阅读说明：本技术 特别适于车辆悬架的具有两个压缩阀的液压减震器 (Hydraulic shock absorber with two compression valves, particularly for vehicle suspensions ) 是由 W·布鲁诺 P·A·孔蒂 F·科托 G·格雷科 S·马尔凯蒂 于 2019-03-01 设计创作，主要内容包括：液压减震器(10)包括：外部圆柱形管(12)；与外部圆柱形管(12)限定环形腔室(16)的内部圆柱形管(14)；主活塞(20),其可滑动地安装在内部圆柱形管(14)中并将内部圆柱形管(14)的内部体积分成延伸腔室(22)和压缩腔室(24),两者均包含不可压缩的阻尼流体；阀组合件(28a,28b),其安装在内部圆柱形管(14)的底壁(72)上,并包括第一压缩阀(28a)和第一吸入阀(28b)；杯形主体(32),其在压缩腔室(24)的内部安装在内部圆柱形管(14)内；以及辅助活塞(34),其刚性地连接到主活塞(20),并且配置成至少在减震器(10)压缩阶段的最后阶段期间在杯形主体(32)中滑动。杯形主体(32)包括侧壁(36)和底壁(38),所述侧壁(36)和所述底壁(38)连同辅助活塞(34)一起限定工作腔室(46)。减震器(10)还包括配置成止回阀的第二压缩阀(68),该第二压缩阀允许阻尼流体仅在从工作腔室(46)朝向压缩腔室(24)的包括在杯形主体(32)的底壁(38)和内部圆柱形管(14)的底壁(72)之间的下部部分的方向上流动。(A hydraulic shock absorber (10) includes: an outer cylindrical tube (12); an inner cylindrical tube (14) defining an annular chamber (16) with the outer cylindrical tube (12); a main piston (20) slidably mounted in the inner cylindrical tube (14) and dividing the inner volume of the inner cylindrical tube (14) into an extension chamber (22) and a compression chamber (24), both containing an incompressible damping fluid; a valve assembly (28a, 28b) mounted on the bottom wall (72) of the inner cylindrical tube (14) and comprising a first compression valve (28a) and a first suction valve (28 b); a cup-shaped body (32) mounted inside the inner cylindrical tube (14) inside the compression chamber (24); and an auxiliary piston (34) rigidly connected to the main piston (20) and configured to slide in the cup-shaped body (32) at least during the final phase of the compression phase of the shock absorber (10). The cup-shaped body (32) comprises a side wall (36) and a bottom wall (38), said side wall (36) and said bottom wall (38) defining, together with the auxiliary piston (34), a working chamber (46). The shock absorber (10) further comprises a second compression valve (68) configured as a check valve allowing the damping fluid to flow only in a direction from the working chamber (46) towards a lower portion of the compression chamber (24) comprised between the bottom wall (38) of the cup-shaped body (32) and the bottom wall (72) of the inner cylindrical tube (14).)

1. A hydraulic shock absorber (10), said hydraulic shock absorber (10) comprising:

an outer cylindrical tube (12) extending along a longitudinal axis (z);

an inner cylindrical tube (14), said inner cylindrical tube (14) being coaxial with the outer cylindrical tube (12) and defining with the outer cylindrical tube (12) an annular chamber (16) filled with a compressible fluid in its top portion;

a rod (18), said rod (18) being arranged coaxially with said outer cylindrical tube (12) and inner cylindrical tube (14) and partially protruding from the top ends of said outer cylindrical tube (12) and inner cylindrical tube (14);

a main piston (20), said main piston (20) being slidably mounted in the inner cylindrical tube (14) along said longitudinal axis (z) and being fixed to the rod (18), the main piston (20) dividing the inner volume of the inner cylindrical tube (14) into an extension chamber (22) and a compression chamber (24), both containing an incompressible damping fluid;

a valve assembly (28a, 28b), said valve assembly (28a, 28b) being mounted on the bottom wall (72) of the inner cylindrical tube (14) and comprising a first compression valve (28a) configured as a check valve and a first suction valve (28b) configured as a check valve, the first compression valve (28a) allowing the damping fluid to flow only in the direction from the compression chamber (24) to the annular chamber (16) during a compression phase of the shock absorber (10), and the first suction valve (28b) allowing the damping fluid to flow only in the direction from the annular chamber (16) to the compression chamber (24) during an extension phase of the shock absorber (10), wherein said first compression valve (28a) comprises at least one first closing element (70), the first closing element (70) being configured to keep normally closed at least one first through hole (74) provided in the bottom wall (72) of the inner cylindrical tube (14), and elastically deformed or displaced according to a given value of pressure in the compression chamber (24) to allow the damping fluid to flow from the compression chamber (24) to the annular chamber (16) through said at least one first through hole (74);

