Hybrid suspension system for a vehicle and vehicle equipped therewith

Abstract

A hybrid suspension system for a two-axle vehicle includes 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

Technical Field

[0001] The present invention is generally in the field of controlling the static / dynamic characteristics of a vehicle; in particular, the present invention relates to a hybrid suspension system for a vehicle and a vehicle equipped with the system. Summary of the invention

[0002] A known solution is to equip the vehicle with a so-called active (or "fully active") type suspension system on both axles (front and rear), which consists of separate actuators (conventionally electro-hydraulic or electromechanical) capable of continuously controlling the forces applied to the suspension according to appropriate control logics (for example, the logic known as "sky hook" and "ground hook" as is well known to those skilled in the art). According to these logics, the active suspension can, for example, be configured to force the associated actuators to extend or compress so that the sprung mass of the vehicle remains at a predetermined height (i.e., avoiding following the contours of the terrain). An example of such a solution can be found in WO 2021 / 240415A1.

[0003] This active suspension is currently the most advanced solution for improving vehicle comfort and handling.

[0004] Another feature of active suspension is the ability to harvest electrical energy when the suspension is operating under controlled damping conditions. On the other hand, in active conditions, the system requires a lot of energy to perform the required functions.

[0005] The main drawback of this system is its high cost, which limits its application to only a few vehicle segments.

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

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

[0008] As known to those skilled in the art, a semi-active suspension is configured to vary the damping coefficient of an actuator and employs an adjustable damping shock absorber capable of varying its damping characteristics under the management of an electronic control unit in order to vary the characteristics of the vehicle suspension system according to, for example, road conditions and vehicle driving conditions. In this sense, a semi-active suspension differs from an active suspension in that it is not possible to apply a force to the suspension that would reverse the direction of the suspension velocity vector. In other words, a semi-active suspension is configured to generate a force that is always opposite to the direction of movement of the wheel relative to the sprung mass by adjusting the damping coefficient of the shock absorber (i.e., the direction of the force applied by the shock absorber is always inconsistent with the direction of the velocity of the wheel relative to the sprung mass), whereas an active suspension is configured, according to a control logic, to generate (if necessary) an actuation force in the same direction as the direction of movement of the wheel relative to the sprung mass. An example of a semi-active suspension is known from document EP 2 232 094 B1.

[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. There may also be at least three vehicle sprung mass vertical acceleration sensors, and / or four wheel hub vertical acceleration sensors (or four suspension travel sensors, one for each suspension of the vehicle), and / or an electrical system with a suitable voltage (e.g. 48V) for managing the active actuators, and / or an electronic control unit for managing the system.

[0010] According to one embodiment, the system can have two configurations, namely a first configuration in which the active suspension is placed on the front axle of the vehicle (and the semi-active suspension is placed on the rear axle), or vice versa (the active suspension is placed on the rear axle and the semi-active suspension is placed on the front axle).

[0011] In the first configuration, the active actuators on the front axle will improve comfort, especially on the front axle. In addition, the movement of the vehicle's sprung masses in both lateral and longitudinal dynamics can be highly controlled. The most critical situation in terms of longitudinal dynamics is limit braking, in which case the load transferred to the front axle will increase the system's ability to control this situation. In lateral dynamic situations, the additional forces that may be applied by the front axle will reduce the roll angle, in which case the situation will be very similar to the situation with a stiffer front anti-roll bar, so that the vehicle's directional characteristics will shift towards a more pronounced understeer tendency. As a result, the full operating capacity of the actuators can be used without the risk of the vehicle being unstable.

[0012] In the second configuration, the active suspension on the rear axle will improve comfort, especially on the rear axle. In this case, the ability to control the sprung masses is reduced relative to the first configuration, both in lateral and longitudinal dynamics. For the longitudinal dynamics of the sprung masses, this configuration mainly improves the load transfer conditions on the rear axle, i.e. the acceleration conditions. Since the acceleration values ​​in this case are usually lower than those under braking, the overall longitudinal control ability is reduced. On the other hand, in the case of lateral dynamics, the additional force exerted by the active actuator on the rear axle can reduce the roll angle of the sprung masses. This situation is very similar to the case of the same vehicle equipped with a stiffer rear anti-roll bar, thus changing the directional characteristics of the vehicle towards a more pronounced oversteer tendency. This configuration may be preferred when the comfort of the rear passengers is a priority or when the rear axle is subject to large changes in load conditions (luxury cars, vans, etc.), but it usually does not allow the full use of the full available force of the actuator, which can lead to the directional characteristics of the vehicle becoming extremely oversteer. On the other hand, a major advantage of this configuration is that the rear actuator can operate without delay based on road condition information for the front wheels, thus enabling it to "pre-alert" the rear axle.

