ES2955102A1 - Shock absorber device for vehicles (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

The invention describes a shock absorber device (1) for vehicles that comprises a cylinder (2) with a longitudinal axis (EL) filled with a non-Newtonian fluid type "shear-thickening" (STF) along which a piston moves longitudinally. (3). The cross section of the piston (3) is smaller than an internal cross section of the cylinder (2) to allow the passage of the STF through a space between said piston (3) and an internal wall of the cylinder (2). Furthermore, the piston (3) is configured in such a way that the force that the STF opposes to the movement of the piston (3) in a first direction of displacement is different from the force that the STF opposes to the movement of the piston (3) in a first direction of displacement. second direction of movement opposite to the first. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

Shock absorber device for vehicles

OBJECT OF THE INVENTION

The present invention belongs generally to the automotive field, and more particularly to vibration damping in vehicles. The object of the present invention is a new damping device having an asymmetric, preferably variable, and even more preferably passively variable, geometry. In this way, a different level of damping is obtained depending on the direction of movement of the shock absorber stem.

BACKGROUND OF THE INVENTION

A vehicle's stability, control and safe operation depend largely on its suspension system. An excessive level of vibrations in the vehicle can compromise not only its comfort but also put the safety of its occupants at risk. Currently, vehicles have active suspension systems, in some cases highly sophisticated from a mechanical point of view, which allow them to optimize their performance on the road, guaranteeing maximum safety for their occupants.

The simplest vehicle shock absorbers on the market are passive devices that use mineral or synthetic oils as the working fluid. The highest-end devices allow the regulation of the degree of damping through the use of active systems that restrict to a greater or lesser extent the passage of oil through the shock absorber valve system, thus modifying its dynamic behavior.

In the last decade, other damping devices have been introduced on the market that allow active regulation of the degree of damping according to driving conditions. Some of them are based on the use of synthetic oils and a mechatronic system incorporated into the body of the shock absorber itself; while others, more modern and even more sophisticated, use so-called magneto-rheological or electro-rheological fluids. These fluids change their physical properties when a magnetic field or electric current is acted upon, respectively. Although both options have great potential when it comes to actively improving the control and stability of the vehicle, they present some problems that complicate their implementation in the market, such as:

- Significant increase in the weight of the shock absorber.

- Technical complexity in its construction.

- Greater need for maintenance.

- Problems with precipitates of magnetic particles in the case of magneto-rheological fluids due to prolonged periods of inactivity of the damper. - Need for an active control system and sensor network in the vehicle. - Higher production costs.

- Wear of its moving elements.

It is at this point where the so-called “shear-thickening” non-Newtonian fluids become interesting. Non-Newtonian shear-thickening fluids (STF), sometimes called "dilating" or "shear-thickening" fluids, are fluids that vary their viscosity depending on the applied shear rate. on them. A high shear speed causes a compaction effect of the fluid particles that increases its resistance to the applied shear stress. Once said stress subsides, the fluid returns to its original properties. A description can be found of the main characteristics of this type of fluids on the website https://es.wikipedia.org/wiki/Dilatante.

In the scientific literature, various works can be found where "shear thickening" fluids are applied to reduce vibrations in mechanical systems by means of shock absorbers with fixed and symmetrical stem geometries. A symmetrical stem geometry implies that the behavior of the shock absorber is equal to traction and compression. Furthermore, since the geometry is also fixed, that is, unalterable, a damping force regulation capacity can only be achieved by altering the properties of the STF used.

Document US2016238100A1 describes a vibration damper based on a shear-thickening fluid. Specifically, the shock absorber is fundamentally formed by a cylinder filled with a shear-thickening fluid along which a flat piston moves. The cylinder includes a partition that divides it into two parts that communicate with each other through a hole. When the plunger moves in one direction or the other, the shear-thickening fluid is forced to pass through the hole to provide the desired damping effect.

In short, there is still a need in this field for shock absorbers that allow greater control of the damping characteristics and that, at the same time, are simple and easier to manufacture and handle.

