Floating piston for single-tube shock absorber

Abstract

A floating piston (10) for a single-tube shock absorber (20) slidably disposed within a tubular sleeve (25) of the shock absorber to separate a sliding chamber (30) and a blind chamber (35) from each other, the floating piston being provided with: an annular support frame (1) made of a metal material; a dynamic lip seal (2) radially outside the frame (1) and configured in sliding contact with a sleeve (25) of the shock absorber (20) such that a radial seal outside the frame (1) is defined; and a central flexible membrane (3) configured so as to sealingly close the central bore (11) and deformable so as to anticipate a full movement of the floating piston (10); the dynamic lip seal (2) and the flexible membrane (3) are made of two elastomeric materials different from each other, and the elastomeric material of the membrane (3) is more flexible and elastic than the elastomeric material of the dynamic lip seal (2).

Description

Technical Field

[0001] The present innovation relates to a floating piston for a single-tube gas shock absorber. In particular, the single-tube shock absorber is used in a vehicle suspension, and the following description will specifically refer to the vehicle suspension without thereby losing its general ( / universal) character. Background Art

[0002] Known types of monotube gas shock absorbers include:

[0003] - sleeve;

[0004] - a floating piston disposed in said sleeve and defining two chambers: a sliding chamber and a blind chamber; and

[0005] - a rod slidable inside said sleeve and provided with an endhead slidable along said sliding chamber.

[0006] In a monotube gas shock absorber of the above-mentioned type, the sliding chamber is usually filled with oil, while the blind chamber is usually filled with gas, and a floating piston is arranged in a sleeve so as to separate the oil from the gas.

[0007] Known types of floating pistons include:

[0008] - a supporting and stiffening core made of metal material and provided with a central hole;

[0009] - a seal, radially outside the metal core and arranged in sliding contact with a sleeve of the monotube shock absorber;

[0010] - a central flexible sleeve configured so as to hermetically close the central bore and capable of deforming so as to anticipate the complete movement of the piston and thus provide greater reactivity and response to the monotube shock absorber during the absorption of smaller roughnesses of the road surface without transmitting them to the vehicle and the driver / rider.

[0011] The flexible membrane of the floating piston must be able to bend towards the sliding chamber, or alternatively towards the blind chamber, according to the pressure changes between the chambers of the shock absorber, and must also be sufficiently flexible to be able to deform before the floating piston starts to shift. Therefore, the fact that the membrane starts to bend, anticipating the movement of the piston, is equivalent to a reduction in the static friction of the floating piston.

[0012] In a floating piston of the type described above, both the radially outer seal and the pliable membrane are made of elastomeric material, and the rigidity of the radially outer seal required to ensure a given static friction against the sleeve (i.e. to ensure a controlled axial sliding action at all times) cannot be easily combined with the flexibility required for the flexible membrane to be able to deform, in particular to deform rapidly. Likewise, the flexibility required for the pliable membrane (such as to allow it to deform, in particular to deform rapidly) cannot be easily combined with the rigidity required for the radially outer seal to ensure a given static friction against the sleeve.

[0013] Therefore, in floating pistons of the above-mentioned known type, there is always a need to find a compromise between the sealing function and the flexibility function at the expense of either function, namely the overall performance of the floating piston itself.

[0014] Innovative content

[0015] In order to basically solve the above technical problems, an object of the present innovation is to provide a floating piston for a single-tube gas shock absorber, which can optimize the performance in terms of sealing effect and flexibility.

[0016] Therefore, according to the present innovation, there is provided a floating piston having the characterizing features indicated in the independent claim attached to this description.

[0017] Further preferred and / or particularly advantageous embodiments of the innovation are described according to the characteristic features indicated in the attached dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present innovation will now be described with reference to the accompanying drawings, which show non-limiting examples of implementation of the present innovation, in which:

[0019] - Figure 1shows a cross section of a floating piston for a monotube gas shock absorber according to a preferred embodiment of the present innovation;

[0020] - Figure 2 is based on Figure 1 A larger scale detail of the floating piston; and

[0021] - Figure 3 Yes Figure 1 A graph comparing the performance of a floating piston of FIG. 5 with the performance of a floating piston implemented according to the prior art. DETAILED DESCRIPTION

[0022] According to this innovation and reference Figure 1 and Figure 2 , a floating piston 10 for a monotube gas shock absorber 20 is provided, wherein the shock absorber 20 has a main axis X and comprises a sleeve 25 and a rod schematically shown and indicated by 26, which can slide in the sleeve 25 and is provided with an end head 27, which can also slide along the sleeve 25.

