Patent Description:
As is well known, farm vehicles are generally equipped with a hydrostatic steering assembly, commonly called hydro steering, which comprises at least one double-action hydraulic jack configured so as to change the orientation of one or more steering elements placed in contact with the ground, typically one or more steering wheels.

The hydraulic jack is supplied with a pressurised operating fluid, typically oil, which is contained inside a reservoir from which it is drawn by means of a pump.

Between the pump and the hydraulic jack is operatively interposed a hydraulic distributor, normally of the rotating type, which can be actuated to address the operator fluid coming from the pump alternatively in one of the two inner chamber of the jack, concurrently putting the other chamber in communication with the reservoir.

In this way, depending on the configuration given to the hydraulic distributor, it is possible to cause a displacement of the piston of the hydraulic jack, to which corresponds a change of the orientation of the steering elements in one direction or in the opposite direction.

The actuation of the hydraulic distributor is carried out by a steering column, which generally has a lower end fastened to the hydraulic distributor and an upper end fastened to a manual steering member, typically a wheel, able to be handled by a driver to cause the rotation of the steering column.

To alleviate the effort required from the driver, or to create particular driving sensations, in the past steering apparatuses were proposed which, in addition to the hydrostatic steering assembly, also comprise and electric servomechanism (EPS).

This electric servomechanism generally comprises an electric motor connected so as to be able to apply a torque to the steering column, and an electronic unit able to control said electric motor, typically controlling the direction and the intensity of the torque generated, based on the angular position of the steering column and/or to the torque imparted by the driver through the steering member. Examples of steering apparatus of this kind are disclosed, for instance, in patent applications <CIT>, <CIT> and <CIT>.

However, if the electric servomechanism were subjected to a sudden malfunction, for example because of a fault or of a failure, the steering of the vehicle would be entirely performed by the driver, with consequent drastic reduction in efficiency and safety, especially in the case of driving at relatively high speed and/or on rough terrain.

In light of the above, an object of the present invention is to provide a steering apparatus able to address the aforementioned drawback of the prior art.

Another object is that of achieving such objective within the context of a simple, rational and relatively cost effective solution.

These and other objects are reached thanks to the characteristics of the invention as set forth in the independent claim <NUM>. The dependent claims outline preferred and/or particularly advantageous aspects of the invention.

In particular, an embodiment of the present invention makes available a steering apparatus for vehicles, preferably for farm vehicles, which comprises:.

wherein said electric servomechanism comprises a first and a second electric motor, each of which is able to apply to the steering column a torque around said axis of rotation independently of the other electric motor.

Thanks to this solution, the electric servomechanism becomes intrinsically redundant so that, if one of the two electric motors stops working or is subjected to a malfunction, the other electric motor can be activated (or remains active), assuring that the steering apparatus as a whole can always continue to operate efficiently even in case of emergency.

According to the present invention, the steering column consists of a single monolithic body or of multiple bodies mutually connected by means of joints that do not allow the selective interruption of the mechanical connection between said bodies.

In practice, the steering column can lack joints, for example friction joints or other types of joints, or any device that can be actuated manually or automatically to interrupt the mechanical connection between the bodies comprising the steering column.

Thanks to this solution, it is assured that, in any condition, there is always a secure mechanical connection between the steering member (e.g. the steering wheel) and the hydrostatic assembly, assuring the possibility of steering the vehicle manually even in the case of failure or malfunction of both electric motors of the electric servomechanism.

According to another aspect of the present invention, the electric servomechanism can comprise a torque sensor able to detect a torque applied to the steering column through the steering member, and an electronic control apparatus connected with said torque sensor and configured to control the first and the second electric motor (for example the direction and the intensity of the torque generated by each of them) on the basis of the signals coming from said torque sensor.

In this way, it is effectively possible to regulate the effect exercised by each motor according to needs.

According to a preferred aspect of the invention, the electronic control apparatus can comprise two distinct control units (ECU), for example two processors or microprocessors, of which a first control unit connected to the torque sensor and configured to control the first electric motor, and a second control unit connected to the torque sensor and configured to control the second electric motor.