DESCRIPTION OF THE INVENTION

The damping device of the present invention solves the above problems thanks to a configuration of the plunger with an asymmetric geometry, preferably variable, and even more preferably variable only in response to the interaction with the STF itself. These characteristics make it possible to provide the damping device of the present invention with greater flexibility in the damping characteristics, allowing it to be different depending on the direction of movement of the piston, without implying an increase in the complexity of the device.

Below are defined some terms that will be used throughout this description.

• STF (Shear Thickening Fluid): This is a fluid whose viscosity increases with the rate of shear deformation. In Spanish it can also be called "shear thickening fluid" or "dilating fluid", although the term most used in scientific documentation is "shear thickening fluid" or directly its acronym STF.

• Longitudinal axis: In a shock absorber equipped with a cylinder through which a piston runs, the longitudinal axis coincides with the main axis of the cylinder along which the piston moves. Naturally, the piston moves along a direction parallel to the longitudinal axis in a first direction or in a second direction opposite to the first.

• Transverse axis: This is an axis contained in a plane perpendicular to the longitudinal axis described above.

• Front surface: This term is used relatively to compare the displacement resistance of various plunger geometries, where a larger front surface implies a greater area of the sole of the plunger in relation to the longitudinal direction and a smaller frontal surface implies a smaller area of the sole of the plunger in relation to the longitudinal direction. Naturally, the larger the front surface, the greater the resistance to displacement of the plunger.

• Lateral surface: This term is also used relatively to compare the displacement resistance of various plunger geometries, where a larger lateral surface implies a greater area of the plunger oriented in the radial direction and a smaller lateral surface implies a smaller area of the plunger. oriented in a radial direction. Naturally, the larger the lateral surface, the greater the resistance to displacement of the plunger.

The present invention is directed to a shock absorber device for vehicles comprising a cylinder with a longitudinal axis filled with an STF along which a piston moves longitudinally. Furthermore, a cross section of the plunger is smaller than an interior cross section of the cylinder to allow passage of STF through a space between said plunger and an interior wall of the cylinder. Naturally, the piston will be connected to a longitudinal rod that protrudes from one or both ends of the cylinder and which connects to the component on which the damping is applied. The damping effect is obtained as a consequence of the interaction between the piston and the STF that takes place due to the movement of the STF from one end of the cylinder to the other in response to the displacements of the piston in one direction or another along the axis longitudinal.

The configuration described in the previous paragraph essentially responds to the characteristics of the damping devices based on STF fluids known from the prior art. However, unlike them, in the damping device of the present invention, the piston is configured in such a way that the force that the STF opposes to the movement of the piston in a first direction of displacement is different from the force that the STF opposes the movement of the piston in a second direction of displacement opposite to the first.

There are different configuration possibilities for the plunger that allow the aforementioned characteristics to be achieved. One option is the use of a plunger that has a non-symmetrical geometry relative to a transverse plane passing through its center, for example a plunger that has a longitudinal end with a first shape and an opposite longitudinal end with a second shape different from the first. A plunger of this type could have, for For example, the first end with a flat shape perpendicular to the longitudinal axis and the second end with a hemispherical shape. Another possibility would be the use of a plunger whose general shape was essentially the same at both ends but where one of them was provided with different surface characteristics, such as roughness, notches, holes, or the like. In any of these cases, the effect of the asymmetry in terms of shape or surface characteristics is that the damping obtained when the piston moves in one direction is different from that obtained when the piston moves in the opposite direction.

This configuration is advantageous because it allows the damping characteristics to be independently selected in one direction or another of movement, thus providing greater operating flexibility to the shock absorber of the invention.

As mentioned above, it is possible to achieve damping with different characteristics depending on the direction of movement by using a piston with a static asymmetric geometry, that is, an asymmetric geometry (for example, in terms of shape or surface characteristics) that remains unchanged during use of the device. However, according to a particularly preferred embodiment of the invention, the piston of the damping device has a variable geometry that alternates between a first geometry when the piston moves in the first direction of movement and a second geometry when the piston moves in the second direction of movement. The change in geometry causes the resistance against the displacement of the piston caused by the STF to be different depending on the direction of displacement. Resistance may vary as a result of a change in the front surface of the plunger, a change in the side surface of the plunger, or a combination of both.