[0013] Overall, as will be shown, both system configurations perform significantly better than if both axles were controlled by pure semi-active suspension, and relatively better than if both axles were controlled by active suspension, while also offering significant cost savings.

[0014] According to one aspect of the invention, the above and other objects and advantages are achieved by a hybrid suspension system for a vehicle and a vehicle equipped with such a system, the system having the characteristics defined in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The functions and structural features of some preferred embodiments of the hybrid suspension system according to the present invention will now be described. With reference to the accompanying drawings, in which:

[0017] - Figure 1 is a schematic diagram of a vehicle hybrid suspension system according to an embodiment of the present invention; and

[0018] - Figure 2 A graph comparing the performance of three suspension systems in controlling the relationship between the vehicle's sprung mass roll angle and lateral acceleration, including a case where both axles are associated with semi-active suspensions, a case where both axles are associated with active suspensions, and a case where one axle is associated with the semi-active suspension and the other axle is associated with the active suspension.

[0019] Detailed Description

[0020] Before explaining in detail the various embodiments of the present invention, it should be clarified that the application of the present invention is not limited to the design details and configurations of the components presented in the following description or shown in the accompanying drawings. The present invention may adopt other embodiments and be implemented or constructed in practice in different ways. It should also be understood that the words and terms have descriptive purposes and should not be interpreted as limiting.

[0021] refer to Figure 1 , the hybrid suspension system of a two-axle vehicle is configured so that one axle of the vehicle is associated with a pair of dedicated active suspensions or shock absorbers, while the other axle is associated with a pair of dedicated semi-active suspensions or shock absorbers. Specifically, the hybrid suspension system according to the present invention includes 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 axle 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 active and one pair of semi-active), each pair being associated with a single axle.

[0022] As is known, an active suspension comprises 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 the wheel hub. The actuator is operable between an active control state, in which the actuator is configured to be electrically driven (e.g. by a battery 14) and to transmit a force to the suspension arm, which causes a relative movement of said suspension arm with respect to the vehicle body (i.e. the sprung mass of the vehicle), thereby performing positive work on the suspension, and a damping state, in which the actuator is configured to transmit a force to the suspension arm, which is opposite to the relative movement of said suspension arm with respect to the vehicle body, thereby performing negative work on the suspension. Conveniently, the actuator is operable between said active control condition and damping condition according to a command from an electronic control unit. Typically, there is also a resilient device, such as a spring, designed to pull the suspension arm back to a predetermined neutral position of static equilibrium relative to the vehicle body.

[0023] According to one embodiment, the actuators of the active suspension 10 may be operated according to the regulation modes described in the following examples.

[0024] Consider a simplified vehicle suspension model, where the body and each wheel of the vehicle are represented schematically by two masses, an upper mass and a lower mass, which are connected to each other via a spring and an actuator mechanically connected in parallel between them.

[0025] Consider a special scenario in which a wheel collides with an obstacle on the road (e.g. a bump in the road surface). The purpose of the control strategy (known per se) is to control the actuator (e.g. the position and torque of the actuator if it is a rotary actuator) so as to always keep the vehicle body at the same vertical height, compensating for the inevitable variations in the spring force due to the vertical displacement of the wheel relative to the vehicle body when passing over the obstacle.

[0026] Fs represents the force applied by the spring on the vehicle body, which is generally considered positive if it points upward, and represents the force applied by the spring on the wheel, which is generally considered positive if it points downward, according to the principle of action and reaction. V represents the relative vertical velocity between the vehicle body and the wheel, which is generally considered positive when extended. F represents the force applied by the actuator on the vehicle body, which is generally considered positive if it points downward, and the actuator applies a force of the same magnitude F on the wheel, which is generally considered positive if it points upward, according to the principle of action and reaction.

