Power steering by wire system using an actuator made transparent by means of a local torque and / or force control loop

Abstract

The invention relates to a steer-by-wire power steering system (1), the system comprising a lower mechanism (10) and an upper mechanism (20), the lower mechanism (10) comprising a servo motor (11) and a steering wheel (12), the upper mechanism (20) comprising a steering wheel (22) and an auxiliary motor (21), the lower mechanism (10) being controlled in a closed loop with zero force through a lower local loop (30), the lower local loop (30) comprising a feedback branch (32), the feedback branch (32) measuring or estimating a contact point located downstream of the servo motor (11) and between the steering wheel (12) and a ground (2). (12C) the actual downstream force (F10_actual) upstream so as to make the servo motor (11) transparent, while the upper mechanism (20) is closed-loop controlled at zero torque through an upper local loop (40), the upper local loop (40) including a feedback branch (42) that measures or estimates the actual driver torque (T20_actual) between the auxiliary motor (21) and the steering wheel (22) so as to make the auxiliary motor (21) transparent, the lower (30) and upper (40) local loops being controlled by a single overall controller (50).

Description

Technical Field

[0001] The present invention relates to the general field of power steering systems for vehicles.

[0002] More specifically, the present invention relates to so-called "steer-by-wire" power steering systems, which are without any mechanical transmission device between an upper mechanism comprising a steering wheel on the one hand and a lower mechanism comprising an auxiliary electric motor acting mechanically on the steering wheel of the vehicle in order to change the yaw direction (i.e. the steering angle) of the steering wheel on the other hand. Background Art

[0003] In such steer-by-wire systems, it is known to ensure servo-control of the position of the underlying mechanism by measuring the angular position of the steering wheel and then defining and transmitting a corresponding set point by means of an electrical link with an auxiliary motor, which drives the underlying mechanism and thus the steering wheel to the desired position.

[0004] In order to ensure feedback to the steering wheel so that the driver can perceive the reaction forces caused in the lower mechanism by the steering operation and the contact of the wheel with the road, a second electric motor is provided in the upper mechanism, which is designed to rotatably drive the steering wheel.

[0005] Nevertheless, known power steering systems, in particular known steer-by-wire systems, often have some disadvantages.

[0006] Firstly, some mechanical phenomena, particularly possibly related to the inertial mass of the lower or upper structure, or to the friction inside said lower or upper structure, can make the driver feel a bit heavy during the operation.

[0007] However, the presence of power steering may make the tactile driving feel relatively unreal, in particular, certain tactile information called "road feel" is not faithfully transmitted to the driver, which intuitively informs the driver about the contact state between the wheels and the ground, in particular about the nature of the road coating (asphalt, gravel...) and the degree of adhesion of the wheels to the ground.

[0008] This feeling can be particularly unnatural in "steer-by-wire" systems, when there is no mechanical connection between the steering wheel and the wheels.

[0009] Therefore, the object of the present invention is to overcome the above-mentioned disadvantages and to provide a new power steering system, in particular a new steer-by-wire system combining light handling performance and faithful feeling of driving conditions. Summary of the invention

[0010] The object of the present invention is achieved by means of a power steering system, which comprises a first mechanism, referred to as the "lower mechanism", which comprises an auxiliary motor and a steering wheel, the auxiliary motor acting on the steering wheel to orient the steering wheel in yaw, the lower mechanism thus defining a lower kinematic chain, which extends from the auxiliary motor to a part of the steering wheel referred to as a contact portion, the contact portion being intended to come into contact with the ground so that the force and movement generated by the auxiliary motor are transmitted to the steering wheel via and along the actuation kinematic chain, the power steering system also comprising a second mechanism, referred to as the "upper mechanism", which comprises the steering wheel and has no mechanical connection with the lower mechanism to form an upper kinematic chain separate from the actuation kinematic chain, or is mechanically connected to the lower mechanism via a coupling member so as to form an auxiliary upper kinematic chain from the steering wheel to the coupling member, the upper kinematic chain forming a fork relative to the actuation kinematic chain, the power steering The system is characterized in that the lower mechanism is servo-controlled in terms of force through a closed loop called "lower local loop", which includes an input branch called "lower loop input branch" that allows defining an input force set point called "lower loop input force set point"; a feedback branch called "lower loop feedback branch" that measures or estimates a force called "actual downstream force" at a reference point called "lower loop reference point" located above the actuation kinematic chain, outside the control kinematic chain, downstream of the auxiliary motor and upstream of the contact of the steering wheel, the force representing at the reference point the force transmitted between the auxiliary motor and the steering wheel through the actuation kinematic chain, and the lower loop feedback branch then applies the actual downstream force in the form of feedback to the lower loop input force set point to form a lower loop actuation set point, which is applied to the auxiliary motor so that the actual downstream feedback force automatically follows the lower loop input force set point.

[0011] Advantageously, the use of a servo-control local loop, in particular a lower local loop suitable for servo-controlling the underlying mechanism in a closed loop and independently (comprising a feedback branch capable of capturing information (in this case force estimation, preferably force measurement) at a reference point remote from the actuator (here remote from the auxiliary motor and therefore closest to the contact between the wheel and the ground) when considering the underlying kinematic chain from upstream to downstream), allows the actuator of the mechanism involved (here the auxiliary motor driving the underlying mechanism) and, more generally, the mechanism to be transparent.

[0012] Transparency in this context refers to the ability of the system, and more specifically to the ability of the underlying mechanism actuated by the auxiliary motor to start moving when a very small external force (or corresponding external torque) is applied to the system, the system being thereby "disengaged" by the action of the external force (or correspondingly by the action of the external torque) without encountering any substantial resistance, thereby servo-controlling the system with zero force (or correspondingly zero torque).

[0013] Advantageously, such a transparent system can thus be manipulated in a responsive manner and without creating a sense of heaviness.

[0014] In particular, phenomena such as inertia or (dry and / or viscous) friction may affect the manipulation of the mechanism, but they are "stuck in the loop", that is, they intervene in a part of the actuation chain belonging to the servo-control closed loop, which is comprised here between the auxiliary motor (included) and the reference point where the feedback branch collects the force information, and the above phenomena therefore have an influence that is divided by the overall gain of the loop, which specifically includes the gain of the feedback branch, for which a very high value can be chosen.

[0015] Thus, said inertia and friction phenomena inside the mechanism are automatically compensated and therefore do not hinder the manipulation of said mechanism.

[0016] Similarly, the lower mechanism can be well-aware of external loads, particularly those applied by the wheels to the road, thereby improving the driver's ability to regain "road feel".

[0017] In addition, the implementation of force servo-control (or, where appropriate, torque servo-control) advantageously imparts to the underlying mechanisms, and more generally to the power steering system, a high degree of sensitivity, accuracy and responsiveness, to the extent that the force servo-control monitors and acts on the force, that is, on the cause of the movement, rather than on the position which is the result of said movement.

[0018] Furthermore, the proposed servo-control of the forces allows to faithfully capture and retransmit to the power steering system, in particular to the steering wheel, all force variations (including fast variations that may reach 20 Hz, 25 Hz, 30 Hz or even more than 30 Hz, such as variations in the external forces exerted by the ground on the wheels, such as those caused by the cycling of the vehicle on gravel-type rough coatings).

[0019] This rich frequency content of the actual downstream force signal obtained and used by the steering system therefore enables the driver to recover a particularly fine and precise road feel, which in particular enables the driver to perceive the properties of the road coating very well.

[0020] Finally, the arrangement provided by the invention is advantageously suitable for managing steering systems of the steer-by-wire type in which, as will be described in detail later, the invention allows, on the one hand, independent servo control of the force aspects of the lower mechanism to be performed solely by means of a lower local loop, and on the other hand, servo control of the torque aspects of the upper mechanism (and therefore also the steering wheel) to be performed solely by means of an upper local loop remote from the lower local loop, and the architecture is completed with a global controller capable of creating a connection between the local loops by generating two input setpoint components, respectively a force setpoint component and a torque setpoint component intended for the lower local loop and the upper local loop, respectively.