a cup-shaped body (32), said cup-shaped body (32) being mounted inside the compression chamber (24) coaxially with the inner cylindrical tube (14) inside the inner cylindrical tube (14); and

an auxiliary piston (34), said auxiliary piston (34) being rigidly connected to the main piston (20) and configured to slide in the cup-shaped body (32) at least during the final phase of the compression phase of the shock absorber (10); and

wherein the cup-shaped body (32) comprises a side wall (36) separate from the internal cylindrical tube (14), and a bottom wall (38), said side wall (36) and said bottom wall (38) defining, together with the auxiliary piston (34), a working chamber (46), wherein the damping fluid is compressed by the auxiliary piston (34) when the auxiliary piston (34) slides in the cup-shaped body (32) towards its bottom wall (38);

characterized in that it further comprises a second compression valve (68) configured as a check valve, which allows the damping fluid to flow only in a direction from the working chamber (46) of the cup-shaped body (32) towards a lower portion of the compression chamber (24) comprised between the bottom wall (38) of the cup-shaped body (32) and the bottom wall (72) of the inner cylindrical tube (14);

wherein said second compression valve (68) comprises at least one second closing element (86), said second closing element (86) being configured to keep normally closed at least one second through hole (48) provided in the bottom wall (38) of the cup-shaped body (32) and to be elastically deformed or displaced according to a given pressure value in the working chamber (46) of the cup-shaped body (32) to allow the damping fluid to flow from the working chamber (46) to said lower portion of the compression chamber (24) through said at least one second through hole (48); and

wherein the at least one second closing element (86) is arranged externally to the cup-shaped body (32), i.e. below the bottom wall (38) of the cup-shaped body (32).

2. Shock absorber according to claim 1, wherein the first compression valve (28a) comprises a plurality of first closing elements (70), which plurality of first closing elements (70) are made as disc-like elements and are stacked one on top of the other on the lower surface of the bottom wall (72) of the inner cylindrical tube (14).

3. Shock absorber according to claim 2, wherein the first closing element (70) is configured as an elastically deformable element, and wherein the first compression valve (28a) further comprises a first locking pin (80), the first locking pin (80) extending through the bottom wall (72) of the inner cylindrical tube (14) to fix the first closing element (70) to the bottom wall (72).

4. Shock absorber according to any one of the preceding claims, wherein said second compression valve (68) comprises a plurality of second closing elements (86) made as disc elements and stacked one on top of the other on the lower surface of the bottom wall (38) of the cup-shaped body (32).

5. Shock absorber according to claim 4, wherein the second closing element (86) is configured as an elastically deformable element, and wherein the second compression valve (68) further comprises a second screw-like locking element (92), the second screw-like locking element (92) extending through the bottom wall (38) of the cup-shaped body (32) to fix the second closing element (86) to the bottom wall (38).

6. Shock absorber according to claims 3 and 5, wherein said first and second screw-like locking elements are formed by the same screw (92) extending through the bottom wall (72) of the inner cylindrical tube (14) and through the bottom wall (38) of the cup-shaped body (32).

7. Damper according to any one of the preceding claims, characterized in that the side wall (36) of the cup-shaped body (32) comprises a first wall portion (36a), a second wall portion (36b) and a third wall portion (36c), the first wall portion (36a) facing the other side opposite the bottom wall (38), the second wall portion (36b) facing the bottom wall (38), the third wall portion (36c) connecting the first and second wall portions (36a, 36b) to each other, wherein the first wall portion (36a) has an outer diameter which is greater than the outer diameter of the second wall portion (36 b).

8. Shock absorber according to claim 7, wherein the first wall portion (36a) has an outer diameter substantially equal to the inner diameter of the inner cylindrical tube (14).

9. Shock absorber according to any of the preceding claims, further comprising a second suction valve (100) configured as a check valve, the second suction valve (100) allowing the damping fluid to flow only in the direction from the lower portion of the compression chamber (24) to the working chamber (46).

Technical Field

The invention relates to a hydraulic shock absorber, in particular to a hydraulic shock absorber with a double-pipe structure.

