Method for indicating a target engine torque determining a corrected target engine torque varying with a correction frequency around an operating value

Abstract

Method for determining a corrected target engine torque (Cmc) for a control motor (M) of a power steering system (1) without mechanical connection, said control motor (M) receiving the corrected target engine torque (Cmc) and exerting an engine torque on an axis of rotation comprising a steering wheel (3), said method comprising: A step of receiving a target engine torque (Cmo), A correction step in which the corrected target engine torque (Cmc) is determined as a function of a result of a comparison between the target engine torque (Cmo) and a normal operating threshold (Sf), said corrected target engine torque (Cmc) varying with a correction frequency (Fc) around a corrected operating value (Vfc) over a corrected operating range (Zc), said corrected operating value (Vfc) being lower than the target engine torque (Cmo). Figure 2

Description

Title of the invention: Method for indicating a target engine torque determining a corrected target engine torque varying with a correction frequency around an operating value Technical field

[0001] The invention relates to the field of power steering and more particularly to a method for indicating a target engine torque, and a power steering without mechanical link implementing such a method. State of the prior art

[0002] A vehicle steering system is intended to enable a driver to control a trajectory of the vehicle by modifying an orientation angle of the vehicle's wheels by means of a steering wheel. The orientation angle of the wheels is in particular linked to an angle of the steering wheel, hereinafter referred to as "steering wheel angle". The driver modifies the steering wheel angle by exerting a force on the steering wheel, hereinafter referred to as "steering wheel torque".

[0003] Generally, a steering system comprises several elements including said steering wheel, a rack, and two wheels each connected to a rod. The rack is the part allowing the wheels to be maneuvered, that is to say allowing the orientation angle of the wheels to be modified, via the rods. The rack transforms a variation in the steering wheel angle into a variation in the vehicle's wheel angle.

[0004] In an electric power steering system without a mechanical link, called "steer-by-wire" in English, the steering wheel is mechanically detached from the rack. In this case, the steering system comprises a steering wheel unit mechanically independent of a rack unit. In other words, a force applied to the steering wheel unit is not mechanically transmitted to the rack unit, and vice versa.

[0005] The rack unit comprises said rack and at least one electronic rack control unit which in particular controls an angular position of the rack so that it is generally consistent with the steering wheel angle. Thus, the driver can steer the vehicle, i.e. modify the angular position of the rack, by means of the steering wheel. The electronic rack control unit comprises a maneuvering regulator which controls a maneuvering motor which exerts a maneuvering motor torque on the rack. More precisely, the steering wheel angle is measured or calculated so as to determine a set maneuvering angle to be reached by the angular position of the rack. In other words, the regulator maneuver controls the angular position of the rack to the set maneuver angle by controlling the maneuvering motor torque exerted by the maneuvering motor on the rack.

[0006] The steering wheel unit comprises said steering wheel and at least one electronic steering wheel control unit which determines in particular a torque to be felt by the driver during a steering wheel maneuver, hereinafter called the target engine torque. The target engine torque is intended in particular to make the driver feel torque information consistent with a life situation in which the vehicle is located (turn, straight line, level of grip, condition of the road surface, etc.). The electronic steering wheel control unit comprises a control regulator which controls the steering wheel torque to the target engine torque by means of a control motor. The control motor then exerts an engine torque on an axis of rotation of the steering wheel.

[0007] The set engine torque varies between a minimum value and a maximum value depending in particular on a maximum torque that can be supplied by the control motor.

[0008] More precisely, the set engine torque varies mainly as a function of a vehicle travel speed, i.e. the vehicle's operating situation, a force acting between the wheels and a rolling surface, and a rack position, in particular when the rack is at its stop. The rack comprises a stop at each end. Said stops may be physical stops mechanically blocking the rack's movement or virtual stops blocking the rack's movement by means of the maneuvering motor. The maximum value is particularly required when the rack is at its stop, i.e. a situation in which, in a power steering system with a mechanical link between the steering wheel unit and the rack unit, the steering wheel can no longer turn.

[0009] By way of illustration, it is assumed that the steering wheel is locked in rotation for a set engine torque of between 30 Nm and 50 Nm. In other words, if the control motor exerts a torque of between 30 Nm and 50 Nm, the driver does not have enough force to turn the steering wheel.

