is provided with a first pair of one-way valves, namely a compensation valve which, during the compression stroke of the shock absorber, controls the flow of the damping fluid from the compression chamber to the extension chamber, and a rebound valve which, during the extension stroke of the shock absorber, controls the flow of the damping fluid from the extension chamber to the compression chamber. A valve assembly is provided on the bottom of the shock absorber and comprises a second pair of one-way valves, namely a compression valve which, during the compression stroke, controls the flow of the damping fluid from the compression chamber to the annular chamber, and an intake valve which, during the extension stroke, controls the flow of the damping fluid from the annular chamber to the compression chamber.

Typically, a hydraulic shock absorber for vehicle suspensions is provided with a first end- of-travel stop member, which is arranged inside the shock absorber and is configured to act during the extension stroke of the shock absorber, and a second end-of-travel stop member, which is arranged on the outside of the shock absorber and is configured to act during the compression stroke of the shock absorber.

The hydraulic stop members are used almost exclusively as end-of-travel devices operating during the extension stroke. However, there are some examples of hydraulic stop members operating during the compression stroke. A hydraulic shock absorber according to the preamble of the independent claim 1 is known from WO 2017/001675 Al in the name of the Applicant. This document discloses a hydraulic shock absorber provided with a hydraulic stop member operating during the compression stroke of the shock absorber, wherein the hydraulic stop member comprises a cup-shaped body mounted in the compression chamber of the shock absorber and an auxiliary piston mounted to an end of the piston rod of the shock absorber (namely, to the end facing the inside of the cylinder of the shock absorber), coaxially therewith, so as to move axially as a single piece with the main piston of the shock absorber, the auxiliary piston being arranged to slide in the cup-shaped body when the shock absorber approaches the end-of-travel position during the compression movement. The cup-shaped body comprises a lateral wall and a bottom wall defining, together with the auxiliary piston, a working chamber in which a damping fluid of the shock absorber (oil) is compressed by the auxiliary piston when the latter slides in the working chamber towards the bottom wall of the cup- shaped body. Moreover, axial channels are provided on the internal surface of the lateral wall of the cup- shaped body to allow the oil to flow out axially from the working chamber when the auxiliary piston slides in the working chamber towards the bottom wall of the cup-shaped body. In such a hydraulic shock absorber the movement of the piston rod of the shock absorber during the compression stroke is thus damped due to the flow of oil from the cup- shaped body of the hydraulic stop member through the axial channels provided in the cylindrical lateral wall of that body.

The hydraulic stop member of the shock absorber known from WO 2017/001675 Al is also provided with a pressure relief valve arranged to allow the discharge of oil from the working chamber through a special bypass channel, so as to avoid an increase in the oil pressure in the working chamber above a predetermined threshold value. The pressure relief valve comprises a closure member which is slidably received inside the auxiliary piston and is held by a spring against a valve seat so as to keep the bypass channel closed as long as the oil pressure inside the working chamber is below the aforementioned threshold value.

It is an object of the present invention to provide a hydraulic shock absorber provided with a hydraulic stop member operating during the compression stroke of the shock absorber, which allows, with the total stroke required for the piston rod of the shock absorber being the same, a reduction in the axial size of the cup- shaped body of the hydraulic stop member, or rather, with the axial size of the cup-shaped body of the hydraulic stop member being the same, an increase in the stroke of the piston rod of the shock absorber. A further object of the present invention is to provide a hydraulic shock absorber of the type identified above, which gives to the designer a wide freedom in setting the damping characteristics of the shock absorber during the compression stroke depending on the design requirements. These and other objects are fully achieved according to the invention by virtue of a hydraulic shock absorber having the features defined in the accompanying independent claim 1.

Advantageous embodiments of the invention are specified in the dependent claims, the subject-matter of which is to be understood as an integrating part of the following description.