[0023] According to the preferred embodiment of the innovation described here, the floating piston 10 is arranged in a cylindrical sleeve 25 so as to separate a sliding chamber 30 filled with oil and engaged by the rod 26 from a blind chamber 35, which is filled with gas and is axially delimited on the one hand by the floating piston 10 and on the other hand by the bottom wall 28 of the sleeve.

[0024] The floating piston 10 is axially movable within the sleeve 25 and comprises:

[0025] - a supporting and reinforcing frame 1 , made of metal material, L-shaped in an axial section passing through the axis X and provided with a central hole 11 ;

[0026] a dynamic lip seal 2 , radially outside the support frame 1 and arranged to be in sliding contact with the sleeve 25 of the shock absorber 20 ; and

[0027] A central pliable membrane ( / flexible diaphragm) 3, configured so as to sealingly close the central hole 11 and capable of deforming so as to anticipate the complete movement of the floating piston 10 and thus provide the monotube shock absorber with greater reactivity and response during the absorption of smaller roughnesses.

[0028] In particular, the support frame 1 comprises a cylindrical wall 12 coaxial with the axis X and an annular wall 13 transverse to the axis X and provided with a radially inner free edge 14 so as to define a central hole 11. The support frame 1 is substantially in the form of a cup-shaped body whose bottom wall is defined by the annular wall 13 and in which Figure 1 and Figure 2 In the preferred example of embodiment shown, the support frame 1 is mounted in the sleeve 25 such that the concavity 15 of the support frame 1 is directed towards the bottom wall 28 of the sleeve 25 .

[0029] The seal 2 is provided with two annular end lips 21 and 22, i.e. a first lip 21 on the oil side and a second lip 22 on the gas side, which are connected together by a cylindrical wall 23 lining the cylindrical wall 12 of the frame 1. The seal 2 is made of a first elastomeric material resistant to high temperatures and co-molded with the supporting frame 1, defining a radial seal outside the frame 1.

[0030] The membrane 3 is integral with the edge 14 of the central hole 11 and is made of a second elastomeric material different from the first elastomeric material of the radial seal 2, having specific properties as described below and also designed to optimize flexibility and strength.

[0031] The floating cylinder 10 is a separator of two fluids, oil and gas. The flexible membrane 3 has the possibility of bending, thus changing the volume of the two chambers, namely the sliding chamber 30 and the blind chamber 35. The purpose of this optimized membrane 3 is to ensure a high degree of flexibility of the membrane, so that it can bend (flex) even after a small pressure change between the two chambers.

[0032] The floating piston 10 can be mounted in the sleeve 25 , wherein the recess 15 of the floating piston 10 is directed toward the bottom wall 28 and its recess 15 is directed toward the rod 26 .

[0033] In order to be able to better understand the importance of the flexibility of the membrane 3, it is mentioned again that the wheels of a motorcycle receive the shocks from contact with the ground and transmit them to the shock absorber. The task of the shock absorber is to absorb these shocks without transmitting them to the vehicle and the driver / rider. In order to absorb them, the shock absorber must try to compensate for the changes in compression / extension that occur due to the pressure changes inside the shock absorber. Therefore, a very flexible membrane ensures a fast and effective response of the shock absorber.

[0034] For this purpose, the second elastomeric material of the flexible membrane ( / pliable film) 3 has been defined by previously unforeseen physical and design characteristics, which are therefore not only the result of a design activity, but the result of an inventive activity that cannot be directly deduced from the technical knowledge in this field. Therefore, the parameters on which this innovative activity is based relate to the choice of the physical characteristics of the second elastomeric material and the design of the membrane 3, in particular the thickness and the form.

[0035] As regards the elastomeric material of the membrane 3, it must possess a series of physical properties in order to ensure good flexibility.

