WO2023214332A1

WO2023214332A1 - Hybrid suspension system for a vehicle, and vehicle equipped with such a system

Info

Publication number: WO2023214332A1
Application number: PCT/IB2023/054607
Authority: WO
Inventors: Piero Monchiero; Giordano Greco; Marco DI VITTORIO; Simone MARCHETTI
Original assignee: Marelli Suspension Systems Italy S.P.A.
Priority date: 2022-05-03
Filing date: 2023-05-03
Publication date: 2023-11-09
Also published as: IT202200008960A1

Abstract

A hybrid suspension system for a two-axle vehicle comprises a pair of active suspensions (10) associated with one of the two axles of the vehicle, and a pair of semi-active suspensions (12) associated with the other of the two axles of the vehicle.

Description

Hybrid suspension system for a vehicle, and vehicle equipped with such a system

Technical field

The present invention is generally in the field of controlling the static/dynamic behavior of a vehicle; in particular, the invention relates to a hybrid suspension system for a vehicle, and a vehicle equipped with such a system.

Summary of the invention

A solution is known of equipping the two axles (front and rear) of a vehicle with suspension systems of the so-called active (or “full-active”) type, consisting of separate actuators (traditionally, electro-hydraulic or electro-mechanical), capable of continuously controlling the force exerted on the suspension according to appropriate control logics (e.g., those referred to as “skyhook” and “groundhook,” which are well known to the person skilled in the art). According to these logics, an active suspension may, for example, be configured to force the relevant actuator to extend or compress so that the sprung mass of the vehicle remains at a predetermined height (i.e., avoiding following the contour of the terrain). An example of such a solution is known from WO 2021/240415 Al.

This active suspension is currently the most advanced solution in terms of improving the comfort and handling of the vehicle.

Another feature of active suspensions is the ability to collect electric energy when the suspension is working under controlled damping conditions. On the other hand, in the active condition, the system requires a significant amount of energy to perform the required function.

A major disadvantage of this type of system is its high cost, which limits its application to few vehicle segments.

One object of the present invention is to overcome this disadvantage while sacrificing as little system performance as possible.

To achieve this, a vehicle suspension system according to the present invention combines active suspension technology, which is applied to a first axle of a vehicle, with semi-active suspension technology, which is applied to a second axle of the vehicle.

As is known to the person skilled in the art, semi-active suspensions are configured to change the damping coefficient of the actuator, and employ adjustable-damping shock absorbers that are capable of varying their damping features under the management of an electronic control unit to change the behavior of the vehicle’s suspension system according to, for example, road surface conditions and vehicle driving conditions. In this sense, semi-active suspensions differ from active suspensions due to the inability of semi-active suspensions to apply a force to the suspension that is able to reverse the direction of the suspension’s velocity vector. In other words, the semi-active suspensions are configured to generate, by modulation of the damping coefficient of the shock absorber, a force that always opposes the movement of the wheel hub relative to the sprung mass (i.e., the force applied by the shock absorber will always have a direction discordant to the velocity of the wheel hub relative to the sprung mass), while active suspensions, according to the control logic, are configured so as to generate, if necessary, an actuator force directed in the same direction as the movement of the wheel hub relative to the sprung mass. An example of a semi- active suspension is known from document EP 2 232 094 Bl.

In particular, a suspension system according to the invention is preferably composed of two active actuators arranged on a first axle of a vehicle and two semi-active shock absorbers arranged on a second axle of a vehicle. There may also be at least three vertical acceleration sensors of the sprung mass of the vehicle, and/or four vertical acceleration sensors of the wheel hub (or four sensors of the suspension travel, one for each suspension of the vehicle), and/or an electric power system characterized by an appropriate voltage, such as 48 V, to manage the active actuators, and/or an electronic control unit to manage the system.

According to one embodiment, the system may have two configurations, respectively, a first configuration wherein the active suspension is placed on the front axle of the vehicle (and the semi-active one on the rear), or vice versa (active on the rear, and semi-active on the front).

