METHOD FOR MANAGING THE STEERING OF A MOTOR VEHICLE BY DAMPING THE RACK

Abstract

METHOD FOR MANAGING A STEERING SYSTEM OF A MOTOR VEHICLE BY DAMPING THE RACK The present invention relates to a method for controlling a steering system (4) of a motor vehicle (2) comprising an electric steering actuator (FWA) of a rack (10) for controlling the angular position of steered wheels (8, 9) of said motor vehicle, remarkable in that said method comprises, upon detection of a failure of the electric steering actuator and when the steered wheels are in an angular steering position, an application of a resistive force on the steering rack, so as to limit a de-steering of said steered wheels. (Figure to be published with the abstract: Figure 1)

Description

Title of the invention: METHOD FOR MANAGING THE STEERING OF A MOTOR VEHICLE BY DAMPING THE RACK Technical field

[0001] The present invention relates to the field of motor vehicles, more particularly to the field of motor vehicle steering systems. Prior art

[0002] Automobile manufacturers are offering more motor vehicles including electric driving functions, also referred to as: “Drive-by-Wire” driving functions, which may in particular include exclusively electrically controlled directional control functions: “Steer-by-Wire” provided by electric power steering units without a steering column, i.e. having no mechanical link between the steering wheel and the wheels.

[0003] This type of electric steering system uses an electric wheel directional actuator, commonly referred to as FWA, an acronym derived from the English name: "Front Wheel Actuator". The latter corresponds to a steering motor engaged with the steering rack to control the rotation angle of the steered wheels.

[0004] Conventionally, modern motor vehicles including autonomous driving functions are also equipped with an electric wheel steering actuator which is combined with a conventional steering system provided with a mechanical link between the steering wheel and the wheels.

[0005] However, electric wheel steering actuators can experience failures, causing a total loss of their operation. In the case where this loss occurs during a bend, and with a sufficiently high vehicle speed, the self-aligning (mechanical) moment then causes a very rapid straightening of the steered wheels (approximately 100 ms), leaving the driver no time to recover when it is autonomous driving (particularly level 3), or even impossible to recover when it is a “Steer-by-Wire” electrically controlled steering system.

[0006] One solution would be to make the steering motor redundant. However, redundancy is expensive and not sufficiently secure, because the recovery of the second motor may be subject to a latency time or to one of the synchronization problems which can suddenly modify the trajectory of the motor vehicle.

[0007] An additional solution is to ensure the steering of the vehicle using a Steer-by-Brake (SbB) steering system, also known as "Brake to Steer", which involves asymmetric braking, for example, by braking the left wheels to create a yaw moment towards the left of the vehicle in order to stay on the trajectory desired by the driver or by the autonomous driving system. However, the performance and effectiveness of this solution depend on the offset of the wheels, known in English as "scrub radius".

[0008] Indeed, a negative or insufficiently positive offset causes a lack of efficiency in the system (SbB) which will have physical difficulty in maintaining the trajectory of the motor vehicle when cornering. Thus, a failure of the steering motor will not leave enough time for the system (SbB) to act on the wheels, and the vehicle risks suddenly straightening up in a straight line in the middle of a bend.

[0009] Published patent document US 2021 / 0086737 A1 discloses a vehicle comprising means acting on the brakes when a failure of the steer-by-wire steering control device is detected, in order to cause the vehicle to move slowly to the side of the road and allow a safe stop.

[0010] However, the solution presented by the document does not make it possible to effectively overcome the drawbacks presented above which are linked to a failure of the electric wheel steering actuator when the motor vehicle is in full turn, the solution therefore has room for improvement in order to make the event of failure of a steering motor more secure. Statement of the invention

[0011] The present invention aims to overcome at least one of the drawbacks of the aforementioned state of the art. More particularly, the invention aims to propose a simple, efficient and economical solution making it possible to secure the operation of a steering system of a motor vehicle provided with an electric wheel steering actuator.

[0012] To this end, the invention relates to a method for controlling the steering of a motor vehicle comprising an electric directional actuator of a rack for controlling the angular position of the steered wheels of said motor vehicle, remarkable in that said method comprises, upon detection of a failure of the electric directional actuator and when the steered wheels are in an angular steering position, an application of a resistive force to the steering rack, so as to limit a de-steering of said steered wheels.

[0013] Advantageously, the electric directional actuator is mechanically engaged directly with the rack of the motor vehicle. The failure comprises a mechanical and / or electrical malfunction of the electric directional actuator, and / or a loss of power supply to said electric directional actuator. Preferably, the failure is detected by detection means which may, for example, comprise an electrical relay configured to be controlled in the event of loss of power supply to the electric directional actuator.