Even though the inventive concept is conceived for application on a vehicle suspension and will be described and illustrated herein with reference to application on a vehicle suspension, the invention is not intended to be limited to this particular application but may be used in other technical fields.

Hydraulic double-tube shock absorbers generally comprise: an outer cylindrical tube; an inner cylindrical tube coaxial with the outer cylindrical tube and defining therewith an annular chamber filled in an upper portion thereof with a compressible fluid (gas); a rod arranged coaxially with and partially protruding from the top ends of the two cylindrical tubes; and a piston slidably mounted in the inner cylindrical tube and fixed to the bottom end of the rod. The piston divides the internal volume of the internal cylindrical tube into an extension chamber and a compression chamber, in which an incompressible damping fluid (oil) is contained. The piston is provided with a first pair of non-return valves, a compensation valve that regulates the flow of damping fluid from the compression chamber to the extension chamber during a compression phase of the shock absorber, and a rebound valve that regulates the flow of damping fluid from the extension chamber to the compression chamber during an extension phase of the shock absorber. A valve assembly is provided on the bottom of the shock absorber that includes a second pair of check valves, a compression valve that regulates the flow of damping fluid from the compression chamber to the annular chamber during the compression phase and a suction valve that regulates the flow of damping fluid from the annular chamber to the compression chamber during the extension phase.

Background

International patent application WO 2016/146660 a1 in the name of the applicant discloses a hydraulic double-tube shock absorber further comprising: a cup-shaped body mounted in and coaxial with the compression chamber of the shock absorber; and an auxiliary piston mounted at the bottom end of the rod of the shock absorber and coaxial with the rod of the shock absorber, so as to slide in the cup-shaped body during the final phase of the compression stroke of the piston of the shock absorber, i.e. when the piston of the shock absorber approaches the end-of-stroke position during the compression phase. The cup-shaped body includes a side wall and a bottom wall, the side wall being separate from the inner cylindrical tube of the shock absorber. The side wall and the bottom wall of the cup-shaped body define, together with the auxiliary piston, a working chamber in which the damping fluid is compressed by the auxiliary piston when the latter slides in the working chamber towards the bottom wall of the cup-shaped body. An axial passage is provided on the inner surface of the side wall of the cup-shaped body for allowing the damping fluid to flow axially out of the working chamber when the auxiliary piston slides in the working chamber towards the bottom wall of the cup-shaped body. The axial channel extends parallel to the longitudinal axis of the cup-shaped body and has a cross-section whose area decreases continuously along said axis towards the bottom wall of the cup-shaped body. The auxiliary piston includes: a cylindrical body fixed to the stem of the shock absorber and having an outer diameter smaller than the inner diameter of the lower wall portion of the cup-shaped body; a sealing ring slidably mounted axially about the cylindrical body and configured to seal against an inner surface of the lower wall portion of the cup-shaped body; and first and second annular abutment elements axially constrained to the cylindrical body and configured to axially limit the axial sliding movement of the sealing ring along the cylindrical body in either direction. The sealing ring, the first abutment element and the second abutment element are configured in such a way that, when the sealing ring slides along the inner surface of the lower wall portion of the cup-shaped body during the compression stroke of the shock absorber, the sealing ring abuts against the first abutment element and there is no passage for the oil to flow from one side of the sealing ring to the other, whereas, during the extension stroke of the shock absorber, the sealing ring abuts against the second abutment element and allows the oil to flow from one side of the sealing ring to the other, i.e. towards the working chamber of the cup-shaped body.

According to this known solution, a plurality of channels are also provided in the bottom wall of the cup-shaped body to allow the outflow of oil from the working chamber of the cup-shaped body to limit the maximum oil pressure in this chamber. Thus preventing the pressure in the working chamber of the cup-shaped body from reaching too high a value. As an alternative or in addition to the passage in the bottom wall of the cup-shaped body, the function of limiting the maximum pressure in the working chamber of the cup-shaped body can be performed by means of a suitably sized recess provided in the sealing ring.

International patent application WO 2017/001675 a1, also in the name of the present applicant, discloses a hydraulic double-tube shock absorber in which the working chamber of the cup-shaped body is connected to the portion of the compression chamber above the sealing ring via a bypass conduit, and in which the shock absorber further comprises a maximum pressure valve configured to keep the bypass conduit normally closed as long as the pressure in the working chamber is below a given limit value, and to open the bypass conduit when the pressure in the working chamber exceeds said limit value, thereby allowing damping fluid to be discharged from the working chamber to the compression chamber through the bypass conduit. With respect to the above known solutions, the hydraulic shock absorbers known from said applications allow to limit the pressure in the working chamber of the cup-shaped body more effectively also at high movements of the stem. On the other hand, the hydraulic shock absorbers known from said application have a more complex structure than the hydraulic shock absorbers of the known solutions described above.

