The invention refers to a suspension with an electromagnetic linear actuator and/or damper, and a vehicle comprising such a suspension. In the field of active suspensions, here taken as an example, it is known to use electromagnetic linear actuators as in WO2010136049 or US 7 427 072. Active suspensions serve to ensure comfort for the occupants of the vehicle despite uneven road conditions, or to maintain wheel contact with the road under load conditions.

Most documents describe the suspension in general terms, neglecting the specific problems encountered during practical implementation or engineering.

Improving this state of the art is the main object of the invention.

A first aspect of the invention concerns an electromagnetic linear actuator comprising: a (e.g. cylindrical) stator defining a central through-cavity that is surrounded by windings, a stem that is housed in a linearly sliding manner in the stator cavity and comprises permanent magnets for reacting to a magnetic field generated by the windings and moving relative to the stator, wherein the stator comprises an outer (e.g. cylindrical) sleeve made of ferromagnetic material, and the windings are consisting only of wires of conductive material insulated from each other, placed inside the cylindrical sleeve (i.e. the cylindrical sleeve contains and surrounds the windings), and devoid of ferromagnetic parts which are arranged in such a way as to axially separate the windings (the windings are axially packed one on top of the other without any separating material, i.e. they are in contact with each other).

The abovementioned stator construction has the advantage that the magnetic field is more concentrated in the stator and leaks less, hence the greater force released by the stem being the current in the windings the same (compared for example to purely ironless architectures). In other words, the cylindrical sleeve lets the magnetic flux lines close, thereby increasing the field strength and reducing outward dispersions.

Another advantage is that the stem suffers less radial forces compared to an ironcore architecture, also benefiting from less wear on the centering guides. A specificity of the ironcore architecture - visible e.g. in EP 3450797 - is that the winding phases are space out with portions of ferromagnetic material (called poles) which have the function to channel and increase the intensity of the flux. In addition, the phases are separated by portions (discs) of magnetic material. This architecture, despite the advantage of concentrating the flux and increasing the force exerted between the windings and the stem, is also characterized by lateral forces that cause wear in the sliding guides, compromising the working life of the component.

On the contrary, the proposed design is free of discs or other (e.g. magnetic) material interposed between the winding phases, so as to reduce the lateral actions due to the presence of poles. In the suspension according to the invention the magnetic material surrounds only the external part of the windings, which are arranged side by side and in contact with each other and without poles.

The windings consist e.g. only of enamelled or painted copper wires or electrically conductive metal wires insulated from each other by means of an electrically insulating coating or film, e.g. a polymer or paint.

In a preferred variant, said sleeve is axially integral with a tubular element, devoid of windings and made of ferromagnetic material, configured to extend the central cavity wherein the stem can make a linear stroke. The advantage of the tubular element is to reduce the magnetic field dispersion towards the outside, in order to prevent the attraction of unwanted ferromagnetic material on the actuator. This is all the more advantageous if the stem is connected to a suspended mass (e.g. a vehicle compartment) and the stator is connected to an unsuspended mass (e.g. a wheel or a levitation element). Since the tubular element would be (more) exposed to the outside environment, the more likely it is that it would attract dirt or foreign bodies during the travel.

In general the ferromagnetic sleeve of the stator may be in one piece with the abovementioned tube. In a different version, the ferromagnetic sleeve and the abovementioned tube are separate and distinct pieces, and coupled to each other thereafter. In a variant embodiment the ferromagnetic sleeve consists of two or more sections with different thickness, wherein one or more sections house the windings, and an end configured for connection to an unsuspended mass, e.g. a wheel or a track or a skid. In a preferred variant the tubular element, on the opposite side of the stator, is connected by a connecting element to a/the unsuspended mass. The connection element may vary depending on the vehicle. E.g. the connecting element is a flange, a ball-joint seat, an elastic-joint seat, or a shaped arm. Preferably the actuator is configured so that one end of the stem slides only inside the tubular element. In this way it is possible to concentrate the winding pack inside said sleeve, for greater concentration of the magnetic flux and/or allowing a stem stroke greater than the axial length of the stator sleeve.

