Hybrid suspension system for vehicles and vehicle equipped with the system

Abstract

A hybrid suspension system for a vehicle, and a vehicle equipped with such a system, is comprised of a pair of active suspensions (10) associated with one of the vehicle's two axles, and a pair of semi-active suspensions (12) associated with the other of the vehicle's two axles.

Description

[Technical field]

[0001] The present invention is generally in the field of controlling the static / dynamic behavior of vehicles, and more particularly, to hybrid suspension systems for vehicles and vehicles equipped with such systems. [Background technology]

[0002] Solutions are known in which the two axles (front and rear) of a vehicle are equipped with suspension systems of the so-called active (or "full active") type. Suspension systems of the (full) active type consist of separate actuators (conventionally electrohydraulic or electromechanical) which allow continuous control of the forces exerted on the suspension according to appropriate control logics (for example the so-called "sky hook" and "ground hook" which are well known to the person skilled in the art). According to these logics, the active suspensions can be configured, for example, to force the associated actuators to extend or compress in such a way that the spring mass of the vehicle remains at a given height (i.e. does not follow the contours of the terrain). An example of such a solution is known from WO2021 / 240415A1.

[0003] This active suspension is currently the most advanced solution when it comes to improving vehicle comfort and handling.

[0004] Another feature of active suspension is that it can harvest electrical energy when the suspension is operating in a controlled damping state, whereas in an active state the system requires a significant amount of energy to perform the required functions.

[0005] The main drawback of this type of system is its high cost, which limits its applicability to certain vehicle segments.

[0006] One of the objectives of the present invention is to overcome this drawback while sacrificing as little system performance as possible.

[0007] To achieve this, the vehicle suspension system of the present invention combines active suspension technology applied to a first axle of the vehicle and semi-active suspension technology applied to a second axle of the vehicle.

[0008] As known to those skilled in the art, semi-active suspensions are configured to change the damping coefficient of the actuators, and thus to change the behavior of the suspension system of the vehicle depending on, for example, road conditions or vehicle driving situations, using adjustable damping shock absorbers whose damping characteristics can be changed under the management of an electronic control unit. In this sense, semi-active suspensions differ from active suspensions, since they cannot apply forces to the suspension that can reverse the direction of the suspension velocity vector. In other words, semi-active suspensions are configured to generate forces that are always opposite to the movement of the wheel hub relative to the sprung mass by adjusting the damping coefficients of the shock absorbers (for example, the forces applied by the shock absorbers always have a direction that is inconsistent with the velocity of the wheel hub relative to the sprung mass), while active suspensions are configured to generate actuator forces, if necessary, directed in the same direction as the movement of the wheel hub relative to the sprung mass, according to a control logic. An example of a semi-active suspension is known from document EP 2 232 094 B1. DISCLOSURE OF THEINVENTION

[0009] In particular, the suspension system according to the invention preferably consists of two active actuators arranged on a first axle of the vehicle and two semi-active shock absorbers arranged on a second axle of the vehicle, and 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 hubs (or four suspension movement sensors, one for each suspension of the vehicle), and / or a power system with suitable voltage characteristics, for example 48V, managing the active actuators, and / or an electronic control unit managing the system.

[0010] According to one embodiment, the systems can each have two configurations: in the first configuration, the active suspension is located on the front axle of the vehicle (and the semi-active suspension is located on the rear axle), or vice versa (active on the rear axle and semi-active on the front axle).

[0011] In the first configuration, the active actuators on the front axle improve comfort, especially on the front axle. Furthermore, a high degree of control of the vehicle's sprung mass movement is possible, both in lateral and longitudinal force relationships. In the case of longitudinal force relationships, the most important condition is the limit braking, in which case the load transfer to the front axle improves the system's ability to control such conditions. In the case of lateral force relationships, the additional forces that may be exerted by the front axle act to reduce the roll angle, in which case the conditions are very similar to those in the presence of a stiffer front anti-roll bar, so that the directional behavior of the vehicle shifts towards a more pronounced tendency towards understeer. This allows the full operating capacity of the actuators to be utilized without risking an unstable state of the vehicle.