[0010] There is a known solution in which the control motor used is a motor directly generating the engine torque on the axis of rotation of the flywheel. This solution requires a control motor capable of generating an engine torque between the minimum value and the maximum value of the set engine torque, i.e. a torque between 30Nm and 50Nm, driving a large motor. In addition, power electronics are required which results in significant current consumption and a high price for the electronic components.

[0011] There is also a solution in which the control motor used comprises a reducer, positioned between the motor and the axis of rotation of the steering wheel, allowing generate a motor torque between the minimum and maximum value of the set motor torque. For example, with a 20 gearbox and 90% efficiency, the maximum value of the set motor torque is 2.8Nm. This solution requires a smaller motor size than the solution above but requires an additional mechanical part, the gearbox, increasing the risk of failure.

[0012] There is therefore a need for a control motor having a reduced size and few mechanical parts. Statement of the invention

[0013] One embodiment relates to a method for indicating a target engine torque determining a corrected target engine torque for a control motor of an electric power steering without mechanical link, said control motor receiving the corrected target engine torque and exerting an engine torque on an axis of rotation comprising a steering wheel, said method being implemented by an electronic steering wheel control unit and comprising: - A step of receiving a set motor torque, - A correction step in which the corrected target engine torque is determined based on a result of a comparison between the target engine torque and a normal operating threshold, said corrected target engine torque varying with a correction frequency around a corrected operating value over a corrected operating range, said corrected operating value being lower than the target engine torque, - An indication step in which the control motor applies the corrected target engine torque to the steering wheel rotation axis

[0014] The control motor is part of a steering wheel unit of an electric power steering system without mechanical connection. The steering wheel unit comprises in particular said steering wheel and at least the electronic steering wheel control unit which determines in particular a torque to be felt by the driver during a steering wheel maneuver, hereinafter called the target engine torque. The target engine torque is intended in particular to make the driver feel torque information consistent with a life situation in which the vehicle is located (turn, straight line, level of grip, condition of the road surface, etc.).

[0015] The electronic steering wheel control unit receives the set engine torque during the reception step, then corrects, in other words modifies, this set engine torque according to certain conditions, during the correction step so as to determine the corrected set engine torque.

[0016] The corrected setpoint motor torque is the motor torque which serves as a setpoint for the control motor.

[0017] During the correction step, the setpoint engine torque is compared to the normal operating threshold, and based on this result, the corrected setpoint engine torque is determined.

[0018] Over the corrected operating range, corresponding to a range of setpoint engine torque values, the corrected setpoint engine torque varies with a correction frequency around a corrected operating value, the corrected operating value being lower than the setpoint engine torque.

[0019] In other words, for a setpoint motor torque included in the corrected operating range, the corrected setpoint motor torque varies around the corrected operating value between a value greater than the corrected operating value and a value less than the corrected operating value.

[0020] Thus, the control motor does not provide, at least permanently, the set engine torque. The control motor provides an engine torque at least partially lower than the set engine torque. The control motor exerting the engine torque directly on the axis of rotation of the steering wheel can therefore have a smaller size than if it had to provide the set engine torque completely. The control motor and the electronic control unit therefore have a small size and low power consumption compared to the state of the art of control motors directly exerting the engine torque on the axis of rotation of the steering wheel.

[0021] The variation of the corrected target engine torque causes a vibration-like sensation in the steering wheel which, according to the applicant's discoveries, makes it possible to simulate a greater engine torque than that actually applied. A driver of the vehicle holding the steering wheel therefore has the impression of a greater resistive torque than that actually applied.

[0022] The subject matter of the present disclosure may also have one or more of the following characteristics taken alone or in combination.

[0023] In some embodiments, the corrected target engine torque is less than or equal to the target engine torque.

[0024] In some embodiments, the corrected target engine torque is less than the target engine torque over the corrected operating range.

[0025] Thus, the control motor has a smaller size than a control motor that has to provide the entire setpoint motor torque. The invention makes it possible to reduce the size and electrical consumption of the control motor compared to the state of the art.

[0026] In some embodiments, the corrected setpoint engine torque varies with a correction amplitude around the corrected operating value.