Indeed, the reference to a variable geometry implies that the piston has one or more elements whose shape changes depending on whether it is moving in one direction or another. To cause this change in shape, it is possible to use active means, that is, external means not directly related to the basic operation of the shock absorber and adequately synchronized to cause the change in the geometry of the piston depending on its direction of travel. These external means could comprise permanent magnets, electromagnets, electrical, pneumatic or hydraulic elements or, in general, any means capable of modifying the geometry of the piston in a synchronized manner with changes in the direction of its movement. Also included here are means in combination with materials capable of modifying the surface characteristics of the plunger. in a sufficiently fast manner, since the surface characteristics of the plunger also have an effect on damping.

This configuration is advantageous because it provides the damping device of the invention with even greater flexibility in terms of the damping characteristics in one direction or another.

As mentioned, changing the geometry of the plunger can be achieved using active means. However, according to another preferred embodiment of the invention, the piston of the damping device is configured to alternate between the first geometry and the second geometry solely because of the force exerted by the STF on said piston when it moves longitudinally along length of the cylinder.

The term “passive” is used in this document to refer to the ability to modify the geometry of the plunger solely in response to the forces exerted by the STF during its displacement, without the need for external means of the type described above. That is, in this case the piston is configured in such a way that the change in geometry occurs solely due to the fluid-dynamic forces on the piston that appear when it moves in one direction or another, without external help of any kind. . When the STF that surrounds the piston moves in one direction in relation to the piston itself, the forces that appear as a consequence of the interaction between the STF and the piston cause some part or element of the piston to adopt a certain shape. On the contrary, when the STF that surrounds the piston moves in the opposite direction to the previous one in relation to the piston (due to the change in the direction of displacement of the piston), said forces cause the aforementioned part or element of the piston to adopt a shape different from the previous one. The change in geometry thus occurs automatically with the change in direction of displacement of the piston, which ensures correct synchronism.

This configuration is particularly advantageous given its greater simplicity in relation to other options that require the use of active means external to the operation of the shock absorber itself.

There are several ways to get the piston to modify its geometry when its direction of travel changes. Two main possibilities are mentioned here: the plunger has moving parts, or the plunger has deformable parts. In this context, it is understood that a moving part is a rigid element that is designed to alternate between two clearly differentiated positions by means of rotations, translations or a combination of rotations and translations. In contrast, a deformable part is one that is designed to change shape, either elastically or plastically.

Below, some examples corresponding to both configurations are described in more detail.

1. Moving parts

According to this preferred embodiment of the invention, the plunger comprises a body and at least one substantially rigid moving part attached to the body. The moving part is configured to adopt a first position when the piston moves in the first direction of movement and a second position when the piston moves in the second direction of movement.

Indeed, in this configuration the piston has moving parts that move in one way or another due to the fluid dynamic force exerted by the STF when the piston moves in one direction or another. When the piston moves in the first direction, the fluid dynamic forces caused by the interaction with the STF cause the moving part to adopt a position such that the piston as a whole has the first geometry, while when the piston moves in the second In this sense, the fluid dynamic forces caused by the interaction with the STF cause the moving part to adopt a position different from the previous one such that the piston as a whole has the second geometry.

The movement of the moving parts could potentially comprise any possible combination of translation and rotation. However, two particularly preferred embodiments are described below that correspond to pure rotation and pure translation.

1.a Rotating moving parts

According to a particularly preferred embodiment of the invention, the moving part is rotatably attached to the body. The change in geometry of the piston occurs here due to a pure rotation of the moving part in relation to the body.

In principle, the moving part can rotate relative to the body around an axis oriented in any possible direction, although two possibilities are specifically mentioned in this document: rotation around the transverse axis, and rotation around the longitudinal axis.

I.a.i Rotation around the transverse axis

According to another preferred embodiment of the invention, the moving part is rotatable relative to the body about a transverse axis. As mentioned previously, the transverse axis is contained in a plane perpendicular to the longitudinal axis along which the piston moves.