[0014] Preferably, when the steered wheels are in the angular steering position, the motor vehicle follows a curved trajectory (for example, in a bend), said motor vehicle comprising a non-zero speed, preferably greater than 20 km / h.

[0015] According to one embodiment, the method further comprises actuating a brake steering control upon detection of the failure of the electric directional actuator.

[0016] Advantageously, the steering control by brake comprises the application of asymmetric braking to the motor vehicle, so as to maintain the latter in its curved trajectory.

[0017] According to one embodiment, the application of the resistive force comprises active or passive damping of a linear displacement of the rack towards a central reference position of said rack.

[0018] Preferably, the central reference position of said rack corresponds to the position at which the steered wheels are in a central position defining a zero angle with a longitudinal direction of the motor vehicle (defining a straight line trajectory of said vehicle).

[0019] According to one embodiment, the active damping of the rack movement comprises a hydraulic device controlled by an electrically controlled valve upon detection of the failure of the electric directional actuator. Preferably, the valve of the hydraulic device corresponds to a normally closed or normally open valve, configured to open or close by electrical control in the event of failure of the electric directional actuator, so as to hydraulically dampen the rack.

[0020] According to one embodiment, the passive damping of the movement of the rack comprises a mechanical resistance means arranged in direct contact with the rack, independently of the angular position of the steered wheels.

[0021] Preferably, the passive damping acts permanently on the rack during all phases of driving of the motor vehicle.

[0022] According to one embodiment, the electric directional actuator comprises an electric motor, and the active damping of the movement of the rack comprises short-circuiting at least two phases of said electric motor, so as to brake a rotation of said electric directional actuator.

[0023] According to one embodiment, the application of the resistive force lasts at least 2 seconds before a return of the rack to a central reference position of said rack.

[0024] Advantageously, the damping of the rack by application of the resistive force makes it possible to ensure a progressive reduction in a yaw speed of the motor vehicle of at most 3° per second, and preferably of at most 27s.

[0025] According to one embodiment, the steering of the motor vehicle is exclusively electrically controlled.

[0026] The invention also relates to a motor vehicle comprising: - steering wheels; - an electric directional actuator of a rack for controlling the angular position of the steered wheels; - a vehicle steering control unit, electrically connected to the electric steering actuator; remarkable in that the control unit is configured to execute the method according to the invention.

[0027] According to one embodiment, said motor vehicle further comprising: - a steering wheel coupled to an electric steering wheel actuator; the steering control unit of the motor vehicle being electrically connected to the electric steering actuator and to the electric steering wheel actuator.

[0028] The measures of the invention are advantageous in that the damping of the rack makes it possible to slow down the return of the rack to its central reference position, thus limiting the deflection of the wheels of the motor vehicle when the latter is in a bend. The joint action of the damping of the rack and the control of the steering by brake makes it possible to maintain the yaw speed of the motor vehicle and to keep it in the bend.

[0029] The method of the invention thus makes it possible to make the driving of the motor vehicle safer, thereby promoting autonomous driving functionalities and / or making it possible to limit, or even do without, redundancy of the electric directional actuators. Brief description of the drawings

[0030] [Fig.l] schematically represents a steering system of a motor vehicle according to the invention, said system comprising an electric directional actuator of a rack of said motor vehicle;

[0031] [Fig.2] illustrates a graph representing the evolution of a steering wheel angle as well as a yaw rate of the motor vehicle in the event of failure of the electric steering actuator, in comparison with or without a resistive force applied to the rack by a method for controlling the steering of the motor vehicle according to the invention. Detailed description

[0032] [Fig.l] schematically represents a steering system 4 of a motor vehicle 2 according to the invention.

[0033] This is an electric power steering system without mechanical connection between the steering wheel 6 and the right 8 and left 9 front steering wheels of the motor vehicle 2.

[0034] It should be noted that the present invention is not limited to a motor vehicle having exclusively electrically controlled “Steer-by-Wire” steering, said steering may be mechanically controlled (conventional) with a connection of the steering wheel by a steering column (not shown) to a steering rack. In this configuration, the motor vehicle preferably comprises an electric steering motor controlling the rack in order to provide autonomous driving functionalities, with the possibility for the driver to manually take over the steering wheel at any time.

[0035] The steering 4 preferably comprises an electric directional actuator of the steered FWA wheels of the motor vehicle 2, said actuator corresponding to an FWA steering motor, said steering 4 also comprising an electric actuator of the steered steering wheel HWA, capable of being driven in rotation in a nominal angular range having two limit angular positions of the steering wheel 6.

[0036] The electric wheel steering actuator is commonly referred to as FWA, an acronym taken from the English name: "Front Wheel Actuator", and the steering wheel actuator is commonly referred to as HWA for: "Hand Wheel Actuator".