In the first configuration, the active actuators on the front axle will improve comfort especially on the front axle. Further, there would be a high degree of control over the movements of the vehicle’s sprung mass in both lateral and longitudinal dynamics. In the case of longitudinal dynamics, the most critical condition is limit braking, in which case the load transfer to the front axle would increase the system’s ability to control such a condition. In the case of lateral dynamics, the additional force that may be exerted by the front axle works to reduce the roll angle, and in this case, the condition will be very similar to that in which a stiffer front anti-roll bar was present, so the directional behavior of the vehicle would shift toward a more pronounced tendency to understeer. For this reason, the full operating capacity of the actuator may be utilized without risking an unstable condition of the vehicle.

In the second configuration, the active suspension on the rear axle would improve comfort especially on the rear axle. In this case, the ability to control the sprung mass is reduced relative to the first configuration under both lateral and longitudinal dynamics. Regarding the longitudinal dynamics of the sprung mass, this configuration is mainly able to improve the load transfer conditions on the rear axle, i.e., the acceleration condition. Since acceleration values are generally lower in this condition than in braking, the overall longitudinal control capacity is reduced. In the case of lateral dynamics, on the other hand, the additional force exerted by the active actuators on the rear axle works to reduce the roll angle of the sprung mass. This condition is very similar to that of the same vehicle with a stiffer rear anti-roll bar, thus changing the directional behavior of the car toward a more pronounced tendency to oversteer. This configuration might be preferred when the priority is the comfort of rear passengers or when the rear axle is subject to large variations in loading condition (limousines, vans, etc.), but it generally does not allow full use of the entire available force of the actuators, which could lead to the car’s directional behavior becoming excessively oversteered. On the other hand, a major advantage of this configuration is that the rear actuators may work without delay due to road profile information from the front wheels, which allows them to “pre-alert” said rear axle. In general, as will be shown, both system configurations perform significantly better than if both axles were controlled by purely semi-active suspension, and proportionally less bad than if both axles were controlled by active suspension, while also benefiting from significant cost savings.

The above and other objects and advantages are achieved, according to one aspect of the invention, by a hybrid suspension system for a vehicle, and to a vehicle equipped with such a system having the features defined in the appended claims.

Brief description of the drawings

The functional and structural features of some preferred embodiments of a hybrid suspension system according to the invention will now be described. Reference is made to the accompanying drawings, wherein:

- Fig. 1 is a schematic diagram of a hybrid suspension system for a vehicle, according to an embodiment of the invention; and

- Fig. 2 is a comparative graph of the performance, in terms of controlling the roll angle of a vehicle’s sprung mass as a function of lateral acceleration, of three suspension systems, respectively, wherein both vehicle axles are associated with semi-active suspensions, wherein both vehicle axles are associated with active suspensions, and wherein one axle is associated with semi-active suspensions and the other axle is associated with active suspensions.

Detailed description

Before explaining in detail a plurality of embodiments of the invention, it should be clarified that the invention is not limited in its application to the design details and configuration of the components presented in the following description or illustrated in the drawings. The invention may assume other embodiments and be implemented or constructed in practice in different ways. It should also be understood that the phraseology and terminology have a descriptive purpose and should not be construed as limiting. Referring illustratively to Fig. 1, a hybrid suspension system for a two-axle vehicle is configured so that one axle of the vehicle is associated with a pair of exclusively active suspensions or shock absorbers, and the other axle is associated with a pair of exclusively semi-active suspensions or shock absorbers. In particular, the hybrid suspension system according to the invention comprises a pair of active suspensions 10 associated with one of the two axles of the vehicle, and a pair of semi-active suspensions 12 associated with the other of the two axles of the vehicle. In this way, the vehicle is equipped with two pairs of shock absorbers or suspensions of different types (one pair of the active type and one pair of the semi-active type), each pair being associated with a single axle.