According to the invention, the operation of the two electric motors is completely independent of each other, obtaining full redundancy in the electric servomechanism.

According to an aspect of the present invention, the first electric motor comprises.

This type of motor has the advantage of having high efficiency and high controllability that make it particularly suitable to be used in the field of assisted steering.

In particular, the first electric motor can be a brushless motor (e.g. a three-phase electric motor) or another motor provided with permanent magnets on the rotor (e.g. an asynchronous motor).

According to the invention, the rotor of the first electric motor is coaxially associated to the steering column and rotatably integral therewith, so as to define therewith a unitary transmission ratio.

For example, the rotor can be directly keyed on the steering column or it can be integrated therein, i.e. a portion of the steering column can serve as a rotor of the first electric motor.

In this way, it is advantageously possible to reduce the dimensions of the steering apparatus.

According to an embodiment of the present invention, the second electric motor can comprise:.

Thanks to this solution, the first electric motor and the second electric motor in practice share the same rotor and the same stator, significantly reducing the overall dimensions of the electric servomechanism, while remaining within the scope of a solution wherein the two electric motors (defined by the respective sets of electric coils) can operate and apply torque to the steering column independently.

In other words, this embodiment provides an electric servomechanism provided with a single rotor and with a single stator that serve as rotor and stator for both electric motors, which are distinguished and are made independent of one another by the fact that they comprise respectively the first and the second set of electric coils.

According to a different embodiment of the present invention, the second electric motor could alternatively comprise:.

In this way, with a generally slightly greater size, it possible to use two substantially standard and, hence, relatively simpler and more economical electric motors.

In particular, the second electric motor can be a brushless motor (e.g. a three-phase brushless motor) or another motor provided with permanent magnets on the rotor (e.g. an asynchronous motor).

In this case, too, the second rotor can be coaxially associated to the steering column and rotatably integral therewith, so as to define therewith a unitary transmission ratio.

For example, the second rotor can be directly keyed on the steering column or it can be integrated therein, i.e. a portion of the steering column can serve as a rotor for an electric servomechanism.

Naturally, the second rotor may be coaxially associated with the steering column in a different axial position with respect to the rotor of the first electric motor.

According to a different aspect of the invention, the hydrostatic steering assembly can comprise:.

This aspect provides a particular effective and efficient solution to make the hydrostatic steering assembly.

Another embodiment of the present invention lastly makes available a vehicle, for example a farm vehicle, comprising the steering apparatus outlined above.

Further features and advantages of the invention will be more apparent after reading the following description provided by way of a non-limiting example, with the aid of the accompanying drawings.

The aforementioned figures show a steering apparatus <NUM> for vehicles, in particular for farm vehicles, for example a farm tractor or any other self-propelled farm machine.

The steering apparatus <NUM> comprises a hydrostatic steering assembly, globally indicated by the numeral <NUM>, which is configured to change the orientation of at least one steering element <NUM>.

The steering element <NUM> is able to stay in contact with the ground, so as to sustain the weight of the vehicle and to change its direction of travel, according to the orientation assumed.

The steering element <NUM> can for example be a steering wheel, which is able to roll on the ground, rotating around a substantially horizontal axis, and it is able to vary its own orientation, rotating around a substantially vertical steering axis.

The orientation of the steering wheel can be quantified in terms of a so-called steering angle, i.e. the angle of rotation effected by the steering wheel, around the steering axis, starting from a pre-set reference position.

The hydrostatic steering assembly <NUM> is configured to cause the rotation of the steering wheel around the steering axis, so as to change the steering angle.

In the example shown, the steering apparatus <NUM> comprises two of said steering wheels and the hydrostatic steering assembly <NUM> is configured to change the steering angle of both steering wheels.

The hydrostatic steering assembly <NUM> can comprise a hydraulic jack <NUM>, which schematically comprises an outer casing <NUM> of preferably cylindrical shape, and a piston <NUM> able to divide the inner volume of the outer casing <NUM> in two separate chambers, of which a first chamber <NUM> and a second chamber <NUM>.