Disclosure of Invention

The object of the present invention is to provide a hydraulic double-tube shock absorber which is simple to manufacture and assemble and which at the same time is able to effectively limit the maximum pressure in the working chamber of the cup-shaped body.

According to the present invention, this and other objects are fully achieved by a hydraulic shock absorber having the features set forth in the appended independent claim 1.

Advantageous embodiments of the invention are defined in the dependent claims, the subject matter of which is considered to form an integral part of the following description.

In short, the present invention is based on the idea of providing a hydraulic shock absorber of the above-mentioned type comprising an additional check valve which allows the damping fluid to flow only in the direction from the working chamber of the cup-shaped body to a portion of the compression chamber of the shock absorber comprised between the bottom wall of said cup-shaped body and the valve assembly on the bottom of the internal cylindrical tube when the pressure in said working chamber exceeds a given threshold, wherein said additional check valve comprises at least one closing element arranged externally of the cup-shaped body, i.e. below the bottom wall of the cup-shaped body, and configured to normally keep closed one or more through holes provided in the bottom wall of the cup-shaped body and to elastically deform or displace when the pressure inside the working chamber of the cup-shaped body increases, until the damping fluid is allowed to flow from the working chamber of the cup-shaped body to the lower portion of the compression chamber through said hole.

Such additional check valve therefore acts as a compression valve (and will therefore be referred to hereinafter as additional compression valve) which affects the pressure variations inside the working chamber of the cup-shaped body once the pressure reaches the above-mentioned threshold value. The use of this additional compression valve, in addition to the compression valve provided on the bottom of the internal cylindrical tube of the shock absorber, also avoids the need to provide a bypass conduit in the cylindrical body of the auxiliary piston and therefore allows the structure of the shock absorber to be simplified, whereas in the prior art discussed above a bypass conduit is provided in the cylindrical body of the auxiliary piston.

The at least one closing element of the additional check valve is preferably configured as an elastically deformable element arranged to be elastically deformed above a given pressure value to allow the damping fluid to flow out of the working chamber of the hydraulic stop member. Alternatively, at least one closing element may be a rigid element on which the elastic element acts to keep the closing element normally closed. By suitably designing the closure element, in the case of at least one elastically deformable closure element, or by suitably designing the elastic element, in the case of at least one rigid closure element, it is possible to obtain a maximum pressure characteristic curve in the working chamber of the cup-shaped body, which depends on the stroke and speed of the damper piston.

Preferably, the additional compression valve has a structure similar to one of the compression valves of the shock absorber on the bottom of the internal cylindrical tube (hereinafter referred to as main compression valve), i.e. with disc-shaped elastically deformable closing elements which are superposed on each other on the lower surface of the bottom wall of the cup-shaped body and are axially fixed to the bottom wall by means of locking elements, in particular screw members, which extend through a central hole provided in each of the elastic closing elements and through a central hole provided on the bottom wall.

Preferably, the same locking element is used to lock the elastic closing elements of the main compression valve and of the additional compression valve, which allows to reduce the total number of parts of the shock absorber.

The additional compression valve is therefore another important element for adjusting the damping level of the shock absorber during the compression stroke, since it allows to obtain, by means of suitable calibration, the desired characteristic curve of the damping force according to the stroke and the speed of the shock absorber piston during the final phase of the compression phase.

Drawings

Other characteristics and advantages of the present invention will become clearer from the following detailed description, given purely by way of non-limiting example with reference to the accompanying drawings, in which:

FIG. 1 is an axial cross-sectional view of a hydraulic dual tube shock absorber, particularly adapted for a vehicle suspension, according to an embodiment of the present invention;

FIG. 2 is an axial cross-sectional view, on an enlarged scale, of the bottom portion of the shock absorber shown in FIG. 1; and

fig. 3 and 4 are an axial sectional view and a perspective view, respectively, of a bottom portion of a hydraulic double tube shock absorber, which is particularly suitable for a vehicle suspension, according to another embodiment of the present invention.