[0021] The invention thus allows the creation of a steer-by-wire system in which both the upper mechanism that actuates the steering wheel (and the steering wheel) and the lower mechanism act in a transparent manner, conferring lightness and precision to the steering while providing an excellent driving feel and a very good sense of contact interaction between the wheel and the ground (road feel). BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other objects, features and advantages of the present invention will appear in more detail when reading the following description and using the accompanying drawings provided for illustrative and non-limiting purposes, in which:

[0023] Figure 1 The principle of transparency of a mechanism with local loop servo control at zero force (or equivalently at zero torque) is shown according to a schematic diagram.

[0024] Figure 2 The schematic diagram shows Figure 1 The response of a transparent mechanism in terms of force (or torque), and therefore in terms of acceleration, as well as in terms of displacement velocity and position.

[0025] Figure 3 An example of a power steering system according to the invention is shown according to a schematic diagram. DETAILED DESCRIPTION

[0026] The present invention relates to a power steering system 1 .

[0027] The power steering system 1 is intended for a vehicle, in particular a motor vehicle, preferably a wheeled motor vehicle comprising at least one steered wheel 12, which may preferably also be a driving wheel.

[0028] In a particularly preferred manner, the steered wheels 12 are the front wheels of the vehicle.

[0029] like Figure 3As shown, the power steering system 1 comprises a first mechanism, referred to as the “lower mechanism” 10, comprising an auxiliary motor 11 and steering wheels 12 (more preferably two steering wheels 12, in this case a left steering wheel 12L and a right steering wheel 12R), the auxiliary motor 11 acting on the steering wheels 12 to orient the steering wheels 12 in yaw.

[0030] The lower mechanism 10 thus allows the desired steering angle A12 to be imparted to the steered wheels 12 .

[0031] In this case, preferably, the lower mechanism thus forms a power mechanism intended to generate a force greater than the manual force applied by the driver.

[0032] Preferably, the auxiliary motor 11 is an electric motor, such as a brushless motor.

[0033] Preferably, it consists of a rotary electric motor.

[0034] The lower mechanism 10 defines a lower kinematic chain L10, which extends from the auxiliary motor 11 to a portion 12C of the steering wheel called the contact portion 12C, which is intended to come into contact with the ground 2 so that the force and movement generated by the auxiliary motor 11 are transmitted to the steering wheel 12 via and along the lower kinematic chain L10.

[0035] As a preferred example, the lower mechanism 10, and more specifically the lower kinematic chain L10, may include a rack 13 driven by an auxiliary motor 11, and at least one end 13L, 13R of the rack 13 is connected to a steering rod 14, which in turn transmits force and displacement to the steering wheel 12.

[0036] Preferably, the rack 13 is mounted in a steering housing 3 fixed to the vehicle and guided in translation according to its longitudinal axis.

[0037] The auxiliary motor 11 may be coupled to the rack 13 via a reducer 15 (or any other suitable mechanical coupling member, such as a gear reducer 15 or a ball screw reducer 15 ).

[0038] Preferably, a steering tie rod 14 connects the rack 13 to a deflectable steering knuckle 16 , which in turn carries the steered wheel 12 .

[0039] According to a possible embodiment, the lower kinematic chain L10 may thus include, from upstream to downstream, Figure 3As shown: an auxiliary motor 11, a reducer 15 (or any other suitable mechanical coupling member), a rack 13 (or at least a portion of the rack 13 located between the reducer 15 and the tie rod 14), a steering tie rod 14, a corresponding steering knuckle 16, and then a steering wheel 12 carried by the steering knuckle 16 (at least the rim of the steering wheel 12).

[0040] Typically, the lower kinematic chain L10 is considered to be in an ascending direction, oriented from upstream to downstream, when moving away from the actuator (here the auxiliary motor 11) along the lower kinematic chain L10 in order to approach the actuator interacting with the external environment of the mechanism 10 under consideration (that is, here approaching the contact portion 12C of the steering wheel 12).

[0041] Therefore, the assist motor 11 preferably forms the upstream end of the lower kinematic chain L10, and the contact portion 12C of the steering wheel 12 forms the downstream end of the lower kinematic chain L10.

[0042] Alternatively, without departing from the scope of the present invention, a shorter lower kinematic chain L10 can of course be considered, in which, for example, the auxiliary motor 11 can act directly on the steering knuckle 16 via the reducer 15, but not through the rack 13, and preferably neither through the rack 13 nor through the steering tie rod 14.

[0043] According to such a variant, a given auxiliary motor 11 can individually and directly control the yaw orientation of a single steered wheel 12 via the steering knuckle 16 .

[0044] Still according to this variant (but this variant will include (at least) two steering wheels 12, typically two front steering wheels), a different auxiliary motor 11 can be associated with each of the steering wheels 12, that is, two different auxiliary motors 11 are provided, which respectively and individually control the yaw direction of the relevant steering wheel 12.

[0045] However, for ease of description, reference is preferably made to a power steering system 1 in which the lower mechanism 10 comprises a rack 13 allowing the actuation of two steering tie rods 14 respectively connected to each of the ends 13L, 13R of said rack, each of which is associated with a steering knuckle 16 and a steered wheel 12.

[0046] like Figure 3 As shown, the power steering system 1 further comprises a second mechanism, referred to as “upper mechanism” 20 .

[0047] The upper structure 20 includes a steering wheel 22 .

[0048] The steering wheel 22 allows the driver to manipulate the power steering system 1 and control a desired steering angle A12 .

[0049] The steering wheel 22 also enables the driver to feel by touch the reactions of the power steering system 1 and thus intuitively infer information about the vehicle's environment ("road feel"), more specifically, information about the properties of the ground 2 on which the vehicle is circling and information about the adhesion of the steering wheel 12 to the ground 2.

[0050] Of course, for convenience, reference will be made to a "steering wheel" 22, bearing in mind that any suitable steering device other than a steering wheel, such as a joystick, may be used for the same purpose.

[0051] Preferably, therefore, the upper mechanism 20 corresponds to the control mechanism (in contrast to the lower mechanism which forms the power mechanism).

[0052] According to a possible implementation, there is no mechanical connection between the upper mechanism 20 and the lower mechanism 10, thereby forming an upper kinematic chain L20 separated from the lower kinematic chain L10.

[0053] In this respect, in a particularly preferred manner, the power steering system 1 forms a power steering system of a “steer-by-wire” configuration without any mechanical connection between the upper structure 20 and the lower structure 10 .

[0054] In such a steer-by-wire system, the steering wheel 22 is not engaged on the underlying structure 20 .

[0055] Therefore, the connection between the steering wheel 22 and the steering wheel 12, and more generally, the functional connection between the upper mechanism 20 and the lower mechanism 10, that is, the connection that allows the position of the steering wheel 22 and the tactile sensation restored by the steering wheel 22 to be associated with the actual position of the steering wheel 12 (the position of the lower mechanism 10) and the forces applied to the steering wheel 12 and the lower mechanism 10, is achieved virtually (exclusively) by electrical signals.

[0056] Alternatively, the upper mechanism 20 may instead be mechanically coupled to the lower mechanism 10 via the coupling member 4 , thereby forming an auxiliary upper kinematic chain L20 from the steering wheel 22 upward to the coupling member 4 , which forms a fork L20B relative to the lower kinematic chain L10 .

[0057] For example, the coupling member 4 may be in the form of a pinion 4 meshing on the rack 13 and fixed to a steering column 5 driven by the steering wheel 22 .

[0058] According to one possible embodiment, it is possible to consider using a clutch device 6 which selectively allows the lower mechanism 10 to be mechanically connected to the upper mechanism 20 or mechanically separated from the upper mechanism 20, thereby being able to select whether to configure the power steering system 1 in a steer-by-wire manner (the device 6 is in a disengaged clutch state) or in a mechanically connected manner (the device 6 is in a clutch state).

[0059] In particular, a power steering system 1 can be provided, which is arranged to operate normally in a steer-by-wire manner, but is nevertheless arranged to mechanically connect the upper mechanism 20 to the lower mechanism 10 again, more specifically, to connect the steering wheel 22 to the steering column 5 again, and in particular to the connecting member 4 connected to the rack 13 as a backup device in the event of failure of the steer-by-wire operation.

[0060] In contrast, as described above, a “pure” steer-by-wire power steering system 1 may be provided that is entirely devoid of any coupling member 4 (and entirely devoid of any steering column 5 engaged on the rack 13 ).

[0061] According to the invention, the lower mechanism 10 is servo-controlled in terms of force by means of a closed loop called “lower local loop” 30 .