[0027] The main phenomena that occur during the obstacle crossing process can be summarized as follows. In the first step, the vehicle is traveling on a flat road, the suspension springs support the vertical load caused by the weight of the vehicle body, the suspension does not move vertically (V = 0), and the force F applied by the actuator is zero. In the second step, the wheel climbs up the obstacle, and the control strategy aims to keep the vehicle body at the same vertical height as in the first step. When the wheel crosses the obstacle and approaches the vehicle body, the suspension is in a compression step (V < 0), and the spring is compressed more than in the first step, thereby applying an additional direct elastic force Fs upward to the vehicle body. In order to compensate for this force Fs, the actuator must apply an equal and opposite force F to the vehicle body, that is, a downward force. According to the principle of action and reaction, the actuator applies an equal and opposite force F to the wheel, thus pointing upward (active operation during compression). In fact, in this step, the actuator actively "helps" the wheel to follow the road bump, pulling the wheel towards the vehicle body, and does not produce a displacement effect on the vehicle body. This way, the actuator does positive work on the suspension, because during this step, the force F applied by the actuator on the wheel is always in the same direction as the vertical velocity of the wheel (the vertical velocity of the vehicle body is theoretically zero, so the work done by the force F applied by the actuator on the vehicle body is also theoretically zero). Note that in this case of relative velocity V between the vehicle body and the negative wheel (compression), the shock absorber (passive or semi-active) resists the relative compressive motion between the vehicle body and the wheel, thus applying an upward force on the vehicle body, which promotes the upward motion of the vehicle body.

[0028] In the third step, the wheel has reached the highest point of the obstacle and the control strategy still aims to keep the vehicle body at the same vertical height as it was in the first or second step. Since the wheel is at the highest point of the obstacle, the relative velocity of the suspension is zero (V=0), but the spring is more compressed than in the second step, thus increasing the value of the elastic force Fs applied upwards to the vehicle body. In order to compensate for this increased force Fs, the actuator must in turn increase the value of the force F it applies downwards to the vehicle body. According to the principle of action and reaction, the actuator applies an equal and opposite force F to the wheel, thus pointing upwards. The actuator operates at zero velocity (active operation at zero velocity) by applying a positive force F. In fact, in this step, the actuator continues to actively keep the wheel at the highest point of the road bump without generating a vertical displacement effect on the vehicle body. It is worth noting that in this case, where the relative velocity V between the vehicle body and the wheel is zero, the reaction force F of the shock absorber (passive or even semi-active) is zero.

[0029] Finally, in the fourth step, the wheel falls from the obstacle and the control strategy again aims to keep the vehicle body at the same vertical height as it was in the previous step. As the wheel drops from the obstacle and away from the vehicle body, the suspension is in the extension step (V>0) and the spring is always compressed, thus exerting an upward elastic force Fs on the vehicle body. To compensate for this force Fs, the actuator must exert an equal and opposite force F on the vehicle body, i.e. a downward force. According to the principle of action and reaction, the actuator exerts an equal and opposite force F on the wheel, thus pointing upwards. The actuator then works in extension by exerting a force F on the vehicle body and the wheel that opposes said extension, so that the actuator acts as a shock absorber (damping operation in extension). In this way, the actuator does negative work on the suspension, because during this step, the force F exerted by the actuator on the wheel is always inconsistent with the vertical velocity of the wheel (the vertical velocity of the vehicle body is theoretically zero, so the work done by the force F exerted by the actuator on the vehicle body is also theoretically zero). During this operation, the actuator regenerates the suspension's kinetic energy into electrical energy, which flows from the actuator to the battery.

[0030] Consider a second special case, in which the wheel enters a depression in the road. Also in this case, the control strategy (known per se) aims to control the actuator so as to always keep the vehicle body at the same vertical height, thus compensating for the inevitable variations in the spring force due to the vertical displacement of the wheel relative to the vehicle body when going over the depression.

[0031] Consider the same conventions regarding the signs of forces and velocities that have already been explained in the case of road bumps.