[0027] The difference between the upper value and the lower value of the corrected target engine torque for a given target engine torque corresponds to the amplitude of correction.

[0028] The correction amplitude influences the feeling of vibrations by the driver.

[0029] In some embodiments, the correction amplitude depends on the torque engine setpoint and / or time.

[0030] For example, the correction amplitude increases with the set motor torque.

[0031] For example, the correction amplitude increases with the time during which the engine torque setpoint is requested.

[0032] In some embodiments, the corrected target engine torque is equal to the target engine torque over a normal operating range.

[0033] Thus, over the normal operating range, the set engine torque is not modified.

[0034] In certain embodiments, the normal operating threshold is equal on the one hand to the maximum of the normal operating range and on the other hand to the minimum of the corrected operating range.

[0035] The normal operating threshold is a setpoint engine torque value that separates the normal operating range from the corrected operating range.

[0036] The normal operating threshold therefore determines from which engine torque the correction applies.

[0037] For example, if the setpoint motor torque is below the normal operating threshold, the setpoint motor torque is within the normal operating range and no correction applies. If the setpoint motor torque is above the normal operating threshold, the setpoint motor torque is within the corrected operating range and the correction applies.

[0038] In certain embodiments, the correction frequency depends on the set motor torque and / or time.

[0039] For example, the correction frequency increases with the set motor torque.

[0040] For example, the correction frequency increases with the time during which the engine torque setpoint is requested.

[0041] In some embodiments, the corrected operating value depends on the setpoint motor torque and / or time.

[0042] For example, the corrected operating value increases with the set engine torque.

[0043] For example, the corrected operating value increases with the time during which the set engine torque is requested.

[0044] In some embodiments, the method determines a torque signal based on the set engine torque.

[0045] The torque signal varies according to the engine torque setpoint to be indicated to the driver.

[0046] In some embodiments, the torque signal is determined based on the corrected target engine torque.

[0047] In some embodiments, the torque signal is a haptic, audible, or visual signal.

[0048] Thus, the driver receives information on the set engine torque by means of other senses.

[0049] In certain embodiments, the method comprises a reset step, subsequent to the correction step, in which a steering wheel angle is determined upon detection of a movement of the steering wheel in a direction opposite to a direction having caused the correction step.

[0050] The invention does not allow the steering wheel to be locked in rotation. Indeed, since the steering wheel is not mechanically connected to the rack, and since the corrected target engine torque is lower than the target engine torque, the driver of the vehicle can continue to turn the steering wheel while the rack is at its stop, for example, or while the wheels are locked. Thus, the driver can make numerous turns in the same direction without causing a change in the position of the rack. In order to avoid the driver having to repeat said numerous turns in an opposite direction before moving the rack in the opposite direction again, the method according to the invention comprises a reset step. For this purpose, the reset step detects counter-steering, or a change in the direction of rotation of the steering wheel, and determines the steering wheel angle consistent with the rack position.

[0051] In certain embodiments, during the reset step, the steering wheel angle is determined based on a result of a comparison between the set engine torque and a stop threshold.

[0052] The stop threshold is the value of the set engine torque for which it is considered that the rack can no longer be moved either because the wheels are blocked in rotation or because the rack is at the stop.

[0053] Thus, the reset step is only carried out, for example, if the set engine torque is greater than the stop threshold. In other words, only if the steering wheel angle can become inconsistent with the actual position of the rack.

[0054] Another aspect of the invention relates to an electric power steering without mechanical link implementing a method according to the invention. Brief description of the drawings

[0055] The invention will be better understood, thanks to the following description, which relates to one or more embodiments according to the present invention, given as non-limiting examples and explained with reference to the appended schematic drawings, in which:

[0056] [Fig.l] is a schematic representation of a power steering system without mechanical linkage;

[0057] [Fig.2] is an illustration of an evolution of a corrected setpoint motor torque as a function of a setpoint motor torque;

[0058] [Fig.3] is a diagram representing a correction frequency and a corrected operating value as a function of the set motor torque. Description of the embodiments

[0059] Only the elements necessary for understanding the invention have been shown. To facilitate reading of the drawings, the same elements bear the same references from one figure to another.