The piston <NUM> can slide forwards and backwards inside the outer casing <NUM>, preferably in parallel direction to the axis thereof, between a first end stop position (rightwards with respect to the view of <FIG>), wherein the volume of the first chamber <NUM> is maximum and the volume of the second chamber <NUM> is minimum, and a second end stop position (leftwards with respect to the view of <FIG>), wherein the volume of the first chamber <NUM> is minimum and that of the second chamber <NUM> is maximum.

To the piston <NUM> can be connected a stem <NUM> that, extending parallel to the sliding direction, projects out of the outer casing <NUM> and is connected to the steering element <NUM>, for example through appropriate lever systems, so that the displacement of said stem <NUM>, due to the sliding of the piston <NUM>, causes a change of the steering angle in one direction or in the opposite direction.

In the example shown, to the piston <NUM> are connected two of said stems <NUM>, which extend and project from opposite parts of the outer casing <NUM> and are individually connected to a respective steering element <NUM>.

However, it is not excluded that, in other embodiments, the piston <NUM> bears a rack gear which, meshing with a pinion, is able to transform the rectilinear motion of the piston <NUM> into a rotation of the pinion itself, which can in turn be keyed with a shaft that, projecting from the outer casing <NUM>, is connected by means of appropriate lever systems to one or both steering elements <NUM>, so as to transform the rotation of the pinion into a change of the steering angle.

The hydrostatic steering assembly <NUM> can also comprise a hydraulic distributor <NUM>, which is provided with an inlet duct <NUM>, with a discharge duct <NUM> and with two supply ducts, of which a first supply duct <NUM> and a second supply duct <NUM>.

The first supply duct <NUM> is in communication with the first chamber <NUM> of the hydraulic jack <NUM>.

The second supply duct <NUM> is in communication with the second chamber <NUM> of the hydraulic jack <NUM>.

The inlet duct <NUM> is connected with the delivery of a hydraulic pump <NUM>, which is able to draw an incompressible operating fluid, typically oil, from a collection reservoir <NUM> and to send it under pressure in the inlet duct <NUM>.

The discharge duct <NUM> is in hydraulic communication with said collection reservoir <NUM>. The hydraulic distributor <NUM> further comprises valve members (not shown in the figure), which can be actuated in at least three configurations, of which a neutral configuration, a first operating configuration and a second operating configuration.

In the neutral configuration, the valve members put in communication the inlet duct <NUM> directly with the discharge duct <NUM>, preferably closing at the same time both the first and the second supply duct <NUM> and <NUM>.

In the first operating configuration, the valve members put in communication the inlet duct <NUM> with the first supply duct <NUM> and the second supply duct <NUM> with the discharge duct <NUM>.

In the second operating configuration, the valve members put in communication the inlet duct <NUM> with the second supply duct <NUM> and the first supply duct <NUM> with the discharge duct <NUM>.

In this way, when the valve members are in the first operating configuration, the pressurised operating fluid coming from the pump <NUM> can flow in the first chamber <NUM> of the hydraulic jack <NUM>, while the operating fluid contained in the second chamber <NUM> can flow towards the collecting reservoir <NUM>, causing a displacement of the piston <NUM> towards the first end stop position (rightwards in <FIG>).

When the valve members are in the second operating configuration, the pressurised operating fluid coming from the pump <NUM> can flow in the second chamber <NUM> of the hydraulic jack <NUM>, while the operating fluid contained in the first chamber <NUM> can flow towards the collecting reservoir <NUM>, causing a displacement of the piston <NUM> towards the second end stop position (leftwards in <FIG>).

When the valve members are in the neutral configuration, the pressurised operating fluid coming from the pump <NUM> can flow directly in the collection reservoir, while the first and the second chamber <NUM> and <NUM> of the hydraulic jack <NUM> can remain closed, assuring that the piston <NUM> remains stably motionless in the previously reached position. The displacement of the valve members between these three configurations can be driven by a steering column <NUM>, which is able to rotate around a pre-set axis of rotation Y and has a first end mechanically connected to the hydraulic distributor <NUM> and a second/opposite end mechanically connected to a steering member <NUM>.