In short, the invention is based on the idea of providing a hydraulic shock absorber of the type specified in the preamble of the independent claim 1, wherein the auxiliary piston comprises

two piston elements telescopic ally coupled to each other, that is to say, a first piston element, which is attached to the piston rod, and a second piston element, which is arranged coaxially with the first piston element, is provided with sealing means arranged to cooperate with the internal surface of the lateral wall of the cup-shaped body, and is axially slidable relative to the first piston element, and

elastic means interposed between the first and second piston elements so as to apply on the second piston element an elastic force tending to urge the second piston element axially towards the cup-shaped body of the hydraulic stop member, i.e. to axially move the second piston element away from the first piston element, and thus from the piston rod.

Thanks to the telescopic configuration of the auxiliary piston, an additional stroke of the piston rod of the shock absorber is obtained, which is given by the axial movement of the second piston element towards the first piston element of the hydraulic stop member against the elastic force generated by the elastic means and therefore, with the axial size of the cup- shaped body being the same, a total stroke of the piston rod greater than that obtainable with a hydraulic shock absorber according to the prior art is obtained.

Moreover, the elastic action exerted by the elastic means interposed between the two piston elements of the hydraulic stop member is added to the viscous action exerted by the oil contained in the working chamber of the cup-shaped body, which allows the designer to calibrate the damping characteristics of the shock absorber during the compression stroke by setting not only the viscous damping characteristics of the stop member (for example, the flow cross-section area of the axial channels) but also the elastic characteristics of the stop member (for example, the stiffness of the elastic means). It is thus possible to obtain, for example, a very progressive increase in the damping force when the auxiliary piston enters the cup- shaped body.

According to one embodiment, the second piston element of the hydraulic stop member is closed at the bottom, i.e. at its end facing the bottom of the cup-shaped body, by a cap. In this embodiment, the force-displacement characteristic of the shock absorber will typically depend, in an initial stage of the compression stroke within the hydraulic stop member, on the elastic characteristics of the elastic means, and only in the final stage of the compression stroke it will depend on the viscous damping characteristics of the hydraulic stop member. According to an alternative embodiment, the lower cap of the second piston element may have one or more holes or be completely dispensed with, thereby allowing the damping fluid contained in the working chamber of the cup-shaped body to flow through the second piston element during the compression stroke. In this alternative embodiment, the force- displacement characteristic will be different from the one according to the first embodiment, since compression of the elastic means will typically occur simultaneously, or successively, to the movement of the auxiliary piston inside the cup-shaped body of the hydraulic stop member.

In the event that the lower cap of the second piston element is open, or even absent, the hydraulic stop member may have a bypass duct configured to connect the working chamber of the cup-shaped body with the portion of the compression chamber of the shock absorber placed above the sealing means of the second piston element and may be further provided with a pressure relief valve configured to keep the bypass duct closed as long as the pressure in the working chamber of the cup-shaped body remains below a given limit value, and to open the bypass duct, thus allowing the discharge of damping fluid through the bypass duct from the working chamber of the cup-shaped body to the compression chamber, when the pressure in the working chamber of the cup-shaped body exceeds the aforesaid limit value.

Preferably, the side wall of the cup-shaped body comprises a first cylindrical wall portion facing the opposite side of the bottom wall of the cup-shaped body, a second cylindrical wall portion facing the bottom wall of the cup-shaped body, and a third tapered wall portion interconnecting the first and second wall portions, wherein the first wall portion has an external diameter substantially equal to the internal diameter of the internal cylindrical tube of the shock absorber and is firmly connected to such tube inside the compression chamber of the shock absorber, wherein the second wall portion has an external diameter smaller than the internal diameter of the internal cylindrical tube, and therefore also smaller than the external diameter of the first wall portion, in such a way as to form an annular passage with such tube, and wherein the third wall portion has a plurality of radial openings or axial passages for putting the portion of the compression chamber comprised between the main piston and the auxiliary piston into communication with the aforesaid annular passage, and therefore with a valve assembly (compression valve and intake valve) arranged on the bottom of the shock absorber. Such an embodiment allows the cup-shaped body to be easily attached, at its first wall portion, to the internal cylindrical tube of the shock absorber, and at the same time, due to the radial openings or the axial passages, does not jeopardize the operation of the shock absorber, since such radial openings or axial passages always ensure communication between the volume of oil comprised between the main piston and the auxiliary piston and the volume of oil comprised in the annular passage, which in turn is in communication with the valve assembly on the bottom of the shock absorber.

