Method for securing a set torque for a motor in a power steering system.
The method for securing setpoint torque in steer-by-wire systems addresses controller failure differentiation by calculating torque values using proportional, integral, and derivative gains, ensuring precise and safe rack control, thus enhancing vehicle safety and comfort.
Patent Information
- Application Number
- FR2023014091
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-12-13
- Publication Date
- 2025-12-26
- Estimated Expiration
- 2043-12-13
AI Technical Summary
Existing power steering systems without mechanical linkages, or 'steer-by-wire' systems, lack effective methods to differentiate between controller failures and other causes of deviations in rack angular position, leading to potential safety issues.
A method involving a controller that determines a setpoint torque for a motor by calculating intermediate and limit values based on angular positions and speeds, using proportional, integral, and derivative gains, and incorporating average motor torque to ensure the setpoint torque remains within a safe range, thereby isolating and mitigating controller malfunctions.
Ensures precise and safe control of the rack angular position by filtering out rapid changes and maintaining consistency between set and actual positions, enhancing vehicle safety and comfort by preventing abrupt deviations.
Smart Images
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Abstract
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 of securing a set torque for an engine. Prior art
[0002] A vehicle steering system is designed to allow a driver to control the vehicle's trajectory by changing the steering angle of the vehicle's wheels using a steering wheel. The driver changes the steering wheel angle by applying force to it.
[0003] Generally, a steering system comprises several elements, including the steering wheel, a rack and pinion, and two wheels, each connected to a tie rod. The rack and pinion is the component that allows the wheels to be steered, that is, allows the steering angle of the wheels to be changed via the tie rods. An angular position of the rack relative to a steering housing, hereafter referred to as the rack angular position, is a representation of the steering angle of the wheels.
[0004] In an electric power steering system without a mechanical linkage, known as "steer-by-wire," the steering wheel is mechanically detached from the rack. In this case, the steering system comprises a steering wheel unit that is 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 includes said steering wheel and at least one means of estimating the steering wheel angle, for example an angle sensor.
[0006] The rack unit comprises said movable rack in the steering housing, 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 may be modified by vehicle functions such as a lane-keeping function or a vehicle parking assist function.
[0007] The electronic control unit determines a setpoint motor torque, or setpoint torque in the following description, enabling it to drive at least one motor that exerts a motor torque on the rack. In other words, the controller regulates the angular position of the rack to the setpoint angular position by determining the setpoint torque of the motor.
[0008] Ensuring the proper functioning of the controller and more particularly the control in position of the rack to ensure consistency between the set angular position and the angular position of the rack, is important in order to guarantee vehicle safety.
[0009] A known solution exists for detecting a malfunction of the rack unit. The rack unit malfunction is defined as a deviation between the rack angular position and the setpoint angular position. When a malfunction is detected, the control is then performed by a backup controller.
[0010] The drawback of this solution is that it does not differentiate the origin of the malfunction. Thus, it is not possible to determine whether the difference between the rack angular position and the setpoint angular position is due to a controller failure or to another cause such as wheel lockup, for example.
[0011] There is therefore a need for more effective security of the controller. Description of the invention
[0012] An 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 a first intermediate value of the setpoint torque is determined as a function of at least one parameter representing a setpoint angular position of the device and at least one parameter representing the angular position of the device; - A second determination step in which a limit value of at least a first intermediate value of the setpoint torque is determined as a function of at least the parameter representing the setpoint angular position and at least the parameter representing the angular position; - A third determination step in which a parameter representative of the average motor 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 motor torque exerted at the previous instant.
[0013] The controller can be an electronic control unit.
[0014] The setpoint torque designates any quantity representative of the setpoint torque allowing the motor to be controlled by torque.
[0015] In some embodiments, the device on which the engine 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 link.
[0017] The first step determines at least one first intermediate value of the setpoint torque. In other words, the setpoint torque can be determined, in certain embodiments, as a function of several intermediate values.
[0018] The first intermediate value is determined based on at least one parameter representing the setpoint angular position of the device and at least one parameter representing the angular position of the device. The parameter representing the setpoint angular position or the parameter representing the angular position may be an angle, a position of the device relative to a point on the motor, or an angular position of the motor. The parameter representing 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 setpoint angular position and the parameter representing the angular position, and then by multiplying the difference by a first gain. The first gain is hereafter referred to as the "proportional gain".
[0020] In some embodiments, the first intermediate value is obtained by an implementation saturation of the product of the difference and the proportional gain. Thus, there is no "overflow" of the first intermediate value, that is to say, the first intermediate value is limited.
