Method for securing a target torque for a motor in a power steering system.

Abstract

Method for securing (100, 200) a target torque for a motor (24, 24') exerting a motor torque (T12, T12') on a device (6) of a power steering system (1), and comprising: A first determination step (ED1) in which a first intermediate value (Ckp) of the target torque is determined; A second determination step (ED2) in which a limit value (Bkpl, Bkpu) of the first intermediate value (Ckp) of the target torque is determined; A third determination step (ED3) in which a parameter representative of the average motor torque exerted at a previous instant (Pfi, Pfc) is determined; A securing step (ES) in which a target value (Ctgs) of the target torque is determined as a function of the first intermediate value (Ckp), the limit value (Bkpl, Bkpu) and the parameter representative of the average motor torque exerted at the previous instant (Pfi, Pfc). Figure 1

Description

Title of the invention: Method for securing a set torque for a motor of a power steering system. Technical field

[0001] The invention relates to the field of vehicles comprising a power steering system and more particularly a method for securing a set torque for an engine. State of the prior art

[0002] A vehicle steering system is intended to enable a driver to control a trajectory of the vehicle by changing an angle of orientation of the vehicle's wheels by means of a steering wheel. The driver changes an angle of the steering wheel by exerting a force on it.

[0003] Generally, a steering system comprises several elements including said steering wheel, a rack, and two wheels each connected to a connecting 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 connecting rods. An angular position of the rack relative to a steering housing, hereinafter called the rack angular position, is an image of the orientation angle of the wheels.

[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 steering wheel unit comprises said steering wheel and at least one means for estimating the angle of the steering wheel, for example an angle sensor.

[0006] The rack unit comprises said movable rack in the steering casing, and at least one electronic control unit which in particular controls the angular position of the rack so that it is consistent with a set angular position. The set angular position is generally consistent with the steering wheel angle, but it can be modified by vehicle functions such as a trajectory tracking function or a vehicle parking assistance function.

[0007] The electronic control unit determines a setpoint motor torque, or setpoint torque in the remainder of the description, making it possible to control at least one motor exerting a motor torque on the rack. In other words, the controller controls the angular position of the rack to the setpoint angular position by determining the setpoint torque of the motor.

[0008] Securing the correct operation of the controller and more particularly the control of the rack position making it possible to ensure consistency between the set angular position and the rack angular position is important in order to guarantee the safety of the vehicle.

[0009] There is a known solution for detecting a malfunction of the rack unit. The malfunction of the rack unit is defined as a difference between the rack angular position and the set angular position. When a malfunction is detected, the control is then carried out by a backup controller.

[0010] The disadvantage of this solution is that it does not discriminate the origin of the operating fault. Thus, it is not possible to determine whether the difference between the rack angular position and the set angular position is due to a failure of the controller or to another cause such as wheel lock, for example.

[0011] There is therefore a need for more efficient security of the controller. Statement of the invention

[0012] One embodiment relates to a method for securing a setpoint torque for a motor, said motor exerting a motor torque on a device of a power steering system of a vehicle so as to modify an angular position of said device, the method being executed by at least one controller and comprising: - A first determination step in which at least one first intermediate value of the setpoint torque is determined as a function of at least one parameter representative of a setpoint angular position of the device and of at least one parameter representative of the angular position of the device; - A second determination step in which a limit value of the at least one first intermediate value of the setpoint torque is determined as a function of at least the parameter representative of the setpoint angular position and at least the parameter representative of the angular position; - A third determination step in which a parameter representative of the average engine torque exerted at a previous instant is determined; - A safety step in which a target value of the setpoint torque is determined as a function of at least the first intermediate value of the setpoint torque, the limit value of the first intermediate value of the setpoint torque and the parameter representing the average engine torque exerted at the previous instant.

[0013] The controller may be an electronic control unit.

[0014] The setpoint torque designates any quantity representative of the setpoint torque allowing the motor to be controlled in torque.

[0015] In some embodiments, the device to which the motor exerts the engine torque is a rack of the power steering system of a vehicle.

[0016] In some embodiments, the power steering system is of the type without mechanical linkage.

[0017] The first step determines at least a first intermediate value of the target torque. In other words, the target torque can be determined, in certain embodiments, as a function of several intermediate values.

[0018] The first intermediate value is determined as a function of at least the parameter representative of the set angular position of the device and at least the parameter representative of the angular position of the device. The parameter representative of the set angular position or the parameter representative of the angular position may be an angle, a position of the device relative to a point of the motor, or an angular position of the motor. The parameter representative of the angular position may be determined, estimated or measured.

[0019] In certain embodiments, the first intermediate value is obtained in particular by calculating the difference between the parameter representing the set angular position and the parameter representing the angular position, then by multiplying the difference by a first gain. The first gain is subsequently referred to as “proportional gain”.

[0020] In some embodiments, the first intermediate value is obtained by an implementation saturation of the product of the difference by the proportional gain. Thus, there is no "overflow" of the first intermediate value, that is to say that the first intermediate value is limited.