Active suspensions are known to comprise an actuator (linear or rotary, pneumatic, electromagnetic, electromechanical, electrohydraulic, etc.) connected on one side to the sprung mass of the vehicle, and on the other side to a suspension arm, which in turn is connected to a wheel hub. The actuator is operable between an active control condition, wherein it is configured to be electrically powered (e.g., by a battery 14) and to transmit to a suspension arm a force that is such that it causes the relative motion of said suspension arm relative to the vehicle body (i.e., the sprung mass of the vehicle), accomplishing positive work on the suspension, and a damping condition, wherein the actuator is configured to transmit to the suspension arm a force that opposes the relative motion of said suspension arm relative to the vehicle body, accomplishing negative work on the suspension. Expediently, the actuator may be operable between these active control and damping conditions on command from an electronic control unit. In general, there is also an elastic means, such as a spring, designed to draw the suspension arm back to a predetermined neutral position of equilibrium of static forces relative to the vehicle body.

According to one embodiment, the actuators of the active suspension 10 are operable according to the adjustment modes described in the examples below.

Let us consider a simplified model of the suspension of the vehicle, wherein the body of the vehicle and each wheel of the vehicle are schematized with two masses, respectively an upper and a lower mass connected to each other via a spring and an actuator mechanically parallel between them. Let us consider the particular scenario wherein the wheel collides with an obstacle on the road, for example a bump. The objective of the control strategy (known per se) is to control the actuator (for example in position and in torque, if the actuator is rotary), so as to always keep the vehicle body at the same vertical height, thus compensating for the inevitable change in force of the spring due to the vertical displacement of the wheel relative to the body of the vehicle when crossing the obstacle.

Fs indicates the force that the spring exerts on the vehicle body, conventionally considered positive if directed upward, and on the wheel, conventionally considered positive if directed downward, due to the action and reaction principle. V indicates the relative vertical velocity between body and wheel, conventionally considered positive in extension. F indicates the force exerted by the actuator on the body, conventionally considered positive if directed downward; by the action and reaction principle, the actuator exerts a force F of the same magnitude on the wheel, which is conventionally considered positive if directed upward.

The main phenomena that occur while crossing the obstacle may be summarized as follows. In a first step, the vehicle moves on a smooth road, the suspension spring supports the vertical load due to the weight of the body, the suspension does not move vertically (V=0), and the actuator exerts a zero force F. In a second step, wherein the wheel climbs the obstacle, the control strategy aims to keep the body at the same vertical height as it had in the first step. As the wheel climbs over the obstacle and approaches the body, the suspension is in the compression step (V<0), the spring is more compressed than it was in the first step and thus exerts an additional direct elastic force Fs on the body upward. To compensate for this force Fs, the actuator must exert an equal and opposite force F on the body, thus directed downward. Due to the action and reaction principle, the actuator exerts an equal and opposite force F on the wheel, thus directed upward (active operation in compression). In practice, in this step the actuator actively “helps” the wheel to follow the bump, pulling the wheel toward the body, and without having a displacement effect on said body. In so doing, the actuator performs positive work on the suspension since the force F exerted by the actuator on the wheel and the vertical velocity of the wheel are always in the same direction during this step (the vertical velocity of the body is theoretically zero, therefore theoretically the work of the force F that the actuator exerts on the body is also zero). Note that in this situation of relative velocity V between the body and the negative wheel (compression), a shock absorber (passive or even semi-active) would have opposed the relative compression motion between body and wheel, thus exerting a force on the body directed upward, which would have facilitated the upward movement of the body.

In a third step, wherein the wheel has reached the apex of the obstacle, the control strategy still has the objective of keeping the body at the same vertical height that it had in the first or second steps. Since the wheel is on the apex of the obstacle, the suspension has zero relative velocity (V=0), but the spring is more compressed than it was in the second step and therefore increases the value of the elastic force Fs exerted on the body upward. To compensate for this increased force Fs, the actuator must in turn increase the value of the force F that it exerts downward on the body. Due to the action and reaction principle, the actuator exerts an equal and opposite force F on the wheel, thus directed upward. The actuator operates at zero speed by exerting a positive force F (active operation with zero speed). In practice, in this step the actuator continues to actively maintain the wheel on the apex of the bump, without having a vertical displacement effect on the body. It should be noted that in this situation of zero relative velocity V between the body and wheel, a shock absorber (passive or even semi-active) would have reacted with a zero force F.