Detailed Description

In the following description and claims, the terms "axial" and "axially" refer to the direction of the longitudinal axis of the shock absorber. Furthermore, the terms "top" and "bottom" refer to the arrangement of the shock absorber shown in fig. 1, wherein the piston of the shock absorber is mounted on the bottom end of the rod, and whereby the rod and the piston move downwards during the compression phase of the shock absorber and upwards during the extension phase of the shock absorber.

Referring initially to fig. 1, a hydraulic dual-tube shock absorber for a vehicle suspension is generally designated 10 and comprises, in a manner known per se: an outer cylindrical tube 12; an inner cylindrical tube 14 arranged coaxially with the outer cylindrical tube 12 and defining with the outer cylindrical tube 12 an annular chamber 16, the annular chamber 16 being filled with a compressible fluid (gas) in a top portion thereof; a rod 18, the rod 18 being arranged coaxially with the two cylindrical tubes 12 and 14 and partially protruding from the top ends of the two cylindrical tubes 12 and 14; and a piston 20 (hereinafter referred to as a master piston) slidably mounted in the inner cylindrical tube 14 and fixed to the bottom end of the rod 18.

The longitudinal axis of shock absorber 10 is designated z.

The main piston 20 divides the interior volume of the inner cylindrical tube 14 into an upper chamber 22, or extension chamber, and a lower chamber 24, or compression chamber, in which an incompressible damping fluid is contained. Oil is commonly used as the damping fluid, and therefore for simplicity the term "oil" will be used hereinafter to refer to the damping fluid. It is however obvious that the invention is not limited to the use of oil as damping fluid, as any other incompressible fluid may be used instead.

Referring also to fig. 2, the main piston 20 is provided, in a manner known per se, with a first valve assembly comprising a pair of check valves 26a and 26b, a so-called compensation valve 26a, which regulates the oil flow from the compression chamber 24 to the extension chamber 22 during the compression phase of the shock absorber, and a so-called rebound valve 26b, which regulates the oil flow from the extension chamber 22 to the compression chamber 24 during the extension phase of the shock absorber.

On the bottom of the shock absorber 10, i.e. on the bottom of the inner cylindrical tube 14, there is provided, in a manner known per se, a second valve assembly comprising a pair of check valves 28a and 28b, a so-called compression valve 28a and a so-called suction valve 28b, the compression valve 28a regulating the oil flow from the compression chamber 24 to the annular chamber 16 during the compression phase, the suction valve 28b regulating the oil flow from the annular chamber 16 to the compression chamber 24 during the extension phase.

Shock absorber 10 further comprises a cup-shaped body 32 and an auxiliary piston 34.

The cup-shaped body 32 extends coaxially with the inner cylindrical tube 14. Furthermore, the cup-shaped body 32 is made as a separate part with respect to the internal cylindrical tube 14 of the shock absorber and is rigidly connected thereto.

The auxiliary piston 34 is preferably connected to the rod 18 of the shock absorber in a removable manner (for example by screwing) so as to be movable along the longitudinal axis z. An auxiliary piston 34 is arranged to slide axially in the cup-shaped body 32 to compress the oil contained therein.

The cup-shaped body 32 is open at its top end, i.e. at its end facing the main piston 20, and comprises a side wall 36 and a bottom wall 38. Preferably, the side walls 36 and the bottom wall 38 are made as separate parts and are firmly connected to each other, for example by press-fit (force-fit) and/or suitable retaining means.

According to the illustrated embodiment, the side wall 36 includes: a first wall portion 36a or inlet wall portion facing the other side opposite to the bottom wall 38, i.e. the side facing the opening of the cup-shaped body 32; a second wall portion 36b or lower wall portion facing the bottom wall 38; and a third wall portion 36c or an intermediate wall portion that connects the inlet wall portion 36a and the lower wall portion 36b to each other. The inlet wall portion 36a has an outer diameter substantially equal to the inner diameter of the inner cylindrical tube 14. The inlet wall portion 36a is securely connected to the inner cylindrical tube 14, such as by press fitting and/or suitable retaining means. The lower wall portion 36b has an outer diameter that is less than the inner diameter of the inner cylindrical tube 14, and thus also less than the outer diameter of the inlet wall portion 36 a. Thus, between the lower wall portion 36b of the cup-shaped body 32 and the internal cylindrical tube 14 of the shock absorber, an annular channel 40 is provided, which is in fluid communication with the portion of the compression chamber 24 below the bottom wall 38 of the cup-shaped body 32. The intermediate wall portion 36c has a plurality of radial openings 42, the radial openings 42 being configured to communicate the portion of the compression chamber 24 comprised between the main piston 20 and the auxiliary piston 34 with the annular channel 40 and thus with the second valve assembly 28 ( check valves 28a and 28b) placed on the bottom of the inner cylindrical tube 14 of the shock absorber.