According to an even more preferred embodiment of the invention, the moving part comprises at least one moving plate, preferably flat, connected to the body through a rotary joint around the transverse axis. Thus, when the piston moves in the first direction of movement, the force exerted by the STF causes the plate to adopt the first position (position in which it forms a first angle in relation to the longitudinal axis), while when the piston moves When moving in the second direction of movement, the force exerted by the STF causes the plate to adopt the second position (a position in which it forms a second angle in relation to the longitudinal axis). The different angle formed by the plate in relation to the longitudinal direction depending on the direction of movement means that the resistance exerted by the STF in one direction or the other is different.

The angles that the plate forms in relation to the longitudinal axis in the first and second geometry could be any as long as they were different and, in this way, the resistance offered by the STF to the passage of the piston was different depending on its direction of movement. . However, according to yet another preferred embodiment of the invention, the moving plate is perpendicular to the longitudinal axis when in the first position and is parallel to the longitudinal axis when in the second position. These are two extreme angular positions that cause the greatest possible difference between the damping obtained in one or the other direction of piston movement.

When the plate is perpendicular to the longitudinal axis, the fluid-dynamic resistance to motion is maximum, while when the plate is parallel to the longitudinal axis, the fluid-dynamic resistance to motion is minimum.

An example of a piston provided with moving parts rotating around a transverse axis will be described later in this document.

I.a.ii Rotation around a longitudinal axis

According to another preferred embodiment of the invention, the moving part of the piston is rotatable relative to the body around an axis parallel to the longitudinal axis.

Even more preferably, the movable part comprises at least a first plate and a second plate, where at least one plate between the first plate and the second plate is connected to the body through a rotary joint about the axis parallel to the longitudinal axis. In this way, when the piston moves in the first direction of movement, the force exerted by the STF causes said at least one plate to rotate to a position in which the first and second plates are separated from each other, while When the piston moves in the second direction of movement, the force exerted by the STF causes said at least one plate to rotate to a position in which the first and second plates are attached to each other. To achieve this, at least the rotating plate can have a certain inclination in relation to the longitudinal axis, thus adopting a shape similar to turbine blades that are forced to rotate when a fluid (in this case the STF) impinges on it. them in longitudinal direction.

An example of a plunger provided with moving parts rotating around a longitudinal axis will be described later in this document.

1.b Sliding moving parts

According to another preferred embodiment of the invention, the moving part of the plunger is attached to the body in a sliding manner. The change in geometry of the piston occurs in this case due to a pure translation of the moving part in relation to to the body.

The slip could occur in any possible direction, including the longitudinal direction, transverse direction, or any other direction not parallel to any of the above. However, according to another preferred embodiment of the invention, the moving part comprises a sliding element along a direction parallel to the longitudinal axis.

More preferably, the body of the plunger has a cylindrical shape and the sliding element is telescopic relative to said body. Thus, when the piston moves in the first direction of displacement, the force exerted by the STF causes the sliding element to come out of the body while, when the piston moves in the second direction of displacement, the force exerted by the STF causes that the sliding element is housed inside the body.

An example of a plunger provided with sliding moving parts will be described later in this document.

2. Deformable parts

According to a preferred embodiment of the invention alternative to the previous ones, the piston of the shock-absorbing device comprises the body and a deformable part attached to the body. The deformable part is configured to adopt a first shape when the piston moves in the first direction of displacement and a second shape when the piston moves in the second direction of displacement. It is not essential that the deformable part be elastic.

According to a particularly preferred embodiment of the invention, the deformable part comprises at least one arm attached to the body and with a free end oriented essentially along the longitudinal axis. In this way, the force exerted by the STF when the piston moves in the first direction of movement causes said arm to open so that the free end moves away from the body, while the force exerted by the STF when the piston moves It moves in the second direction of movement and causes said arm to close so that the free end approaches the body.

An example of a plunger provided with deformable parts will be described later in this document.

According to yet another preferred embodiment, the plunger comprises at least one hole through which the STF can pass when said plunger moves in at least one of the two directions of movement. The orifice can be located in any position (for example, with outlet ports located at the ends of the piston and/or on the lateral surface of the piston), it can have any shape that is not necessarily rectilinear longitudinal with a constant section (for example, presenting curves and/or changes in cross section), and have outlets oriented in any orientation (for example, oriented at an angle to the longitudinal direction), provided that the STF passes through them in at least one of the two directions of displacement.