Further features 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 accompanying drawings, wherein:

Figure 1 is an axial sectional view of a double-tube hydraulic shock absorber for a vehicle suspension provided with a hydraulic stop member operating during the compression stroke according to a first embodiment of the present invention, in a first operating position;

Figure 2 is an axial sectional view showing, on an enlarged scale, the hydraulic stop member of the shock absorber of Figure 1, in the aforesaid first operating position;

Figure 3 is an exploded view of the hydraulic stop member of the shock absorber of Figure 1;

Figure 4 is an axial sectional view showing, on an enlarged scale, the hydraulic stop member of the shock absorber of Figure 1, in a second operating position;

Figure 5 is an axial sectional view showing, on an enlarged scale, the hydraulic stop member of the shock absorber of Figure 1, in a third operating position;

Figure 6 shows an example of a force-displacement characteristic, during the compression stroke, of the shock absorber of Figure 1;

Figure 7 is an axial sectional view of a variant embodiment of the hydraulic stop member of a hydraulic shock absorber for a vehicle suspension according to the present invention, in an operating position similar to the aforesaid first operating position of Figures 1 and 2; Figure 8 is an axial sectional view of the hydraulic stop member of Figure 7, in an operating position similar to the aforesaid second operating position of Figure 4;

Figure 9 is an axial sectional view of the hydraulic stop member of Figure 7, in an operating position similar to the aforesaid third operating position of Figure 5; and

Figure 10 is an axial sectional view of a further variant embodiment of the hydraulic stop member of a hydraulic shock absorber for a vehicle suspension according to the present invention, in an operating position similar to the aforesaid third operating position of Figure 5. In the following description and claims, the terms "axial" and "axially" identify the direction of the longitudinal axis of the shock absorber, as well as of the longitudinal axis of the hydraulic stop member. Moreover, terms such as "upper" and "lower" are to be understood as referring to the arrangement of the shock absorber shown in Figure 1, wherein the main piston of the shock absorber is mounted at the lower end of the piston rod and therefore the piston rod and the piston move downwards during the compression stroke of the shock absorber and upwards during the extension stroke of the shock absorber.

As already mentioned above, the present description of the invention relates to a double- tube hydraulic shock absorber. However, the invention is not to be considered as being limited to such an architecture of the shock absorber, as it is also applicable, for example, to a single-tube hydraulic shock absorber.

With reference first to Figure 1, a double-tube hydraulic shock absorber, particularly for vehicle suspensions, is generally indicated at 10 and comprises, in a manner known per se, an external cylindrical tube 12, an internal cylindrical tube 14 coaxial with the external cylindrical tube 12 and defining with the latter an annular chamber 16 filled in an upper portion thereof with gas, a piston rod 18 which is arranged coaxially with the two cylindrical tubes 12 and 14 and protrudes partially therefrom, and a main piston 20 (hereinafter referred to as the main piston) which is slidably mounted in the internal cylindrical tube 14 and is fixed to the lower end of the piston rod 18. The main piston 20 separates the internal volume of the internal cylindrical tube 14 into an upper chamber 22, or extension chamber, and a lower chamber 24, or compression chamber, in which a damping fluid is contained. Oil is typically used as a damping fluid and therefore, for simplicity, oil will be used hereinafter to indicate the damping fluid. It is clear, however, that the present invention is not limited to the use of oil as damping fluid.