[0060] It will be noted that in this document, the terms "right" and "left", used to describe a direction of rotation of the wheels of a vehicle, and "clockwise" and "counterclockwise", used to describe a direction of rotation of a steering wheel of the vehicle, refer to this direction relative to the vehicle in a forward driving situation, that is to say the direction considered by a driver positioned normally in front of the steering wheel.

[0061] The invention relates to a method for indicating a target engine torque determining a corrected target engine torque Cmc for a control motor M of a power steering system 1 for a vehicle 2, and more particularly for a motor vehicle 2 intended for the transport of people.

[0062] The control motor M will preferably be an electric motor, with two directions of operation, and preferably a rotary electric motor, of the brushless type. The control motor M engages directly on an axis of rotation of a steering wheel 3, for example by means of a pinion. For example, the control motor M has a maximum motor torque of less than 5Nm, for example 4Nm, preferably 3Nm. Thus, the size of the control motor M is less than 10cm*10cm, for example approximately 8cm*8cm and a current consumption should be less than 70A.

[0063] In a manner known per se, and as can be seen in [Fig. 1], said power steering system 1 comprises the steering wheel 3 on which a driver can exert a force, called "steering wheel torque". An angle 03 and a direction of rotation of the steering wheel 3 is measured by an angle sensor 23.

[0064] The steering wheel torque T3, the angle 03 and the direction of rotation of the steering wheel 3 are transmitted to an electronic rack control unit 20 and an electronic steering wheel control unit 21.

[0065] Said steering wheel 3 is not mechanically linked to a steering rack 6, which is itself guided in translation in a steering casing 7 fixed said vehicle 2. In other words, the steering wheel 3 is mechanically detached from the steering rack 6. In this case, the steering system 1 comprises a steering wheel unit mechanically independent of a rack unit. In other words, a force applied to the steering wheel unit is not mechanically transmitted to the rack unit, and vice versa. The power steering system 1 is of the “without mechanical link” or “steer-by-wire” type.

[0066] The steering wheel unit comprises said steering wheel 3 and at least the electronic steering wheel control unit 21 which determines in particular a torque to be felt by the driver during a maneuver of the steering wheel 3, hereinafter called the set engine torque Cmo. The set engine torque Cmo is intended in particular to make the driver feel torque information consistent with a life situation in which the vehicle 2 is located (turn, straight line, level of grip, condition of the road surface, etc.). The electronic steering wheel control unit 21 controls the steering wheel torque to the set engine torque Cmo by means of the control motor M. The control motor M then exerts an engine torque on the axis of rotation of the steering wheel so that the steering wheel torque is close to or equal to the set engine torque Cmo.

[0067] The rack unit comprises said rack 6 and at least the electronic rack control unit 20 which in particular controls an angular position of the rack 6 so that it is consistent with a set angular position. The set angular position is generally consistent with the angle of the steering wheel 03, but it can be modified by functions of the vehicle 2 such as a trajectory tracking function or a parking assistance function of the vehicle 2.

[0068] The electronic rack control unit 20 determines a setpoint rack torque enabling the control of a maneuvering motor 24 exerting a motor torque T12 on the rack 6. In other words, the electronic rack control unit 20 controls the angular position of the rack 6 to the setpoint angular position by determining the setpoint rack torque of the maneuvering motor 2.

[0069] The angular position of the rack 6 can be deduced from an angular position 012 of the maneuvering motor 24.

[0070] Preferably, the ends of the rack 6 are each connected to a steering rod 8, 9 connected to the steering knuckle of a steered wheel 10, 11 (respectively a left wheel 10 and a right wheel 11), such that the longitudinal translational movement of the rack 6 makes it possible to modify a steering angle (yaw angle) of the steered wheels 10, 11. The steered wheels 10, 11 may also preferably be drive wheels.

[0071] The maneuvering motor 24 will preferably be an electric motor, with two operating directions, and preferably a rotary electric motor, of the brushless type.

[0072] The maneuvering motor 24 can engage directly on the rack of direction 6, for example by means of a 13 pinion.