[0062] For the convenience of description, the set formed by the lower-level mechanism 10 and the lower local loop 30 that manipulates it may be referred to as a "lower-level subsystem".

[0063] Advantageously, the choice of servo control in terms of force or, equivalently, torque, allows the actuation of the lower mechanism 10 to be adjusted by aligning the desired stress state with the reference point P10 of the lower mechanism (that is, by aligning the magnitude of the force transmitted by means of the lower kinematic chain L10 with the reference point P10).

[0064] This force servo control allows detecting and managing the forces applied to the lower mechanism 10, more specifically the external forces generated by the reaction of the ground 2 on the steering wheels 12 and transmitted through the lower mechanism 10 along the lower kinematic chain L10.

[0065] As described above, by having a force-based servo control, i.e., based on the movement of the underlying mechanism 10 which can be immediately perceived in real time rather than on the cause of a displacement (position change) (the above movement is the result of the application of a force which can only be perceived later, and a certain delay is required to complete a movement of sufficient magnitude), a servo control with a particularly rapid and accurate reaction force is advantageously obtained.

[0066] Furthermore, this type of servo control allows the actuator of the lower mechanism 10 (ie the auxiliary motor 11) and, more generally, the lower mechanism 10 to be made transparent, as will be described in detail later.

[0067] The lower local loop 30 comprises an input branch, called “lower loop input branch” 31 , which allows defining an input force setpoint, called “lower loop input force setpoint” F10_set.

[0068] The lower local loop 30 also comprises a feedback branch 32 , called “lower loop feedback branch”, which measures or estimates a force, called “actual downstream force” F10_actual, at a reference point, called “lower loop reference point” P10 .

[0069] The actual downstream force F10_actual represents, at the reference point P10 , the force transmitted between the auxiliary motor 11 and the steering wheel 12 via the lower kinematic chain L10 (or conversely, represents the force transmitted from the steering wheel 12 to the auxiliary motor 11 ).

[0070] In practice, this actual downstream force F10_actual corresponds to the force provided by the lower mechanism 10 at the time considered to counteract (in particular, in balance while maintaining a given steering angle A12, or even in excess while changing the steering angle A12) the resistance force called “external force” F_ext exerted on said lower mechanism 10 by the vehicle's environment, in particular by the ground 2.

[0071] In practice, the external force F_ext is substantially caused by the contact between the contact portion 12C of the steering wheel 12 and the ground 2 , or by the contact between the steering wheel 12 and an obstacle present in the environment of the steering wheel 12 .

[0072] In general, the actual downstream force F10_actual may correspond to a tensile or compressive force exerted by the associated steering tie rod 14 on the ends 13L, 13R of the rack connected to said tie rod 14 .

[0073] Preferably, the actual downstream force F10_actual is measured by means of a suitable force sensor 17 placed at the lower circuit reference point P10.

[0074] For example, the force sensor 17 may include a strain gauge, or may include a photoelasticity measuring optical sensor.

[0075] Preferably, if Figure 3 As shown, two force sensors 17L, 17R can be used, namely a first left force sensor 17L, which allows measuring the force applied to the left end 13L of the rack 13 by the left steering rod 14L (connected to the left steering wheel 12L), and a second right force sensor 17R, which allows measuring the force applied to the opposite right end 13R of the rack 13 by the opposite right steering rod 14R (connected to the right steering wheel 12R).

[0076] In such a configuration, the actual downstream force F10_actual may be determined more accurately by means of the actual downstream force calculation unit 70 , advantageously from two measurements performed simultaneously on each of the two force sensors 17L, 17R.

[0077] For example, the actual downstream force F10_actual may be considered to be the sum or difference (depending on the sign of the captured information) of the value of the force F10_actual_L measured by the left force sensor 17L and the value of the force F10_actual_R measured by the right force sensor 17R.

[0078] It should be noted that the left F10_actual_L and right F10_actual_R forces should have opposite signs because one of the tie rods (the left tie rod 14L when the power steering system 1 turns left) is in compression and the other tie rod (the right tie rod when turning left) is in tension.

[0079] According to a variant of realization of the invention, instead of carrying out the measurement of the actual downstream force F10_actual by the force sensor 17 , it is possible to use an estimate of said actual downstream force F10_actual provided by a suitable algorithm designed to provide a true estimate of said actual downstream force at the reference point P10 considered.

[0080] Such an algorithm allows to virtually estimate the forces at the lower-loop reference point P10 from data other than the force measurements already performed at said reference point 10. Thus, the power steering system 1 may, where appropriate, not have any force sensor 17 at the lower-loop reference point P10.

[0081] For example, if the lower circuit reference point P10 used is located at the end 13L of the rack 13 and / or at the height of the steering tie rod 14, then a force estimation algorithm at the tie rod can be used, as described in the application WO-2016 / 005671 filed by the applicant.

[0082] Thus, a physical measurement is preferably performed by using a force sensor 17 or several force sensors 17 (preferably two force sensors 17L, 17R, one on each side of the rack 13), rather than a virtual estimation by an algorithm, in order to obtain a better performance of the system according to the invention.

[0083] Furthermore, regardless of whether the actual downstream force P10_actual is measured by means of the sensor 17 or evaluated by means of an appropriate algorithm, the lower loop reference point P10 is located on the lower kinematic chain L10 and outside the upper kinematic chain L20 , downstream of the auxiliary motor 11 and upstream of the contact portion 12C of the steering wheel 12 .

[0084] In practice, the reference point P10 should be chosen such that the actual downstream force P10_set evaluated therein actually represents the force exerted on the steered wheel 12 by the underlying kinematic chain L10 .

[0085] In practice, in order to obtain a true estimate of the force and improve the transparency of the lower mechanism 10, the lower loop reference point P10 is preferably placed as far downstream as possible along the lower motion chain L10, farthest from the actuator (auxiliary motor 11), and closest to the steering wheel 12, more specifically, closest to the contact area 12C, that is, the closest area, here referring to the (downstream) terminal area of ​​the lower motion chain L10, where the external environment of the vehicle applies an external force F_ext to the lower mechanism 10.

[0086] Thus, the actuator branch for executing the force setpoint can be included in the lower local circuit 30 , which is the longest possible part of the lower kinematic chain L10 .

[0087] In this case, a portion of the lower layer kinematic chain L10 is thereby integrated into the lower local loop 30, that is to say is "stuck in the loop", extending from the auxiliary motor 11, which forms the upstream input point of this layer, in which the force set points F10_set, F10_mot can be adjusted and applied to the actuator (auxiliary motor 11), until a downstream reference point P10 forming the output point of the loop, the reference point P10 being located downstream of the auxiliary motor and downstream of a portion of the actuator member (specifically the rack 13) driven by the auxiliary motor 11.

[0088] At the level of the reference point P10 , the actual effect on the tie rod 14 and the steering wheel 12 is monitored by the implementation of the force setpoints F10_set, F10_mot by the auxiliary electric motor 11 .

[0089] More generally, at the level of the reference point P10, the effects of the combined actions of the actuator (auxiliary motor 11) and the environment of the system 1 on the elements of the lower kinematic chain L10 outside the lower local loop 30 are monitored, when these elements are located downstream of the reference point P10, beyond the part of the lower kinematic chain L10 included in the lower local loop 30.

[0090] Preferably and specifically, if the lower kinematic chain L10 passes through an intermediate member between the auxiliary motor 11 and the steering knuckle 16 , for example through the rack 13 , the lower loop reference point P10 , and more specifically the force sensor 17 used for the feedback branch 32 , is different from and physically distant from a possible torque sensor integrated on the shaft of the auxiliary motor 11 .

[0091] Similarly, the lower loop reference point P10, and more specifically the force sensor 17 used by the feedback branch 32, is different from and physically distant from a possible steering wheel torque sensor 27 that would be associated with the steering wheel 22, which is located on the steering column carrying the steering wheel and is specifically used to measure the torque T_driver applied by the driver to the steering wheel 22.

[0092] According to the invention, the lower-loop feedback branch 32 then applies the actual downstream force F10_actual in the form of feedback at the lower-loop input force set point F10_set, thereby forming the lower-loop actuation set point F10_mot, which is applied to the auxiliary motor 11, so that the actual downstream feedback force F10_actual automatically follows the lower-loop input force set point F10_set.