[0036] In the case of elastomeric materials, flexibility can be defined, for example, as being inversely proportional to the hardness of Shore A. The preselected elastomeric material of the membrane 3 is a butadiene and acrylonitrile copolymer and has a hardness between 55 Shore A and 70 Shore A. This makes it necessarily different from the first elastomeric material used for the seal 2, for which the hardness exhibits much greater values ​​in the range between 70 Shore A and 85 Shore A.

[0037] It is also important that the elastic modulus of the elastomeric material of the membrane 3 be chosen to be between 0.5 MPa and 4 MPa, while the elastic modulus of the elastomeric material of the seal 2 is not less than 1 MPa.

[0038] Furthermore, the two elastomeric materials differ from each other with respect to the choice of elongation at break value. In particular, the elongation at break of the elastomeric material of the membrane 3 must be between 200% and 400%, while the elongation at break of the elastomeric material of the seal 2 is not greater than 170%.

[0039] Operating in synergy with each other, all the above physical properties (hardness, elastic modulus and elongation at break) contribute to the required flexibility, i.e. keeping the extensional rigidity of the membrane within predetermined limits and equal to 49 N / mm. 49 N is the maximum permissible force for obtaining an axial displacement of 1 mm of the membrane.

[0040] Regarding the design of membrane 3 and also referring to Figure 2 , due to the high elongation at break value of the material, the thickness s of the flexible membrane 3 can conveniently be reduced and assume a value between 2 mm and 3.1 mm. Thus, due to this design rule, the exchange of volume between the two fluids can be further increased.

[0041] Preferably, still in order to maximize the volume exchange between the two fluids, the area of ​​the membrane must be maximized. However, the pressing of the metal frame 1 must ensure a firm support for the membrane 3. To this end, the inner diameter D of the frame 1 can be related to the inner diameter D of the sleeve 25 according to the following relationship:

[0042] D–15mm<d<D–5mm

[0043] All these selected design parameters interact with the technical characteristics of the material and contribute to defining a predetermined extension stiffness value which the membrane 3 must not exceed.

[0044] Figure 3 is a graph relating to the tests carried out, which shows the extensional rigidity of the membrane of the floating piston plotted against the working pressure during operation. In the graph, the x-axis shows the pressure value in millibar [mbar] and the y-axis shows the rigidity value expressed as force / displacement in [N / mm]. In addition, the graph shows a first curve 100 relating to a membrane using an elastomeric material of known type (for example, the elastomeric material of the dynamic seal of the floating piston), a second curve 200 relating to a membrane using an elastomeric material according to the innovation and having the above-mentioned physical characteristics, and a straight dashed line 300 representing a limit value of the extensional rigidity equal to 49 N / mm.

[0045] It can be seen that the curve 200 associated with the membrane 3 according to the innovation always remains well below the predetermined limit value of stiffness as the operating pressure varies.

[0046] It can also be understood from this graph that the elastomeric material defined for the membrane 3 cannot be the same material as that used for the dynamic seal 2, because the dynamic lips 21, 22 will not be able to withstand the working pressure. Therefore, an optimized elastomeric material can be used for the membrane 3, while an elastomeric material of a known type can remain for the dynamic lips 21, 22, and more generally, for the seal 2.

[0047] Preferably, the different elastomeric materials of the radially external seal 2 and of the flexible membrane 3 are injected simultaneously into the mould for producing the floating piston 10 and merge together above the annular portion 13 of the frame 1, but in practice are separated from each other by a constriction zone 31 which serves to separate the flows of the two materials during the simultaneous injection. Therefore, the two materials will merge together to a limited extent in this zone.

[0048] Furthermore, in the floating piston 10 according to the present innovation, the different elastomeric materials of the radially outer seal 2 and the flexible membrane ( / pliable film) 3 must satisfy a number of conditions:

[0049] a) they must be chemically stable with respect to each other; since a merging (albeit limited) of the two materials occurs in the contraction zone 31, these elastomeric materials must be stable (i.e. non-reactive) with respect to each other, so as to maintain their own chemical composition and associated physical properties;

[0050] b) have similar viscosity values, allowing mold injection operations to be performed in similar times;

[0051] c) have similar cure times so that they can be molded together.

[0052] If conditions a) and b) are not observed, the result will be a severe contamination of the elastomeric material of the dynamic lip envelope and vice versa. This will adversely affect the functioning of the floating piston and its aesthetic appearance.

[0053] If condition c) is not observed, separation of the elastomeric material from the contraction zone may occur, resulting in defects.