In the illustrated embodiment, the steering member <NUM> is in the form of a steering wheel, which can be coaxially keyed directly to the second end of the steering column <NUM>.

However, in other embodiments, the steering member <NUM> can be any other member able to be gripped and handled manually by a driver to impart to the steering column <NUM> a torque able to make it rotate.

In this way, when the steering column <NUM> is motionless, the valve members of the hydraulic distributor <NUM> can remain in neutral configuration, when the steering column <NUM> is rotated in one direction, the valve members can move to the first operating configuration and, when the steering column is rotated in the opposite direction, the valve members can move to the second operating configuration.

In more detail, the hydraulic distributor <NUM> can be rotary and the valve members can comprise for example two cylinders coaxially inserted one in the other, of which an inner cylinder coaxially keyed to the first end of the steering column <NUM> and an outer cylinder able to rotate with respect to the inner cylinder for a limited angle in both directions.

When the steering column <NUM> is motionless, appropriate spring-operated return systems maintain the outer cylinder in a predetermined angular position with respect to the inner cylinder, which corresponds to the neutral configuration of the hydraulic distributor <NUM>.

When the steering column <NUM> is set in rotation in one direction, the inner cylinder of the hydraulic distributor <NUM> overcomes the elastic strength of the spring-operated system and performs a small rotation with respect to the outer cylinders, reaching the first operating configuration.

In this way, so long as the steering column <NUM> is maintained in rotation in said direction, the hydraulic distributor <NUM> puts in communication the pump <NUM> with the first chamber <NUM> of the hydraulic jack <NUM> and the second chamber <NUM> with the collecting reservoir <NUM>, causing the sliding of the piston <NUM> towards the first end stop position.

If the steering column <NUM> is stopped, the outer cylinder of the hydraulic distributor <NUM> is brought back to the neutral configuration by the spring-operated system, stopping the sliding of the piston <NUM>.

Reversing the direction of rotation of the steering column <NUM>, the inner cylinder of the hydraulic distributor <NUM> overcomes the elastic strength of the spring-operated system and performs another small rotation with respect to the outer cylinder, but this time in the opposite direction with respect to the previous case, reaching the second operating configuration.

In this way, so long as the steering column <NUM> is maintained in rotation in this reverse direction, the hydraulic distributor <NUM> puts in communication the pump <NUM> with the second chamber <NUM> of the hydraulic jack <NUM> and the first chamber <NUM> with the collecting reservoir <NUM>, causing the sliding of the piston <NUM> towards the second end stop position.

As shown in the figures, the steering column <NUM> can be in the form of a monolithic body, which is able to rotate solely around the axis of rotation Y.

However, in other embodiments, the steering column <NUM> can comprise multiple parts or separate bodies, which can be mutually connected by means of the appropriate mechanical joints able to transfer the torque from one body to the other.

These mechanical joints can be rigid, for example as a sleeve, a shell or flanged discs, or they can be at least partially elastic, for example with torsion bar.

In some cases it is also possible for the bodies comprising the steering column <NUM> not to be perfectly aligned but to have mutually inclined axes of rotation and to be connected by means of universal joints or other joints able to allow this non-alignment.

In any case, the mechanical joints do not allow the selective interruption of the mechanical connection between the bodies comprising the steering column <NUM>, so that any torque applied to one of said bodies is always necessary transferred also to all the other bodies and vice versa.

In other words, the steering column <NUM> is totally free of joints, for example of friction joints or of any other type of joint, which can be driven manually or automatically in at least one configuration in which they are able to interrupt the mechanical connection between two parties or bodies of the steering column <NUM>.

The steering apparatus <NUM> further comprises an electric servomechanism, indicated globally by the numeral <NUM>, which is configured to apply to the steering column <NUM> a torque around the axis of rotation Y.