In its simplest version, the orifice may be a longitudinal orifice of uniformly circular cross section passing through the plunger longitudinally from one end to the other. However, options are possible where the hole does not have a straight longitudinal direction, but instead presents changes in cross section inside. For example, a plunger could be designed with a longitudinal axis hole but with a conical shape, so that the outlet at one end of the plunger had a larger cross section than the outlet at the opposite end. In this way, the resistance to displacement exerted by the hole in both directions of displacement would be different.

Options are also possible where the hole does not have a rectilinear longitudinal direction, but rather has an inclined direction in relation to the longitudinal direction, or has a non-rectilinear direction that includes one or more internal changes of direction. Thus, an adequate design of these changes in direction could serve to adjust the resistance offered by the STF in one or both directions of movement.

As has also been mentioned, it is not necessary that the orifice have its outlets at the ends of the plunger, but one or both could be located on the lateral surface of the plunger. Thus, by properly orienting the outlet located on the lateral surface, it could be achieved that the fluid entered the orifice only in one of the two directions of movement. For example, a plunger could be devised with an orifice that had one outlet located at one end and the other on the side surface, and where the side surface outlet was oriented perpendicular to the direction of travel of the plunger. Thus, when this piston moved in the direction in which it finds the end outlet, the STF would enter the hole, but when it moved in the opposite direction, the STF would not enter the hole.

It would also be possible to provide the orifice with a sealing plate articulated to an edge or side wall of the orifice in such a way that the interaction with the STF would cause its closure in one of the two directions of movement. Thus, when the plunger moves in one direction of travel, the STF keeps the seal plate open and the fluid enters the orifice, while when the plunger moves in the opposite direction of travel, the STF causes the closure of the blanking plate and the fluid does not enter the orifice.

The number of options regarding the internal hole of the plunger is enormous, thus providing a large number of possibilities with regard to adjusting the resistance exerted by the STF in one direction or another of movement of the plunger.

In short, in the present invention damping devices with different piston configurations have been described. The particularity that the pistons have is that they are asymmetrical depending on the direction of displacement, preferably thanks to a variable geometry, and more preferably where the change in geometry occurs solely due to the interaction with the STF. This allows for very flexible shock absorbers in terms of damping characteristics in one direction or another of movement.

BRIEF DESCRIPTION OF THE DRAWINGS

The Figs. 1a and 1b respectively show an exterior perspective view and a longitudinal section of an example of a device according to the present invention.

The Figs. 2a and 2b show perspective views of an example of a plunger according to the present invention respectively in the first and second geometry.

The Figs. 3a and 3b show perspective views of another example of a plunger according to the present invention respectively in the first and second geometry.

The Figs. 4a and 4b show perspective views of yet another example of a plunger according to the present invention respectively in the first and second geometry.

The Figs. 5a and 5b show perspective views of yet another example of a plunger according to the present invention respectively in the first and second geometry.

Fig.6 shows a graph of applied force in relation to travel speed corresponding to an example of a device according to the invention.

Fig. 7 shows a graph of applied force in relation to displacement distance corresponding to an example of a device according to the invention.

PREFERRED EMBODIMENT OF THE INVENTION

Some examples of shock-absorbing devices (1) according to the present invention are described below with reference to the attached figures. In these examples, the ascending or upward direction coincides with the so-called “first direction of movement”, while the descending or downward direction coincides with the so-called “second direction of movement”.

The Figs. 1a and 1b show an example of a damping device (1) according to the present invention. The device (1), whose exterior appearance is similar to that of prior art damping devices, comprises a cylinder (2) through which a piston runs. The piston (3) is attached to a rod (4) whose ends protrude from both sides of the cylinder (2). The cylinder (2) is also filled with an STF in which the piston (3) is immersed. Furthermore, unlike what happens in other devices formed by the cylinder-piston/piston assembly, in this case the piston (3) does not touch the interior walls of the cylinder (2). Therefore, as can be seen in Fig. 1b, the piston (3) does not separate the cylinder (2) into two hermetic cavities separated from each other. On the contrary, there is a space between the radially outer edges of the piston (3) and the inner walls of the cylinder (2), such that when the piston (3) moves along the cylinder (2), the STF that fills the cylinder (2) is forced to pass through said space from one cavity to another. The interaction between the STF and the plunger (3) during this process is responsible for the damping effect provided by the device (1).