This construction also allows other functionalities. In particular, said end of the stem comprises an abutment element made of non ferromagnetic (e.g. elastomeric) material that has a diameter greater than two abutment portions arranged inside the cavity of the tubular element at two axially opposite points, so that the abutment portions constitute an obstacle to the movement of the abutment element - and therefore of the stem - and each defines a mechanical end-stop to limit the stroke of the stem. In an alternative variant, the system may be without such mechanical end-of-travel and the end of the stem can slide inside the stator winding slot. This is achieved by continuous sliding bearings inside the slot.

In a preferred variant, the permanent magnets of the stem are cylindrical rings, with axial or radial flux direction, mounted on a central support shaft and/or a cylindrical outer shell that contains them. This gives a constructive advantage in terms of simplified production and assembly.

Preferably the central support shaft is made of non-ferromagnetic material in order not to short-circuit the flux lines within it.

Preferably, the suspension comprises an elastic element mounted to act in parallel to the stem and release an elastic force between the suspended mass and the actuator. Thus the elastic element acts as a support that supports the static load, without burdening the stem which can work for only corrective actions.

In a preferred variant, the elastic element is connected directly to the stator or to the outside of the stator so as not to burden the stem. In a preferred variant, the elastic element is coaxial to the translation axis of the stem, for construction compactness and symmetry for the stresses.

In a preferred variant, the stator comprises two flanges or end-caps placed at the axial ends of the sleeve to contain the windings, wherein the flanges are made of non ferromagnetic material. The advantage is to reduce the phenomenon of cogging torque, due to the channeling of the magnetic flux into ferromagnetic materials. In this case, said flanges avoid that along the stroke of the stem resistance points are created due to flux concentration, thus avoiding jerks in the advance.

In a more preferred variant, the stator, for the stem centering, comprises a friction bearing (or bushings) placed on one or each of the two flanges. In particular, one or each of the two flanges comprises a seat for housing the friction bearing (or bushing).

In a variant, the stator comprises a single continuous friction bearing.

In a preferred variant, the stator inside the sleeve, or at a slit in the sleeve to allow the passage of magnetic flux, comprises a sensor to detect the magnetic field strength and infer the position of the stem, hence the opening of the suspension.

In a preferred variant, the suspension comprises an accelerometer sensor attached to the stator and/or the stem, the accelerometer sensor being configured to measure the acceleration - respectively - of the unsuspended mass and/or the suspended mass.

The above actuator is advantageous when used alone, and even more so when used as a component in a more sophisticated dynamic system. In fact, a second aspect of the invention concerns a suspension comprising the abovementioned electromagnetic linear actuator and/or damper, in particular a suspension for vehicle, such as a car, train or other.

In general the suspension equipped with the abovementioned actuator and/or damper can be applied between a suspended mass, e.g. a compartment, and an unsuspended mass, e.g. a wheel or a track or a levitation skid.

Another application possibility is in systems for reducing the vibrations of a suspended mass, such as a vibrating motor on supports. In this case the suspension can be directly connected to the ground. The second aspect of the invention may have as variants those above for the isolated actuator.

In particular, the actuator and/or the suspension comprise means for adjusting the dynamics of the stem so that the stem and/or the actuator exerts a damping force between the two points to which it is applied. These means may comprise position and/or speed and/or acceleration sensors for the stem, and/or an electronic circuit (e.g. microprocessor-based and preferably connected to the sensors to receive signals from them) configured to electrically drive the stator windings to impose a desired dynamics on the stem.

A third aspect of the invention concerns a vehicle, such as a car or train or other, comprising the abovementioned suspension.

The advantages of the invention will be clearer from the following description of a preferred embodiment of a actuator, referring to the attached drawing in which

- Fig. 1 shows a three-dimensional, vertical cross-sectional view of a first actuator, - Fig. 2 shows a side view in vertical cross-section of the actuator in Fig. 1 ;

- Fig. 3 shows a vertical cross-sectional view of a second actuator;

- Fig. 4 shows a vertical cross-sectional view of a third actuator.