Preferably, a plurality of axial channels 44 are provided on the inner surface of lateral wall 36 of cup-shaped body 32, in particular on the inner surface of lower wall portion 36b, and possibly also on the inner surface of intermediate wall portion 36c, so as to allow oil to flow in an axial direction out of a chamber (hereinafter referred to as working chamber) 46 enclosed by lower wall portion 36b and comprised between auxiliary piston 34 and bottom wall 38, when auxiliary piston 34 is moved towards bottom wall 38. The axial channel 44 extends parallel to the longitudinal axis of the cup-shaped body 32 (coinciding with the longitudinal axis z of the shock absorber 10), and therefore extends along the direction of movement of the auxiliary piston 34.

The axial passage 44 preferably has a cross-section that continuously decreases in area toward the bottom wall 38. More specifically, axial passage 44 preferably has a width (i.e., a dimension in the circumferential direction) that continuously (e.g., linearly) decreases toward bottom wall 38. The depth (i.e., the dimension in the radial direction) of the axial passage 44 may also decrease continuously, e.g., linearly, toward the bottom wall 38. The area of the flow section through which the oil can flow out of the working chamber 46 therefore continuously decreases as the auxiliary piston 34 moves in the cup-shaped body 32 towards the bottom wall 38. The reduction in the cross-sectional flow area results in a gradual increase in the damping force generated on the auxiliary piston 34 and, therefore, on the rod 18 to which the auxiliary piston 34 is fixed. By suitably defining the number and/or cross-section of the axial channels 44, it is thus possible to obtain a given law of variation of the damping force as a function of the travel of the auxiliary piston 34 in the cup-shaped body 32. Axial passage 44 may be replaced by, or alternatively combined with, calibrated holes suitably sized to obtain a given law of variation of the damping force as a function of the travel of auxiliary piston 34 in cup-shaped body 32.

The bottom wall 38 of the cup-shaped body 32 has at least one through hole 48 for allowing the outflow of oil from the cup-shaped body 32 to limit the increase of the oil pressure in the working chamber 46 during the compression phase. Preferably, as in the embodiment shown in the figures, the bottom wall 38 has a plurality of through holes 48, the respective axes of which are positioned, for example, angularly equally spaced, along a circumference having a centre on the longitudinal axis z.

The auxiliary piston 34 comprises a cylindrical body 50, which cylindrical body 50 extends coaxially with the cup-shaped body 32 and is connected to the rod 18 of the shock absorber, for example by a threaded coupling 52, so as to be movable along the longitudinal axis z together with the rod 18. Cylindrical body 50 has an outer diameter that is less than the inner diameter of lower wall portion 36b of cup-shaped body 32.

Auxiliary piston 34 also comprises a sealing ring 54 arranged to seal against the inner surface of lower wall portion 36b of cup-shaped body 32 so as to close working chamber 46 at the top end. In the embodiment presented herein, the sealing ring 54 is axially slidably mounted about the cylindrical body 50. In addition, the seal ring 54 may have a notch to allow a small amount of oil to flow from one side of the seal ring to the other.

The auxiliary piston 34 further comprises a pair of annular abutment elements 56 and 58, namely an upper abutment element 56 and a lower abutment element 58, the upper abutment element 56 being arranged above the sealing ring 54, i.e. on the side of the sealing ring facing the piston 20 of the shock absorber, and the lower abutment element 58 being arranged below the sealing ring 54, i.e. on the side of the sealing ring facing the working chamber 46. The assembly formed by the two abutment elements 56 and 58 is axially fixed to the cylindrical body 50 by means of a pair of retaining rings 60 and 62, which retaining rings 60 and 62 are housed in respective circumferential grooves 64 and 66 provided in the cylindrical body 50. The upper abutment element 56 forms an axial abutment surface facing axially downwards, i.e. towards the lower abutment element 58, against which the sealing ring 54 abuts during the compression phase. The lower abutment element 58 comprises: an upper portion 58a, the sealing ring 54 being disposed about the upper portion 58 a; and a lower portion 58b having an outer diameter greater than that of the upper portion 58a to form an axial abutment surface against which the seal ring 54 abuts during the extension phase. Thus, the seal ring 54 is axially movable between the axial abutment surfaces of the upper and lower abutment elements 56, 58.