[0021] In certain embodiments, the first determination step determines the at least one first intermediate value of the target torque also as a function of the speed of the vehicle.

[0022] More specifically, the proportional gain may depend on the vehicle speed.

[0023] Thus, the proportional gain modifies a speed with which the vehicle wheels will follow the set angular position. At the vehicle level, this modifies a precision with which the driver can control a wheel orientation angle. By decreasing the proportional gain, this precision decreases but driving comfort increases because this filters out higher frequency wheel orientation movements.

[0024] It is common for vehicles to be fitted with a rack with a variable ratio depending on the vehicle speed between the set angular position and the wheel orientation angle. In other words, at 20 km / h, the rack ratio is substantially direct, that is to say that the wheel orientation angle varies significantly. possibly proportional to the set angular position, because the vehicle's trajectory evolves slowly. At high speed, the rack ratio is not very direct, that is to say that the wheel orientation angle varies less than the set angular position, because the slightest variation in the wheel orientation angle causes the car to deviate / shake significantly.

[0025] According to one embodiment, the proportional gain increases with the vehicle speed.

[0026] Thus, at 20 km / h, the proportional gain is reduced so as to degrade the precision of steering the wheel orientation angle but to improve driving comfort, for example in the case of rapid variations in the set angular position, i.e. if the driver swings the steering wheel.

[0027] At high speed, for example 130 km / h, the rack ratio is not very direct, it is therefore important to maintain good precision and therefore a significant proportional gain.

[0028] The second step determines the limit value of the at least one first intermediate value of the setpoint torque. When several intermediate values ​​are determined, the second step determines several limit values. In other words, for each intermediate value determined by the first determination step, the second determination step determines a limit value.

[0029] In certain embodiments, the limit value is obtained in particular by calculating the difference between the parameter representing the set angular position and the parameter representing the angular position, then by multiplying the difference by a first limit gain. The first limit gain is subsequently referred to as the “limit proportional gain”.

[0030] The limit value may be a limit value pair comprising an upper limit value and a lower limit value. Alternatively, only one of the upper limit value or the lower limit value may be determined, and the other of the upper or lower limit value is calculated by symmetry.

[0031] In certain embodiments, the second determination step determines the limit value of the at least one first intermediate value of the setpoint torque as a function of the vehicle speed.

[0032] More specifically, the limiting proportional gain may depend on the vehicle speed.

[0033] The third step determines the parameter representative of the average engine torque exerted at the previous instant.

[0034] By previous instant is meant a moment located in the past in relation to the calculation of the target value of the current setpoint torque. The previous instant depends in particular on a speed of implementation of the safety process.

[0035] Finally, the securing step combines the at least one first intermediate value of the setpoint torque, the limit value of the at least one first intermediate value of the setpoint torque and the parameter representative of the average engine torque exerted at the previous instant so as to determine the target value of the setpoint torque.

[0036] The parameter representing the average engine torque can be obtained in various ways, such as for example by a low-pass filter. Using the parameter representing the average engine torque makes it possible to ignore rapid changes in the engine torque.

[0037] The target value of the setpoint torque is the torque value that we want the motor to exert on the device. This is a secure setpoint torque. In other words, the securing step makes it possible to guarantee that the requested setpoint torque, corresponding to the target value of the setpoint torque, is included in a defined interval around the parameter representing the average motor torque exerted at a previous instant. In other words, there is a framework for the target value of the setpoint torque. There can therefore be no significant and sudden deviation from the requested setpoint torque. Thus, we avoid errors linked to a malfunction of the controller implementing at least the first step or we limit the effects of a failure without switching to another regulation strategy such as for example a back-up law, or another controller.

[0038] In certain embodiments, the parameter representative of the average engine torque exerted at the previous instant is determined as a function of at least the parameter representative of the set angular position and at least the parameter representative of the angular position of the device.

[0039] One of the ways of determining the parameter representative of the average engine torque is to use at least the parameter representative of the set angular position and at least the parameter representative of the angular position of the device.

[0040] In certain embodiments, the parameter representative of the average engine torque is obtained in particular by calculating the difference between the parameter representative of the set angular position and the parameter representative of the angular position, then by multiplying the difference by a gain designated, subsequently, by the terms “integral gain”.

[0041] In certain embodiments, the parameter representative of the average engine torque is obtained by an implementation saturation and an integration of the product of the difference by the integral gain. Thus, there is no "overflow" of the parameter representative of the average engine torque, that is to say that the parameter representative of the average engine torque is limited.

[0042] In certain embodiments, the parameter representative of the average engine torque is determined at least as a function of the vehicle speed.

[0043] More specifically, the integral gain may depend on the vehicle speed.

[0044] In certain embodiments, the parameter representative of the average engine torque exerted at the previous instant is determined as a function of the target value of the setpoint torque at the previous instant or as a function of a measurement of a parameter representative of the engine torque exerted at the previous instant.