Finally, in a fourth step, wherein the wheel descends from the obstacle, once again the control strategy aims to keep the body at the same vertical height it had in the previous step. Since the wheel descends from the obstacle and moves away from the body, the suspension is in the extension step (V>0), the spring is always compressed and therefore exerts an elastic force Fs directed upward on the body. To compensate for this force Fs, the actuator must exert an equal and opposite force F on the body, thus directed downward. Due to the action and reaction principle, the actuator exerts an equal and opposite force F on the wheel, thus directed upward. The actuator then works in extension by exerting a force F on the body and wheel that opposes said extension, whereby the actuator is functioning as a shock absorber (damping operation in extension). In so doing, the actuator performs negative work on the suspension, since the force F exerted by the actuator on the wheel and the vertical velocity of the wheel are always of discordant direction during this step (the vertical velocity of the body is theoretically zero, therefore theoretically the work of the force F that the actuator exerts on the body is also zero). During this operation, the actuator then regenerates the kinetic energy of the suspension into electric energy, with a flow of electric energy going from the actuator to the battery.

Let us consider then a second particular scenario, wherein the wheel enters a dip on the road. Also in this case, the objective of the control strategy (known per se) is to control the actuator, so as to always keep the body of the vehicle at the same vertical height, thus compensating for the inevitable change in force of the spring due to the vertical displacement of the wheel relative to the body of the vehicle when crossing the dip.

Let us consider the same conventions on the signs of forces and velocity already illustrated for the case of the bump.

The main phenomena that occur while crossing the dip may be summarized as follows. In a first step, the vehicle moves on a smooth road, the suspension spring supports the vertical load due to the weight of the body, the suspension does not move vertically (V=0), and the actuator exerts a zero force F. In a second step, wherein the wheel enters the dip, the control strategy aims to keep the body at the same vertical height that it had in the first step. As the wheel descends inside the dip and moves away from the body, the suspension is in the extension step (V>0), the spring becomes more extended than it was in step 1 and therefore exerts an additional elastic force Fs on the body directed downward. To compensate for this force Fs, the actuator must exert an equal and opposite force F on the body, thus directed upward. Due to the action and reaction principle, the actuator exerts an equal and opposite force F on the wheel, thus directed downward (active operation in extension). In practice, in this step the actuator actively “helps” the wheel to follow the profile of the dip, pushing the wheel in the direction opposite to the body, and without having a displacement effect on said body. In so doing, the actuator performs positive work on the suspension since the force F exerted by the actuator on the wheel and the vertical velocity of the wheel are always in the same direction during this step (the vertical velocity of the body is theoretically zero, therefore theoretically the work of the force F that the actuator exerts on the body is also zero). It should be noted that in this situation of relative velocity V between body and positive wheel (extension), a shock absorber (passive or even semi-active) would have opposed the relative motion of extension between body and wheel, thus exerting a force on the body directed downward, which would have facilitated the movement toward the bottom of the body.

In a third step, wherein the wheel has reached the lowest point of the dip, the control strategy still has the objective of keeping the body at the same vertical height as it had in the previous steps. Since the wheel is at the lowest point of the dip, the suspension has zero relative velocity (V=0), but the spring is more extended than it was in the second step and therefore increases the value of the elastic force Fs exerted on the body downward. To compensate for this increased force Fs, the actuator must in turn increase the value of the force F that it exerts upward on the body. Due to the action and reaction principle, the actuator exerts an equal and opposite force F on the wheel, thus directed downward. The actuator operates at zero speed by exerting a negative force F (active operation with zero speed). In practice, in this step the actuator continues to actively keep the wheel on the lowest point of the dip, without the effect of vertical displacement on the body. It should be noted that in this situation of zero relative velocity V between the body and wheel, a shock absorber (passive or even semi-active) would have reacted with a zero force F.