[0012] In the second configuration, the active suspension of the rear axle improves comfort, especially at the rear axle. In this case, the ability to control the sprung mass is reduced compared to the first configuration, both in the lateral and longitudinal force relationships. With regard to the longitudinal force relationship of the sprung mass, this configuration can mainly improve the load transfer conditions of the rear axle, e.g. under acceleration conditions. In this condition, the acceleration values ​​are generally lower than under braking, so the overall longitudinal control ability is reduced. On the other hand, in the case of the lateral force relationship, the additional force applied to the rear axle by the active actuator serves 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, which changes the directional behavior of the car to a more pronounced oversteer tendency. This configuration may be preferred when prioritizing the comfort of the rear passengers or when the load conditions of the rear axle are highly variable (limousines, vans, etc.), but usually it is not possible to fully use all the available forces of the actuators, which may lead to excessive oversteer in the directional behavior of the car. However, the main advantage of this configuration is that road profile information from the front wheels allows the rear actuators to be activated without delay, providing "advance warning" to the rear axle.

[0013] In general, as will be shown below, both system configurations perform significantly better than when both axles are controlled by pure semi-active suspensions, relatively no worse than when both axles are controlled by active suspensions, and benefit from significant cost savings.The above and other objects and advantages are achieved according to one aspect of the present invention by a hybrid suspension system for a vehicle, and a vehicle equipped with such a system having the features defined in the appended claims. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram of a hybrid suspension system for a vehicle according to an embodiment of the present invention. [Diagram 2]FIG. 2 is a comparative graph of the performance of three suspension systems in terms of controlling the roll angle of a vehicle's sprung mass as a function of lateral acceleration: when both vehicle axles are associated with semi-active suspensions, when both vehicle axles are associated with active suspensions, and when one axle is associated with semi-active suspension and the other axle is associated with active suspension. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The functional and structural features of several preferred embodiments of the hybrid suspension system according to the present invention are described below.

[0016] Before describing several embodiments of the present invention in detail, it should be made clear that the present invention is not limited in its application to the design details and configuration of components set forth in the following description or illustrated in the drawings. The present invention contemplates other embodiments and may actually be implemented or constructed in different ways. It is also to be understood that these phrases and terminology are for the purpose of description and not for the purpose of limitation.

[0017] With reference to Fig. 1, a hybrid suspension system for a two-axle vehicle is configured such that one axle of the vehicle is associated with only one set of active suspensions or shock absorbers and the other axle is associated with only one set of semi-active suspensions or shock absorbers. In particular, the hybrid suspension system according to the present invention includes a set of active suspensions 10 associated with one of the two axles of the vehicle and a set of semi-active suspensions 12 associated with the other of the two axles of the vehicle. Thus, the vehicle is equipped with two sets of shock absorbers or suspensions of different types (one set of active type and the other set of semi-active type), each set associated with a single axle.

[0018] An active suspension is 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. The suspension arm is connected to the wheel hub. The actuator is electrically driven (e.g. by the battery 14) and is operable between an active control state, in which the actuator is configured to transmit to the suspension arm a force which induces a relative movement of the suspension arm with respect to the vehicle body (e.g. the sprung mass of the vehicle) resulting in a positive effect on the suspension, and a damping state, in which the actuator is configured to transmit to the suspension arm a force which opposes the relative movement of the suspension arm with respect to the vehicle body resulting in a negative effect on the suspension. Conveniently, the actuator is operable between these active control and damping states in response to a command from an electronic control unit. Typically, it also comprises elastic means, such as a spring, designed to return the suspension arm to a predefined neutral position of equilibrium of static forces with respect to the vehicle body.

[0019] According to one embodiment, the actuators of the active suspension 10 are operable according to a modulation mode, which is described in the following example.

[0020] Considering a simplified model of a vehicle suspension, the body and each wheel are depicted as two masses, an upper mass and a lower mass, which are interconnected via a spring and a mechanically parallel actuator between them.

[0021] Consider the specific scenario where a wheel hits an obstacle on the road, e.g. a bump. The objective of the control strategy (known per se) is to control the actuators (e.g. position and torque if the actuators are rotary) to keep the body at the same vertical height at all times and to compensate for the inevitable change in spring force due to the vertical displacement of the wheel relative to the body as it traverses the obstacle.

[0022] Fs is the force the spring exerts on the body, which due to the principle of action and reaction is conventionally considered positive when directed upwards, and the force on the wheel is conventionally considered positive when directed downwards. V is the relative vertical velocity of the body and wheel, which is conventionally considered positive when extended. F is the force the actuator exerts on the body, which is conventionally considered positive when directed downwards. Due to the principle of action and reaction, the actuator exerts an equal force F on the wheel, which is conventionally considered positive when directed upwards.