This electric servomechanism <NUM> comprises two electric motors, of which a first electric motor <NUM> and a second electric motor <NUM>, each of which is able to apply to the steering column <NUM> a torque around the axis of rotation Y, independently and autonomously with respect to the other.

The first electric motor <NUM> can be a brushless motor, for example a three-phase brushless motor.

The first electric motor <NUM> comprises a stator <NUM> with substantially annular shape, which surrounds and receives within it a rotor <NUM> having a pre-set axis of rotation.

In particular, the rotor <NUM> is coaxially associated and rotatably integral with the steering column <NUM>, so that the axis of rotation of the rotor <NUM> coincides with the axis of rotation Y of the steering column <NUM> and that the transmission ratio between the rotor <NUM> and the steering column <NUM> is unitary, i.e. that to each rotation of the rotor <NUM> corresponds an equal rotation of the steering column <NUM> and vice versa.

For example, the rotor <NUM> can be shaped as an annular body directly keyed on the steering column <NUM> or can be integrated therein, or can be made in a single body with the steering column <NUM> or with a portion thereof.

In any case, the rotor <NUM> can bear a plurality of permanent magnets, which can be distributed circumferentially around the axis of rotation and angularly equidistant from each other.

The permanent magnets of the rotor <NUM> can interact with a plurality of electric coils, indicated as <NUM> in the diagram A, which are installed on the stator <NUM> and are individually able to define a phase (or pole) of the first electric motor <NUM>.

The electric coils <NUM> can also be distributed circumferentially around the axis of rotation of the rotor <NUM>, with respect to which they are angularly equidistant from each other.

In the illustrated example, the first electric motor <NUM> is a three-phase brushless motor and, consequently, it comprises three electric coils <NUM> angularly separated by <NUM>° from each other.

However, in other embodiments, the first electric motor <NUM> can have a different number of phases.

In the embodiment illustrated in <FIG>, the second electric motor <NUM> can also be a brushless motor, for example a three-phase brushless motor, altogether similar to the first electric motor <NUM>.

In particular, the second electric motor <NUM> can comprise a stator <NUM> with substantially annular shape, which surrounds and receives within it a rotor <NUM> having a pre-set axis of rotation.

The stator <NUM> and the rotor <NUM> of the second electric motor <NUM> can be physically separate with respect to the stator <NUM> and to the rotor <NUM> of the first electric motor <NUM>.

The rotor <NUM>, too, can be coaxially associated and rotatably integral with the steering column <NUM>, so that the axis of rotation of the rotor <NUM> coincides with the axis of rotation Y of the steering column <NUM> and that the transmission ratio between the rotor <NUM> and the steering column <NUM> is unitary, i.e. that to each rotation of the rotor <NUM> corresponds an equal rotation of the steering column <NUM> and vice versa.

The rotor <NUM> of the second electric motor <NUM> can be associated with the steering column <NUM> in a different axial position with respect to the rotor <NUM> of the first electric motor <NUM>, for example between the rotor <NUM> of the first electric motor <NUM> and the hydraulic distributor <NUM>.

The rotor <NUM> can bear a plurality of permanent magnets, which can be distributed circumferentially around the axis of rotation and angularly equidistant from each other.

The permanent magnets of the rotor <NUM> can interact with a plurality of electric coils, indicated as <NUM> in the diagram B, which are installed on the stator <NUM> and are individually able to define a phase (or pole) of the second electric motor <NUM>.

In the illustrated example, the second electric motor <NUM> is a three-phase brushless motor and, consequently, it comprises three electric coils <NUM> angularly separated by <NUM>° from each other.

However, in other embodiments, the second electric motor <NUM> can have a different number of phases.

The stators <NUM> and <NUM> of the first and of the second electric motor <NUM> and <NUM> can be supported and enclosed within a single outer casing <NUM>, which can be traversed by the steering column <NUM> and can be fixed to the hydraulic distributor <NUM> of the hydrostatic steering assembly <NUM>.

The electric servomechanism <NUM> can further comprise one or more sensors able to measure the operating parameters of the steering apparatus <NUM>.