[0045] The measurement of the engine torque exerted can be carried out directly or indirectly on the device or on the engine.

[0046] In certain embodiments, the parameter representative of the average engine torque exerted at the previous instant is determined by applying a low-pass filter to the target value of the setpoint torque at the previous instant or to the measurement of the parameter representative of the engine torque exerted at the previous instant.

[0047] In some embodiments, the low-pass filter is 2nd order.

[0048] Thus, we obtain a static part of the engine torque exerted, that is to say that we removes rapid variations in the engine torque exerted. The low-pass filter allows a sort of “average” engine torque to be obtained.

[0049] In certain embodiments, the parameter representative of the average engine torque exerted at the previous instant is obtained by a multiplication of the target value of the setpoint torque at the previous instant filtered or the measurement of the parameter representative of the engine torque exerted at the previous instant filtered, with a gain subsequently designated by “static gain”.

[0050] In some embodiments, the static gain depends on the vehicle speed.

[0051] In some embodiments, the securing method comprises:

[0052] - a first evaluation step in which a temporary value of the torque setpoint is evaluated as a function of at least one first intermediate value of the setpoint torque and the parameter representative of the average motor torque exerted at the previous instant, and

[0053] - a second evaluation step in which a limit value of the value temporary value of the setpoint torque is determined as a function of the limit value of at least one first intermediate value of the setpoint torque and of the parameter representative of the average motor torque exerted at the previous instant;

[0054] the securing step determining the target value of the setpoint torque as a function of at least the temporary value of the setpoint torque and the limit value of the temporary value of the setpoint torque.

[0055] For example, the first evaluation step sums the at least one first intermediate value of the setpoint torque and the parameter representative of the average engine torque exerted at the previous instant. In other words, if several intermediate values ​​are determined, the first evaluation step sums the plurality of intermediate values ​​of the setpoint torque and the parameter representative of the average engine torque exerted at the previous moment.

[0056] For example, the second evaluation step sums the limit value of the first intermediate value of the setpoint torque and the parameter representing the average engine torque exerted at the previous instant. In other words, if several intermediate values ​​are determined, therefore if several limit values ​​are determined, the second evaluation step sums the plurality of limit values ​​and the parameter representing the average engine torque exerted at the previous instant.

[0057] The securing step then performs a limitation of the temporary value of the setpoint torque by the limit value of the temporary value of the setpoint torque so that the temporary value of the setpoint torque is included in the limit value of the temporary value.

[0058] In certain embodiments, the first determination step, the third determination step and the first evaluation step are carried out by a position controller of the device, and the second determination step, the third determination step, the second evaluation step and the securing step are carried out by a securing controller receiving in particular as input the temporary value of the setpoint torque of the position controller.

[0059] Thus the safety controller is positioned independently and after the position controller. It is therefore possible on the one hand to make modifications or adjustments to the position controller independently of the safety controller and on the other hand to position the safety controller in a partition of an electronic control unit that is more robust to failures than that of the position controller. Securing the setpoint torque of the motor is therefore ensured.

[0060] In some embodiments, the method comprises: - A first securing step in which at least one target value of the at least one first intermediate value of the setpoint torque is determined as a function of the at least one first intermediate value of the setpoint torque and the limit value of the at least one first intermediate value of the setpoint torque;

[0061] the securing step determining the target value of the setpoint torque as a function of at least the target value of the at least one first intermediate value of the setpoint torque and of the parameter representative of the average engine torque exerted at the previous instant.

[0062] The first securing step consists for example of a limitation of the at least one first intermediate value of the setpoint torque by the limit value of the at least one first intermediate value of the setpoint torque. Thus the target value of the at least one first intermediate value of the setpoint torque is at most or at least equal to the limit value of the at least one first intermediate value of the torque setpoint.

[0063] In the case where several intermediate values ​​are determined, each intermediate value is limited by the appropriate limit value.

[0064] The securing step determines the target value of the setpoint torque as a function of at least the target value of the at least one first intermediate value of the setpoint torque and the parameter representative of the average engine torque exerted at the previous instant.

[0065] For example, the target value of the setpoint torque is obtained by the sum of the at least one target value of the at least one first intermediate value of the setpoint torque and the parameter representative of the average engine torque exerted at the previous instant. In the case where several target values ​​of several intermediate values ​​have been determined, the target value of the setpoint torque is obtained by the sum of all the target values ​​of the intermediate values ​​and the parameter representative of the average engine torque exerted at the previous instant.

[0066] In certain embodiments, the first determination step also determines a second intermediate value of the setpoint torque as a function of at least one parameter representative of a setpoint speed of said device and a parameter representative of a speed of said device, and the second determination step also determines a limit value of the second intermediate value of the setpoint torque as a function of at least the parameter representative of the setpoint speed of said device and the parameter representative of the speed of said device.

[0067] The parameter representing the set speed of said device or the parameter representing the speed of said device can be determined on the basis of the parameter representing the set angular position or the parameter representing the angular position of the device or be measured directly or indirectly on the motor or on the device.