[0093] Therefore, reference Figure 3 , preferably having:

[0094] F10_mot = F10_set - F10_actual

[0095] The signs + (positive) and − (negative) are chosen here merely by convention to indicate the corrective effect of the feedback branch 32 .

[0096] like Figure 3 As shown, the lower-circuit local controller 33 converts the lower-circuit actuation setpoint F10_mot into a current setpoint applied to the auxiliary motor 11 .

[0097] Preferably, the lower loop local controller 33 uses a law or a map at this time, which may also depend on vehicle-related parameters, such as the longitudinal speed, lateral acceleration, yaw speed, etc. of the vehicle.

[0098] The law or map may also depend on parameters specific to the power steering system 1 , in particular specific to the underlying subsystems 10 , 30 , such as the rotational speed of the auxiliary motor 11 , the torque generated by the auxiliary motor 11 , the inertial mass of all or part of the components of the underlying mechanism 10 , etc.

[0099] These parameters (related to the vehicle and / or power steering system) are Figure 3 The relevant inputs of the power steering system 1 are shown labeled “data”.

[0100] For example, the parameter “data” may be provided to the power steering system 1 by other onboard systems (such as an electronic stability program (ESP) or an anti-lock braking system (ABS)) on the vehicle through an onboard computer network.

[0101] Preferably, according to a feature that may constitute the invention in its own right, when considering a power steering system 1 comprising a closed lower local loop 30, the lower local loop 30 comprises a sub-branch 31A of the lower loop input branch 31, said sub-branch introducing a lower loop input reference F10_ref representing an input force setpoint having a zero value, so as to enable servo-control of the lower local loop 30 with zero force:

[0102] F10_ref=0

[0103] This input reference F10_ref having a zero value (preferably a constant) allows to impart a high transparency on the lower mechanism 10 , and more specifically on the lower kinematic chain portion L10 captured in the lower local loop 30 .

[0104] In practice, when the lower mechanism 10 is initially in a state of equilibrium, a change in the external force F_ext acting on the steering wheel 12, and more generally on a part of the lower kinematic chain L10 not included in the lower local circuit 30, occurs, for example because the steering wheel 12 hits an obstacle present on the ground 2. This change in the external force F_ext results in a change in the value of the actual downstream force F10_actual at the reference point P10, which therefore deviates in practice from the input force set point F10_set at the time considered.

[0105] Since the feedback branch 32 changes the actuation set point F10_mot by reflecting the change in the actual downstream force F10_actual, the auxiliary motor 11, which is automatically adjusted in an independent manner by the lower local loop 30, then immediately corrects its action, so that the auxiliary motor 11, more generally, the part of the lower mechanism 10 included in the lower local loop 30, is disengaged under the action of the external force F_ext without any resistance to absorb the change in the magnitude of the external force F_exet, thereby returning the actual downstream force F10_actual to the value of the desired input force set point F10_set.

[0106] Advantageously, in the absence of another (non-zero) force setpoint component at the input 31 of the lower loop 30 , the lower loop input reference F_ref is applied by default, here having the value zero.

[0107] Therefore, in this case, the auxiliary motor 31 is servo-controlled to keep the actual downstream force F10_actual at a zero value or a substantially zero value.

[0108] Therefore, when the external force F_ext tends to cause the application of a non-zero actual downstream force, the feedback branch 32 immediately detects and transmits this change in the actual downstream force F10_actual so as to generate an actuation set point F_mot which, when applied to the auxiliary motor 11, enables the latter to act on the lower mechanism 10 to absorb the effect of the external force F_ext, thereby returning the actual downstream force F10_actual to zero.

[0109] Therefore, in practice, the auxiliary motor 11 reacts so as not to oppose any resistance to the variation of the external force F_ext, but rather to accompany the variation of the external force F_ext so as to avoid the generation of stresses and, in this case, the emergence or maintenance of a non-zero actual downstream force F10_actual.

[0110] Therefore, once a small external force F_ext is applied thereto, the lower structure 10 moves spontaneously in a desired direction under the action of the external force F_ext.

[0111] A similar principle applies when, in addition to the input reference value F10_ref having the value zero, the lower-loop input setpoint F10_set also takes into account, by means of a second sub-branch 31B of the input branch 31, a component of the force setpoint called "lower-loop force setpoint dynamic component" F10_dyn (generally allowing the driver's steering intention and, more generally, the driver's operation of the steering wheel 22 to be reflected).

[0112] Again, when a change in the external force F_ext occurs (temporarily causing the actual downstream force F10_actual to move away from the input force setpoint value F10_set, which, in equilibrium, is equal to the dynamic component F10_dyn (constant at the time considered), the feedback branch 32 allows the actuation setpoint F10_mot to be changed so that the auxiliary motor 11 causes the lower mechanism 10 to disengage and the actual downstream force F10_actual to return to the dynamic component value F10_dyn.

[0113] Therefore, the auxiliary motor 11 does not resist any resistance to the displacement of the lower mechanism 10 necessary and sufficient to absorb the changes in the external force F_ext, thus allowing the difference between the actual downstream force F10_actual and the input force set point F10_set, i.e. the difference here between the actual downstream force F10_actual and the force set point dynamic component F10_dyn, to be maintained at a substantially zero value.

[0114] In any case, the lower local loop 30, which is servo-controlled at zero force, therefore allows the action of the auxiliary motor 11 to be corrected in real time with high responsiveness, so that the auxiliary motor 11 has almost no resistance to the displacement of the lower mechanism 10 caused by the change of the external force F_ext, thereby promoting the disengagement of the lower mechanism 10 with the help of the change of the external force F_ext.

[0115] This self-regulation gives the underlying mechanism 10 a high degree of transparency and in particular enables it to react to all variations in the external force F_ext, being sensitive to the interaction between the steering wheel 12 and the ground characterized by the “road feel” and restoring this interaction in a very clear and recognizable way.

[0116] This same self-regulation performed with zero force also enables the driver to operate the power steering system 1 effortlessly, in particular without being disturbed by the inertia of the lower mechanism or by the internal friction occurring in the portion of the lower mechanism 10 included in the lower local circuit 30 .

[0117] For ease of presentation, the friction, specifically the dry friction (Coulomb friction) F_dry, T_dry and the viscous friction F_visc, T_visc (proportional to the displacement speed of the mechanism 10 under consideration, more specifically to the displacement speed of the rack 13) is Figure 1 and 3 Indicated by friction pad.

[0118] It should be noted that, according to a variant, the lower-loop input reference F10_ref may be set to a non-zero offset value in order to introduce a corrective effect in the lower-loop input setpoint F10_set.

[0119] In order to better understand the present invention, reference will be made to Figure 1 and 2 Describe the concept of "transparency" in more detail.

[0120] According to the present invention, Figure 1 and 2 The transparency concept shown in is advantageously applied (or adapted) to the lower mechanism 10 , or the upper mechanism 20 , or preferably to each of the two mechanisms 10 , 20 , which is actuated by the auxiliary motor 11 .

[0121] For the sake of convenience, reference will therefore be made to the constituent elements of the mechanisms 10 , 20 .

[0122] Figure 1 Mechanisms 10 , 20 driven by actuators, represented as electric motors 11 , 21 are illustrated.

[0123] The mechanisms 10 , 20 are servo-controlled by closed loops called “local loops” 30 , 40 .

[0124] Servo control is performed in terms of force (identified by the letter "F"), or equivalently, in terms of torque (identified by the letter "T").

[0125] To this end, the local circuit 30 , 40 comprises an input branch 31 , 41 for defining an input setpoint (force setpoint or respectively torque setpoint), and a feedback branch 32 , 42 .

[0126] The input branches 31 , 41 here allow defining an input reference F10_ref, T20_ref representing zero force (correspondingly zero torque) for performing a servo control with zero force (correspondingly zero torque).

[0127] The feedback branches 32 , 42 evaluate (eg by means of a suitable algorithm) or preferably measure the actual force F10_actual (eg actual torque T20_actual) at the reference point P10 , P20 of the mechanism 10 , 20 , eg by means of a suitable force sensor 17 (eg torque sensor 27 ).

[0128] The gain applied by the force sensor 17 (respectively the torque sensor 27 ) or the evaluation algorithm is denoted by “K”.

[0129] The reference point P10 , P20 is located downstream of the actuator (electric motor) 11 , 21 along a kinematic chain L10 , L20 which couples said actuator 11 , 21 to an actuator 12 , 22 , here typically a steering wheel 12 or a steering wheel 22 .