These sensors can include a torque sensor <NUM> able to measure the torque applied on the steering column <NUM> by the driver through the steering member <NUM>.

The torque sensor <NUM> can be applied to a segment of the steering column <NUM> between the steering member <NUM> and the rotor <NUM> of the first electric motor <NUM>.

The torque sensor <NUM> can comprise for example a torsion bar able to connect two contiguous portions of the steering column <NUM> and a sensitive element able to measure the angular phase difference between said two portions.

The sensors can also include at least one position sensor, for example a resolver, which is able to measure the angular position of the steering column <NUM> with respect to a pre-set initial reference position.

In the example shown, the sensors include two of said position sensors, of which a first position sensor <NUM> applied to a segment of the steering column <NUM> between the steering member <NUM> and the torque sensor <NUM>, and a second position sensor <NUM> applied to a segment of the steering column <NUM> between the torque <NUM> and the hydraulic distributor <NUM> of the hydrostatic steering assembly <NUM>, specifically between the rotor <NUM> of the second electric motor <NUM> and the hydraulic distributor <NUM>.

The torque sensor <NUM> and the position sensors <NUM> and <NUM> can be contained and protected inside the casing <NUM>.

The sensors can further include an angular sensor <NUM> able to measure the steering angle of at least one of the steering elements <NUM>.

Each sensor is preferably connected with an electronic control apparatus, indicated globally as <NUM>, which is configured to control the first and the second electric motor <NUM> and <NUM> on the basis of the signals coming from the sensors.

In particular, the electronic control apparatus <NUM> is configured to command and control the electric current that is supplied to the electric coils <NUM> of the first motor <NUM> and to the electric coils <NUM> of the second motor <NUM>, so as to impose a direction and an intensity to the torque that each of these electric motors <NUM> and <NUM> is able to generate and to apply to the steering column <NUM>.

Preferably, the electronic control apparatus <NUM> comprises two distinct electronic control units (ECU), for example two processors or microprocessors, of which a first electronic control units <NUM> configured to control the first electric motor <NUM>, i.e. the electric current that powers the electric coils <NUM>, and a second electronic control unit <NUM> configured to control the second electric motor <NUM>, i.e. the electric current that powers the electric coils <NUM>.

To do so, the first electronic control unit <NUM> can be connected with the electric coils <NUM> and with the torque sensor <NUM>.

The first electronic control unit <NUM> may be connected also with the angular sensor <NUM> and/or with at least one of the position sensors <NUM> and <NUM>, for example with the first position sensor <NUM>.

On the basis of the signals (i.e. of the information) coming from the torque sensor <NUM>, and possibly on the basis of the signal (i.e. of the information) coming from the position sensor and/or from the angular sensor <NUM>, the first electronic control unit <NUM> can be configured to establish the direction and the intensity of the torque that the first electric motor <NUM> has to generate and apply to the steering column <NUM>.

On the basis of the direction and of the value of torque thus established, and possibly on the basis of the signals (or of the information) coming from the position sensor, the first electronic control unit <NUM> can then be configured to supply electric current to the electric coils <NUM> so as to obtain from the first electric motor <NUM> a torque having the desired direction and intensity.

Similarly, the second electronic control unit <NUM> can be connected with the electric coil <NUM> and with the torque sensor <NUM>.

The second electronic control unit <NUM> may be connected also with the angular sensor <NUM> and/or with at least one of the position sensors <NUM> and <NUM>, for example with the second position sensor <NUM>.

On the basis of the signals (i.e. of the information) coming from the torque sensor <NUM>, and possibly on the basis of the signal (i.e. of the information) coming from the position sensor and/or from the angular sensor <NUM>, the second electronic control unit <NUM> can be configured to establish the direction and the intensity of the torque that the second electric motor <NUM> has to generate and apply to the steering column <NUM>.

On the basis of the direction and of the value of torque established, and possibly on the basis of the signals (or of the information) coming from the position sensor, the second electronic control unit <NUM> can then be configured to supply electric current to the electric coils <NUM> so as to obtain from the second electric motor <NUM> a torque having the desired direction and intensity.