[0037] In this configuration, each of the wheel and steering wheel actuators may comprise a receiver (angular position sensor) and a transmitter (actuator), so as to actuate the front wheels 8, 9 by means of a rack 10 following receipt of an angular position of the steering wheel, and vice versa.

[0038] Preferably, the electric steering system 4 is controlled by a control unit 12 of the motor vehicle 2, directly connected to each of the actuators FWA and HWA, respectively by means of an input 12.1 for a signal representative of the angular position of the steering wheel 6, and an output 12.2 for a signal controlling the steered wheels 8, 9.

[0039] The control unit 12 further comprises a control signal output to the steering wheel 6 and a signal input representative of the angular position of the steered wheels 8, 9.

[0040] The steering wheel 6 may comprise physical or virtual stops. Preferably, the HWA actuator of the steering wheel 6 is configured to generate maximum force feedback at the two limit angular positions of the steering wheel 6, so as to form two virtual end-of-travel stops of the steering wheel. Advantageously, the steering wheel 6 is also capable, thanks to the HWA actuator, of providing force feedback between the two limit angular positions.

[0041] The present invention proposes a method for controlling the steering system 4 by means of the control unit 12, so as to make the driving of the motor vehicle 2 safer, in particular when the latter is moving along a curved trajectory (for example, in a bend), and when a failure of the electric directional actuator FWA occurs.

[0042] In such a situation, the method according to the invention advantageously proposes applying a resistive force to the steering rack 10 in order to limit a deflection of the steered wheels 8, 9 and thus to be able to maintain the motor vehicle 2 for as long as possible in its initial curved trajectory in the bend.

[0043] In this regard, the application of the resistive force comprises a damping of a linear displacement of the rack towards a central reference position of said rack, at which the steered wheels 8, 9 are aligned with a longitudinal direction of the motor vehicle 2.

[0044] Since the failure of the electric directional actuator FWA may be due to a loss of electrical power supply, then the means or means for providing damping to the rack 10 is advantageously independent of said electrical power supply.

[0045] Preferably, the damping of the movement of the rack 10 is active or passive, and makes it possible to slow down said movement (linear translation) in order to keep the motor vehicle 2 turning for as long as possible in the event of a failure.

[0046] The passive damping of the rack movement may comprise a mechanical resistance means arranged in direct contact with the rack (for example, a spring, or a jack, etc.), said damping being independent of the angular position of the steered wheels, i.e., regardless of the orientation of the wheels and the rolling phase of the motor vehicle. This type of damping makes it possible to guarantee a permanent application of the resistive force on the rack, but requires the electric directional actuator FWA (before its failure) to counter said passive resistive force during the steering of the wheels.

[0047] Alternatively, the active damping of the movement of the rack 10 may comprise a hydraulic device controlled by a normally closed or normally open valve, said valve being electrically controlled to open or close upon detection of the failure of the electric directional actuator FWA. Thus, in the event of loss of electrical power, the valve opens or closes and the active damping is applied to the rack 10. This type of damping, unlike passive damping, does not require a counter-force applied by the directional actuator FWA.

[0048] In another alternative, the active damping of the movement of the rack 10 comprises a short-circuiting of at least two phases of the electric motor of the directional actuator FWA, so as to brake the rotation of a shaft 14 of said electric directional actuator FWA. This braking advantageously corresponds to a resistive force at the end of the shaft 16 which is directly engaged with the rack 10. Preferably, the short-circuiting of the phases is ensured by a normally closed electrical relay which is configured to allow an electrical connection of said phases, in particular in the event of loss of power supply to the electric directional actuator FWA.

[0049] The present invention is not limited to a particular example of damping. Indeed, the latter may include any other technical solution which may be mechanical or electrical and which makes it possible to generate a resistive force (permanent or conditioned by the loss of power supply) on the rack 10, limiting its return speed to its central reference position. The method according to the invention may also provide a combination of several damping solutions.

[0050] Damping alone makes it possible to slow down the deviation of the vehicle after a total loss of the steering motor when cornering, however, and in order to completely maintain the initial trajectory of the motor vehicle 2 preceding the failure of the FWA steering motor, the method according to the invention preferably further comprises the actuation of steering control by brake as soon as the failure of the FWA electric steering actuator is detected.

[0051] Advantageously, the steering control by brake is ensured by a steering system of the “Steer-by-Brake” (SbB) type, also called in English: “Brake to Steer” corresponding to asymmetric braking capable of individually controlling the angle of rotation of each wheel of the motor vehicle 2.

[0052] Alternatively, the method of the invention may be limited to the damping of the rack and allow the driver of the motor vehicle 2 to regain control of the steering wheel 6, in particular when the steering 4 is mechanically controlled and capable of providing autonomous driving. To this end, the damping of the rack 10 makes it possible to maintain the latter outside its central reference position (nominal position) for at least 2 seconds, a duration which is advantageously sufficient for the driver to regain control of his vehicle.