To use this device (1), normally the cylinder (2) is rigidly fixed to the body of the vehicle in question, for example a motorcycle, while the rod (4) is fixed to the component to be damped. The vibrations that occur in the longitudinal direction are transmitted through the stem (4) to the piston (3) which, as a consequence, tends to move longitudinally along the cylinder (2). Fig. 1a explicitly shows the longitudinal axis (LE). These vibrations are damped thanks to the effect of the STF on the piston (3) that has been described in the previous paragraph.

Fig.2 shows an example of a piston (3) provided with moving parts by rotation in relation to a transverse axis (ET). In particular, the piston (3) here has an essentially hollow cylindrical body (31), that is, the piston (3) is provided with a cylindrical interior hole with a longitudinal axis. At an upper end of the plunger there is a moving part (32) formed by two essentially semicircular plates. Each of these plates (32) is rotatable around a respective transverse axis (ET) and has a stop positioned appropriately to limit rotation in one of the two directions of rotation. Thus, when the piston (3) moves upward, as seen in Fig. 2a, the fluid dynamic forces caused by the downward displacement of the STF in relation to the piston (3) cause the two plates (32) to rotate until reach their stop where they are contained in a horizontal plane, that is, perpendicular to the longitudinal axis (EL). Furthermore, the plates (32) are sized and positioned in such a way that, when in this position, they completely close the interior cavity of the cylindrical body (31). Therefore, when the piston (3) moves in the first direction (upwards), the front surface is maximum, and consequently the resistance to displacement offered by the STF is maximum. On the contrary, when the piston moves downwards, as seen in Fig. 2b, the fluid dynamic forces caused by the upward movement of the STF in relation to the piston (3) cause the two plates to rotate again until they are positioned correctly. naturally in a plane parallel to the longitudinal axis (EL). In this position, the STF can pass through the interior cavity of the cylindrical body (31) without the plates (32) offering substantial resistance. Therefore, when the piston moves in the second direction (down), the front surface is minimal, and consequently the resistance to displacement offered by the STF is minimal.

Fig. 3 shows an example of a piston (3) provided with parts that move by rotation around an axis parallel to the longitudinal axis (EL). In this case, the piston (3) is formed by an essentially cylindrical body (31) oriented in a longitudinal direction from which four plates (32a, 32b) emerge radially. Each of these plates (32a, 32b) has an essentially rectangular shape and is arranged essentially parallel to the longitudinal axis (EL) although with a certain inclination in the tangential direction. This inclination causes that, when the piston (3) moves in the longitudinal direction, the STF exerts a force on them that tends to make them rotate around the longitudinal axis (EL). Two of the plates, in this example the plates (32b), are rigidly fixed to the body (31), while the two other plates, in this case the plates (32a) are fixed to the body (31) in a rotary manner around the longitudinal axis (EL). Thanks to this configuration, when the piston (3) moves upward as shown in Fig. 3a, the fluid dynamic forces caused by the downward displacement of the STF in relation to the piston (3) tend to make the plates ( 32a) rotate counterclockwise, so that they rotate to the position shown in the figure. The plates (32b), being fixed, remain in the position shown. Therefore, the resistance offered by the STF in the first direction (upwards) is given by the geometry of the piston (3) shown in Fig. 3a. On the contrary, when the piston (3) moves downward, the fluid dynamic forces caused by the upward movement of the STF in relation to the piston (3) tend to cause the plates (32a) to rotate in the clockwise direction. clock, reaching the position shown in Fig. 3b. As can be seen, in Fig. 3b both plates (32a) have rotated 90° in relation to the position shown in Fig. 3a. Since the plates (32b) do not move because they are fixed in a fixed manner, the result is that each plate (32a) remains attached to a corresponding plate (32b). With this second geometry, it is clearly seen that there is a reduction in both the front surface and the lateral surface of the piston (3). Consequently, the resistance offered by the STF in the second direction (downwards) given by the geometry of the piston (3) shown in Fig. 3b is, therefore, significantly lower than that offered by the piston (3) with the geometry shown in Fig. 3a.

