The present invention concerns a mount for damping oscillations, in particular a hydraulic mount. This component can be applied, for example, to contribute in connecting the engine to the chassis of a road vehicle, but it can also have many other applications.

Background art

Hydraulic mounts as such are known and are characterised by the presence of an incompressible fluid (e.g. water and glycol) which, following stresses on the mount, moves between a first and a second chamber through a narrow conduit.

The common feature to ail hydraulic mounts is the capacity to obtain a dynamic stiffening and a drastic increase in damping at a specific frequency.

For example, they allow an increase in rigidity in the event of stresses induced by movement such as a sudden swerve or slamming on the brakes while maintaining at the same time excellent damping for stresses such as the vibrations induced by a running engine.

Hydraulic mounts are typically distinguished as bushings (wherein there is mainly or exclusively radial application of the load) and cones (wherein there is mainly or exclusively axial application of the load).

Each hydraulic mount has a predetermined response to stresses deriving from the geometry thereof. Different types of mounts are known which, according to the geometry, offer different responses to stresses. In consideration of the specific requirement, designers therefore choose the most appropriate mount.

Disclosure of the invention

In this context, the technical task underpinning the present invention is to provide a hydraulic mount that offers maximum operating flexibility allowing its response to be modulated over time, according to desired parameters.

The defined technical task and the specified aims are substantially achieved by a hydraulic mount, comprising the technical characteristics set forth in one or more of the appended claims,

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Further characteristics and advantages of the present invention will become more apparent from the approximate and thus non-limiting description of a preferred, but not exclusive, embodiment of a mount, as illustrated in the accompanying drawings, of which:

- figure 1 illustrates a detail of a mount according to the present invention;

- figures 2, 3, 4 show a perspective view and according to two orthogonal sections of an embodiment according to the present invention;

- figure 5 shows a detail of a component of the mount of figures 2, 3, 4;

- figure 6 shows a sectional view of a further embodiment according to the present invention;

- figures 7 and 8 show respectively the modulus and phase of the dynamic rigidity of the mount according to the frequency of the stress.

Detained description of preferred embodiments of the invention

In the accompanying figures, reference number 1 denotes a mount for damping oscillations.

Such mount 1 comprises a first chamber 40 deformable under the action of said oscillations. The mount 1 also comprises a second chamber 5; appropriately, also the second chamber 5 is at least in part deformable.

The mount 1 further comprises a conduit 60 that sets the first and the second chamber 40, 5 into communication. The conduit 60 is a narrow passage that is interposed between the first and the second chamber 40,

5.

Appropriately, the mount 1 comprises an incompressible fluid suitable for moving between the first and the second chamber 40, 5 through the conduit 60.

The fluid is a magnetorheologicai fluid. A magnetorheological fluid is a material that displays a change in rheological behaviour following the application of a magnetic field. The application of a magnetic field and the intensity thereof are therefore able to substantially change, in a reversible way, the viscosity of a similar fluid (whereas the density is not changed). The mount 1 comprises a means 12 for exciting a magnetic field forexciting the magnetorheoiogical fluid, !t is part of the means 1 1 for regulating the dynamic behaviour of the mount 1 itself. Dynamic behaviour means the response of the mount 1 to the dynamic vibrations and stresses received. With a low energy value supplied, magnetorheoiogical fluids allow a consistent variation in viscosity to be obtained; furthermore, the change in viscosity is almost instantaneous, in the order of a few milliseconds. The interesting aspect is that the change in the viscosity of the fluid determines a change in the response of the mount 1 to stresses while maintaining the geometry of the mount 1 unaltered. Figures 7 and 8 show the modulus and phase of the dynamic rigidity of the mount, respectively, as a function of the frequency of the stress; the curves indicated by reference "a" relate to a higher viscosity value, and the curves indicated by reference "b" relate to a lower viscosity value.

Appropriately, magnetorheoiogical fluids comprise ferromagnetic particles suspended in a carrier fluid, very often an organic solvent or water. The ferromagnetic nano-particies are coated by a surfactant to prevent them caking. A non-binding example of a magnetorheoiogical fluid is MR Fluid MRF-132DG Lord Corporation.

The means 12 for generating a magnetic field for exciting the magnetorheoiogical fluid may comprise a first electromagnetic circuit. It therefore allows an active mount 1 to be obtained in which the response of the mount 1 can be modified as a function of the commands imparted by the means 12 for generating a magnetic field. Such commands could be imparted, for example, as a function of detections made by one or more sensors.