[0073] The indication method according to the invention implements a step of receiving the setpoint engine torque Cmo, then a correction step so as to obtain the corrected setpoint engine torque Cmc, and finally an indication step in which the control motor M applies the corrected setpoint engine torque Cmc to the axis of rotation of the steering wheel. The corrected setpoint engine torque Cmc is the engine torque which serves as a setpoint for the control motor M.

[0074] In the correction step, the corrected target engine torque Cmc is determined as a function of a result of a comparison between the target engine torque Cmo and a normal operating threshold Sf. In other words, during the correction step, the target engine torque Cmo is compared to the normal operating threshold Sf, and as a function of this result, the corrected target engine torque Cmc is determined.

[0075] In certain embodiments, and as illustrated in [Fig.2] and 3, the normal operating threshold Sf is equal on the one hand to the maximum of a normal operating range Zf and on the other hand to the minimum of a corrected operating range Zc. The normal operating threshold Sf is a setpoint engine torque value Cmo which separates the normal operating range Zf from the corrected operating range Z c*

[0076] The normal operating threshold Sf determines from which setpoint motor torque Cmo a correction of the setpoint motor torque Cmo is applied.

[0077] For example, if the setpoint motor torque Cmo is lower than the normal operating threshold Sf, the setpoint motor torque Cmo is in the normal operating range Zf and no correction applies. Thus, the corrected setpoint motor torque Cmc is equal to the setpoint motor torque Cmo over the normal operating range Zf.

[0078] If the set engine torque Cmo is greater than the normal operating threshold Sf, the set engine torque Cmo is in the corrected operating range Zc and a correction is made by the electronic steering wheel control unit 21.

[0079] Over the corrected operating range Zc, the corrected setpoint motor torque Cmc varies over time with a correction frequency Fc around a corrected operating value Vfc.

[0080] In certain embodiments, the correction frequency Fc depends on the set motor torque Cmo as illustrated in [Fig.2] or 3 and / or on time.

[0081] In Figures 2 and 3, the correction frequency increases with the set motor torque.

[0082] In certain embodiments, the correction frequency Fc increases with the time during which the set motor torque Cmo is requested.

[0083] The corrected operating value Vfc corresponds to the torque value around which oscillates the corrected setpoint motor torque Cmc. The corrected operating value Vfc is chosen to be lower than the setpoint motor torque Cmo.

[0084] In certain embodiments, the corrected operating value Vfc depends on the set motor torque Cmo and / or time.

[0085] For example, the corrected operating value Vfc increases with the set motor torque Cmo as illustrated in [Fig.3].

[0086] For example, the corrected operating value Vfc increases with the time during which the set motor torque Cmo is requested.

[0087] In certain embodiments, the corrected setpoint motor torque Cmc varies with a correction amplitude around the corrected operating value Vfc.

[0088] The difference between the upper value and the lower value of the corrected target motor torque Cmc for a given target motor torque Cmo corresponds to the correction amplitude.

[0089] The correction amplitude influences the feeling of vibrations by the driver.

[0090] In some embodiments, the correction magnitude depends on the torque motor setpoint Cmoet / or time.

[0091] For example, the correction amplitude increases with the set motor torque Cmo

[0092] For example, the correction amplitude increases with the time during which the engine torque setpoint Cmoest requested.

[0093] In certain embodiments, the corrected setpoint motor torque Cmc is less than or equal to the setpoint motor torque Cmo.

[0094] In certain embodiments, the corrected setpoint motor torque Cmc is less than the setpoint motor torque Cmo over the corrected operating range Zc.

[0095] Thus, the control motor M does not provide, at least permanently, the set engine torque Cmo. The control motor M provides an engine torque at least partially lower than the set engine torque Cmo. Thus, the control motor M has a smaller size than a control motor that has to provide the entire set engine torque Cmo. The invention makes it possible to reduce the size and electrical consumption of the control motor M and of the electronic control unit compared to the state of the art of a control motor exerting the torque directly on the axis of rotation of the steering wheel.

[0096] The variation of the corrected target engine torque Cmc causes a vibration-like sensation in the steering wheel 3 which, according to the applicant's discoveries, makes it possible to simulate a greater engine torque than that actually applied. A driver of the vehicle holding the steering wheel 3 therefore has the impression of a greater resistive torque than that actually applied.

