The present invention relates to a vehicle wheel suspension, of the kind comprising a spring, such as e.g. a helical spring or a similar elastic element, interposed between the wheel and the body of the vehicle, and a damper, also interposed between the wheel and the body of the vehicle, in parallel with the spring.

While designing a vehicle wheel suspension of the kind identified above, the designer shall find each time the best compromise, depending on the specific application, between two contrasting requirements, that is road-holding (and thus safety) and comfort. In particular, the two parameters involved in the definition of the characteristics of the suspension, and thus in the determination of the optimal compromise between road-holding and comfort, are the stiffness of the spring and the damping of the damper. The design choice- is generally determined by the kind of use for which the vehicle has been designed. In sport vehicles, road-holding is naturally preferred, to the detriment of comfort, while for example in city- cars comfort is preferred, to the detriment of road-holding.

Since the operating conditions for which road-holding shall be preferred are generally discernible from the conditions for which comfort shall be preferred, it is known to use suspension active adjustment systems allowing to actively adjust, in real time, the characteristics of the suspensions depending on the vehicle driving conditions.

Suspension active adjustment systems are known, which allow for example to change the force-speed characteristic of the damper to change the force between the sprung mass and the unsprung mass of the vehicle during the transient phase of the dynamics of the vehicle.

Suspension active adjustment systems are also known, which allow to change in a controlled manner the stiffness of the spring to change the force exerted between the sprung mass and the unsprung mass of the vehicle, not only during the transient phase of the dynamics of the vehicle, but also at steady state, for example during cornering. As they are able to vary the overall stiffness of the suspension, these adjustmenbt systems further allow, in steady conditions, to change the attitude of the vehicle both to accomplish several comfort or road-holding targets and to adapt the attitude of the vehicle to any load variations.

The present inventions relates to this second category of suspension active adjustment systems and aims at providing a vehicle wheel suspension that is provided with an active adjustment system, improved with respect to the prior art, for continuously adjusting, in a controlled manner, the overall stiffness of the suspension, that is the ratio of the force exerted between the sprung mass and the unsprung mass of the vehicle to the relative position of the sprung mass with respect to the unsprung mass of the vehicle, at that wheel. ,

This and other objects are fully achieved according to the invention by virtue of a vehicle wheel suspension having the features set forth in the attached independent claim 1.

Advantageous embodiments of the invention are defined in the dependent claims, the subject-matter of which is to be considered as forming an integral part of the following description.

In short, the invention is based on the idea of providing a suspension of the type mentioned above comprising, in addition to the main spring and the damper:

a first reaction element acting between the cylinder and the rod of the damper, in parallel with the main spring, to generate, in the extension phase or in the compression phase of the damper, a reaction force opposing the extension or compression movement of the damper, respectively,

first abutment means which are associated with the first reaction element and are adjustable to vary the point of intervention of the first reaction element during the expansion stroke or the compression stroke of the damper, respectively, and

adjustment means for adjusting in a controlled manner the position of said first abutment means. By virtue of such a configuration, a suspension according to the invention allows to adjust, in a controlled manner, the point of intervention of the first reaction element during the extension or compression phase, and thus to adjust, in a controlled manner, the overall stiffness of the suspension. By providing all the wheels of a vehicle with such a suspension, it is thus possible to adjust the overall stiffness of every single corner of the vehicle in order to adjust the overall roll stiffness of each of the two axes of the vehicle, or to adjust the attitude of the vehicle.

According to an embodiment, the first reaction element is arranged to act during the extension phase of the damper and the suspension further comprises a second reaction element acting between the cylinder and the rod of the damper, in parallel with the main spring, to generate, during the compression phase of the damper, a reaction force opposing the compression movement, as well as second abutment means which are associated with the second reaction element and are adjustable to vary the point of intervention of the second reaction element during the compression stroke of the damper, the adjustment means being, in this case, also arranged to adjust, in a controlled manner, the position of the second abutment means.

Preferably, the first and/or second reaction elements are elastic elements, in particular mechanical springs.

Preferably, the first abutment means include a first fixed abutment member and a first movable abutment member, and the adjustment means are arranged to adjust the position of the first movable abutment member with respect to the first fixed abutment member along a longitudinal axis of the damper. Likewise, the second abutment means include a second fixed abutment member and a second movable abutment member and the adjustment means are arranged to adjusti the position of the second movable abutment member with respect to the second fixed abutment member along a longitudinal axis of the damper.