[0068] In certain embodiments, the second intermediate value is obtained in particular by calculating the difference between the parameter representing the set speed and the parameter representing the speed of the device, then by multiplying the difference by a second gain. The second gain is subsequently referred to as the “derived gain”.

[0069] In some embodiments, the second intermediate value is obtained by an implementation saturation of the product of the difference by the derived gain. Thus, there is no "overflow" of the second intermediate value, i.e. the second intermediate value is limited.

[0070] In certain embodiments, the first determination step determines the second intermediate value of the target torque also as a function of the vehicle speed.

[0071] More specifically, the derived gain may depend on the vehicle speed.

[0072] Thus, the derivative gain modifies a speed with which the vehicle wheels will follow the set angular position. At the vehicle level, this modifies a precision with which the driver can control a wheel orientation angle. By reducing the derivative gain, this precision decreases but driving comfort increases because this filters out higher frequency wheel orientation movements.

[0073] According to one embodiment, the derived gain increases with the vehicle speed.

[0074] Thus, at 20 km / h, the derived gain is reduced so as to degrade the precision of steering the wheel orientation angle but to improve driving comfort, for example in the case of rapid variations in the set angular position, i.e. if the driver oscillates the steering wheel.

[0075] At high speed, for example 130 km / h, the rack ratio is not very direct, it is therefore important to maintain good precision and therefore a significant derivative gain.

[0076] In certain embodiments, the limit value of the second intermediate value of the setpoint torque is obtained in particular by calculating the difference between the parameter representing the setpoint speed and the parameter representing the speed, then by multiplying the difference by a second limit gain. The second limit gain is subsequently designated by the terms “limit derivative gain”.

[0077] In certain embodiments, the second determination step determines the limit value of the second intermediate value of the setpoint torque as a function of the vehicle speed.

[0078] More specifically, the limit derivative gain may depend on the vehicle speed.

[0079] Another aspect of the invention relates to a vehicle comprising a power steering system of the type without mechanical link implementing a securing method according to the invention. Brief description of the drawings

[0080] The invention will be better understood, thanks to the following description, which relates to several embodiments according to the present invention, given as non-limiting examples and explained with reference to the appended schematic drawings, in which:

[0081] [Fig.l] is a schematic representation of a first embodiment of the invention;

[0082] [Fig.2] is a schematic representation of a first part of the first embodiment;

[0083] [Fig.3] is a schematic representation of a second part of the first embodiment;

[0084] [Fig.4] is a schematic representation of a second embodiment;

[0085] [Fig.5] is a schematic representation of a vehicle comprising a system of power steering without mechanical link. Description of the embodiments

[0086] Only the elements necessary for understanding the invention have been shown.

[0087] The invention relates to a method 100, 200 for securing a set torque for a pair of assistance motors 24, 24' of a power steering system 1 for a vehicle 2, and more particularly for a motor vehicle 2 intended for the transport of people.

[0088] In a manner known per se, and as can be seen in [Fig. 5], said power steering system 1 comprises a steering wheel 3 on which a driver can exert a force, called “steering wheel torque” T3. An angle 03 of the steering wheel 3 is measured by an angle sensor 23.

[0089] The steering wheel torque T3 and the angle 03 of the steering wheel are transmitted to an electronic rack control unit 20.

[0090] 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 to 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 T3 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.

[0091] The steering wheel unit comprises said steering wheel 3 and at least one electronic steering wheel control unit, not shown, which determines in particular a torque to be felt by the driver during a maneuver of the steering wheel 3, hereinafter called the target control torque. The target control torque 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 surface, etc.). The electronic steering wheel control unit controls the steering wheel torque T3 to the target control torque by means of a control motor, not shown. The control motor then exerts a control motor torque so that the steering wheel torque T3 is close to or equal to the target control torque.

[0092] In certain embodiments, the securing method 100, 200 according to the invention can be exercised on the control engine.

[0093] The rack unit comprises said rack 6 and at least the electronic rack control unit 20 which in particular controls an angular position Pc of the rack mesh 6 so that it is consistent with a set angular position Ptg. The set angular position Ptg is generally consistent with the steering wheel angle 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.

[0094] The electronic rack control unit 20 determines a setpoint motor torque, or setpoint torque in the remainder of the description, making it possible to control the pair of assistance motors 24, 24' which exert a motor torque T12, T12' on the rack 6. In other words, the electronic rack control unit 20 controls the angular position Pc of the rack 6 to the setpoint angular position Ptg by determining the setpoint torque of the pair of motors 24, 24'.

[0095] The angular position Pc of the rack 6 can be deduced from an angular position 012, 012' of each motor 24, 24'.

[0096] 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.

[0097] Each assistance motor 24, 24' will preferably be an electric motor, with two operating directions, and preferably a rotary electric motor, of the brushless type.

[0098] Each assistance motor 24, 24' can engage directly on the steering rack 6, for example by means of a pinion 13, 13'.