[0021] In some embodiments, the first determination step determines at least one first intermediate value of the setpoint torque also as a function of the vehicle speed.
[0022] More specifically, the proportional gain may depend on the speed of the vehicle.
[0023] Thus, the proportional gain modifies the speed at which the vehicle's wheels follow the set angular position. At the vehicle level, this modifies the precision with which the driver can control the wheel steering angle. By decreasing the proportional gain, this precision decreases, but driving comfort is increased because it filters out higher-frequency wheel steering movements.
[0024] It is common for vehicles to be equipped with a rack and pinion with a variable ratio that varies according to the vehicle's speed between the set angular position and the wheel steering angle. In other words, at 20 km / h, the rack and pinion ratio is essentially direct, meaning that the wheel steering angle varies in a linear fashion. The steering ratio is likely proportional to the set angular position, as the vehicle's trajectory changes slowly. At high speeds, the rack and pinion ratio is not very direct, meaning 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 vehicle speed.
[0026] Thus, at 20km / h, the proportional gain is reduced so as to degrade the precision of steering the angle of orientation of the wheels but to improve driving comfort, for example in the case of rapid variations of the set angular position, i.e. if the driver oscillates the steering wheel.
[0027] At high speed, for example 130km / h, the ratio of the rack is not very direct, so it is important to maintain good precision and therefore a significant proportional gain.
[0028] The second step determines the limit value of 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 setpoint angular position and the parameter representing the angular position, and then multiplying the difference by a first limit gain. The first limit gain is hereafter referred to as the "limit proportional gain".
[0030] The limit value may be a pair of limit values comprising an upper limit value and a lower limit value. Alternatively, only one of the upper or lower limit values may be determined, and the other of the upper or lower limit value is calculated by symmetry.
[0031] In some embodiments, the second determination step determines the limit value of at least a first intermediate value of the setpoint torque as a function of vehicle speed.
[0032] More specifically, the limiting proportional gain may depend on the vehicle speed.
[0033] The third step determines the parameter representing the average motor torque exerted at the previous instant.
[0034] The previous instant is understood to be a moment situated in the past with respect to the calculation of the target value of the setpoint torque currently being calculated. The previous instant depends in particular on the execution speed of the safety process.
[0035] Finally, the securing step combines at least one first intermediate value of the setpoint torque, the limit value of at least one first intermediate value of the setpoint torque and the parameter representing the average motor torque exerted at the previous instant so as to determine the target value of the setpoint torque.
[0036] The parameter representing the average motor torque can be obtained in various ways, such as by a low-pass filter. Using the parameter representing the average motor torque makes it possible to disregard rapid changes in motor torque.
[0037] The target torque setpoint is the desired torque value for the motor on the device. This is a safe setpoint torque. In other words, the safety step ensures that the requested setpoint torque, corresponding to the target torque setpoint value, is within a defined range around the parameter representing the average motor torque applied at a previous instant. In other words, the target torque setpoint value is bounded. Therefore, there can be no significant and abrupt deviation from the requested setpoint torque. Thus, errors related to a controller malfunction are avoided by implementing at least the first step, or the effects of a failure are limited without switching to another control strategy, such as a backup law or another controller.
[0038] In certain embodiments, the parameter representing the average motor torque exerted at the previous instant is determined as a function of at least the parameter representing the setpoint angular position and at least the parameter representing the angular position of the device.
[0039] One way to determine the representative parameter of the average motor torque is to use at least the representative parameter of the setpoint angular position and at least the representative parameter of the device angular position.
[0040] In certain embodiments, the parameter representing the average motor torque is obtained in particular by calculating the difference between the parameter representing the setpoint angular position and the parameter representing the angular position, and then by multiplying the difference by a gain designated, hereafter, by the terms "integral gain".
[0041] In certain embodiments, the representative parameter of the average motor torque is obtained by implementation saturation and integration of the product of the difference and the integral gain. Thus, there is no "overflow" of the representative parameter of the average motor torque; that is, the representative parameter of the average motor torque is limited.
[0042] In some embodiments, the parameter representing 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 representing the average motor 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 representing the motor torque exerted at the previous instant.
[0045] The measurement of the applied motor torque can be carried out directly or indirectly on the device or on the motor.
[0046] In certain embodiments, the parameter representing the average motor 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 representing the motor torque exerted at the previous instant.
[0047] In some embodiments, the low-pass filter is of the 2nd order.