According to an embodiment, the adjustment means include a linear actuator comprising a fixed element, fixed to the cylinder or to the rod of the damper, and a movable element to which the first movable abutment member is drivingly connected for translation along the longitudinal axis of the damper. When provided, the second movable abutment member is also drivingly connected to the movable element of the linear actuator for translation along the longitudinal axis of the damper.

Further features and advantages of the present invention will become apparent from the following detailed description, given purely by way of non-limiting example, with reference to the appended drawings, where:

Figure 1 is a schematic representation of a vehicle wheel suspension arrangement according to a first embodiment of the present invention;

Figure 2 is a section view schematically showing an embodiment of the suspension arrangement of Figure 1 ;

Figure 3 is a schematic representation of a vehicle wheel suspension arrangement according to a second embodiment of the present invention;

Figure 4 is a section view schematically showing an embodiment of the suspension, arrangement of Figure 3;

Figure 5 is a schematic representation of a vehicle wheel suspension arrangement according to a third embodiment of the present invention; and

Figure 6 is a section view schematically showing an embodiment of the suspension arrangement of Figure 5.

With reference initially to Figures 1 and 2, a vehicle wheel suspension according to an embodiment of the present invention basically comprises:

a main spring 10 (hereinafter simply referred to as spring), which is preferably, even though not necessarily, made as a mechanical spring, in particular as a cylindrical helical spring, and is interposed between the body of the vehicle (or, more generally, the sprung mass of the vehicle) and the wheel of the vehicle (or, more generally, the unsprung mass of the vehicle);

a damper 12, which is preferably, even though not necessarily, made as a hydraulic damper and comprises, in a per-se-known manner, a cylinder 14, a piston 16 slidably accommodated in the cylinder 14 so as to divide the latter into a compression chamber and an extension chamber, and a rod 18 rigidly connected to the piston 16 and protruding out of the cylinder 14 (in the embodiment shown, protruding upwards so as to be connected to the body of the vehicle), the damper 12 also being interposed between the body and the wheel of the vehicle, in parallel with the spring 10;

a first reaction element 20 acting between the cylinder 14 and the rod 18 of the damper 12 to generate, during the extension phase of the damper, a reaction force opposing the extension movement; and

a second reaction element 22 acting between the cylinder 14 and the rod 18 of the damper 12 to generate, during the compression phase of the damper, a reaction force opposing to the compression movement.

The spring 10 insists, for example, at its bottom end against a bottom spring plate 1 la fixed to the cylinder 14 of the damper 12 and at its top end against a top spring plate 1 lb fixed to the rod 18 of the damper 12.

The first reaction element 20 is preferably made as an elastic element arranged to generate an elastic reaction force. In particular, the first reaction element 20 is formed by a mechanical spring, such as a cylindrical helical spring, which is conveniently radially interposed between the cylinder 14 of the damper 12 and the spring 10.

The first reaction element 20 rests at its bottom on a first fixed abutment member 24, which is made for example as a spring plate and is rigidly connected to the rod 18 of the damper 12. The term "fixed abutment member" shall be intended, for the purposes of the present invention, as referring to an abutment member whose position is fixed, the position of the piston with respect to the cylinder of the damper remaining unchanged. A first movable abutment member 26 carried by the cylinder 14 of the damper 12 is also associated to the first reaction element 20. The term "movable abutment member" shall be intended, for the purposes of the present invention, as referring to an abutment member whose position is adjustable, the position of the piston with respect to the cylinder of the damper remaining unchanged. The first movable abutment member 26 is adjustable in its position with respect to the cylinder 14 of the damper 12 along the longitudinal axis z of the latter. By adjusting the position of the first movable abutment member 26 on the cylinder 14 of the damper 12, the distance between the first reaction element 20 and this abutment member is adjusted. It is thus possible to adjust the length of the extension stroke the piston 16 of the damper 12 has to cover with respect to the cylinder 14 to bring the first reaction element 20, namely the top end of this element, into abutment against the first movable abutment element 26, and thus adjust the point of intervention of the first reaction element 20 (i.e. the point at which the first reaction element starts to exert a reaction force between the cylinder 14 and the rod 18 of the damper 12) during the extension stroke of the damper 12.