[0023] The main phenomena occurring when going over an obstacle can be summarized as follows: In the first step, the vehicle moves on a smooth road, the suspension springs support the vertical load due to the weight of the body, the suspension does not move vertically (V=0), and the force F exerted by the actuator is zero. In the second step, when the wheel climbs the obstacle, the control strategy aims to keep the body at the same vertical height as in the first step. When the wheel goes over the obstacle and approaches the body, the suspension is in the compression phase (V<0) and the springs are more compressed than in the first phase, so they exert an additional direct elastic force Fs upwards on the body. To compensate for this force Fs, the actuator must exert an equal and opposite force F on the body, which results in a downward force. Due to the action-reaction principle, the actuator exerts an equal and opposite force F on the wheel, which results in an upward force (active action during compression). In effect, in this phase the actuator actively "assists" the wheel to follow the bump, pulling it towards the body without any displacement effect on the body. In doing so, the actuator performs positive work on the suspension, since at this stage the force F exerted by the actuator on the wheel and the vertical velocity of the wheel are always in the same direction (the vertical velocity of the body is theoretically zero, so theoretically the work of the force F exerted by the actuator on the body is also zero). It should be noted that in this situation of relative velocity V between the body and the negative wheel (compression), the shock absorber (passive or semi-active) opposes the relative compression movement between the body and the wheel, exerting an upward force on the body and promoting the upward movement of the body.

[0024] In the third step, when the wheel has reached the apex of the obstacle, the control strategy still has the goal of keeping the vehicle body at the same vertical height as in the first or second step. Since the wheel is at the apex of the obstacle, the relative velocity of the suspension is zero (V=0), but the spring is more compressed than in the second step, so the value of the elastic force Fs exerted upwards on the vehicle body increases. To compensate for this increased force Fs, the actuator needs to increase the value of the force F exerted downwards on the vehicle body. Due to the principle of action and reaction, the actuator exerts an equal and opposite force F on the wheel, which is directed upwards. The actuator operates at zero velocity by exerting a positive force F (active operation at zero velocity). In fact, in this step, the actuator actively keeps the wheel at the apex position of the bump without exerting any vertical displacement effect on the vehicle body. It should be noted that in this situation, where the relative velocity V between the vehicle body and the wheel is zero, the shock absorber (passive or semi-active) reacts with a zero force F.

[0025] Finally, in the fourth step, when the wheel descends from the obstacle, the control strategy again aims to keep the body at the same vertical height as in the previous step. As the wheel descends from the obstacle and leaves the body, the suspension is in an extension step (V>0) and the spring is always compressed, so an upward elastic force Fs acts on the body. To compensate for this force Fs, the actuator needs to apply an equal and opposite force F to the body, directed downwards. Due to the principle of action and reaction, the actuator applies an equal and opposite force F to the wheel, directed upwards. Then, during extension, the actuator works by applying a force F to the body and the wheel that opposes its extension, so that the actuator acts as a shock absorber (damping action during extension). By doing so, the actuator does a negative work on the suspension. This is because during this step, the force F that the actuator exerts on the wheel and the vertical velocity of the wheel are always in the opposite direction (since the vertical velocity of the body is theoretically zero, the work of the force F that the actuator exerts on the body is also theoretically zero). During this operation, the actuator converts the kinetic energy of the suspension into electrical energy, with the flow of electrical energy being from the actuator to the battery.