The main piston 20 is provided, in a manner known per se, with a first valve assembly 26 comprising a pair of one-way valves, namely a compensation valve which, during the compression stroke of the shock absorber, controls the flow of oil from the compression chamber 24 to the extension chamber 22, and a rebound valve which, during the extension stroke of the shock absorber, controls the flow of oil from the extension chamber 22 to the compression chamber 24. On the bottom of the shock absorber 10, and specifically on the bottom of the internal cylindrical tube 14, there is provided, in a manner known per se, a second valve assembly 28 comprising a pair of one-way valves, namely a compression valve which, during the compression stroke, controls the flow of oil from the compression chamber 24 to the annular chamber 16, and an intake valve which, during the extension stroke, controls the flow of oil from the annular chamber 16 to the compression chamber 24. The longitudinal axis of the shock absorber 10 is indicated at z. The shock absorber 10 is provided with a hydraulic stop member, generally indicated at 30, operating during the compression stroke of the shock absorber to hydraulically dissipate the kinetic energy of the suspension when the shock absorber approaches the end-of-travel position in compression. As shown in Figure 1, the hydraulic stop member 30 is arranged in the compression chamber 24 of the shock absorber, in particular on the bottom of the internal cylindrical tube 14.

With reference also to Figures 2 and 3, the hydraulic stop member 30 basically comprises a cup-shaped body 32 and a piston 34 (hereinafter referred to as auxiliary piston).

The cup-shaped body 32 is fixed to the internal cylindrical tube 14 of the shock absorber and extends coaxially therewith.

The auxiliary piston 34 comprises a first piston element 36 having an approximately cylindrical shape and in any case extending axially, which element is attached, for example by threaded coupling 40, to the bottom end of the piston rod 18, below the main piston 20. The auxiliary piston 34 further comprises a second piston element 38, of tubular shape, which is placed around the first piston element 36, coaxially therewith. The second piston element 38 is mounted so as to be axially slidable with respect to the first piston element 36 along an external cylindrical wall 36a of the first piston element 36. The second piston element 38 is provided with a sealing ring 42 arranged to seal against the internal surface of a lateral wall 44 of the cup-shaped body 32.

The cup-shaped body 32 is open at the top, i.e. towards the main piston 20, and comprises, in addition to the lateral wall 44, a bottom wall 46. Preferably, the lateral wall 44 and the bottom wall 46 are made as separate pieces from each other and are firmly connected to each other, for example by force-fit and/or suitable retaining means. According to the illustrated embodiment, the lateral wall 44 comprises a first wall portion 44a, or upper wall portion, which faces away from the bottom wall 46, i.e. towards the side of the opening of the cup-shaped body 32, a second wall portion 44b, or lower wall portion, which faces towards the bottom wall 46, and a third wall portion 44c, or intermediate wall portion, which interconnects the upper wall portion 44a and the lower wall portion 44b. The upper wall portion 44a has an external diameter substantially equal to the internal diameter of the internal cylindrical tube 14. The upper wall portion 44a is firmly connected to the internal cylindrical tube 14, for example by force-fit and/or suitable retaining means. The lower wall portion 44b has an external diameter smaller than the internal diameter of the internal cylindrical tube 14, and thus also smaller than the external diameter of the upper wall portion 44a. Between the lower wall portion 44b of the cup-shaped body 32 and the internal cylindrical tube 14 of the shock absorber there is therefore an annular passage 48 (Figure 1), which is in fluid communication with the portion of the compression chamber 24 below the bottom wall 46 of the cup-shaped body 32.

On the internal surface of the side wall 44 of the cup-shaped body 32, in particular on the internal surface of the lower wall portion 44b, and possibly also of the intermediate wall portion 44c, a plurality of axial channels 50 (Figure 2) are provided to allow the oil to flow out in the axial direction from a working chamber 52 enclosed by the lower wall portion 44b and comprised between the second piston element 38 and the bottom wall 46, when the auxiliary piston 34 moves towards the bottom wall 46 of the cup-shaped body 32. The axial channels 50 extend parallel to the axis z (longitudinal axis of the cup-shaped body 32), and therefore along the direction of movement of the auxiliary piston 34.