In order to allow to continuously adjust the position of the first movable abutment member 26 with respect to the cylinder 14 of the damper 12, a linear actuator 28, for example a double-acting hydraulic linear actuator, is mounted on the cylinder 14to control the movement of the first movable abutment member 26 with respect to the cylinder 14 along the longitudinal axis z. The linear actuator 28 comprises a fixed element 30, acting as a cylinder, which is rigidly connected to the cylinder 14 of the damper 12 and a movable element 32, acting as a piston, which is movable with respect to the fixed element 30 and to which the first movable abutment member 26 is drivingly connected for translation along the longitudinal axis z. When the linear actuator 28 is made as a hydraulic actuator, like in the embodiment illustrated in Figures 1 and 2, the linear actuator 28 is connected to a hydraulic supply circuit comprising a reservoir T, a hydraulic pump P and a control valve V, for example a four-way two-position solenoid valve, arranged to control the connection of the two working chambers of the actuator 28 with the reservoir T and with the hydraulic pump P.

The second reaction element 22 is preferably made as an elastic element, in particular as a conventional bump stop (typically made in a polyurethane-based microcellular elastomer) of the kind normally provided in vehicle wheel suspensions to elastically resist the compression of the damper when the latter comes into abutment against the top end of the cylinder of the damper. The second reaction element 22 is mounted on a second fixed abutment member 34, fixed to the rod 18 of the damper 12, so as to insist at its top against said abutment member. Preferably, the second fixed abutment member 34 is formed in one piece with the first fixed abutment member 24, as shown in Figure 2.

A second movable abutment member 36 carried by the cylinder 14 of the damper 12 is also associated to the second reaction element 22. The second movable abutment member 36 is adjustable in its position with respect to the cylinder 14 of the damper 12 along the longitudinal axis z. By adjusting the position of the second movable abutment member 36 on the cylinder 14 of the damper 12 the distance between the second reaction element 22 and said abutment member is adjusted. It is thus possible to adjust the length of the compression stroke the piston 16 of the damper 12 has to cover with respect to the cylinder 14 to bring the second reaction element 22 into abutment against the second movable abutment member 36 and thus adjust the point of intervention of the second reaction element 22 during the compression stroke of the damper 12.

The position of the second movable abutment member 36 with respect to the cylinder 14 of the damper 12 is adjusted by means og a linear actuator, for example a double-acting hydraulic linear actuator, which is conveniently (as in the proposed embodiment) the same linear actuator 28 that controls the movement of the first movable abutment member 26 also.

In the embodiment illustrated in Figures 1 and 2, therefore, the second movable abutment member 36 is rigidly connected for translation along the longitudinal axis z with the movable element 32 of the linear actuator 28. By controlling the position of the movable element 32 of the linear actuator 28 by means of the control valve V, it is thus possible to control the relative position both of the first movable abutment member 26 and of the second movable abutment member 36 along the longitudinal axis z with respect to the cylinder 14 of the damper 12, and thus the points of interventions both of the first reaction element 20 and of the second reaction element 22, during the extension stroke and during the compression stroke of the damper 12, respectively. The control valve V of the hydraulic supply circuit is connected, in a per-se-known manner, to an electronic control unit (not shown) that is arranged to manage the operation of the suspension, in particular to adjust the overall stiffness of the suspension by adjusting the position of the first movable abutment member 26 and of the second movable abutment member 36 in the way illustrated above, depending on predetermined parameters representative of the driving conditions of the vehicle.

A second embodiment of a vehicle wheel suspension according to the present invention is shown in Figures 3 and 4, where parts and elements identical or corresponding to those of Figures 1 and 2 have been given the same reference numbers.

This second embodiment differs from the first one in that the second reaction element 22 is formed (like the first reaction element 20) by a mechanical spring, such as in particular a cylindrical helical spring, which is preferably radially interposed between the cylinder 14 of the damper 12 and the spring 10. The second movable abutment member 36 is made as a spring plate, against which the bottom end of the second reaction element 22 rests. Also in this case, the second fixed abutment member 34 is rigidly connected to the rod 18 of the damper 12, while the second movable abutment member 36 is drivingly connected for translation with the movable element 32 of the linear actuator 28, so that the position of said abutment member along the longitudinal axis z with respect to the cylinder 14 of the damper 12 may be adjusted by controlling the position of the movable element 32 of the linear actuator 28. Preferably, the second fixed abutment member 34 is formed by the same member acting as first fixed abutment member 24.