[0026] Now consider a second specific scenario, where the wheel enters a pothole. In this case too, the aim of the control strategy (known per se) is to control the actuators to keep the vertical height of the body the same at all times and to compensate for the inevitable change in the spring force due to the vertical displacement of the wheel relative to the body when crossing the pothole. Consider the same rules for the signs of forces and velocities already given for the case of a bump. The main phenomena occurring when crossing a pothole can be summarized as follows: In the first step, the vehicle moves on a smooth road, the suspension springs support the vertical load due to the weight of the body, the suspension does not move vertically (V=0) and the actuators exert a zero force F. In the second step, the wheel enters the pothole, but the control strategy aims to keep the body at the same vertical height as in the first step. As the wheel descends in the pothole and leaves the body, the suspension goes through an extension step (V>0) and the springs are more extended than in the first step, so they exert an additional downward elastic force Fs on the body. To compensate for this force Fs, the actuator must exert an equal and opposite force F on the body, resulting in an upward movement. By the principle of action and reaction, the actuator exerts an equal and opposite force F on the wheel, resulting in a downward movement (active action during extension). In effect, in this step, the actuator actively "assists" the wheel to follow the profile of the incline, pushing the wheel in the opposite direction to the body, with no displacement effect on the body. In doing so, the actuator performs positive work on the suspension. This is because during this step, the force F exerted by the actuator on the wheel and the vertical velocity of the wheel are always in the same direction (since the vertical velocity of the body is theoretically zero, theoretically the work of the force F exerted by the actuator on the body is also zero). It should be noted that in this situation of relative velocity V between the body and the positive wheel (extension), the shock absorber (passive or semi-active) opposes the relative motion of the extension between the body and the wheel, exerting a downward force on the body and facilitating the movement of the body to the bottom.

[0027] In the third step, the wheel reaches the bottom of the depression, but the objective of the control strategy is to maintain the vehicle body at the same vertical height as in the previous step. Since the wheel is at the bottom of the depression, the relative velocity of the suspension is zero (V=0), but the spring is more stretched than in the second step, so the value of the elastic force Fs exerted downwards on the vehicle body increases. To compensate for this increased force Fs, the actuator needs to increase the value of the force F it exerts upwards on the vehicle body. Due to the principle of action and reaction, the actuator exerts an equal and opposite force F on the wheel, directed downwards. The actuator operates at zero velocity by exerting a negative force F (active operation at zero velocity). In fact, in this step, the actuator actively continues to maintain the wheel at the bottom of the depression, unaffected by any vertical displacement with respect to the vehicle body. It should be noted that in this situation, where the relative velocity V between the vehicle body and the wheel is zero, the shock absorber (passive or semi-active) should react with a zero force F.

[0028] Finally, in the fourth step, when the wheel rises from the dip, the control strategy again aims to keep the body at the same vertical height as in the previous step. As the wheel rises from the dip and approaches the body, the suspension is in a compression step (V<0) and the spring is always stretched, so it exerts a downward elastic force Fs on the body. To compensate for this force Fs, the actuator needs to exert an equal and opposite force F on the body, which will be directed upwards. Due to the principle of action and reaction, the actuator exerts an equal and opposite force F on the wheel, which will be directed downwards. The actuator then works in compression by exerting a force F on the body and the wheel that opposes the compression (damping action in compression). In doing so, the actuator does negative work on the suspension. This is because during this step, the force F that the actuator exerts on the wheel and the vertical velocity of the wheel are always in the opposite direction (since the vertical velocity of the body is theoretically zero, the work of the force F that the actuator exerts on the body is also theoretically zero). During this operation, the actuator converts the kinetic energy of the suspension into electrical energy, and a flow of electrical energy flows from the actuator to the battery.

[0029] According to the above embodiment, the actuator can be switched from active operation to damping operation (preferably regenerative).

[0030] In particular, when a wheel encounters a bump or when a wheel encounters a pothole (starting from a neutral state of static suspension force equilibrium), in a first step the actuator is powered to perform an active adjustment of the suspension action until the peak of the bump or the deepest point of the pothole is reached, after which, in a second step, the power supply is interrupted and the actuator is made to operate as a generator, acting as a suspension damper. According to one embodiment, the semi-active suspension 12 may instead include a typically adjustable damping shock absorber including a pressure tube surrounding a pressure chamber in which a hydraulic damping fluid (oil) is contained, a piston slidably mounted to divide the pressure chamber of the pressure tube into a lower pressure chamber and an upper pressure chamber, an outer tube, an annular chamber called a reservoir chamber between the pressure tube and the outer tube (the lower part of this chamber is filled with the same hydraulic fluid (oil) and the upper part is filled with a compressible fluid (e.g. air, nitrogen, etc.) pressurized to a predetermined pressure value), an intermediate tube attached to the pressure tube and surrounding a bypass chamber communicating with the upper pressure chamber through a communication hole provided in the pressure tube, and a control valve (usually a solenoid valve) hydraulically connected on one side to the bypass chamber and on the other side to the reservoir chamber and configured to control the passage of fluid between the bypass chamber and the reservoir chamber.