[0048] Thus, we obtain a static part of the applied motor torque, that is to say that we It eliminates rapid variations in the applied motor torque. The low-pass filter allows for a sort of "average" motor torque.
[0049] In certain embodiments, the parameter representing the average motor torque exerted at the previous instant is obtained by multiplying the target value of the setpoint torque at the previous instant filtered or the measurement of the parameter representing the motor torque exerted at the previous instant filtered, with a gain hereafter referred to as "static gain".
[0050] In some embodiments, the static gain depends on the vehicle speed.
[0051] In some embodiments, the securing process comprises:
[0052] - a first evaluation step in which a temporary value of the torque The setpoint is evaluated based on at least one initial intermediate value of the setpoint torque and the parameter representing the average motor torque exerted at the previous instant, and
[0053] - a second evaluation step in which a limit value of the value temporary setpoint torque is determined as a function of the limit value of at least a first intermediate value of the setpoint torque and the parameter representing 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 at least one first intermediate value of the setpoint torque and the parameter representing the average motor 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 representing the average motor 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 motor torque applied at the previous instant. In other words, if several intermediate values are determined, and therefore if several limit values are determined, the second evaluation step sums the plurality of limit values and the parameter representing the average motor torque applied 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 some embodiments, the first determination step, the third determination step and the first evaluation step are carried out by a controller in the position 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 from the controller in position.
[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 faults than that of the position controller. The securing of the motor's setpoint torque is therefore ensured.
[0060] In some embodiments, the process comprises: - A first safety step in which at least one target value of at least one first intermediate value of the setpoint pair is determined as a function of at least one first intermediate value of the setpoint pair and the limit value of at least one first intermediate value of the setpoint pair;
[0061] the securing step determining the target value of the setpoint torque as a function of at least the target value of at least a first intermediate value of the setpoint torque and the parameter representing the average motor torque exerted at the previous instant.
[0062] The first safety step consists, for example, of limiting 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 couple instructions.
[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 at least a first intermediate value of the setpoint torque and the parameter representing the average motor torque exerted at the previous instant.
[0065] For example, the target value of the setpoint torque is obtained by summing at least one target value of at least one first intermediate value of the setpoint torque and the parameter representing the average motor torque applied 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 summing all the target values of the intermediate values and the parameter representing the average motor torque applied 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 representing a setpoint speed of said device and a parameter representing 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 representing the setpoint speed of said device and the parameter representing the speed of said device.
[0067] The representative parameter of the setpoint speed of said device or the representative parameter of the speed of said device can be determined on the basis of the representative parameter of the setpoint angular position or the representative parameter of 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 setpoint speed and the parameter representing the device speed, and then multiplying the difference by a second gain. The second gain is hereafter 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 and the derived gain. Thus, there is no "overflow" of the second intermediate value, that is to say, the second intermediate value is limited.
[0070] In some embodiments, the first determination step determines the second intermediate value of the setpoint torque also as a function of the vehicle speed.
[0071] More specifically, the derived gain may depend on the speed of the vehicle.
[0072] Thus, the derived gain modifies the speed at which the vehicle's wheels follow the set angular position. At the vehicle level, this modifies the precision with which the driver can control the wheel steering angle. By decreasing the derived gain, this precision decreases, but driving comfort is increased because it filters out higher-frequency wheel steering movements.
[0073] According to one embodiment, the derived gain increases with vehicle speed.
[0074] Thus, at 20km / h, the derived gain is reduced so as to degrade the precision of steering the angle of orientation of the wheels but to improve driving comfort, for example in the case of rapid variations of the set angular position, i.e. if the driver oscillates the steering wheel.
[0075] At high speed, for example 130km / h, the ratio of the rack is not very direct, so it is important to maintain good accuracy and therefore a significant derived gain.
[0076] In certain embodiments, the limiting 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, and then multiplying the difference by a second limiting gain. The second limiting gain is hereafter referred to as the "limiting derivative gain".
[0077] In some 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 limiting derived gain may depend on the vehicle speed.
[0079] Another aspect of the invention relates to a vehicle comprising a mechanically linkless power steering system implementing a safety method according to the invention. Brief description of the drawings
[0080] The invention will be better understood from the following description, which relates to several embodiments according to the present invention, given by way of non-limiting examples and explained with reference to the accompanying schematic drawings, in which:
[0081] [Fig.1] 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 implementation methods
[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 assist motors 24, 24' of a power steering system 1 for a vehicle 2, and more particularly for a passenger vehicle 2.