In order to allow the oil to flow out of the working chamber 46 downwards, i.e. towards the portion of the compression chamber 24 comprised between the bottom wall 38 of the cup-shaped body 32 and the second valve assembly ( check valves 28a and 28b), when a given value of the oil pressure in the working chamber 46 is exceeded, according to the invention the shock absorber 10 also comprises a check valve 68 (hereinafter referred to as additional compression valve, since it has a structure and operation similar to that of the compression valve 28a on the bottom of the inner cylindrical tube 14) mounted outside the cup-shaped body 32, i.e. below the bottom wall 38 of the cup-shaped body 32.

As described above, the additional compression valve 68 has a structure and operation similar to the structure and operation of compression valve 28 a.

In particular, the compression valve 28a comprises a plurality of closing elements 70, preferably made as elastically deformable elements, mounted on a bottom wall 72, in particular on the lower surface of the bottom wall 72, the bottom wall 72 closing on the bottom the internal cylindrical tube 14. The compression valve 28a is normally closed, since in the undeformed condition of the closing element 70, the closing element 70 prevents the oil from flowing through the through hole 74 provided in the bottom wall 72, the through hole 74 preferably being arranged with its respective axis positioned along a circumference having a centre on the longitudinal axis z. The closure elements 70 are preferably made as disc-shaped elements and stacked on each other. The closure elements 70 may differ from each other in terms of outer diameter and thickness so that they have different flexibility characteristics (flexilbility characteristics) from each other. By varying the number and/or type of closure elements, it is possible to provide the compression valve with desired characteristics, for example in terms of the pressure value at which the compression valve starts to open.

The group of closure elements 70 cooperates with an annular projection 76 formed by the lower surface of the bottom wall 72 to generally close a space 78 defined between the group of closure elements 70 and the bottom wall 72, and the through-hole 74 opens into the space 78.

The group of closure elements 70 is fixed to the bottom wall 72 in a manner known per se, for example by means of a rivet coupling obtained by a locking pin 80, which locking pin 80 extends through a through hole 82 at the centre of the bottom wall 72 and is riveted to a nut 84 on the other side of the bottom wall 72 opposite the group of closure elements 70.

When the oil pressure in the portion of the compression chamber 24 comprised between the bottom wall 38 of the cup-shaped body 32 and the bottom wall 72 of the inner cylindrical tube 14 exceeds a given threshold value, which depends on the elastic characteristics and the preload of the group of closing elements 70 of the compression valve 28a, the group of closing elements 70 starts to deform, lifting away from the annular projection 76, allowing the fluid to flow out of the compression chamber 24 towards the annular chamber 16 through the through holes 74 in the bottom wall 72.

Similarly, the additional compression valve 68 comprises a plurality of closing elements 86, preferably made as elastically deformable elements, mounted on the lower surface (i.e. the outwardly facing surface) of the bottom wall 38 of the cup-shaped body 32. Obviously, such an arrangement of the closing element 86 does not take up additional space inside the cup-shaped body 32 and therefore allows to maximize the working stroke of the auxiliary piston 34, while the axial dimensions of the cup-shaped body 32 remain unchanged.

The additional compression valve 68 is normally also closed, and therefore the closing element 86 prevents oil from flowing through the through hole 48 in the bottom wall 38 without deformation of the closing element 86. The closure elements 86 are also preferably made as plate-like elements and stacked on one another. The closure elements 86 may differ from each other in diameter and thickness such that they have different flexibility characteristics from each other. By varying the number and/or type of closure elements, it is thus possible to provide additional compression valves with desired characteristics, for example in terms of the pressure value at which the valve starts to open.

The set of closure elements 86 cooperate with an annular projection 88 formed by the lower surface of bottom wall 38 to generally close an annular space 90 defined between the set of closure elements 86 and bottom wall 38, and through-hole 48 opens into annular space 90.

The set of closure elements 86 is secured to the bottom wall 38 by means of locking elements 92, such as locking screws. The locking screw 92 extends through a through hole 94 at the centre of the bottom wall 38 and is fixed to the bottom wall 38 on the other side of said wall opposite the set of closing elements 86 by a nut 96. Alternatively, for the additional compression valve 68, the same type of riveted coupling (i.e., coupling by means of a locking pin 80 caulk on a nut 84) as used for the compression valve 28a may also be used.

The additional compression valve 68 operates as follows.