[0130] The actuators 12 , 22 form a (terminal) interface between the mechanisms 10 , 20 and the external environment of the mechanisms 10 , 20 , through which the external environment (here usually the ground 2 or the corresponding vehicle driver) can apply an external force F_ext and a corresponding external torque T_ext to the mechanisms 10 , 20 in response to the actuators (motors) 11 , 21 .

[0131] The mass or equivalent moment of inertia of a portion of the mechanism 10, 20 included in the local loop 30, 40, that is, the upstream portion of the kinematic chain L10, L20 extending from the actuator (motor) 11, 21 to the reference point P10, P20 is denoted by J1.

[0132] The mass or equivalent moment of inertia of the (remaining) part of the mechanism 10, 20 is denoted as J2, and the remaining part of the mechanism 10, 20 is located outside the local loop 30, 40, that is, in the downstream part of the motion chain L10, which extends from the reference points P10, P20 to the (terminal) interface of the mechanism 10, 20 with the external environment, more specifically, to the contact area with the actuator 12, 22 and the external environment (ground 2, corresponding driver).

[0133] The total gain of the local loops 30, 40 is represented by G A .

[0134] For simplicity, the total gain G A This is represented here in the form of a single transfer function placed on the feedback branches 32 , 42 .

[0135] When the motion of the actuator 12, 22 is a rotational motion, the angular position, angular velocity and angular acceleration of the actuator 12, 22, more specifically the steering wheel 22, are expressed as θ J2 , and

[0136] Similarly, with respect to translational motion, the linear position, linear velocity, and linear acceleration of the actuators 12, 22 will be represented as X and J2 , and

[0137] It should be emphasized that, in the case where the lower mechanism 10 includes a rack 13, and in particular taking into account the (relative) stiffness of the rack 13 and of the kinematic chain portion L10 connecting the rack 13 to the steering knuckle 16, the position, velocity and acceleration of the rack 13 can advantageously be regarded as representing the position, velocity and acceleration of the downstream portion of the lower mechanism 10 including the tie rod 14, the steering knuckle 16 and the steering wheel 12.

[0138] The force, respectively the torque, of the viscous friction (proportional to the displacement speed of the mechanical member under consideration) exerted on the (upstream) portion of the mechanism 10 , 20 comprised in the local circuit 30 , 40 is denoted F_visc, respectively T_visc.

[0139] The force or respectively the torque of dry friction exerted on the (upstream) portion of the mechanism 10 , 20 comprised in the local circuit 30 , 40 is denoted F_dry, respectively T_dry.

[0140] We believe that R1 = T_visc + T_sec

[0141] “s” represents the Laplace variable.

[0142] refer to Figure 1 We obtain the following expression:

[0143]

[0144] If a sufficiently high overall gain G is chosen A or approaching infinite total gain, the above expression can be simplified to obtain, in a first approximation:

[0145]

[0146] Therefore, the reaction of the mechanism 10, 20 to the application of the external force F_ext, T_ext, and more specifically the reaction of the displacement of the (downstream) part of the mechanism 10, 20 located outside the local circuit 30, 40 depends only on the inertia J2 of said downstream part outside the local circuit 30, 40.

[0147] The upstream part of the mechanism 10 , 20 extending from the actuator (motor) 11 , 21 up to the reference point P10 , P20 thus becomes transparent since it does not present any resistance to movement against variations in the external forces F_ext, T_ext.

[0148] Advantageously, if Figure 2 As shown, the transparency enables the mechanism 10 , 20 to react immediately to the application of the external forces F_ext, T_ext by spontaneous displacement.

[0149] In particular, the external force step F_ext, T_ext will be transformed without delay into an acceleration step which is proportional to the external force step F_ext, T_ext (according to the inverse of the product of the inertial mass J2).

[0150] Therefore, a velocity ramp and a position correction quadratic curve are obtained, also without any delay.

[0151] Furthermore, the formula simplification given above allows the elimination of the expression R1 from the equation, that is to say automatically compensating for the influence of the friction F_dry, T_dry, F_visc, T_visc inside the portion of the mechanism 10 , 20 included in the local circuit 30 , 40 , thus making said friction insignificant.

[0152] When considering the application of this transparency principle to the lower local circuit 30 and the lower mechanism 10 actuated by the auxiliary motor 11, we obtain:

[0153]

[0154] in:

[0155] X_rack refers to the position of the rack 13 (here, the linear position translated along the steering housing 3);

[0156] J_rod represents the inertial mass of a portion of the lower mechanism 10 located downstream of the reference point P10, and more specifically, represents the inertial mass of a portion of the lower mechanism 10 located downstream of the force sensor 17. Therefore, J_rod can represent the inertial mass of the subassembly formed by the tie rod 14, the steering knuckle 16, and the steering wheel 12.

[0157] Similarly, when considering the application of transparency to the servo control of the upper mechanism 20 in terms of torque through a closed loop, the following formula can be obtained, where in addition to the steering wheel 22, the upper mechanism 20 also includes an auxiliary motor 21, which is arranged to actuate the upper mechanism 20 to restore the force representing the reaction force of the lower mechanism to the steering wheel 22:

[0158]

[0159] in:

[0160] θ SW refers to the angular position of the steering wheel 22;

[0161] T_driver refers to the external torque T_ext applied to the steering wheel 22 by the driver.

[0162] J SW refers to the moment of inertia of a portion of the upper structure 20 situated downstream of the reference point P20, which in this case comprises the steering wheel 22 and, where appropriate, the portion of the steering column on which said steering wheel 22 is mounted.

[0163] It should also be noted that the smaller the inertial mass J2 of the downstream portion of the mechanism 10, 20 that is not included in the local loop 30, 40, the smaller the resistance of the mechanism 10, 20 to movement, and therefore the better the reaction of the mechanism 10, 20 to the application of external forces F_ext, T_ext, that is, the higher the sensitivity of the mechanism 10, 20, and therefore the stronger the ability of the system 1 to restore a better road feel.

[0164] In order to minimize the inertial mass J2, as described above, we will seek to include the largest possible portion of the mechanism 10, 20 in the local loop 30, 40, thereby placing the reference points P10, P20 of the feedback branches 32, 42 as far downstream as possible of the corresponding kinematic chains L10, L20, so as to include the longest possible portion of the kinematic chains L10, L20 in the local loop 30, 40.

[0165] We will therefore seek to correctly position the reference points P10 , P20 , and more specifically the force and / or torque sensors 17 , 27 downstream of the electric motors 11 , 21 .

[0166] Therefore, in the case of the lower mechanism 10, we will seek to place the lower loop reference point P10 downstream of the auxiliary motor 11, and preferably, if the mechanism 10 includes a member 4 for connecting to the upper kinematic chain L20, L20B, then along the lower kinematic chain L10, downstream of the connecting member 4 (downstream of the bifurcation between the lower kinematic chain and the upper kinematic chain), closest to the contact area 12C between the steering wheel 12 and the ground 2.

[0167] Therefore, if preferably, the lower-level motion chain L10 includes a rack 13 driven by an auxiliary motor 11, and at least one end 13L, 13R of the rack 13 is connected to a steering rod 14, and the steering rod 14 in turn transmits the force and displacement to the steering wheel 12, then the lower loop reference point P10 for measuring or estimating the actual downstream force F10_actual is preferably located downstream of the rack 13 in the direction of the steering wheel 12, for example, at the junction between one end 13L of the rack and the steering rod 14, on the steering rod 14, or downstream of the steering rod 14.

[0168] As mentioned above, if an algorithm allowing virtual estimation is selected, the lower loop reference point P10 corresponds to a point on the hierarchy where the algorithm estimates the actual downstream force F10_actual.

[0169] If the force is measured physically by means of force sensor 17 , reference point P10 corresponds to the physical position of force sensor 17 .

[0170] By the way, regardless of whether the lower-level mechanism 10 includes a rack 13 and / or one (or several) tie rods 14, if the lower-level motion chain L10 includes a steering knuckle 16 that carries the steering wheel 12, the lower-loop reference point P10 for measuring or estimating the actual downstream force F10_actual can advantageously be located on the steering knuckle 16.

[0171] The steering knuckle 16 embodies an orientation axis of the steered wheel 12 , here a yaw axis, by means of which the steering angle of the steered wheel 12 can be varied.