Finally, in a fourth step, wherein the wheel rises out of the dip, once again the control strategy aims to keep the body at the same vertical height that it had in the previous steps. As the wheel rises out of the dip and approaches the body, the suspension is in the compression step (V<0), the spring is always extended and therefore exerts an elastic force Fs on the body directed downward. To compensate for this force Fs, the actuator must exert an equal and opposite force F on the body, thus directed upward. Due to the action and reaction principle, the actuator exerts an equal and opposite force F on the wheel, thus directed downward. The actuator then operates in compression by exerting a force F on the body and wheel that opposes said compression (damping operation in compression). In so doing, the actuator performs negative work on the suspension, since the force F exerted by the actuator on the wheel and the vertical velocity of the wheel are always of discordant direction during this step (the vertical velocity of the body is theoretically zero, therefore theoretically the work of the force F that the actuator exerts on the body is also zero). During this operation, the actuator then regenerates the kinetic energy of the suspension into electric energy, with a flow of electric energy going from the actuator to the battery.

According to the embodiments described above, the actuator may switch from active operation to damping operation (preferably regenerative).

In particular, both when (starting from a neutral condition of equilibrium of static suspension forces) the wheel encounters a bump and when the wheel encounters a dip, the actuator is in a first step powered to perform an active adjustment of the suspension motion until it reaches the apex of the bump or the deepest point of the dip after which, in a second step, the power supply is interrupted and the actuator is made to work as a generator, thus functioning as a damper for the suspension.

According to one embodiment, the semi-active suspension 12 may instead comprise a typical adjustable-damping shock absorber, which, for example, includes a pressure tube enclosing a pressure chamber wherein a hydraulic damping fluid (oil) is contained, a piston mounted to be slidable within the pressure chamber of the pressure tube so as to divide it into a lower pressure chamber and an upper pressure chamber, an outer tube, an annular chamber called a reservoir chamber and comprised between the pressure tube and the outer tube, wherein said chamber is filled in its lower part with the same hydraulic fluid (oil) and in its upper part with a compressible fluid (e.g., air, nitrogen, etc.) pressurized to a pre-determined pressure value, an intermediate tube that is fitted on the pressure tube and encloses therewith a by-pass chamber in communication with the upper pressure chamber through communication holes provided in the pressure tube, and a control valve, typically a solenoid valve, hydraulically connected on one side to the by-pass chamber and on the other side to the reservoir chamber, and arranged to control the passage of fluid between the by-pass chamber and the reservoir chamber.

According to one embodiment, the pair of active suspensions 10 is associated with the rear axle of the vehicle (in the forward direction of the vehicle), and the pair of semi-active suspensions 12 is associated with the front axle (in the forward direction of the vehicle). According to an alternative embodiment, the pair of active suspensions 10 is associated with the front axle of the vehicle, and the pair of semi-active suspensions 12 is associated with the rear axle of the vehicle.

A hybrid suspension system according to the invention may further comprise at least three vertical acceleration sensors of the sprung mass of vehicle , and/or four vertical acceleration sensors of the wheel hub, and/or four sensors of the suspension travel, one for each suspension of the vehicle, and/or an electric power supply system 14 characterized by an appropriate voltage, e.g., 48 V, able to power the actuators of the active suspension 10, and/or an electric power system 16 characterized by another appropriate voltage, e.g., 12 V, able to power the actuators of the semi-active suspension 12, and/or an electronic control unit 18 for centralized control of the hybrid suspension system (actuators of the active suspension 10 and actuators of the semi-active suspension 12).

According to one aspect of the invention, a vehicle is provided that comprises a pair of axles 8, 9 each associated with a pair of wheels, a sprung mass, supported by said axles 8, 9, and a hybrid suspension system according to any of the embodiments described above, said hybrid suspension system being associated with said pair of axles 8, 9 in such a way as to control the transmission of shocks from said axles 8, 9 to the sprung mass of the vehicle.