[0099] A distribution of the set torque Ctgs on each of the motors 24, 24' is carried out for example as a function of the availability of each of the motors.

[0100] In the remainder of the description, reference will be made to only one motor 24 of the pair of motors. However, it is clear that the invention can also be applied to the other motor 24'.

[0101] Figures 1, 2 and 3 illustrate a first embodiment 100, while [Fig.4] illustrates a second embodiment 200 of the method according to the invention. However, to facilitate reading of the drawings, the same elements bear the same references from one figure to another.

[0102] The invention relates more specifically to the method 100, 200 for securing the setpoint torque for the motor 24. As described above, said motor 24 exerts the engine torque T12 on the rack 6 of the power steering system 1 of the vehicle 2 so as to modify the angular position Pc of the rack. The method 100, 200 is executed by the electronic rack control unit 20 and comprises a first step of determining EDI in which a first intermediate value Ckp of the setpoint torque is determined as a function of at least one parameter representative of a setpoint angular position Ptg of the rack 6 and at least one parameter representative of the angular position Pc of the rack 6.

[0103] The setpoint torque designates any quantity representative of the setpoint torque making it possible to control the torque of the motor 24.

[0104] The parameter representative of the set angular position Ptg or the parameter representative of the angular position Pg can be an angle, a position of the rack relative to a point of the motor 24, or an angular position 012 of the motor 24. The parameter representative of the angular position Pg can be determined, estimated or measured.

[0105] In each of the embodiments illustrated in the figures, the first intermediate value Ckp is obtained in particular by calculating the difference of the parameter representing the set angular position Ptg and the parameter representing the angular position Pg, then by multiplying the difference by a first gain Kp. The first gain Kp is designated, subsequently, by the terms “proportional gain”. Then the first intermediate value Ckp is obtained by an implementation saturation Sat of the product of the difference by the proportional gain Kp. Thus, there is no “overflow” of the first intermediate value Ckp, that is to say that the first intermediate value Ckp is limited.

[0106] The first EDI determination step determines the first intermediate value Ckp of the target torque also as a function of the speed V of the vehicle 2.

[0107] More specifically, the proportional gain Kp depends on the speed V of the vehicle 2. Thus, the proportional gain Kp modifies a speed with which the wheels of the vehicle will follow the set angular position. At the vehicle level, this modifies a precision with which the driver can control a wheel orientation angle. By decreasing the proportional gain Kp, this precision decreases but driving comfort increases because this filters out higher frequency wheel orientation movements.

[0108] It is common for vehicles to be equipped with a rack with a variable ratio depending on the speed V of the vehicle between the set angular position and the wheel orientation angle. In other words, at 20 km / h, the rack ratio is substantially direct, that is to say that the wheel orientation angle varies substantially proportionally to the set angular position, because the trajectory of the vehicle evolves slowly. At high speed, the rack ratio is not very direct, that is to say that the wheel orientation angle varies less than the set angular position Ptg, because the slightest variation in the wheel orientation angle causes the car to deviate / shake significantly.

[0109] According to one embodiment, the proportional gain Kp increases with the speed V vehicle 2.

[0110] Thus, at 20 km / h, the proportional gain Kp is reduced so as to degrade the precision of steering the wheel orientation angle but to improve driving comfort, for example in the case of rapid variations in the set angular position, i.e. if the driver oscillates the steering wheel.

[0111] At high speed, for example 130 km / h, the rack ratio is not very direct, it is therefore important to maintain good precision and therefore a significant proportional gain Kp.

[0112] The first determination step EDI also determines a second intermediate value Ckd of the setpoint torque as a function of at least one parameter representative of a setpoint speed Vctg of the rack 6 and of a parameter representative of a speed Vc of the rack 6.

[0113] The parameter representative of the set speed Vctg of the rack or the parameter representative of the speed Vc of the rack can be determined on the basis of the parameter representative of the set angular position Ptg or of the parameter representative of the angular position Pc of the rack or be measured directly or indirectly on the motor 24 or on the rack.

[0114] The second intermediate value Ckd is obtained in particular by calculating the difference between the parameter representing the set speed Vctg and the parameter representing the speed Vc of the rack, then by multiplying the difference by a second gain Kd. The second gain Kd is subsequently referred to as “derived gain”.

[0115] The second intermediate value Ckd is obtained by an implementation saturation Sat of the product of the difference by the derived gain Kd. Thus, there is no “overflow” of the second intermediate value, that is to say that the second intermediate value Ckd is limited.

[0116] The first EDI determination step determines the second intermediate value Ckd of the target torque also as a function of the speed V of the vehicle 2.

[0117] More specifically, the derivative gain Kd may depend on the speed V of the vehicle 2. Thus, the derivative gain Kd modifies a speed with which the wheels of the vehicle will follow the set angular position. At the level of the vehicle 2, this modifies a precision with which the driver can control a wheel orientation angle. By decreasing the derivative gain Kd, this precision decreases but driving comfort increases because this filters out higher frequency wheel orientation movements.