[0172] According to another possibility, it is possible to consider placing the lower circuit reference point P10 on the steering wheel 12 itself, for example on the rim of the steering wheel or even at the level of the tire of said steering wheel 12, closest to the rolling tread of said tire and therefore to the contact area 12C with the ground 2.

[0173] According to a preferred feature which may constitute the invention in its own right, in particular according to whether the lower mechanism 10 is servo-controlled by means of a closed lower local circuit 30 as described above, the upper mechanism 20 comprises, in addition to the steering wheel 22 , an auxiliary electric motor 21 .

[0174] The auxiliary motor 21 is different from the auxiliary motor 11 of the lower mechanism 10 .

[0175] In particular, this separation allows the creation of a servo control loop 40 dedicated to the upper mechanism 20 , distinct from the lower local loop 30 , and forming, where appropriate, a “steer-by-wire” steering system.

[0176] Preferably, if Figure 3 As shown, the upper mechanism 20 can be servo-controlled in terms of torque by means of a closed loop called an “upper local loop” 40 .

[0177] For the convenience of description, the set formed by the upper-level mechanism 2 and the manipulation thereof may be referred to as an "upper-level subsystem".

[0178] As indicated above with specific address with reference to the lower local loop 30 , servo-control in terms of torque (like servo-control in terms of force) allows imparting responsiveness and transparency to the upper mechanism 20 .

[0179] The steering wheel 22 is therefore light and easy to handle, since it offers almost no “parasitic” inherent resistance to the external torque Text=T_driver applied by the driver (in particular, there is no resistance associated with the internal friction T_visc, T_dry of the upper structure 20 or with the appropriate inertial mass of said upper structure 20 ), while being able to precisely and accurately transmit the road feel to the driver.

[0180] The upper local loop 40 comprises an input branch, called “upper loop input branch” 41 , which allows defining an input torque setpoint, called “upper loop input torque setpoint” T20_set.

[0181] The upper local loop 40 also includes a feedback branch called the “upper loop feedback branch” 42, which measures or estimates a torque called the “actual driver torque” T20_actual at a reference point called the “upper loop reference point” P20 located between the auxiliary motor 21 and the steering wheel 22 (more specifically, located between the downstream of the auxiliary motor 21 and the upstream of the steering wheel 22), which at the reference point P20 represents the torque T_driver applied by the driver to the upper mechanism 20 via the steering wheel 22.

[0182] In practice, one may consider T20_actual = T_driver, with T_driver taking a non-zero value, for example when the driver actively acts on the steering wheel to achieve or maintain a desired steering angle, or taking a zero value, typically when the vehicle is traveling in a straight line.

[0183] Preferably, the upper loop reference point P20 is located in close proximity to the steering wheel 22 , for example, on the steering column portion that carries the steering wheel 22 .

[0184] Again, it may be considered to use a steering wheel torque estimation algorithm to virtually estimate the actual driver torque T20_actual based on other parameters.

[0185] Nevertheless, preferably, the actual driver torque T20_actual will be measured by a suitable torque sensor 27, such as a torque electromagnetic sensor measuring the deformation of a torsion bar placed on the steering column.

[0186] The position of the torque sensor 27 physically corresponds to the upper loop reference point P20.

[0187] It should be emphasized that the upper loop reference point P20 is different from the lower loop reference point P10 and therefore, where appropriate, the force sensor 17 used in the lower local loop 30 is different and remote from the torque sensor 27 used in the upper local loop 40 .

[0188] More generally, therefore, the upper local circuit 40 and the lower local circuit 30 are well separated so as to be able to operate independently of each other and in particular to be able to servo-control their respective actuators (motors) 11 , 21 in an independent manner.

[0189] Advantageously, after estimating or measuring the actual driver torque T20_actual, the upper-loop feedback branch 42 then applies said actual driver torque T20_acutal in the form of feedback to the upper-loop input force setpoint T20_set to form the upper-loop actuation setpoint T20_mot, which is applied to the auxiliary drive 21 so that the actual driver torque T20_acutal (and the driver torque T_driver) automatically follows the upper-loop input torque setpoint T20_set.

[0190] It should be emphasized that the characteristics, operation and advantages of the upper local loop 40 may be advantageously inferred from those described with reference to the lower local loop 30 , mutatis mutandis.

[0191] In fact, we find similar functions and advantages in the upper local loop 40 as in the lower local loop 30 .

[0192] Therefore, reference Figure 3 , preferably having:

[0193] T20_mot = T20_set - T20_actual

[0194] The signs + (positive) and − (negative) are chosen here merely by convention to indicate the corrective effect of the feedback branch 42 .

[0195] like Figure 3 As shown, an upper-loop local controller 43 , which is preferably different from the lower-loop local controller 33 , converts the upper-loop actuation setpoint T20_mot into a current setpoint applied to the auxiliary electric motor 21 .

[0196] Preferably, at this time, the upper loop local controller 43 uses a law or a mapping diagram, which may also depend on vehicle-related parameters "data", such as longitudinal speed, lateral acceleration, yaw speed, etc. and / or parameters "data" specific to the power steering system 1, more specifically, parameters specific to the upper-level subsystems 20, 40, such as the rotational speed of the auxiliary motor 21, the torque generated by the auxiliary motor 21, the inertial mass of all or part of the components of the upper-level mechanism 20, etc.

[0197] Preferably, the upper local loop 40 comprises a sub-branch 41A of the upper loop input branch 41 introducing an upper loop input reference T20_ref representing an input torque setpoint having a zero value, so as to servo-control the upper local loop with zero torque.

[0198] Therefore, here, T20_ref=0.

[0199] As indicated previously with reference to the lower mechanism 10 providing a servo control of zero force, the servo control of the upper mechanism 20 with zero torque allows making said upper mechanism 20 transparent and increasing its reactivity and sensitivity.

[0200] Again, the servo control at zero torque enables the upper mechanism 20 to not resist any parasitic resistance of the driver's manipulation of the steering wheel 22 , while faithfully restoring the reactions of the road and the lower mechanism 10 in said steering wheel 22 .

[0201] It should be emphasized that the architecture of the power steering system 1 includes, on the one hand, a lower local circuit 30, which is used to servo-control the lower mechanism 10 that mechanically acts on the steering wheel orientation, and on the other hand, a separate upper local circuit 40, which is used to servo-control the upper mechanism 20 that allows the driver to manipulate and feel the manipulation of the vehicle, and this circuit is particularly suitable for the wire-controlled steering system 1.

[0202] Preferably, if Figure 3 As shown, the power steering system 1 comprises a controller called “global controller” 50 which, as a function of parameters representative of the conditions of the upper mechanism 20 and of the conditions of the lower mechanism 20, generates, individually on the one hand, a dynamic component of a lower circuit force setpoint F10_dyn applied to the lower local circuit 30 and, on the other hand, a dynamic component of an upper circuit torque setpoint T20_dyn applied to the upper local circuit 40.

[0203] The dynamic component of the force set point F10_dyn, the corresponding torque set point T20_dyn, is adjusted in real time to adapt the reaction of the power steering system 1 to the vehicle service life conditions at the time considered and to the driver's actions (control) at the time considered, and thus to manage the steering assistance according to a predetermined assistance law, which can be stored in a diagram within the global controller 50, for example.

[0204] In the case of a steer-by-wire power steering system 1 , the global controller advantageously ensures a virtual coupling between the upper local circuit 40 associated with the upper mechanism 20 and the lower local circuit 30 associated with the lower mechanism 10 by means of electrical signals.

[0205] Among the parameters (specific to the power steering system 1 ) representing the condition of the superordinate mechanism 20 and used by the global controller 50 , the angular position θ of the steering wheel 22 may be considered in particular. 22 , and / or the angular velocity of the steering wheel

[0206] Among the parameters (specific to the power steering system 1 ) representing the condition of the underlying mechanism 10 and used by the global controller 50 , the angular position θ of the shaft of the auxiliary motor 11 may be considered in particular. 11 and / or the angular velocity of the auxiliary motor

[0207] In addition, the global controller 50 may also take into account parameters “data” related to the vehicle (and external to the power steering system 1 ), such as longitudinal speed, lateral acceleration, yaw rate, etc.

[0208] For example, the global controller 50 may determine a basic set point T_basic based on all or part of these various parameters.