Fig. 4 shows an example of a piston (3) provided with moving parts by sliding along a direction parallel to the longitudinal axis (EL). The piston (3) here comprises a hollow cylindrical body (31), that is, the piston (3) is provided with a cylindrical interior hole with a longitudinal axis. The plunger (3) also comprises a set of sliding mobile parts (32) that also have a hollow cylindrical shape and that are arranged telescopically in relation to the body (31) and in relation to each other. In particular, there are three cylindrical-shaped sliding elements configured to alternate between two positions: an open position in which each of the cylindrical elements is housed in the immediately adjacent cylindrical element and where all of them are, in turn, housed within the cylindrical body (31); and a closed position in which each cylindrical element protrudes slightly from the immediately adjacent cylindrical element and where all of them protrude from the cylindrical body (31). This is essentially a conventional telescoping setup. When the plunger (3) moves upward, the fluid dynamic forces caused by the downward displacement of the STF in relation to the plunger (3) drive the sliding elements downward until they adopt the open position shown in Fig. 4a. On the contrary, when the plunger moves downward, the forces Fluid dynamics caused by the upward displacement of the STF in relation to the piston (3) drive the sliding elements upward until they adopt the closed position shown in Fig. 4b. The change in geometry does not essentially cause any change in the front surface of the piston (3), but in its lateral surface: the lateral surface is noticeably larger in the first geometry than in the second. As a consequence, the resistance offered by the STF in the second direction (downwards) given by the geometry of the piston (3) shown in Fig. 3b is, therefore, significantly lower than that offered by the piston (3) with the geometry shown in Fig. 3a.

Fig. 5 shows an example of a piston (3) provided with deformable parts. The piston (3) here comprises a body (31) and a set of at least two deformable elements (33). In this example, the deformable elements (33) have the shape of arms that are rigidly attached to the body (31) and that, after emerging from it in an essentially radial direction, curve upward until they adopt an essentially longitudinal direction at their ends. When the plunger (3) moves upward, the relative downward displacement of the STF forces the arms (33) to “open” such that their ends move away from the body (31) as shown in Fig. 5a. On the contrary, when the plunger (3) moves downward, the upward displacement of the STF causes the arms (33) to “close” to the geometry shown in Fig. 5b. The arms (33) can optionally be elastic, so that the geometry of the plunger (3) shown in Fig. 5b is the geometry at rest and only adopts the geometry shown in Fig. 5a when the STF pushes the arms outwards. during upward movement. In either case, it can be seen that the front surface of the piston (3) when it moves upwards (first direction) is larger than when it moves downwards (second direction). In this case, in addition to the variation in the front surface, there is also an evident change in the fluid-dynamic characteristics of the piston (3) depending on the direction of travel. As a consequence, the resistance offered by the STF in the second direction (downwards) given by the geometry of the piston (3) shown in Fig. 3b is, therefore, significantly lower than that offered by the piston (3) with the geometry shown in Fig. 3a.

Finally, they are shown in Figs. 6 and 7 graphic paths showing the damping force exerted by the STF in relation respectively to the speed and displacement of the piston (3). Fig. 6 shows how the force on the piston (3) is not symmetrical in the compression or traction path (that is, in the first or second direction of movement), unlike what occurs in a symmetrical fixed damping device of the conventional type.

Claims (16)