[0118] According to one embodiment, the derived gain Kd increases with the speed V of vehicle 2.

[0119] Thus, at 20km / h, the derived gain Kd is reduced so as to degrade the precision of control of the wheel orientation angle but to improve driving comfort, for example in the case of rapid variations in the set angular position, i.e. if the driver swings the steering wheel.

[0120] At high speed, for example 130km / h, the rack ratio is not very direct, it is therefore important to maintain good precision and therefore a significant derivative gain Kd.

[0121] The method 100, 200 comprises a second determination step ED2 in which a limit value Bkpb Bkpu of the first intermediate value Ckp of the setpoint torque is determined as a function of the parameter representative of the setpoint angular position Ptg and of the parameter representative of the angular position Pc.

[0122] The limit value Bkpb Bkpu is obtained in particular by calculating the difference between the parameter representing the set angular position Ptg and the parameter representing the angular position Pc, then by multiplying the difference by a first limit gain Bkp. The first limit gain Bkp is subsequently designated by the terms “limit proportional gain”.

[0123] The limit value Bkpb Bkpu may be a limit value pair comprising an upper limit value Bkpu and a lower limit value Bkpb. Alternatively, only one of the upper limit value Bkpu or the lower limit value Bkpi may be determined, and the other of the upper limit value Bkpu or the lower limit value Bkpi is calculated by symmetry.

[0124] The second determination step ED2 determines the limit value Bkpb Bkpu of the first intermediate value Ckp of the setpoint torque as a function of the speed V vehicle 2. More specifically, the limit proportional gain Bkp can depend on the speed V vehicle 2.

[0125] The second determination step ED2 also determines a limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint torque as a function of the parameter representative of the setpoint speed Vctg and of the parameter representative of the speed Vc of the rack 6.

[0126] The limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint torque is obtained in particular by calculating the difference of the parameter representing the setpoint speed Vctg and the parameter representing the speed Vc, then by multiplying the difference by a second limit gain Bkd. The second limit gain Bkd is designated, subsequently, by the terms “limit derivative gain”.

[0127] The second determination step ED2 determines the limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint torque as a function of the speed V vehicle 2. More specifically, the limit derivative gain Bkd can depend on the speed V vehicle 2.

[0128] The method comprises a third determination step ED3 in which a parameter representative of the average engine torque exerted at a previous instant Pfc, Pfl is determined.

[0129] By previous instant is meant a moment located in the past with respect to the calculation of a target value Ctgs of the current setpoint torque. The previous instant depends in particular on a speed of implementation of the safety method 100, 200. Use of the parameter representing the average engine torque Pfc, Pfl makes it possible not to take into account rapid changes in the engine torque T12.

[0130] Figures 2 and 4 illustrate a first embodiment in which the parameter representative of the average engine torque exerted at a previous instant Pflest is determined as a function of the parameter representative of the set angular position Ptg and of the parameter representative of the angular position Pc of the rack.

[0131] The parameter representing the average engine torque Pfl is obtained in particular by calculating the difference between the parameter representing the set angular position Ptg and the parameter representing the angular position Pc, then by multiplying the difference by a gain K; designated, subsequently, by the terms “integral gain”.

[0132] The parameter representing the average engine torque Pfl is obtained by an implementation saturation Sat and an integration Int of the product of the difference by the integral gain K;. Thus, there is no “overflow” of the parameter representing the average engine torque Pfi, that is to say that the parameter representing the average engine torque Pfi is limited.

[0133] In certain embodiments, the parameter representative of the average engine torque Pfl is determined as a function of the speed V of the vehicle 2. More specifically, the integral gain K; may depend on the speed V of the vehicle 2.

[0134] [Fig.3] illustrates a second embodiment in which the parameter represents representative of the average engine torque exerted at the previous instant Pfc is determined as a function of the target value of the set torque at the previous instant or as a function of a measurement of a parameter representative of the engine torque exerted at the previous instant Cmot carried out directly or indirectly on the rack 6 or on the motor 24.

[0135] More precisely, the parameter representative of the average engine torque exerted at the previous instant Pfc is determined by applying a low-pass filter Moy to the target value of the setpoint torque at the previous instant or to the measurement of the parameter representative of the engine torque exerted at the previous instant Cmot. For example, the low-pass filter Moy is of the 2nd order.

[0136] Thus, a static part of the exerted engine torque T12 is obtained, that is to say that rapid variations in the exerted engine torque are eliminated. The low-pass filter Moy makes it possible to obtain a sort of “average” engine torque.

[0137] The parameter representing the average engine torque exerted at the previous instant Pfc is obtained by multiplying the target value of the setpoint torque at the instant previous filtered or the measurement of the parameter representative of the engine torque exerted at the previous instant Cmot filtered, with a gain Ks subsequently designated by “static gain”. The static gain Ks depends on the speed V vehicle 2.