[0209] As a (non-limiting) example, the global controller 50 may determine the basic setpoint T_basic using a calculation law which in practice corresponds to a virtual torsion bar:

[0210]

[0211] in:

[0212] Δθ=θ22 -θ 11

[0213] k1 is the uniform gain with (torsion) elastic stiffness,

[0214]

[0215] k2 is the uniform gain with viscosity,

[0216] Thus, the first term k1*Δθ corresponds to the torsional elastic deformation torque component,

[0217] The second corresponds to the dissipated torque component.

[0218] However, whatever the law used to calculate the basic setpoint T_basic, said basic setpoint T_basic is preferably converted into a lower-circuit force setpoint dynamic component F10_dyn and an upper-circuit torque setpoint dynamic component T20_dyn by the first and second subcontrollers 51 and 52 , respectively.

[0219] The global controller 50 thus forms a common core that branches on a hierarchy of sub-controllers 51 , 52 in order to distribute the dynamic setpoints F10_dyn, T20_dyn to each of the upper local loop 40 and the lower local loop 30 .

[0220] Therefore, in general, the power steering system 1, more specifically the steer-by-wire system 1, preferably has the following architecture: the architecture comprises two (closed) local loops 30, 40 (i.e. a force servo-controlled lower local loop 30 dedicated to the lower mechanism 10 actuating the steering wheel 12, and a torque servo-controlled upper local loop 40 dedicated to the upper mechanism 20 acting on the steering wheel 22), the local loops 30, 40 being connected to each other and controlled by a (same) global controller 50 (which defines the torque T20_dyn and force F10_dyn dynamic set points that can be applied by each of these local loops 30, 40, respectively).

[0221] Advantageously, the power steering system 1 according to the invention specifically allows for steer-by-wire to be achieved by associating lower subsystems 10, 30 and upper subsystems 20, 40, which are different from one another and each of which is capable of self-regulating (corresponding torque) independently of the others, via (preferably only via) a global controller 50.

[0222] More specifically, the present invention relates to a steer-by-wire power steering system 1, which comprises: a lower mechanism 10 and an upper mechanism 20, the lower mechanism 10 comprising an auxiliary motor 11 and a steering wheel 12, the upper mechanism 20 comprising a steering wheel 22 and an auxiliary motor 21, the lower mechanism 10 being servo-controlled with zero force on a closed loop via a lower local loop 30, the lower local loop 30 comprising a feedback branch 32, which measures or estimates an actual downstream force F10_actual located downstream of the auxiliary motor 11 and upstream of a contact 12C between the steering wheel 12 and the ground 2 to make the auxiliary motor 11 transparent, and the upper mechanism 20 being servo-controlled with zero torque on a closed loop via an upper local loop 40, the upper local loop 40 comprising a feedback branch 42, which measures or estimates an actual driver torque T20_actual between the auxiliary motor 21 and the steering wheel 22 to make the auxiliary motor 21 transparent, the lower local loop 30 and the upper local loop 40 being preferably controlled by the same global controller 50.

[0223] Preferably, as described above, each torque T20_dyn and force F10_dyn dynamic component completes the input reference F10_ref, T20_ref provided by the first input sub-branch 31A, 41A (different from the second input sub-branch 31B, 41B) by means of the second input sub-branch 31B, 41B of the local circuit 30, 40 under consideration.

[0224] Therefore, both a zero reference F10_ref, T20_ref (which enables zero force / torque servo control) and a dynamic component F10_dyn, T20_dyn reflecting active manipulation of the steering system 1 (by the driver, or by an automated driving system providing driving assistance) can be considered.

[0225] Therefore, preferably, the lower-loop input force setpoint F10_set is derived from the algebraic sum of the dynamic component of the lower-loop input reference F10_ref representing zero force and the lower-loop force setpoint F10_dyn from the global controller 50 , 51 .

[0226] Preferably, if Figure 3 As shown, the lower-loop input force setpoint F10_set is derived from the algebraic sum of the dynamic components of the lower-loop input reference F10_ref representing zero force and the lower-loop force setpoint F10_dyn from the global controller 50 , 51 .

[0227] To this end, the first input sub-branch 31A and the second input sub-branch 31B may be combined by means of a summation block.

[0228] Preferably, the summation block may also receive an actual downstream force value F10_actual from the feedback branch 32 , which will be subtracted from the input force setpoint F10_set (according to the sign convention used) to form the lower loop actuation setpoint F10_mot.

[0229] It should be noted that in the absence of a lower-loop force setpoint dynamic component F10_dyn, or if said dynamic component F10_dyn is zero, the lower local loop 30 servo-controls the lower mechanism 10 to an input reference value F10_ref, here preferably F10_ref=0.

[0230] As an alternative or in addition to the above-described calculation of the lower-loop input force setpoint F10_set, the upper-loop input torque setpoint T20_set is preferably derived from a combination of an upper-loop input reference T20_ref representing zero torque and an upper-loop torque setpoint dynamic component T20_dyn from the global controller 50 , 52 .

[0231] More preferably, the upper loop input torque setpoint T20_set is derived from the algebraic sum of an upper loop input reference T20_ref representing zero torque and an upper loop torque setpoint dynamic component T20_dyn from the global controller 50 , 52 .

[0232] Analogously to what has been described with respect to the lower local loop 30 , a summer may again be used at the level of the upper local loop 40 to connect the two input sub-branches 41A, 41B and the feedback loop 42 .

[0233] According to a preferred possibility of the invention, outside the lower local loop 30, the actual downstream force F10_act measured or estimated at the lower loop reference point P10 is used, by means of a function called "feedforward" 60, as a component for determining the upper loop input force setpoint T20_set and / or equivalently as a component for determining or adjusting the upper loop actuation setpoint T20_mot intended to be applied to the auxiliary motor 21.

[0234] This "feed-forward" function 60 is distinct from the lower and upper loop feedback loops 32, 42 and is Figure 3 Indicated by dotted line.

[0235] Advantageously, this feedforward function 60 allows the road feel caused by the variation of the external force F_ext applied to the steering wheel 12 and the lower mechanism 10 to be transmitted directly from the lower mechanism 10 to the upper local circuit 40, more specifically to the auxiliary motor 21, the above-mentioned road feel being sensed at the level of the lower circuit reference point P10 and more specifically by the force sensor 17.

[0236] The “road feel” restored by the reaction of the auxiliary electric motor 21 can thereby be improved according to the influence of the set point adjustment caused by the “feedforward” function 60 .

[0237] Depending on the possible application, the feed-forward function 60 may be configured to not pass a predetermined frequency range in order to accentuate the perception of responses falling within that frequency range.

[0238] For this purpose, for example, a bandpass filter can be used which has an amplification gain in the frequency range.

[0239] Therefore, assuming that the set formed by the upper mechanism 20, the upper local loop 40, the lower mechanism 10 and the lower local loop 30 does not inherently have sufficient dynamic performance to restore the interaction between the steering wheel 12 and the ground 2 in a satisfactory manner within a given frequency range, the feedforward function 60 can be used to amplify the signal generated by the interaction between the steering wheel 12 and the ground within this frequency range to improve the steering wheel feel.

[0240] Therefore, the feedforward function 60 allows the road feel to be set more finely.

[0241] According to another possible application, as an alternative or in addition to the foregoing, a feed-forward function 60 configured to selectively attenuate or eliminate frequency sensations within a given frequency range may be used.

[0242] To this end, by means of the feed-forward function 60 , a signal can be injected which has the same frequency as the perceived signal which is to be neutralized, but which is in the opposite phase (phase shifted by 180 degrees) with respect to said perceived signal.

[0243] By way of example, the perceived effect of an imbalance phenomenon associated with a balance defect of the steering wheel 12 can thus be limited.

[0244] Therefore, in any case, the feed-forward function 60 has the potential to provide additional fine-tuning.

[0245] Thus, in the case where the set formed by the upper mechanism 20, the upper local loop 40, the lower mechanism 10 and the lower local loop 30 has sufficiently high dynamics, it is not necessary to use the feedforward function 60.

[0246] Furthermore, the actual downstream force F10_actual is preferably measured at the lower loop reference point P10 with a bandwidth extending (from 0 Hz) to at least 20 Hz, at least 25 Hz, at least 30 Hz, or even beyond 30 Hz.