For the rest, what has already been said above with reference to the first embodiment shown in Figures 1 and 2 still applies.

Also in this second embodiment, therefore, by adjusting the position of the first and second movable abutment members by means of the linear actuator, it is possible to modify the points of intervention of the first and second reaction elements, respectively, during the extension stroke and during the compression stroke, and thus to adjust the overall stiffness of the suspension both in extension and in compression.

A third embodiment of a vehicle wheel suspension according to the present invention is shown in Figures 5 and 6, where parts and elements identical or corresponding to those of Figures 1 and 2 have been given the same reference numbers.

This third embodiment differs from the first one in that the fixed element 30 of the linear actuator 28 is rigidly connected to the rod 18, instead of to the cylinder 14, of the damper 12. In this case, the second reaction element 22 (that is also preferably formed by a conventional bump stop) is mounted on the second movable abutment member 36, which is drivingly connected for translation along the longitudinal axis z with the movable element 32 of the linear actuator 28, so as to insist at its top against said abutment member. The second fixed abutment member 34 is, instead, formed by the top face of the cylinder 14 of the damper 12 or, alternatively, by a dedicated member mounted on the top face of the cylinder 14.

The first reaction element 20 is formed, as in the embodiment of Figures 1 and 2, by a mechanical spring, in particular a cylindrical helical spring, which insists at its top end against the first fixed abutment member 24 and at its bottom end against the first movable abutment member 26.

For the rest, what has already been said above with reference to the first embodiment shown in Figures 1 and 2 still applies.

Therefore, also in this third embodiment, by adjusting the position of the first and of the second movable abutment members by means of the linear actuator it is possible to modify the points of intervention of the first and second reaction elements, respectively, during the extension stroke and during the compression stroke and thus to adjust the overall stiffness of the suspension both in extension and in compression.

As it is clear from the description given above, by virtue of a suspension according to the present invention it is possible to actively adjust the overall stiffness of the suspension by conveniently adjusting the relative position between the fixed abutment members and the movable abutment members associated to the reaction elements acting in parallel with respect to the main spring of the suspension and, thus, adjusting the points of interventions of said reaction elements in compression and in extension. By controlling the overall stiffness of the suspension of each of the vehicle wheels, it is possible to implement an active control of the vehicle sprung mass motions, both those induced by the road surface and those resulting from the driving manoeuvres.

Such a suspension allows, for example, to control the roll angle and thus conveniently modulate the understeer and oversteer effects of the vehicle during the changes of direction.

Furthermore, the suspension allows to continuously adjust the overall stiffness, both in the compression phase and in the rebound phase, by using a single actuator and thus minimizing the complexity and the cost of the adjustment system.

Adjusting the overall stiffness of the suspension requires very little power, i.e. just the one required to control the movable element of the actuator.

The stiffness adjustment system the suspension according to the invention is provided with further allows to adjust the relative position of the rod with respect to the cylinder of the damper, and thus the height of the vehicle from the ground. Indeed, compression of the elastic element acting in extension results in a compression also of the main spring of the suspension and, thus, in a retraction of the rod of the cylinder of the damper, with resulting reduction in the height of the vehicle from the ground. A reduction of the height of the vehicle from the ground corresponds then an increase in the stiffness of the suspension in the extension phase, and, therefore, an improvement in the road-holding performance of the vehicle, that is precisely what it is desirable to ensure when the height of the vehicle from the ground is reduced, since this is typically done for high-speed driving conditions, e.g. for driving in a highway. With respect to suspensions provided with vehicle height adjustment systems acting in series with the main spring of the suspension, the suspension according to the invention allows to obtain longer strokes.

Naturally, the principle of the invention remaining unchanged, the embodiments and constructional details may vary widely from those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the enclosed claims.

For example, even if in the embodiments described and illustrated herein two reaction elements are provided, which act in the extension phase and in the compression phase of the damper, respectively, the suspension may also comprise only one reaction element, acting either in the extension phase or in the compression phase.