It is shown that a suspension system according to the invention achieves a significantly better performance compared to the case where both axles of the vehicle are combined with semiactive suspensions, given a modest reduction in performance compared to the case where both axles of the vehicle are combined with active suspensions. In fact, as will be observed below, the performance gain (compared to the case where both vehicle axles are associated with semi-active suspensions) is 50% greater than the loss that occurs compared to the case where both vehicle axles are associated with active suspensions. Such a compromise also allows, without unduly impairing performance, significant cost savings.

In particular, Fig. 2 is a comparative graph of the performance, in terms of the roll angle (expressed in degrees) of the sprung mass of a vehicle as a function of the lateral acceleration (expressed in m/s²) of the vehicle, of three suspension systems, respectively, wherein both axles of the vehicle are associated with semi-active suspensions (red curve at top), wherein both axles of the vehicle are associated with active suspension (yellow curve at the bottom), and wherein one axle is associated with a semi-active suspension and the other axle is associated with an active suspension (intermediate blue curve, corresponding to a suspension system according to the invention). The curves are obtained for a circular trajectory of the center of gravity of the vehicle with a radius of 100 m.

The graph shows that, with a suspension system according to the invention, the improvement in roll angle reduction, compared to the case where both vehicle axles are associated with semi-active suspensions, is on average much greater than the performance loss, compared to the case where both vehicle axles are associated with active suspensions. For example, at 8 m/s², the gain in terms of roll angle reduction, compared to the case where both vehicle axles are associated with semi-active suspensions, is 27%, given a performance loss, compared to the case where both vehicle axles are associated with active suspensions, of only 18%. It may be deduced from this that the coupling of active- and semi-active suspensions allows for an effect other than their simple performance average, thus demonstrating the existence of a synergistic effect that allows the performance of a system with only semi-active suspensions to be significantly improved, reducing the performance of a system with only active suspensions to a lesser extent, while important economic savings are achieved (due to the replacement of a pair of expensive active suspensions with a pair of cheaper semi-active suspensions).

Various aspects and embodiments of a hybrid suspension system for a vehicle, and a vehicle equipped with such a system, according to the invention have been described. It is understood that each embodiment may be combined with any other embodiment. Moreover, the invention is not limited to the embodiments described, but may be varied within the scope defined by the appended claims.

Claims

1. A hybrid suspension system for a two-axle vehicle, comprising a pair of active suspensions (10) associated with one of the two axles of the vehicle, and a pair of semiactive suspensions (12) associated with the other of the two axles of the vehicle, so that each axle of the vehicle is associated with a pair of respective exclusively active or semi-active suspensions.

2. The system according to claim 1, wherein the pair of active suspensions (10) is associated with the rear axle of the vehicle, and the pair of semi-active suspensions (12) is associated with the front axle of the vehicle.

3. The system according to claim 1, wherein the pair of active suspensions (10) is associated with the front axle of the vehicle, and the pair of semi-active suspensions (12) is associated with the rear axle of the vehicle.

4. The system according to any one of the preceding claims, comprising at least three vertical acceleration sensors of the sprung mass of the vehicle, and/or four vertical acceleration sensors of the wheel hub, and/or four sensors of the suspension travel, and/or an electric power supply system (14) able to power the actuators of the active suspension (10), and/or an electric power supply system (16) able to power the actuators of the semiactive suspensions (12), and/or an electronic control unit (18) for centralized control of the hybrid suspension system.

5. A vehicle comprising:

- a pair of axles (8, 9) each associated with a pair of wheels;

- a sprung mass supported by said axles (8, 9); and

- a hybrid suspension system according to any one of the preceding claims, said hybrid suspension system being associated with said pair of axles (8, 9) in such a way as to control the transmission of shocks from said axles (8, 9) to the sprung mass of the vehicle.