[0247] Thus, the force sensor 17 will generate a useful signal with a very rich frequency content and will therefore contain a lot of information (particularly accurate) about the variation of the external force F_ext and thus about the state of the interaction between the ground surface 2 and the steered wheel 12 .

[0248] Of course, the lower loop feedback branch 32 will be able to transmit the signal with at least equal bandwidth so that frequency information is not lost.

[0249] Advantageously, the wide bandwidth confers a high tactile sensitivity to the power steering system 1, to such an extent that, whatever the frequency, even if it is very high, the external force F_ext generated by the road coating (ground 2) when acting on the tire (and therefore on the steering wheel 12 and the lower mechanism 10) causes disturbances and variations which themselves immediately attract attention and are therefore transmitted again to the steering wheel (via the global controller 50 and / or via the feedforward function 60 and then via the upper local loop 40 and the upper mechanism 50), thus providing the driver with a very good road feel; in addition, this extent allows, for situations occurring in the case of servo control in terms of position, disturbances to be filtered out conversely in order to maintain a stable steering position.

[0250] Of course, all controllers 50, 51, 52, 33, 43, and more generally the servo control structure of the local loops 30, 40, may be implemented by any suitable electronic and / or computer calculation.

[0251] Furthermore, the invention itself covers a vehicle, in particular a motor vehicle, equipped with a power steering system 1 as described above.

[0252] Incidentally, the present invention is not limited to the above-mentioned variants, and a person skilled in the art can in particular freely isolate or combine one of the aforementioned features, or replace them with equivalents.

Claims

1. A power steering system (1) comprising a first mechanism, referred to as "lower mechanism" (10), comprising an auxiliary motor (11) and a steering wheel (12), said auxiliary motor (11) acting on said steering wheel to orient said steering wheel in yaw, said lower mechanism (10) thus defining a lower kinematic chain (L10) extending from said auxiliary motor (11) to a portion of said steering wheel, referred to as "contact portion" (12C), said contact portion being intended to come into contact with the ground (2), so that the forces and movements generated by said auxiliary motor (11) are transmitted to said steering wheel (12) via and along said lower kinematic chain (L10) The power steering system (1) further comprises a second mechanism called "upper mechanism" (20), the second mechanism comprising a steering wheel (22), and the second mechanism has no mechanical connection with the lower mechanism (10) to form an upper kinematic chain (L20) separated from the lower kinematic chain (L10), or the second mechanism is mechanically connected to the lower mechanism (10) via a connecting member (4) to form an auxiliary upper kinematic chain from the steering wheel (22) to the connecting member, the auxiliary upper kinematic chain forming a fork (L20B) relative to the lower kinematic chain (L10), the power steering system (1) is characterized in that the lower mechanism (10) The force servo control is performed by a closed loop called "lower local loop" (30), comprising an input branch called "lower loop input branch" (31) which allows defining an input force set point called "lower loop input force set point" (F10_set); a feedback branch called "lower loop feedback branch" (32) which measures or estimates a force called "actual downstream force" (F10_set) at a reference point called "lower loop reference point" (P10) located above the lower kinematic chain (L10), outside the upper kinematic chain (L20), downstream of the auxiliary motor (11) and upstream of the contact (12C) of the steering wheel (12). The invention relates to a lower loop feedback branch (32) for generating a force of the auxiliary motor (11) (F10_actual) which represents the force transmitted between the auxiliary motor (11) and the steering wheel (12) through the lower kinematic chain (L10) at the reference point (P10), and the lower loop feedback branch (32) then applies the actual downstream force (F10_actual) to the lower loop input force set point (F10_set) in the form of feedback to form a lower loop actuation set point (F10_mot), which is applied to the auxiliary motor (11) so that the actual downstream feedback force (F10_actual) automatically follows the lower loop input force set point (F10_set).

2. The power steering system according to claim 1, characterized in that: The lower local loop (30) comprises a sub-branch (31A) of the lower loop input branch, which introduces a lower loop input reference (F10_ref) representing an input force setpoint having a zero value, so as to enable servo control of the lower local loop (30) at zero force.

3. The power steering system according to claim 1 or 2, characterized in that: The lower kinematic chain (L10) comprises a rack (13) driven by the auxiliary motor (11), and at least one end (13L) of the rack is connected to a steering tie rod (14), which in turn transmits force and displacement to the steering wheel (12) and is used to measure or estimate the actual downstream force (F10_actual) at the lower loop reference point (P10), the lower loop reference point (P10) being located at the junction between one end (13F) of the rack and the steering tie rod (14), above the steering tie rod (14), or downstream of the steering tie rod (14).

4. The power steering system according to claim 1, characterized in that: The lower kinematic chain (L10) comprises a steering knuckle (16) which carries the steering wheel (12) and embodies the orientation axis of the steering wheel, and the lower loop reference point (P10) for measuring or estimating the actual downstream force (F10_actual) is located on the steering knuckle (16).

5. The power steering system according to claim 1, characterized in that: A power steering system is formed in a "steer-by-wire" configuration without any mechanical connection between the upper mechanism (20) and the lower mechanism (10).

6. The power steering system according to claim 1, characterized in that: In addition to the steering wheel (22), the upper mechanism (20) also includes a second auxiliary motor (21) different from the auxiliary motor (11) of the lower mechanism (10), and the upper mechanism (20) is servo-controlled in terms of torque via a closed loop called an "upper local loop" (40), the upper local loop (40) comprising an input branch called an "upper loop input branch" (41) which allows defining an input torque set point called an "upper loop input torque set point" (T20_set), and a feedback branch called an "upper loop feedback branch" (42) which measures or estimates an input torque called an "actual driver torque" (T20_actual) at a reference point called an "upper loop reference point" (P20) between the second auxiliary motor (21) and the steering wheel (22). ), which torque represents the torque applied by the driver to the upper mechanism (20) via the steering wheel (22) at the reference point, and the upper loop feedback branch (42) then applies the actual driver torque (T20_actual ) to the upper loop input torque set point (T20_set) in the form of feedback to form an upper loop actuation set point (T20_mot), which is applied to the second auxiliary motor (21) so that the actual driver torque (T20_actual) automatically follows the upper loop input torque set point (T20_set).

7. The power steering system according to claim 6, characterized in that: The upper local loop (40) comprises a sub-branch (41A) of the upper loop input branch, which introduces an upper loop input reference (T20_ref) representing an input torque setpoint having a zero value, so as to enable servo control of the upper local loop (40) at zero torque.

8. The power steering system according to claim 6, characterized in that: It comprises a controller called "global controller" (50) which, according to parameters representing the conditions of the upper mechanism (20) and the conditions of the lower mechanism (10), generates, on the one hand, a dynamic component of a lower circuit force setpoint (F10_dyn) applied to the lower local circuit (30) and, on the other hand, a dynamic component of an upper circuit torque setpoint (T20_dyn) applied to the upper local circuit (40).

9. The power steering system according to claim 8, characterized in that: The lower local loop (30) comprises a sub-branch (31A) of the lower loop input branch, the sub-branch introducing a lower loop input reference (F10_ref) representing an input force setpoint having a zero value so as to enable servo control of the lower local loop (30) at zero force, and the lower loop input force setpoint (F10_set) is derived from a combination of the lower loop input reference (F10_ref) representing zero force and a dynamic component of the lower loop force setpoint (F10_dyn) from the global controller (50).

10. The power steering system according to claim 8, characterized in that: The upper local loop (40) comprises a sub-branch (41A) of the upper loop input branch, the sub-branch introducing an upper loop input reference (T20_ref) representing an input torque setpoint having a zero value so as to enable servo control of the upper local loop (40) at zero torque, and the upper loop input torque setpoint (T20_set) is derived from a combination of the upper loop input reference (T20_ref) representing zero torque and a dynamic component of the upper loop torque setpoint (T20_dyn) from the global controller (50).

11. The power steering system according to any one of claims 6 to 10, characterized in that: The actual downstream force (F10_actual) measured or estimated at the lower loop reference point (P10) is used, outside the lower local loop (30), by means of a function called "feedforward" (60), as a component for determining the upper loop input torque setpoint (T20_set) or as a component for determining or adjusting the upper loop actuation setpoint (T20_mot) intended to be applied to the second auxiliary motor (21).

12. The power steering system according to claim 1, characterized in that: The actual downstream force (F10_actual) is measured at the lower loop reference point (P10) over a bandwidth extending to at least 20 Hz.

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