[0138] Finally, the method 100, 200 comprises a securing step ES in which the target value Ctgs of the setpoint torque is determined as a function of the first intermediate value Ckp of the setpoint torque, of the second intermediate value Ckd of the setpoint torque, of the limit value Bkpb Bkpu of the first intermediate value Ckp of the setpoint torque, of the limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint torque and of the parameter representative of the average engine torque exerted at the previous instant Pfl, Pfc.

[0139] The target value Ctgs of the setpoint torque is the torque value that the motor 24 is desired to exert on the rack. This is a secure setpoint torque. In other words, the security step ES makes it possible to guarantee that the requested setpoint torque, corresponding to the target value Ctgs of the setpoint torque, is included in a defined interval around the parameter representative of the average motor torque exerted at a previous instant Pfi, Pc. There can therefore be no significant and sudden deviation from the requested setpoint torque. Thus, errors linked to a malfunction of the controller implementing at least the first step are avoided.

[0140] In the embodiment illustrated in Figures 1, 2 and 3, the method 100 comprises a first evaluation step EE1 in which a temporary value Ctg of the setpoint torque is evaluated as a function of the first intermediate value Ckp of the setpoint torque, the second intermediate value Ckd of the setpoint torque and the parameter representative of the average engine torque exerted at the previous instant Pfl. The first evaluation step EE1 sums the first intermediate value Ckp of the setpoint torque, the second intermediate value Ckd of the setpoint torque and the parameter representative of the average engine torque exerted at the previous instant Pfi.

[0141] The method also comprises a second evaluation step EE2 in which a limit value Bu, Bi of the temporary value Ctg of the setpoint torque is determined as a function of the limit value Bkpb Bkpu of the first intermediate value Ckp of the setpoint torque, of the limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint torque and of the parameter representing the average engine torque exerted at the previous instant Pfc. More particularly, the second evaluation step EE2 sums the limit value Bkpb Bkpu of the first intermediate value Ckp of the setpoint torque, the limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint torque and the parameter representing the average engine torque exerted at the previous instant Pfc.

[0142] The securing step determines the target value Ctgs of the setpoint torque as a function of the temporary value Ctg of the setpoint torque and the limit value Bu, Bi of the value temporary Ctg of the setpoint torque. More precisely, the safety step then performs a limitation of the temporary value of the setpoint torque by the limit value of the temporary value of the setpoint torque so that the temporary value of the setpoint torque is included in the limit value of the temporary value.

[0143] The embodiment illustrated in [Fig. 1], 2 and 3 allows the first determination step EDI, the third determination step ED3 and the first evaluation step EE1 to be carried out by a controller in the AFC position of the rack, and the second determination step ED2, the third determination step ED3, the second evaluation step EE2 and the securing step ES to be carried out by a securing controller AFS receiving in particular as input the temporary value Ctg of the setpoint torque of the controller in the AFC position. Thus the securing controller AFS is positioned independently and after the controller in the AFC position.It is therefore possible on the one hand to make modifications or adjustments to the AFC position controller independently of the AFS safety controller and on the other hand to position the AFS safety controller in a partition of an electronic control unit that is more robust to failures than that of the AFC position controller. Securing the motor's setpoint torque is therefore ensured.

[0144] In the embodiment illustrated in [Fig.4], the method 200 comprises a first securing step ES 1 in which a target value Ckps of the first intermediate value Ckp of the setpoint torque is determined as a function of the first intermediate value Ckp of the setpoint torque and the limit value Bkpb Bkpu of the first intermediate value Ckp of the setpoint torque, and a target value Ckds of the second intermediate value Ckd of the setpoint torque is determined as a function of the second intermediate value Ckd of the setpoint torque and the limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint torque,

[0145] The first ESI security step consists more precisely of a limitation of the first intermediate value Ckp of the setpoint torque by the limit value Bkpb Bkpu of the first intermediate value Ckp of the setpoint torque, and of a limitation of the second intermediate value Ckd of the setpoint torque by the limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint torque. Thus the target value Ckps of the first intermediate value Ckp of the setpoint torque is at most or at least equal to the limit value Bkpb Bkpu of the first intermediate value Ckp of the setpoint torque, and the target value Ckds of the second intermediate value Ckd of the setpoint torque is at most or at least equal to the limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint torque.

[0146] Then, the securing step ES determines the target value Ctgs of the setpoint torque as a function of the target value Ckps of the first intermediate value Ckp of the setpoint torque, of the target value Ckds of the second intermediate value Ckd of the torque setpoint and the parameter representing the average motor torque exerted at the previous instant Pfl. For example, the target value Ctgs of the setpoint torque is obtained by the sum of the target value Ckps of the first intermediate value Ckp of the setpoint torque, the target value Ckds of the second intermediate value Ckd of the setpoint torque and the parameter representing the average motor torque exerted at the previous instant Pfl.

[0147] 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.

[0148] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a method.