[0053] [Fig.2] illustrates a graph 100 representing, in dotted lines, the evolution of a steering wheel angle Ar as well as a yaw rate VI of a motor vehicle of the state of the art (not controlled by the method of the invention), after a failure D of the electric directional actuator of its steering system.

[0054] Graph 100 also illustrates for comparison purposes, and in continuous line plots, the evolution of a steering wheel angle Ar' as well as a yaw speed VI', at the following the application of a resistive force to the rack according to the method of the invention.

[0055] Preferably, the developments Ar' and VI' also result from steering control by brake of the motor vehicle as soon as the fault D occurs.

[0056] At t < 0 s: the vehicle is turning with an average angle of the two steered wheels equal to 2.5° and a yaw rate of 117s.

[0057] At t = 0 s: occurrence of the complete failure D of the electric directional actuator. The method of the invention then directly applies the resistive force to the rack, and preferentially triggers progressively the control of the steering by brake. Preferably, the resistive force is proportional to a speed of movement of the rack.

[0058] At t > 0 s: it can be seen that the wheels of the state-of-the-art motor vehicle suddenly deflect after failure D (with reference to plot Ar), followed by an equally sudden straightening of the vehicle in a straight line (with reference to plot VI showing a rapid reduction in yaw rate despite a “Steer-by-brake” steering solution).

[0059] It can also be seen in a comparative manner that the damping of the rack according to the method of the invention combined with the steering control by brake, makes it possible to ensure a progressive reduction of the rotation angle of the wheels and the yaw rate of the motor vehicle, said reduction in the yaw rate being advantageously at most 37s and preferably at most 27s.

[0060] Advantageously, the joint action of the damping of the rack and the steering control by brake makes it possible to maintain the yaw speed of the motor vehicle and keep it in the bend.

[0061] The method for controlling the direction of the motor vehicle preferably corresponds to a computer algorithm which can be executed in the form of lines of code readable by a computer (which can correspond to the control unit 12 of [Fig.l]).

[0062] Advantageously, the steering control by brake makes it possible to impart a yaw moment in the direction desired by the driver or by the autonomous driving system of the motor vehicle. The damping of the rack provided by the method of the invention makes it possible to considerably improve the efficiency of said steering control by brake, particularly when the ground offset of the wheels is negative or is not sufficiently positive, or with degraded ground grip.

Claims

Claims

1. Method for controlling a steering of a motor vehicle (2) comprising an electric directional actuator (FWA) of a rack (10) for controlling the angular position of steered wheels (8, 9) of said motor vehicle (2), characterized in that said method comprises, upon detection of a failure of the electric directional actuator (FWA) and when the steered wheels (8, 9) are in an angular steering position, an application of a resistive force on the steering rack, so as to limit a deflection of said steered wheels (8, 9).

2. The method of claim 1, wherein the method further comprises actuating brake steering control upon detection of failure of the electric steering actuator (FWA).

3. Method according to one of claims 1 and 2, in which the application of the resistive force comprises an active or passive damping of a linear displacement of the rack (10) towards a central reference position of said rack.

4. Method according to claim 3, in which the active damping of the movement of the rack (10) comprises a hydraulic device controlled by an electrically controlled valve upon detection of the failure of the electric directional actuator (FWA).

5. A method according to claim 3, wherein the passive damping of the movement of the rack (10) comprises a mechanical resistance means arranged in direct contact with the rack (10), independently of the angular position of the steered wheels (8, 9).

6. Method according to one of claims 3 and 4, in which the electric directional actuator (FWA) comprises an electric motor, and the active damping of the movement of the rack (10) comprises a short-circuiting of at least two phases of said electric motor, so as to brake a rotation of said electric directional actuator (FWA).

7. Method according to one of claims 1 to 6, in which the application of the resistive force lasts at least 2 seconds before a return of the rack (10) towards a central reference position of said rack (10).

8. Method according to one of claims 1 to 7, in which the steering of the motor vehicle (2) is exclusively electrically controlled.

9. Motor vehicle (2) comprising: - steered wheels (8, 9); - an electric directional actuator (FWA) of a rack (10) for controlling the angular position of the steered wheels (8, 9); - a control unit (12) for steering the vehicle (2), electrically connected to the electric directional actuator (FWA); characterized in that the control unit (12) is configured to execute the method according to one of claims 1 to 8.

10. Motor vehicle (2) according to claim 9, further comprising: - a steering wheel (6) coupled to an electric steering wheel actuator (HWA); the steering control unit (12) of the motor vehicle (2) being electrically connected to the electric steering actuator (FWA) and to the electric steering wheel actuator (HWA).

Images