Thanks to this solution, the two electric motors <NUM> and <NUM> can function in a totally autonomous and mutually independent way.

For example, in normal operating conditions, steering assistance may be provided by the first electric motor <NUM>, whose electronic control unit <NUM> will power the electric coils <NUM> in the ways outlined above.

In these conditions, the second electric motor <NUM> may remain deactivated, i.e. the electric coils <NUM> may never be powered, so that the second electric motor <NUM> may not apply any torque to the steering column <NUM>.

The second electric motor <NUM> may automatically come into operation, according to the procedures outlined above, if the first motor <NUM> stops operating, for example in case of failure or fault or a failure, assuring electric steering assistance even in case of emergency.

In this way, the second electric motor <NUM> would represent an element of redundancy that replaces the first electric motor <NUM> only in case of need.

However, in other embodiments, the first and the second motor <NUM> and <NUM> can be reversed, or, in normal operating conditions, both electric motors <NUM> and <NUM> can be active concurrently, thereby assuring that, in case of failure or fault of one of the two electric motors, at least the other electric motor can always remain in operation.

<FIG> shows a second embodiment of the steering apparatus <NUM>, which differs from the one described previously only by the aspects that are described in detail below.

In this case, the first electric motor <NUM> and the second electric motor <NUM> can share the same rotor and the same stator.

More specifically, as in the previous case, the first electric motor <NUM> can comprise a stator <NUM> with substantially annular shape, which surrounds and receives within it a rotor <NUM> having a pre-set axis of rotation.

The rotor <NUM> can be coaxially associated and rotatably integral with the steering column <NUM>, so that the axis of rotation of the rotor <NUM> coincides with the axis of rotation Y of the steering column <NUM> and that the transmission ratio between the rotor <NUM> and the steering column <NUM> is unitary, i.e. that to each rotation of the rotor <NUM> corresponds an equal rotation of the steering column <NUM> and vice versa.

The permanent magnets of the rotor <NUM> can interact with a plurality of electric coils, indicated as <NUM> in the diagram C, which are installed on the stator <NUM> and are individually able to define a phase (or pole) of the first electric motor <NUM>.

For example, the first electric motor <NUM> can be a brushless motor, specifically a three-phase brushless motor that comprises three electric coils <NUM> angularly separated by <NUM>° from each other.

In this embodiment, the second electric motor <NUM> can comprise a plurality of electric motor, indicated with the numeral <NUM> in the diagram C, which are installed on the same stator <NUM> on which are also installed the electric coils <NUM> of the first electric motor <NUM>. For example, the electric coils <NUM> can be distributed circumferentially around the axis of rotation of the rotor <NUM>, with respect to which they are angularly equidistant from each other, and each of them can be angularly interposed and preferably equidistant from two consecutive electric coils <NUM> of the first motor <NUM>.

The electric coils <NUM> can interact with the same permanent magnets of the sole rotor <NUM> and they are individually able to define a phase (or pole) of the second electric motor <NUM>.

The second electric motor <NUM> can thus be for example a brushless motor, specifically a three-phase brushless motor that comprises three electric coils <NUM> angularly separated by <NUM>° from each other.

In practice, on the sole sector <NUM> can be globally installed a plurality of electric coils arranged circumferentially around the axis of rotation of the sole rotor <NUM> and angularly equidistant from each other, of which a first set of electric coils <NUM> that define the phases (or poles) of the first electric motor <NUM> and a second set of electric coils <NUM>, alternated to the previous ones, that define the phases (or poles) of the second electric motor <NUM>.

In the illustrated example, since the first electric motor <NUM> and the second electric motors <NUM> are configured as two three-phase brushless electric motors, on the sole stator <NUM> is present a set of six electric coils angularly separated by <NUM>° from each other, which define six phases (or poles), of which three phases belong to the first motor <NUM> and the other three phases, alternated to the previous ones, belong to the second motor <NUM>.