[0054] Basically, the choice of a specific elastomeric material for the membrane of the floating piston provides the following advantages:

[0055] - By keeping the extension stiffness of the membrane below 49 N / mm, the membrane acquires a high degree of flexibility, thus increasing the sensitivity of the shock absorber. This means that the membrane also reacts to small changes in pressure, which improves the performance of the shock absorber in terms of driver / rider comfort (improved damping effect) and static friction of the shock absorber (absorption of changes in pressure). In fact, the technical function of the floating piston is to maintain the pressure balance in the two shock absorber chambers: when an external load in one of the two chambers increases the pressure in one of the two chambers, the piston moves until the pressure in the two chambers is balanced. If the same elastomeric material as that of the radially external seal is used for the flexible membrane, the flexible membrane can ensure only a limited axial displacement and therefore only a limited volume of displacement fluid (gas / oil). In contrast, the use of specific elastomeric materials for the flexible membrane allows a larger volume of fluid to be displaced.

[0056] - Because if the radially outer sealing lip is made of a material different from the material of the membrane, the radially outer sealing lip retains good properties in terms of dynamic sealing and resistance to high pressure peaks.

[0057] In addition to the embodiments of the present innovation as described above, it must be understood that there are many other variations. It must also be understood that these embodiments are merely examples and do not limit the scope of the present innovation, its application or its possible configurations. On the contrary, although the above description allows those skilled in the art to implement the present innovation at least according to one of the examples of the embodiments of the present innovation, it must be understood that many variations of the described components are possible without departing from the scope of the present innovation as defined in the attached claims, which are interpreted literally and / or according to their legal equivalents.

Claims

1. A floating piston (10) for a monotube shock absorber (20), wherein: The floating piston is slidably disposed in a tubular shock absorber sleeve (25) to separate a sliding chamber (30) and a blind chamber (35) from each other, and the floating piston comprises: - an annular support frame (1) made of metal material, having an L-shaped cross section and provided with a central hole (11); a dynamic lip seal (2) radially outside the frame (1) and arranged to be in sliding contact with a sleeve (25) of the shock absorber (20) so as to define a radial seal outside the frame (1), and - a central flexible membrane (3) configured so as to sealingly close the central hole (11) and deformable so as to anticipate the full movement of the floating piston (10); The floating piston (10) is characterized in that the dynamic lip seal (2) and the flexible membrane (3) are made of two different elastomeric materials, the elastomeric material of the membrane (3) being more flexible and elastic than the elastomeric material of the dynamic lip seal (2).

2. The floating piston (10) according to claim 1, characterized in that: The elastomeric material of the membrane (3) has a hardness between 55 and 70 Shore A, an elastic modulus between 0.5 and 4 MPa and an elongation at break between 200 and 400%.

3. The floating piston (10) according to claim 1 or 2, characterized in that: The thickness (s) of the film (3) is between 2 mm and 3.1 mm.

4. A floating piston (10) according to any one of the preceding claims, characterised in that The inner diameter (D) of the radial inner edge (14) of the frame (1) is related to the inner diameter (D) of the sleeve (25) according to the following relationship: D–15mm<d<D–5mm.

5. The floating piston (10) according to claim 4, characterized in that The frame (1) comprises a cylindrical wall (12) and an annular wall (13), the annular wall (13) being provided with the edge (14), radially inside and defining the central hole (11).

6. The floating piston (10) according to claim 6, characterized in that The seal (2) is provided with two annular end lips (21, 22) which are connected to each other via a cylindrical wall (23) lining the cylindrical wall (12) of the frame (1).

7. A floating piston (10) according to any one of the preceding claims, characterised in that The membrane (3) has an extension stiffness of less than 49 N / mm.

8. A floating piston (10) according to any one of the preceding claims, characterised in that The first elastomeric material of the seal (2) and the second elastomeric material of the membrane (3) are chemically stable with respect to one another.

9. A floating piston (10) according to any one of the preceding claims, characterised in that The first elastomeric material of the seal (2) and the second elastomeric material of the membrane (3) have similar viscosity values.

10. The floating piston (10) according to any one of the preceding claims, characterized in that The first elastomeric material of the seal (2) and the second elastomeric material of the membrane (3) have similar vulcanization times.

Images