The third wall portion 44c has a plurality of radial openings 54 (and/or a plurality of axial passages, not provided for in the illustrated embodiment) for putting the portion of the compression chamber 24 comprised between the main piston 20 of the shock absorber 10 and the cup-shaped body 32 of the hydraulic stop member 30 into communication with the aforesaid annular passage 48, and therefore with the valve assembly 28 (compression valve and intake valve) arranged on the bottom of the shock absorber 10.

The first piston element 36 forms a lower abutment surface 56 adapted to cooperate with a lower abutment surface 58 of the second piston element 38 to define a lower end-of-travel position (fully extended position) of the second piston element 38 (Figure 2), and an upper abutment surface 60 adapted to cooperate with an upper abutment surface 62 of the second piston element 38 to define an upper end-of-travel position (fully retracted position) of the second piston element 38 (Figure 5). The second piston element 38 is thus axially movable with respect to the first piston element 36 between the aforesaid upper and lower end-of- travel positions. Elastic means are axially arranged between the first piston element 36 and the second piston element 38 to apply on the second piston element 38 an elastic force which is directed towards the bottom wall 46 of the cup-shaped body 32 and therefore tends to urge the second piston element 38 into the aforesaid lower end-of-travel position. These elastic means are preferably formed by a spring 64, and will be therefore hereinafter referred to simply as spring, but might be formed by any other suitable elastic means. In the illustrated embodiment, the spring 64 is a cylindrical coil spring, but could be a spring of any other type. For example, if a high- stiffness spring was required a pack of Belleville springs could be provided instead of a cylindrical coil spring.

The spring 64 is in contact at its upper end against a first abutment surface integral with the first piston element 36, said first abutment surface coinciding, for example, with the aforementioned upper abutment surface 60. The spring 64 is in contact at its lower end against a second abutment surface 66a integral with the second piston element 38. Said second abutment surface 66a is formed, for example, by an annular element 66 which is arranged around the second piston element 38 and rests at its bottom against a shoulder 68 of such piston element.

In the embodiment shown in Figures 1 to 5, the second piston element 38 is closed at the bottom by a cap 70.

The second piston element 38 further comprises a pair of annular abutment elements 72 and 74, namely a first annular abutment element 72, which is arranged above the sealing ring 42, i.e. on the side of the sealing ring 42 facing towards the main piston 20, and a second annular abutment element 74, which is arranged beneath the sealing ring 42, i.e. on the side of the sealing ring 42 facing the bottom wall 46 of the cup-shaped body 32. The assembly formed by the two annular abutment elements 72 and 74 is axially coupled to the second piston element 38 on one side (bottom side) by means of the cap 70 and on the opposite side (upper side) by means of a retaining ring 76 housed in a circumferential groove 78 provided in the second piston element 38. The first annular abutment element 72 forms an axial abutment surface 72a, axially facing downwards, i.e. towards the second annular abutment element 74, against which the sealing ring 42 abuts during the compression stroke. The second annular abutment element 74 comprises an upper portion 80, around which the sealing ring 42 is placed, and a lower portion 82 having an external diameter greater than that of the upper portion 80. The lower portion 82 of the second annular abutment element 74 forms a shoulder 82a, axially facing upwards, i.e. towards the first annular abutment element 72, on which a plurality of protrusions 84 are provided against which the sealing ring 42 abuts during the extension stroke. The sealing ring 42 is thus axially movable between the axial abutment surface 72a of the first annular abutment element 72 and the upper face of the protrusions 84 of the second annular abutment element 74.

The operation of the hydraulic stop member 30 described above will now be described, with reference in particular to Figures 2, 4 and 5, it being understood that the operation of the hydraulic stop member is the same also for the other embodiments of the invention which will be described further on.