[0097] However, the corrected target engine torque Cmc does not allow the steering wheel to be locked. rotating steering wheel. In other words, the driver, despite the vibrations felt, can continue to turn the steering wheel 3 indefinitely in one direction without changing the position of the rack 6. In order to avoid the driver having to make numerous turns in the opposite direction before moving the rack 6 in the opposite direction again, the method according to the invention comprises a reset step.

[0098] The reset step following the correction step determines the steering wheel angle 03 upon detection of a movement of the steering wheel 3 in a direction opposite to a direction that caused the correction step. In other words, the reset step detects a counter-steering, or a change in the direction of rotation of the steering wheel 3, and determines the steering wheel angle 03 consistent with the position of the rack 6.

[0099] In certain embodiments, during the reset step, the steering wheel angle 03 is determined as a function of a result of a comparison between the set engine torque Cmo and a stop threshold Sb.

[0100] The stop threshold Sb is the value of the set engine torque Cmo for which it is considered that the rack 6 can no longer be moved either because the wheels 10, 11 are blocked in rotation or because the rack 6 is at the stop.

[0101] Thus, the reset step is only carried out, for example, if the set engine torque Cmo is greater than the stop threshold Sb. In other words, only if the steering wheel angle 03 can become inconsistent with the actual position of the rack 6.

[0102] The method also determines a torque signal which depends on the set engine torque Cmo. This torque signal, in addition to the corrected set engine torque Cmc, indicates to the driver the set engine torque Cmo which should be felt.

[0103] In some embodiments, the torque signal is determined based on the corrected target motor torque Cmc.

[0104] In some embodiments, the torque signal is a haptic, audible, or visual signal.

[0105] Thus, the driver receives information on the set engine torque by means of other senses.

[0106] Although the present invention has been described with reference to specific embodiments, it is obvious that modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0107] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and vice versa, all the characteristics described with reference to a device are transposable, alone or in combination, to a process.

Claims

Claims

1. Method for indicating a target engine torque determining a corrected target engine torque (Cmc) for a control motor (M) of an electric power steering (1) without mechanical link, said control motor (M) receiving the corrected target engine torque (Cmc) and exerting a motor torque on an axis of rotation comprising a steering wheel (3), said method being implemented by an electronic steering wheel control unit (21) and comprising: - A step of receiving a target engine torque (Cmo), - A correction step in which the corrected target engine torque (Cmc) is determined as a function of a result of a comparison between the target engine torque (Cmo) and a normal operating threshold (Sf), said corrected target engine torque (Cmc) varying with a correction frequency (Fc) around a corrected operating value (Vfc) over a corrected operating range (Zc),said corrected operating value (Vfc) being lower than the setpoint engine torque (Cmo), - An indication step in which the control motor (M) applies the corrected setpoint engine torque (Cmc) to the axis of rotation of the steering wheel.,

2. An indication method according to claim 1, wherein the corrected target engine torque (Cmc) varies with a correction amplitude around the corrected operating value (Vfc).

3. Indication method according to claim 2, in which the correction amplitude depends on the set motor torque (Cmo) and / or time.

4. An indication method according to any one of the preceding claims, wherein the corrected target engine torque (Cmc) is equal to the target engine torque (Cmo) over a normal operating range (4).

5. Indication method according to claim 4, in which the normal operating threshold (Sf) is equal on the one hand to the maximum of the normal operating range (Zf) and on the other hand to the minimum of the corrected operating range (Zc).

6. An indicating method according to any one of the preceding claims- preceding, in which the correction frequency (Fc) depends on the set motor torque (Cmo) and / or time.

7. Indication method according to any one of the preceding claims, determining a torque signal as a function of the set engine torque (Cmo).

8. An indication method according to any one of the preceding claims, comprising a resetting step, subsequent to the correction step, in which a steering wheel angle (03) is determined upon detection of a movement of the steering wheel (3) in a direction opposite to a direction having caused the correction step.

9. Indication method according to claim 8, wherein during the reset step, the steering wheel angle (03) is determined as a function of a result of a comparison between the set engine torque (Cmo) and a stop threshold (Sb).

10. Electric power steering (1) without mechanical link implementing a method according to any one of the preceding claims.

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