Claims

Claims

1. Method for securing (100, 200) a target torque for a motor (24, 24'), said motor (24, 24') exerting a motor torque (T12, T12') on a device (6) of a power steering system (1) of a vehicle (2) so as to modify an angular position of said device (6), the method being executed by at least one controller (20) and comprising: - A first determination step (EDI) in which at least one first intermediate value (Ckp) of the target torque is determined as a function of at least one parameter representative of a target angular position (Ptg) of the device (6) and of at least one parameter representative of the angular position (Pc) of the device (6);- A second determination step (ED2) in which a limit value (Bkpb Bkpu) of the at least one first intermediate value (Ckp) of the setpoint torque is determined as a function of at least the parameter representing the setpoint angular position (Ptg) and at least the parameter representing the angular position (Pc); - A third determination step (ED3) in which a parameter representing the average engine torque exerted at a previous instant (Pfl, Pfc) is determined; - A safety step (ES) in which a target value (Ctgs) of the setpoint torque is determined as a function of at least the first intermediate value (Ckp) of the setpoint torque, the limit value (Bkpb Bkpu) of the first intermediate value (Ckp) of the setpoint torque and the parameter representing the average engine torque exerted at the previous instant (Pfi, Pfe).;

2. Securing method (100, 200) according to claim 1, in which the parameter representative of the average engine torque exerted at the previous instant (Pfi) is determined as a function of at least the parameter representative of the set angular position (Ptg) and at least the parameter representative of the angular position (Pc) of the device (6).

3. Securing method (100, 200) according to claim 1, in which the parameter representative of the average engine torque exerted at the instant previous (Pfc) is determined based on the target value (Ctgs) of the set torque at the previous instant or based on a measurement of a parameter representative of the motor torque exerted at the previous instant (C

4. word / * Securing method (100, 200) according to claim 3, in which the parameter representative of the average engine torque exerted at the previous instant (Pfc) is determined by applying a low-pass filter (Moy) to the target value (Ctgs) of the setpoint torque at the previous instant or to the measurement of the parameter representative of the engine torque exerted at the previous instant (Cmot).

5. Securing method (100, 200) according to any one of the preceding claims, in which the first determination step (EDI) determines the at least one first intermediate value (Ckp) of the set torque also as a function of the speed (V) of the vehicle (2).

6. Securing method (100, 200) according to any one of the preceding claims, in which the second determination step (ED2) determines the limit value (Bkpi, Bkpu) of the at least one first intermediate value (Ckp) of the set torque as a function of the vehicle speed (V) (2).

7. Securing method (100) according to any one of the preceding claims, comprising: - a first evaluation step (EE1) in which a temporary value (Ctg) of the setpoint torque is evaluated as a function of the at least one first intermediate value (Ckp) of the setpoint torque and the parameter representative of the average engine torque exerted at the previous instant (Pfl, Pfc), and - a second evaluation step (EE2) in which a limit value (Bu, Bi) of the temporary value (Ctg) of the setpoint torque is determined as a function of the limit value (Bkpb Bkpu) of the at least one first intermediate value (Ckp) of the setpoint torque and the parameter representative of the average engine torque exerted at the previous instant (Pfl, Pfc); the safety step (ES) determining the target value (Ctgs) of the setpoint torque as a function of at least the temporary value (Ctg) of the setpoint torque and the limit value (Bu, Bi) of the temporary value (Ctg) of the setpoint torque.

8. Securing method (100) according to claim 7, wherein the first determination step (EDI), the third determination step (ED3) and the first evaluation step (EE1) are carried out by a position controller (AFC) of the device (6), and the second determination step (ED2), the third determination step (ED3), the second evaluation step (EE2) and the securing step (ES) are carried out by a securing controller (AFS) receiving in particular as input the temporary value (Ctg) of the setpoint torque of the position controller (AFC).

9. Securing method (200) according to any one of claims 1 to 6, comprising: - A first securing step (ESI) in which at least one target value (Ckps) of the at least one first intermediate value (Ckp) of the setpoint torque is determined as a function of the at least one first intermediate value (Ckp) of the setpoint torque and the limit value (Bkpb Bkpu) of the at least one first intermediate value (Ckp) of the setpoint torque; the securing step (ES) determining the target value (Ctgs) of the setpoint torque as a function of at least the target value (Ckps) of the at least one first intermediate value (Ckp) of the setpoint torque and the parameter representative of the average engine torque exerted at the previous instant (Pfl, P

10. fc / * Securing method (100, 200) according to any one of the preceding claims, in which the first determination step (EDI) also determines a second intermediate value (Ckd) of the setpoint torque as a function of at least one parameter representative of a setpoint speed (Vctg) of said device (6) and a parameter representative of a speed (Vc) of said device (6), and the second determination step (ED2) also determines a limit value (Bkdb Bkdu) of the second intermediate value (Ckd) of the setpoint torque as a function of at least the parameter representative of the setpoint speed (V rtg) of said device (6) and the parameter representative of the speed (Vc) of said device (6).

11. Vehicle (2) comprising a power steering system (1) of the type without mechanical link implementing a securing method (100, 200) according to any one of the preceding claims.

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