During the compression stroke of the shock absorber, when the sealing ring 42 carried by the second piston element 38 of the auxiliary piston 34 begins to slide along the internal surface of the lower wall portion 44b of the cup-shaped body 32, the oil contained in the working chamber 52 is forced to flow axially out of this chamber through the axial channels 50. As a result of the resistance provided by the oil when flowing out of the working chamber 52 through the axial channels 50, the oil pressure in the working chamber 52 increases, thereby leading to an increase in the force exerted by the oil on the second piston element 38 and thus, via the spring 64, also on the first piston element 36, which, as stated above, is drivingly connected with the piston rod 18.

On the other hand, the second piston element 38, in addition to the force (directed upwards) generated by the oil contained in the working chamber 52, is also subject to the elastic force (directed downwards) generated by the spring 64. The behavior of the second piston element 38, and thus of the hydraulic stop member 30, depends therefore on these forces.

Figures 2, 4 and 5 show the behavior of the hydraulic stop member assuming that the spring 64 has a low stiffness, so that the elastic force applied by the spring 64 on the second piston element 38 is less than the force generated by the oil pressure in the working chamber 52.

Figure 2 shows the hydraulic stop member in a first operating position, wherein the sealing ring 42 is located at the upper end of the lower wall portion 44b of the cup-shaped body 32. In such a position, the second piston element 38 is still held by the spring 64 in the lower end-of-travel position. From this point on, since the elastic force applied by the spring 64 on the second piston element 38 is less than the force generated by the oil contained in the working chamber 52, the further compression movement of the piston rod 18 does not substantially lead to a downward movement of the second piston element 38, but only to a relative movement of the second piston element 38 with respect to the first piston element 36 against the elastic force of the spring 64, which is being compressed.

Figure 4 shows a second operating position wherein the second piston element 38, and therefore the sealing ring 42, is substantially in the same position as in Figure 2 with respect to the cup-shaped body 32, while the first piston element 36 has moved downwards, along with the piston rod 18, with respect to the second piston element 38, thereby compressing the spring 64, until the upper abutment surfaces 60 and 62 of the first piston element 36 and of the second piston element 38, respectively, are brought into contact with one another. When shifting from the first operating position of Figure 2 to the second operating position of Figure 4 (which phase will be hereinafter referred to as elastic compression phase), the resistance acting against the compression movement of the shock absorber is only the elastic resistance due to the spring 64, which is being compressed.

Once the two piston elements 36 and 38 are in abutment with one another with the respective upper abutment surfaces 60 and 62 (upper end-of-travel position), in the further compression movement of the shock absorber the two piston elements 36 and 38 behave as a single body. When shifting from the second operating position of Figure 4 to a third operating position (Figure 5), wherein the shock absorber is in the maximum compression condition, with the cap 70 of the auxiliary piston 34 abutting against the bottom wall 46 of the cup-shaped body 32, the hydraulic stop member 30 thus behaves as a known hydraulic stop member (such as, for example, the hydraulic stop member disclosed in the aforementioned document WO 2017/001675). This phase is indicated hereinafter as viscous damping phase.

Depending on the stiffness of the spring 64, the above-described elastic compression phase and viscous damping phase may occur in succession in this order, in succession in the reverse order, or simultaneously (throughout the compression stroke or through just a portion of the compression stroke). In this regard, Figure 6 shows two different force-displacement characteristics of a shock absorber according to the present invention, obtainable with a higher or lower stiffness of the spring 64. If the spring 64 has a low stiffness, the first part of the characteristic shows a nearly linear trend, indicating an almost purely elastic behavior, while the second part of the characteristic, with a non-linear trend, represents the viscous damping phase. On the other hand, if the spring 64 has a high stiffness, the spring is compressed only at the end of the compression stroke, when the second piston element 38 comes into abutment against the bottom wall 46 of the cup-shaped body 32. In this case, the first part of the characteristic represents the viscous damping phase, whereas when the second piston element 38 comes into abutment against the bottom wall 46 of the cup-shaped body 32, there is a further increase in force due both to the compression of the spring 64 and to the damping effect of the oil contained in an internal chamber 86 of the second piston element 38, as the oil can flow out only through the seals of the telescopic coupling between the first and second piston elements 36 and 38.