[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, referred to as "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] The steering wheel 3 is not mechanically linked to a steering rack 6, which is itself guided in translation within a steering housing 7 fixed to the 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 that is mechanically independent of a rack unit. That is to say, a force applied T3 to the steering wheel unit is not mechanically transmitted to the rack unit, and vice versa. The power steering system 1 is of the "mechanically unlinked" 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 steering wheel maneuver 3, hereinafter referred to as the setpoint control torque. The purpose of the setpoint control torque is, in particular, to provide the driver with torque information consistent with the real-world conditions of the vehicle 2 (curve, straight line, level of grip, road surface condition, etc.). The electronic steering wheel control unit regulates the steering wheel torque T3 to the setpoint control torque by means of a control motor, not shown. The control motor then applies a control motor torque so that the steering wheel torque T3 is close to or equal to the setpoint control torque.
[0092] In certain embodiments, the securing method 100, 200 according to the invention can be exercised on the control motor.
[0093] The rack unit comprises said rack 6 and at least the electronic rack control unit 20 which controls, in particular, an angular position Pc of the rack mesh 6 so that it is consistent with a setpoint angular position Ptg. The setpoint angular position Ptg is generally consistent with the steering wheel angle 03, but it can be modified by vehicle 2 functions such as a trajectory following function or a vehicle 2 parking assist function.
[0094] The electronic rack control unit 20 determines a setpoint motor torque, or setpoint torque in the following description, enabling the control of the pair of assist 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 stub axle of a steering wheel 10, 11 (respectively a left wheel 10 and a right wheel 11), such that the longitudinal translational movement of the rack 6 allows a steering angle (yaw angle) of the steering wheels 10, 11 to be modified. The steering wheels 10, 11 can also preferably be drive wheels.
[0097] Each assistance motor 24, 24' will preferably be an electric motor, with two directions of operation, and preferably a rotary electric motor, of the brushless type.
[0098] Each assistance motor 24, 24' can engage directly with the steering rack 6, by means of, for example, a pinion 13, 13'.
[0099] A distribution of the setpoint torque Ctgs on each of the motors 24, 24' is carried out for example according to the availability of each of the motors.
[0100] In the following 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 the drawings, the same elements bear the same reference numerals from one figure to another.
[0102] The invention relates more specifically to the method of securing 100, 200 the setpoint torque for the motor 24. As described above, said motor 24 exerts the motor 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 carried out by the electronic rack control unit 20 and comprises a first EDI determination step in which a first intermediate value Ckp of the The setpoint torque is determined as a function of at least one parameter representing a setpoint angular position Ptg of the rack 6 and at least one parameter representing the angular position Pc of the rack 6.
[0103] The setpoint torque designates any quantity representative of the setpoint torque allowing the motor 24 to be controlled in torque.
[0104] The representative parameter of the setpoint angular position Ptg or the representative parameter 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 representative parameter 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 between the parameter representing the setpoint angular position Ptg and the parameter representing the angular position Pg, and then by multiplying the difference by a first gain Kp. The first gain Kp is hereafter referred to as the "proportional gain". The first intermediate value Ckp is then obtained by an implementation saturation Sat of the product of the difference and the proportional gain Kp. Thus, there is no "overflow" of the first intermediate value Ckp; that is, the first intermediate value Ckp is limited.
[0106] The first EDI determination step determines the first intermediate value Ckp of the setpoint torque also as a function of the vehicle speed V 2.
[0107] More specifically, the proportional gain Kp depends on the speed V of vehicle 2. Thus, the proportional gain Kp modifies the rate at which the vehicle's wheels follow the set angular position. At the vehicle level, this modifies the precision with which the driver can control the wheel orientation angle. By decreasing the proportional gain Kp, this precision decreases, but driving comfort is increased because it filters out higher-frequency wheel orientation movements.
[0108] It is common for vehicles to be equipped with a rack and pinion system with a variable ratio depending on the vehicle's speed V between the set angular position and the wheel steering angle. In other words, at 20 km / h, the rack and pinion ratio is essentially direct, meaning that the wheel steering angle varies in a manner substantially proportional to the set angular position, because the vehicle's trajectory changes slowly. At high speeds, the rack and pinion ratio is less direct, meaning that the wheel steering angle varies less than the set angular position Ptg, because the slightest variation in the wheel steering angle causes the car to deviate / shake significantly.
[0109] According to one embodiment, the proportional gain Kp increases with speed V vehicle 2.