[0032] The main phenomena that occur when going over a depression can be summarized as follows. In the first step, the vehicle is traveling on a flat road, the suspension springs support the vertical load caused by the weight of the vehicle body, the suspension does not move vertically (V=0), and the force applied by the actuator is zero. In the second step, the wheel enters the depression and the control strategy aims to keep the vehicle body at the same vertical height as it was in the first step. When the wheel descends into the depression and away from the vehicle body, the suspension is in the extension step (V>0), the spring is extended more than in the first step, and therefore exerts an additional elastic force Fs downward on the vehicle body. To compensate for this force Fs, the actuator must apply an equal and opposite force F to the vehicle body, that is, an upward force. According to the principle of action and reaction, the actuator applies an equal and opposite force F to the wheel, thus pointing downward (active operation during extension). In fact, in this step, the actuator actively "helps" the wheel to follow the contour of the depression, pushing the wheel in the opposite direction to the vehicle body, and without generating a displacement effect on the vehicle body. In this way, the actuator does positive work on the suspension, because during this step, the force F applied by the actuator to the wheel is always in the same direction as the vertical velocity of the wheel (the vertical velocity of the body is theoretically zero, so the work done by the force F applied by the actuator to the body is theoretically zero). It should be noted that in the case of a relative velocity V between the body and the wheel in the positive direction (extension), the shock absorber (passive or even semi-active) will resist the relative movement of the extension between the body and the wheel, thus applying a downward force on the body, thus promoting movement towards the bottom of the body.

[0033] In the third step, the wheel has reached the lowest point of the depression and the control strategy still aims to keep the vehicle body at the same vertical height as it was in the previous step. Since the wheel is at the lowest point of the depression, the suspension has a relative velocity of zero (V=0), but the spring is stretched more than it was in the second step, thus increasing the value of the elastic force Fs exerted downward on the vehicle body. In order to compensate for this increased force Fs, the actuator must in turn increase the value of the force F it exerts upward on the vehicle body. According to the principle of action and reaction, the actuator applies an equal and opposite force F to the wheel, thus pointing downward. The actuator operates at zero velocity (active operation at zero velocity) by applying a negative force F. In fact, in this step, the actuator continues to actively keep the wheel at the lowest point of the depression without affecting the vertical displacement of the vehicle body. It is worth noting that in the case of zero relative velocity V between the vehicle body and the wheel, the reaction force F of the shock absorber (passive or even semi-active) is zero.

[0034] Finally, in the fourth step, the wheel is lifted from the depression and the control strategy is again aimed at keeping the body at the same vertical height as it was in the previous steps. When the wheel is lifted from the depression and approaches the body, the suspension is in a compression step (V<0) and the spring is always extended, thus exerting a 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, that is, an upward force. According to the principle of action and reaction, the actuator exerts an equal and opposite force F on the wheel, thus pointing downward. The actuator then performs a compression operation by exerting a force F on the body and the wheel that opposes the compression (damping operation during compression). In this way, the actuator performs negative work on the suspension because during this step, the force F exerted by the actuator on the wheel is always inconsistent with the vertical velocity of the wheel (the vertical velocity of the body is theoretically zero, so the work done by the force F exerted by the actuator on the body is also theoretically zero). During this operation, the actuator regenerates the kinetic energy of the suspension into electrical energy, which flows from the actuator to the battery.

[0035] According to the above-described embodiment, the actuator can be switched from active operation to damping operation (preferably regenerative operation).

[0036] Specifically, when the wheel encounters a bump in the road surface (starting from a balanced neutral state of static suspension forces) and when the wheel encounters a depression, in a first step, the actuator is activated to perform active adjustment of the suspension movement until the highest point of the bump or the deepest point of the depression is reached, after which in a second step, the power supply is interrupted and the actuator works as a generator, thereby acting as a shock absorber for the suspension.

[0037] According to one embodiment, the semi-active suspension 12 may alternatively include a typical adjustable damping shock absorber, which shock absorber, for example, includes a pressure tube surrounding a pressure chamber, containing a hydraulic damping fluid (oil); a piston, which is installed to be slidable in the pressure chamber of the pressure tube, thereby dividing the pressure chamber into a lower pressure chamber and an upper pressure chamber; an outer tube; an annular chamber, which is called a reservoir chamber, located between the pressure tube and the outer tube, wherein the chamber is filled with the same hydraulic fluid (oil) at its lower part and a compressible fluid pressurized to a predetermined pressure value (for example, air, nitrogen, etc.) at its upper part; an intermediate tube, which is installed on the pressure tube and surrounds a bypass chamber, which is connected to the upper pressure chamber through a connecting hole provided in the pressure tube; and a control valve, typically a solenoid valve, which is hydraulically connected to the bypass chamber on one side and to the reservoir chamber on the other side, and is arranged to control the passage of fluid between the bypass chamber and the reservoir chamber.