However, in other embodiments, the first and the second electric motor <NUM> and <NUM> can have a different number of phases, preferably equal to each other.

The stator <NUM> can be supported and enclosed within an outer casing <NUM>, which can be traversed by the steering column <NUM> and can be fixed to the hydraulic distributor <NUM> of the hydrostatic steering assembly <NUM>.

In this embodiment, too, the electric servomechanism <NUM> can further comprise one or more sensors able to measure the operating parameters of the steering apparatus <NUM>. These sensors can include a torque sensor <NUM> able to measure the torque applied on the steering column <NUM> by the driver through the steering member <NUM>.

The torque sensor <NUM> can be positioned in a segment of the steering column <NUM> between the steering member <NUM> and the sole rotor <NUM> of the electric servomechanism <NUM>.

In the example shown, the sensors include two of said position sensors, indicated respectively with the numerals <NUM> and <NUM>, which can both be applied to a segment of the steering column <NUM> between the rotor <NUM> and the hydraulic distributor <NUM> of the hydrostatic steering assembly <NUM>.

On the basis of the direction and of the value of torque established, and possibly on the basis of the signals (or of the information) coming from the position sensor, the first electronic control unit <NUM> can then be configured to supply electric current to the electric coils <NUM> so as to obtain a torque having the desired direction and intensity.

On the basis of the direction and of the value of torque established, and possibly on the basis of the signals (or of the information) coming from the position sensor, the second electronic control unit <NUM> can then be configured to supply electric current to the electric coils <NUM> so as to obtain a torque having the desired direction and intensity.

Thanks to this solution, although the two electric motors <NUM> and <NUM> share the same rotor <NUM> and the same stator <NUM>, can function in a totally autonomous and mutually independent way.

For example, in normal operating conditions, steering assistance may be provided only by the first electric motor <NUM>, whose electronic control unit <NUM> will power the electric coils <NUM> in the ways outlined above.

In these conditions, the second electric motor <NUM> may be deactivated, i.e. the electric coils <NUM> may never be powered, so that the second electric motor <NUM> may not apply any torque to the steering column <NUM>.

In this way, the second electric motor <NUM> would represent in practice an element of redundancy that replaces the first electric motor <NUM> only in case of need.

Although the previous description always refers in particular to brushless motors, in other embodiments the first and the second motor <NUM> and <NUM> can be motors of other types, for example electric motors having permanent magnets on the rotor, for example asynchronous motors.

Claim 1:
A steering apparatus (<NUM>) for vehicles, which comprises:
- a steering column (<NUM>) having at least one axis of rotation (Y),
- a manually actuated steering member (<NUM>) mechanical connected to one end of the steering column (<NUM>),
- a hydrostatic steering assembly (<NUM>) mechanically connected to an opposite end of the steering column (<NUM>) and configured to transform a rotation of the steering column (<NUM>) around said axis of rotation (Y) in a change of an orientation of at least one steering element (<NUM>) able to stay in contact with the ground, and
- an electric servomechanism (<NUM>) configured to apply to the steering column (<NUM>) a torque around said axis of rotation (Y),
wherein said electric servomechanism (<NUM>) comprises a first and a second electric motor (<NUM>, <NUM>), each of which is able to apply to the steering column (<NUM>) a torque around said axis of rotation (Y) independently of the other electric motor,
wherein the first electric motor (<NUM>) comprises:
- a rotor (<NUM>) having a pre-set axis of rotation (Y),
- a stator (<NUM>) that surrounds the rotor (<NUM>), and
- a first set of electric coils (<NUM>) arranged on the stator (<NUM>) angularly equidistant around the axis (Y) of the rotor (<NUM>), each of which defines a phase of the first electric motor (<NUM>),
wherein the rotor (<NUM>) is coaxially associated to the steering column (<NUM>) and rotatably integral therewith, so as to define therewith a unitary transmission ratio,
characterised in that the steering column (<NUM>) consists of a single monolithic body or of multiple bodies mutually connected by means of joints that do not allow the selective interruption of the mechanical connection between said bodies.