A variant embodiment of the invention is shown in Figures 7 to 9, where parts and elements identical or corresponding to those of Figures 1 to 5 are indicated with the same reference numbers.

Such a variant embodiment differs from that of Figures 1 to 5 substantially only in that the second piston element 38 is open at the bottom, instead of being closed by the cap 70, so that the working chamber 52 of the cup-shaped body 32 is in fluid communication with the internal chamber 86 of the second piston element 38. Apart from that, what has been stated above with reference to Figures 1 to 5 applies to this variant embodiment as well.

This variant of the invention makes it possible to obtain a force-displacement characteristic that may be very different from the one obtainable with the embodiment of Figures 1 to 5, since in this case the effective surface of the second piston element 38 on which the oil contained in the working chamber 52 of the cup-shaped body 32 acts is much smaller than that of the embodiment described above. With this variant embodiment, therefore, compression of the spring will typically occur simultaneously, if not even subsequently, to the movement of the second piston element 38 inside the cup-shaped body 32.

Finally, a further embodiment of the invention is shown in Figure 10, where parts and elements identical or corresponding to those of the preceding Figures are indicated with the same reference numbers.

Such an embodiment differs from that of Figures 1 to 5 first in that the cap 70 has a through hole 88, via which the working chamber 52 of the cup-shaped body 32 is in communication with the internal chamber 86 of the second piston element 38.

Moreover, according to the embodiment of Figure 10 the auxiliary piston 34 is provided with a pressure relief valve arranged to limit the pressure in the working chamber 52 of the cup-shaped body 32 up to a given maximum value. This valve comprises a closure member 90, which is made, for example, as a ball and is normally held by a spring 92 against a respective seat 94 communicating with the internal chamber 86 of the second piston 38 through an axial duct 96. When the closure member 90 is lifted from its seat 94, the axial duct 96 is in fluid communication, through radial holes 98 provided in the first piston element 36 and through radial holes 100 provided in the second piston element 38, with the portion of the compression chamber 24 located above the sealing ring 42. A bypass path is therefore defined by the axial duct 96, the holes 98 and the holes 100.

In the normal operating condition, the closure member 90 is urged by the spring 92 against the seat 94. When the pressure in the working chamber 52 of the cup-shaped body 32 exceeds a given limit value, such as to overcome the preload of the spring 92, the closure member 90 is lifted from its seat 94, thereby leaving the above-defined bypass path free and allowing in this way the oil to flow out from the working chamber 52 to the compression chamber 24, with a resulting reduction in the pressure in the working chamber 52. This avoids the risk of damages or losses due to an excessively high pressure in the working chamber 52.

As is evident from the above description, a hydraulic shock absorber for vehicle suspensions provided with a hydraulic stop member according to the present invention allows to generate a damping force on the piston of the hydraulic stop member, and therefore on the piston rod of the shock absorber, whose law of variation as a function of the stroke may be defined in advance by properly defining not only the hydraulic parameters of the stop member, but also the stiffness of the spring 64.

Moreover, thanks to the possibility of relative movement of the second piston element 38 with respect to the first piston element 36, it is possible to reduce the axial size of the cup- shaped body 32, with the total stroke of the hydraulic shock absorber being the same, or rather increase the total stroke of the hydraulic shock absorber, with the axial size of the cup-shaped body 32 being the same.

Naturally, the principle of the invention remaining unchanged, the embodiments and details of implementation may vary widely with respect to those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the accompanying claims.