[0038] According to one embodiment, a pair of active suspensions 10 are associated with the rear axles of the vehicle (in the forward direction of the vehicle), while a pair of semi-active suspensions 12 are associated with the front axles (in the forward direction of the vehicle).

[0039] According to an alternative 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.

[0040] The hybrid suspension system according to the present invention may also include at least three vehicle sprung mass vertical acceleration sensors, and / or four wheel hub vertical acceleration sensors, and / or four suspension travel sensors (one for each suspension of the vehicle), and / or an electric power supply system 14 with an appropriate voltage (e.g. 48V) capable of powering the actuators of the active suspension 10, and / or an electric power system 16 with another appropriate voltage (e.g. 12V) capable of powering the actuators of the semi-active suspension 12, and / or an electronic control unit 18 for centrally controlling the hybrid suspension system (the actuators of the active suspension 10 and the actuators of the semi-active suspension 12).

[0041] According to one aspect of the present invention, a vehicle is provided, comprising: a pair of axles 8, 9, each axle being associated with a pair of wheels; a sprung mass supported by the axles 8, 9; and a hybrid suspension system according to any of the above-described embodiments, the hybrid suspension system being connected to the pair of axles 8, 9 so as to control the transmission of impacts from the axles 8, 9 to the sprung mass of the vehicle.

[0042] The results show that the suspension system of the present invention achieves significantly better performance than when both axles of the vehicle are equipped with semi-active suspension, while the performance is moderately reduced compared to when both axles of the vehicle are equipped with active suspension. In fact, as will be seen below, the performance gain (compared to when both axles of the vehicle are associated with semi-active suspension) is 50% higher than the loss caused by when both axles of the vehicle are associated with active suspension. Such a trade-off can also save a lot of cost without excessively compromising performance.

[0043] Specifically, Figure 2 The three suspension systems are respectively based on the vehicle's sprung mass roll angle (in degrees) and the vehicle's lateral acceleration (in m / s 2 , including the case where both axles of the vehicle are associated with semi-active suspension (the top red curve), the case where both axles of the vehicle are associated with active suspension (the bottom yellow curve), and the case where one axle is associated with semi-active suspension and the other axle is associated with active suspension (the middle blue curve, corresponding to the suspension system according to the invention). The above curves are obtained with a circular trajectory of the center of gravity of the vehicle with a radius of 100 meters.

[0044] This figure shows that, with the suspension system according to the invention, the improvement in roll angle reduction compared to the case where both axles are associated with semi-active suspensions is, on average, much greater than the performance loss compared to the case where both axles are associated with active suspensions. 2 , the gain in roll angle reduction compared to the case where both axles are associated with semi-active suspensions is 27%, while the performance loss compared to the case where both axles are associated with active suspensions is only 18%. It can be inferred from this that the combination of active and semi-active suspensions can produce effects other than the simple average of their performances, demonstrating the existence of synergies that can allow a significant improvement in the performance of a system that only adopts semi-active suspensions, and to a lesser extent a reduction in the performance of a system that only adopts active suspensions, while achieving important economic savings (this is due to replacing a pair of expensive active suspensions with a pair of cheaper semi-active suspensions).

[0045] Various aspects and embodiments of a vehicle hybrid suspension system according to the invention and a vehicle equipped with such a system have been described. It should be understood that each embodiment can be combined with any other embodiment. Furthermore, the invention is not limited to the described embodiments but can 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 semi-active suspensions (12) associated with the other of the two axles of the vehicle, such that each axle of the vehicle is associated with a pair of corresponding dedicated active suspensions or semi-active suspensions.

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

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

4. A system according to any of the preceding claims, comprising at least three vehicle sprung mass vertical acceleration sensors, and / or four wheel hub vertical acceleration sensors, and / or four suspension travel sensors, and / or a power supply system (14) capable of powering the actuators of the active suspension (10), and / or a power supply system (16) capable of powering the actuators of the semi-active suspension (12), and / or an electronic control unit (18) for centrally controlling the hybrid suspension system.

5. A vehicle comprising: - a pair of axles (8, 9), each axle being associated with a pair of wheels; - a sprung mass supported by said axles (8, 9); as well as - A hybrid suspension system according to any one of the preceding claims, associated with a pair of said axles (8, 9) so as to control the transmission of impacts from said axles (8, 9) to the sprung mass of the vehicle.

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