The means 12 for generating a magnetic field for exciting the magnetorheological fluid comprises a first bobbin 121 that, in turn, comprises a plurality of turns. The first bobbin 121 also comprises a first insert 123 positioned at least partially within the turns. Appropriately, such first insert 123 is made of ferromagnetic material, preferably steel. Thanks to the magnetic permeability value of the first insert 123 it is possible to reach high magnetic field values with a low amperage value circulating within the first bobbin 121 . The first bobbin 121 is external to the conduit 80. The first insert 123 is in contact with the fluid. Appropriately, the first insert 123 crosses a wall of the conduit 60 and projects internally to the conduit 60 to come into contact with the fluid.

The first insert 123 skims the fluid along said conduit 60. The first insert 123 is positioned in a first zone of the conduit 60,

The means 12 for generating a magnetic field for exciting the magnetorheological fluid comprises a second bobbin 122 that, in turn, comprises a plurality of turns and a second insert 124 positioned at least partially within the turns. Appropriately, the second insert 124 is ferromagnetic. It also skims the fluid along said conduit 60. The second insert 124 therefore comes into contact with the fluid.

Advantageously, the conduit 60 comprises at least a wall with a first hole that is crossed by the first insert 123. At least at such first hole, the conduit

60 is made of diamagnefic or paramagnetic material.

Appropriately, also the second insert 124 crosses a wall that delimits the conduit 60 (advantageously, but not necessarily, the same wail crossed by the first insert 123).

As exemplified in figure 1 or 5, the conduit 60 comprises an annular component in which a groove is afforded in which the operating fluid flows (known in the technical sector as "inertia track"). The first and/or the second inserts 123, 124 cross such component.

The above-indicated measures allow the magnetic field to be concentrated. In proximity to the first insert 123 (and the second insert 124 and all the other inserts if present) the magnetorheological fluid becomes thicker, increasing the average viscosity value of the fluid and changing the dynamic behaviour of the hydraulic mounts.

In figures 2-6 the generating means 12 is not explicitly illustrated, but has been omitted for simplicity (it could be positioned as in figure 1 or project outwards into the left part of figures 4 and 6).

The mount 1 is advantageously a damping bushing 10. The bushing 10 comprises a first element 2 (which is a sleeve or a shaft), a second element 3 (which is a sleeve) enclosing the first element 2 and an eiastomeric body 4 interposed between the first and the second element 2, 3. The eiastomeric body 4 is radially interposed between the first and the second element 2, 3. Appropriately, the eiastomeric body 4 is in contact both with the first and the second element 2, 3, It is advantageously made of rubber, preferably vulcanized. As exemplified in the accompanying figures, the eiastomeric body 4 is in turn a hollow element that encloses the first element 2 about a longitudinal axis of the latter. The first and the second element 2, 3 have mutually parallel longitudinal axes of extension. The first and the second elements 2, 3 are advantageously made of metal material. The first chamber 40 is at least in part delimited by the eiastomeric body 4. In particular, the first chamber 40 is defined by a concavity afforded internally to the eiastomeric body 4. The first chamber 40 is defined by the combination of the eiastomeric body 4 and the second element 3.

The conduit 60 preferably extends according to a curved path. The conduit 60 optionally comprises at least one spiralling section. Appropriately the various turns are copianar. In an alternative solution, the conduit comprises a labyrinth-shaped path in which several arches (in communication with one another) follow on inside one another. Advantageously, such arches are concentric and/or copianar. The above- indicated measures allow the path to be extended, while however limiting the dimensions.

Reference is to be made to a solution illustrated in figures 2, 3, 4. The second chamber 5 is not in contact with said elastomeric body 4. In particular, the second chamber 5 is delimited at least in part by a flexible membrane 50. In fact, the second chamber 5 is a flexible chamber in which the flexible membrane 50 moves to compensate the movement of the incompressible fluid. Appropriately, the second chamber 5 is annular. The second expansion chamber 5 encloses a compartment 7. The bushing 1 comprises a bottom 70 of such compartment 7 which is interposed between the compartment 7 itself and the elastomeric body 4. The bottom 70 therefore separates the compartment 7 and the elastomeric body 4.

Advantageously, the flexible membrane 50 separates the second chamber 5 from an external zone to the bushing 1 in which there is air at atmospheric pressure.