1. Shock-absorbing device (1) for vehicles comprising a cylinder (2) with a longitudinal axis (EL) filled with a non-Newtonian shear-thickening fluid (STF) along which a piston (3) moves longitudinally. ), where a cross section of the piston (3) is smaller than an internal cross section of the cylinder (2) to allow the passage of the STF through a space between said piston (3) and an internal wall of the cylinder (2), characterized in that the piston (3) is configured in such a way that the force that the STF opposes to the movement of the piston (3) in a first direction of displacement is different from the force that the STF opposes to the movement of the piston (3) in a second direction of displacement opposite to the first. 2. Shock absorber device (1) for vehicles according to claim 1, wherein the piston (3) has a variable geometry that alternates between a first geometry when the piston (3) moves in the first direction of movement and a second geometry. when the piston (3) moves in the second direction of movement 3. Shock absorber device (1) for vehicles according to claim 2, wherein the piston (3) is configured to alternate between the first geometry and the second geometry solely because of the force exerted by the STF on said piston (3). when it moves longitudinally along the cylinder (2). 4. Shock-absorbing device (1) for vehicles according to claim 3, wherein the piston (3) comprises a body (31) and at least one substantially rigid moving part (32) joined to the body (31) and configured to adopt a first position when the piston (3) moves in the first direction of movement and a second position when the piston (3) moves in the second direction of movement. 5. Shock-absorbing device (1) for vehicles according to claim 4, wherein the mobile part (32) is rotatably attached to the body (31). 6. Shock-absorbing device (1) for vehicles according to claim 5, wherein the mobile part (32) is rotatable in relation to the body (31) around a transverse axis (ET), the transverse axis (ET) being contained in a plane perpendicular to the longitudinal axis (EL) along which the piston (3) moves. 7. Shock-absorbing device (1) for vehicles according to claim 6, wherein the mobile part (32) comprises at least one mobile plate connected to the body (31) through a rotary joint around the transverse axis (ET), of so that when the piston (3) moves in the first direction of movement, the force exerted by the STF causes the mobile plate to adopt the first position, while when the piston (3) moves in the second direction of movement, The force exerted by the STF causes the moving plate to adopt the second position. 8. Shock absorber device (1) for vehicles according to claim 7 where, in the first position, the mobile plate is perpendicular to the longitudinal axis (EL) while, in the second position, the mobile plate is parallel to the longitudinal axis (EL). HE) 9. Shock-absorbing device (1) for vehicles according to claim 5, wherein the mobile part (32) is rotatable in relation to the body (31) around an axis parallel to the longitudinal axis (EL). 10. Shock absorber device (1) for vehicles according to claim 9, wherein the moving part (32) comprises at least a first plate (32a) and a second plate (32b), where at least one plate among the first plate (32a) and the second plate (32b) is connected to the body (31) through a rotary joint around the axis parallel to the longitudinal axis (EL) so that, when the piston (3) moves in the first direction of displacement, the force exerted by the STF causes said at least one plate to rotate to a position in which the first (32a) and second plates (32b) are separated from each other, while when the piston (3) moves In the second direction of movement, the force exerted by the STF causes said at least one plate to rotate to a position in which the first (32a) and second (32b) plates are attached to each other. 11. Shock-absorbing device (1) for vehicles according to claim 4, wherein the mobile part (32) is attached to the body (31) in a sliding manner. 12. Shock-absorbing device (1) for vehicles according to claim 11, wherein the moving part (32) comprises a sliding element along a direction parallel to the longitudinal axis (EL). 13. Shock absorber device (1) for vehicles according to claim 12, wherein The body (31) of the piston (3) has a cylindrical shape and the sliding element (32) is telescopic in relation to said body (31), so that when the piston (3) moves in the first direction of movement, the force exerted by the STF causes the sliding element (32) to leave the body (31) while, when the piston (3) moves in the second direction of movement, the force exerted by the STF causes the sliding element (32) to move out of the body (31). lodges inside the body (31). 14. Shock-absorbing device (1) for vehicles according to claim 3, wherein the piston (3) comprises the body (31) and a deformable part (33) joined to the body (3), where the deformable part (33) is configured to adopt a first shape when the piston (3) moves in the first direction of movement and a second shape when the piston (3) moves in the second direction of movement. 15. Shock-absorbing device (1) for vehicles according to claim 14, wherein the deformable part (33) comprises at least one arm attached to the body (31) and with a free end oriented essentially along the longitudinal axis (EL) , so that the force exerted by the STF when the piston (3) moves in the first direction of movement causes said arm to open so that the free end moves away from the body (31), while the force exerted by The STF when the piston (3) moves in the second direction of movement causes said arm to close so that the free end approaches the body (31). 16. Shock-absorbing device (1) for vehicles according to any of the preceding claims, wherein the piston (3) comprises at least one hole through which the STF can pass when said piston (3) moves in at least one of both directions of movement.