[0031] In one embodiment, a pair of active suspensions 10 are associated with the rear axles (towards the front of the vehicle) of the vehicle, and a pair of semi-active suspensions 12 are associated with the front axles (towards the front of the vehicle). In another embodiment, a pair of active suspensions 10 are associated with the front axles of the vehicle, and a pair of semi-active suspensions 12 are associated with the rear axles of the vehicle.

[0032] The hybrid suspension system according to the present invention may further comprise at least three vertical acceleration sensors of the vehicle's sprung mass, and / or four vertical acceleration sensors of the wheel hubs, and / or four sensors of suspension travel, one for each suspension of the vehicle, and / or a power supply system 14 characterized by a suitable voltage (e.g. 48 V) capable of supplying power to the actuators of the active suspension 10, and / or a power system 16 characterized by another suitable voltage (e.g. 12 V) capable of supplying power to the actuators of the semi-active suspension 12, and / or an electronic control unit 18 for centralized control of the hybrid suspension system (the actuators of the active suspension 10 and the actuators of the semi-active suspension 12).

[0033] According to one aspect of the present invention, there is provided a vehicle comprising a pair of axles 8, 9 respectively 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 above embodiments, said hybrid suspension system being associated with said pair of axles 8, 9 and controlling the transmission of shocks from said axles 8, 9 to the sprung mass of the vehicle.

[0034] The suspension system according to the present invention has been shown to achieve significantly better performance than both vehicle axles combined with semi-active suspension, with only a slight loss in performance compared to when both vehicle axles are combined with active suspension. In fact, as shown below, the gain in performance (compared to when both vehicle axles are combined with semi-active suspension) is 50% greater than the loss incurred compared to when both vehicle axles are combined with active suspension. Such a compromise also allows for significant cost savings without undue loss in performance.

[0035] In particular, Figure 2 is a graph comparing the performance of three suspension systems in terms of the roll angle of the sprung mass of the vehicle (expressed in degrees) as a function of the lateral acceleration of the vehicle (expressed in m / s2) when both axles of the vehicle are associated with a semi-active suspension (upper red curve), when both axles of the vehicle are associated with an active suspension (lower yellow curve) and when one axle is associated with a semi-active suspension and the other axle is associated with an active suspension (middle blue curve, corresponding to the suspension system according to the invention). These curves are obtained for a circular trajectory of the center of gravity of the vehicle with a radius of 100 m.

[0036] The graph shows that for the suspension system according to the invention, the improvement in roll angle reduction compared to when both axles are associated with semi-active suspension is on average much greater than the performance loss compared to when both axles are associated with active suspension. For example, at 8 m / s2, the gain in terms of roll angle reduction compared to when both axles are associated with semi-active suspension is 27%, but the performance loss compared to when both axles are associated with active suspension is only 18%. From this, it can be inferred that the combination of active and semi-active suspensions results in more than just a simple performance average, demonstrating the existence of synergies that significantly improve the performance of a system with only semi-active suspensions and achieve important economic savings (arising due to the replacement of an expensive pair of active suspensions with a cheaper pair of semi-active suspensions) without significantly decreasing the performance of a system with only active suspensions.

[0037] Various aspects and embodiments of the hybrid suspension system for a vehicle according to the present invention and of a vehicle equipped with such a system have been described. It will be understood that each embodiment can be combined with other embodiments. Moreover, the invention is not limited to the described embodiments, but can be modified within the scope defined by the appended claims.

Claims

1. 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 a vehicle; A pair of semi-active suspensions (12) associated with the other of the two axles of the vehicle; With A hybrid suspension system in which each axle of the vehicle is associated with its own pair of said active suspensions (10) or said pair of said semi-active suspensions (12).

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

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

4. 4. The hybrid suspension system according to claim 1, further comprising at least three vertical acceleration sensors of the vehicle's sprung mass, and / or four vertical acceleration sensors of the wheel hub, and / or four sensors of suspension travel, and / or a power supply system (14) capable of supplying power to actuators of the active suspension (10), and / or a power supply system (16) capable of supplying power to actuators of the semi-active suspension (12), and / or an electronic control unit (18) for centralized control of the hybrid suspension system.

5. A pair of axles (8, 9) respectively associated with a pair of wheels; a sprung mass supported by said axle (8, 9); A hybrid suspension system according to any one of claims 1 to 3; Equipped with The hybrid suspension system is associated with the pair of axles (8, 9) to control the transmission of shocks from the axles (8, 9) to the sprung mass of the vehicle.

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