Appropriately, a hollow space 43 not affected by the incompressible fluid is interposed between the first and the second element 2, 3. Advantageously, the hollow space 43 is interposed between the elastomeric body 4 and the second element 3. The body 4 delimits the hollow space 43 at least in part. Such hollow space 43 is diametrically opposed to the first chamber 40 with respect to the first element 2.

The elastomeric body 4 comprises a first portion 41 and a projection 42 that projects in a cantilever fashion towards the first portion 41. The first portion 41 extends perimetra!!y lying against the second element 3. The hollow space 43 extends between the first portion 41 and the projection 42. Preferably, the hollow space 43 encloses the projection 42 on three sides.

In the absence of external forces acting on the bushing 10, the first element 2 is eccentric with respect to the second element 3.

In fact, since the elastomeric body 4 does not contribute to defining the second chamber 5, the first element 2 can be positioned eccentrically in the absence of external forces on the bushing 1 . In fact, with reference to figure 3 the first element 2 will have space to move upwards and will be able to do so without compressing the second chamber 5. This allows a soft bushing 10 to be obtained in static conditions. Once associated with the masses to be dampened, the first and the second element 2, 3 become coaxial (in static conditions).

The radial movement of the second element 3 with respect to said first element 2 alternatively pumps the fluid from the first chamber 40 towards the second chamber 5 and recalls by depression the fluid from the second chamber 5 towards the first chamber 40. The second chamber 5 collects the incompressible fluid, but does not exert a pumping or suction force, or, even so, such action is certainly lower with respect to that of the first chamber 40. The fluid acts as a resonance element and allows an increase in rigidity at a predetermined frequency range of the oscillations to be dampened.

The second chamber 5 extends radially between an internal annular edge 81 and an external annular edge 82. The bushing 1 comprises a metal flap 80 that extends radially and connects the internal annular edge 81 and the external annular edge 82. The flap 80 comprises a hole 83 for the introduction of the incompressible fluid into the second chamber 5. An obturator (preferably irremovable) obstructs the hole 83. In order to introduce the incompressible fluid, a vacuum is first generated within the second chamber 5 and the first chamber 40. At this point, the incompressible fluid is introduced and then everything is closed (e.g. by forcing the obturator into the hole 83). Such obturator is preferably a metal plug inserted by interference into the hole 83. Advantageously, the bushing 1 comprises an additional flexible membrane 51 that delimits the expansion chamber 5. As can be noted in figure 2, the membrane 50 and the additional membrane 51 delimit a same face of the expansion chamber 5. The membrane 50 and the additional membrane 51 in the exemplified solution illustrated extend like two arches. They are separated by the flap 80 previously described and appropriately also by an additional flap 800.

The membrane 50 and/or the additional membrane 51 are free to move according to the pressure in the expansion chamber 5.

Reference is now made to an alternative solution illustrated in figure 6, The eiastomeric body 4 in that case delimits at least partially the first and the second chamber 40, 5. The first element 2 extends along a longitudinal axis 20, The bushing 10 along a direction identified by said longitudinal axis 20 extends between a first and a second end 21 , 22. The minimum axial distance between the conduit 60 and the first end 21 is shorter by 1/5 of the length of the entire mount 1 measured along said longitudinal axis 20. The conduit 60 is therefore in proximity to an end of the first element 2 so as to be able to be easily accessible in order to facilitate the insertion of the magnetorheological fluid. Furthermore, this facilitates the housing of the means 12 for generating a magnetic field, minimizing its dimensions.

The conduit 60 in the preferred solution is delimited by a plug 61 located at an axial end of the conduit 60. The plug 61 further comprises a hole for access to the inside of said conduit 60, said hole being occluded by an irremovable obturator. Such hole allows the suction of the air present in the conduit 60 and the introduction of the magnetorheological fluid. Subsequently, the hole is occluded by the irremovable plug.

The invention as it is conceived enables achieving multiple advantages. First of all, it allows the active control of the mount as a function of specific commands from a control unit (e.g. a vehicle control unit). This allows active control that is variable over time, for adapting to specific situations. Acting on the viscosity of the fluid rather than on the inertia track 60 has the advantage of increasing the dynamic rigidity modulus without changing its shape and without varying the characteristic resonance frequency of the mount. Furthermore, in this way, the use of electromagnetic parts is avoided, with the advantage of increasing the strength of the final product. The invention as it is conceived is susceptible to numerous modifications, ail falling within the scope of the inventive concept characterising it.

Further, all the details can be replaced with other technically-equivalent elements. In practice, all the materials used, as well as the dimensions, can be any according to requirements.