During the compression phase of the shock absorber, when the sealing ring 54 of the auxiliary piston 34 starts to slide along the inner surface of the lower wall portion 36b of the cup-shaped body 32, the oil contained in the working chamber 46 is forced to flow out of this chamber in an axial direction through the axial passage 44. As previously explained, the area of the flow section formed by the axial channel 44 preferably decreases continuously as the auxiliary piston 34 moves towards the bottom wall 38 of the cup-shaped body 32. Thus, the pressure exerted on the auxiliary piston 34 and therefore on the stem 18 increases.

As the auxiliary piston 34 moves towards the bottom wall 38 of the cup-shaped body 32, and therefore the volume of the working chamber 46 decreases, the pressure of the oil contained in the working chamber 46 increases. As long as the pressure value in working chamber 46 remains below the threshold value of additional compression valve 68, which can be set to the desired value by suitably adjusting the group of closing elements 86, additional compression valve 68 remains closed, preventing the oil from flowing from working chamber 46 to the portion of compression chamber 24 below bottom wall 38 of cup-shaped body 32. The additional compression valve 68 may allow at most oil to flow through calibrated passages provided directly on the set of closure elements 86. Conversely, when the value of the pressure in the working chamber 46 exceeds said threshold value, the group of closing elements 86 begins to deform, lifting away from the annular projection 88, allowing the oil to flow from the working chamber 46 to the portion of the compression chamber 24 below the bottom wall 38.

Another embodiment of a hydraulic shock absorber according to the present invention is shown in fig. 3 and 4, in which parts and elements identical or corresponding to those of fig. 1 and 2 are identified by the same reference numerals.

This further embodiment differs from the embodiment described above with reference to fig. 1 and 2 mainly in that the additional compression valve 68 and the compression valve 28a share a locking element with which the respective set of closing elements 70 and 86 is fixed to the respective bottom wall 72 and 38. In other words, the screws 92 and the corresponding nuts 96 are used to fix the group of closing elements 70 of the compression valve 28a to the bottom wall 72 and the group of closing elements 86 of the additional compression valve to the bottom wall 38, with a spacer member 98 interposed between the group of closing elements 70 and the group of closing elements 86. By tightening the screw 92 onto the nut 96, the set of closure elements 70 and 86 of the compression valve 28a and 68 are both locked, and thus simplify both the structure and assembly of the shock absorber. Moreover, since the bottom wall 38 of the cup-shaped body 32 and therefore the entire cup-shaped body 32 is axially fixed to the bottom wall 72 of the inner cylindrical tube 14, a rigid coupling between the side wall 36 of the cup-shaped body 32 and the inner cylindrical tube 14 is no longer necessary, for example by means of a press fit and/or suitable retaining means. Obviously, this contributes to further simplifying the assembly of the shock absorber.

Furthermore, with respect to the embodiment of fig. 1 and 2, the upper abutment element 56 of the auxiliary piston 34 is not fixed to the cylindrical body 50 by a retaining ring, but is fixed to the cylindrical body 50 by plastic deformation of the upper edge portion 56a of this element, so as to engage with an annular groove 64 provided in the cylindrical body 50. This way of locking the upper abutment element 56 to the cylindrical body 50 can also be used in the shock absorber of figures 1 and 2.

In addition, as shown in fig. 4, the shock absorber may include an additional check valve 100, the check valve 100 acting as a suction valve (and, therefore, referred to hereinafter as an additional suction valve) that operates similar to the suction valve 28b on the bottom of the inner cylindrical tube 14 during the extension phase to allow oil to flow to the working chamber 46 to ensure proper filling thereof.

The additional suction valve 100 comprises at least one elastically deformable closing element 102, preferably made as a disc-shaped element, mounted on the bottom wall 38 of the cup-shaped body 32, in particular on the upper surface of the bottom wall 38, and cooperating with a plurality of through holes 104 provided in the wall. The additional suction valve 100 is also normally closed and therefore prevents oil from flowing through the through hole 104 in the bottom wall 38 without deformation. When a plurality of the closure elements 102 are provided, the closure elements may be different from each other in diameter and thickness so as to have different flexibility characteristics from each other. Advantageously, at least one closing element 102 is fixed to the bottom wall 38 of the cup-shaped body 32 by the same nut 96, so that no further locking means are required for the closing element 102 of the additional suction valve 100.

What has been explained above with reference to the embodiments of fig. 1 and 2 still applies.

Naturally, the principle of the invention remaining the same, the embodiments and construction details may be widely varied 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.