In the figures equal numbers indicate equal or conceptually similar parts. In order not to crowd the figures, some equal elements are not numbered. The linear actuator MC1 comprises a stator 10 and a stem 30 which is linearly translatable back and forth along an axis X, an axis that coincides with that of an internal cavity of the stator 10 housing the stem 30.

Inside the stator 10, around the cavity, there are windings 26 that are used to generate (in a known way) a magnetic field that, by interacting with permanent magnets 34 mounted on a central shaft 32 of the stem 30, determines the translation of the stem 30.

An electronic circuit 18, mounted on the outside of stator 20, controls the currents circulating in the windings 26. In particular, the electronic circuit 18 also comprises a magnetic flux and/or position sensor for the stator 30. The permanent magnets 34 are cylindrical rings with axial or radial flux direction.

The stator 10 encloses the windings 26 with a cylindrical outer sleeve 12 made of ferromagnetic material, so that the magnetic field is more concentrated in the stator 10.

The stator 10 comprises two end flanges 14 made of non-ferromagnetic material placed at the axial ends of the sleeve 12 to contain axially the windings 26. The flanges 14 reduce the phenomenon of cogging torque during the movement of the stem 30. As can be seen in the figures, the windings 26 are all packed and in contact with each other inside the sleeve 12, so there are no statoric poles between one winding 26 and the other.

For centering the stem 30, the stator 10 is equipped with a friction bearing 28 (or bushings) mounted in a seat of each flange 14.

The sleeve 12 is axially integral with a tubular element 20, devoid of windings and made of ferromagnetic material, which extends the central cavity of the sleeve 12 so that the stem 30 can make a wider linear stroke. The tubular element 20 is able to reduce the magnetic field dispersion toward the outside, in order to prevent the attraction of unwanted ferromagnetic material onto the actuator.

In a preferred application, the stem 30 is connected to a suspended mass (e.g. a vehicle compartment) and the stator 10 is connected to an unsuspended mass (e.g. a wheel or a levitation element). For this purpose, the tubular element 20 is integral with a connecting element 50, which is used for coupling with the unsuspended mass and may vary depending on the vehicle.

One end of the stem 30 slides only inside the tubular element 20. On this end of the stem 30 is mounted a disc 36 made of non-ferromagnetic material (e.g. elastomeric or aluminum or non-ferromagnetic stainless steel) that has a diameter greater than two shoulders 24, 26 of the element 20 that act as an obstacle and abutment portions for the disc 36. Thus the disc 36 and the shoulders 24, 26 together form the two opposite mechanical end-stops for the stroke of the stem 30.

A variant is shown in fig. 3. The actuator MC2 is the same as the actuator MC1 , but as a difference it comprises an elastic element 70.

The elastic element 70 is not always necessary, and is mounted to act in parallel with the stem 30.

The elastic element 70 may be a helical spring, as in fig. 3, or another type of mechanical deformation spring, or a gas spring.

Especially when the actuator MC1 is used in an active-suspension application for vehicle, the variant MC2 is preferable because the elastic element 70 generates an elastic force between the suspended mass and the actuator so that the static load can be sustained without burdening the stem 30. For this purpose, the elastic element 70 is directly connected to radial flanges 16 (optional in the actuator MC1) which are integral with the outer surface of the stator 10. Thus the force expressed by the elastic element 70 is directed along the X axis, discharges on the chassis of the stator 30 and does not generate unwanted moments/forces on the stem 30.

Another variant is shown in fig. 4. The actuator MC3 is the same as the actuator MC1 , but as a difference it comprises a different connection element 60, in the example shown in the form of a ring (useful for fixation to other mechanical organs, e.g. ball- or elastic joints).

The connection element 60 may, for example, replace the element 50 in fig. 2.

As an option, the actuator MC3 can also be equipped with the flanges 16 and the elastic element 70.