[0110] Thus, at 20km / h, the proportional gain Kp is reduced so as to degrade the precision of steering the angle of orientation of the wheels but to improve driving comfort, for example in the case of rapid variations of the set angular position, i.e. if the driver oscillates the steering wheel.
[0111] At high speed, for example 130km / h, the ratio of the rack is not very direct, so it is important to maintain good accuracy and therefore a significant proportional gain Kp.
[0112] The first EDI determination step 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 a parameter representative of a speed Vc of the rack 6.
[0113] The representative parameter of the setpoint speed Vctg of the rack or the representative parameter of the speed Vc of the rack can be determined on the basis of the representative parameter of the setpoint angular position Ptg or the representative parameter 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 setpoint speed Vctg and the parameter representing the rack speed Vc, and then by multiplying the difference by a second gain Kd. The second gain Kd is hereafter referred to as the "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, the second intermediate value Ckd is limited.
[0116] The first EDI determination step determines the second intermediate value Ckd of the setpoint torque also as a function of the vehicle speed V 2.
[0117] More specifically, the derived gain Kd can depend on the speed V of vehicle 2. Thus, the derived gain Kd modifies the speed at which the vehicle's wheels follow the set angular position. At the level of vehicle 2, this modifies the precision with which the driver can control the steering angle of the wheels. By decreasing the derived gain Kd, this precision decreases, but driving comfort is increased because it filters out higher-frequency wheel steering movements.
[0118] According to one embodiment, the derived gain Kd increases with the vehicle speed V 2.
[0119] Thus, at 20 km / h, the derived gain Kd is reduced so as to degrade the accuracy of steering the angle of the wheels 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.
[0120] At high speed, for example 130km / h, the rack ratio is not very direct, so it is important to maintain good accuracy and therefore a significant derived gain Kd.
[0121] The method 100, 200 includes 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 representative parameter of the setpoint angular position Ptg and the representative parameter of the angular position Pc.
[0122] The limit value Bkpb Bkpu is obtained in particular by calculating the difference between the parameter representing the setpoint angular position Ptg and the parameter representing the angular position Pc, and then by multiplying the difference by a first limit gain Bkp. The first limit gain Bkp is hereafter referred to as the "limit proportional gain".
[0123] The limit value Bkpb Bkpu can be a pair of limit values 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 can be determined, and the other of the upper limit value Bkpu or 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 representative parameter of the setpoint speed Vctg and the representative parameter of the speed Vc of the rack 6.
[0126] The limiting value Bkdb Bkdu of the second intermediate value Ckd of the setpoint torque is obtained in particular by calculating the difference between the parameter representing the setpoint speed Vctg and the parameter representing the speed Vc, and then by multiplying the difference by a second limiting gain Bkd. The second limiting gain Bkd is hereafter referred to as the "limiting 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 includes a third determination step ED3 in which a parameter representative of the average motor torque exerted at a previous instant Pfc, Pfl is determined.
[0129] The term "previous instant" refers to a moment in the past relative to the calculation of a target value Ctgs of the current setpoint torque. The previous instant depends, in particular, on the execution speed of the safety process (100, 200). Using the parameter representing the average motor torque Pfc, Pfl allows for the exclusion of rapid changes in motor torque T12.
[0130] Figures 2 and 4 illustrate a first embodiment in which the representative parameter of the average motor torque exerted at a previous instant Pflest is determined as a function of the representative parameter of the setpoint angular position Ptg and the representative parameter of the angular position Pc of the rack.
[0131] The representative parameter of the average motor torque Pfl is obtained in particular by calculating the difference of the representative parameter of the setpoint angular position Ptg and the representative parameter of the angular position Pc, then by multiplying the difference by a gain K; designated, hereafter, by the terms "integral gain".
[0132] The representative parameter of the average motor 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 representative parameter of the average motor torque Pfi, that is to say that the representative parameter of the average motor torque Pfi is limited.
[0133] In some embodiments, the parameter representing the average motor torque Pfl is determined as a function of the vehicle speed V 2. More specifically, the integral gain K; can depend on the vehicle speed V 2.
[0134] Figure 3 illustrates a second embodiment in which the parameter represents The average motor torque exerted at the previous instant Pfc 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 motor torque exerted at the previous instant Cmot carried out directly or indirectly on the rack 6 or on the motor 24.
[0135] More specifically, the parameter representing the average motor 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 representing the motor torque exerted at the previous instant, Cmot. For example, the low-pass filter, Moy, is of the second order.
[0136] Thus, a static portion of the applied motor torque T12 is obtained, meaning that rapid variations in the applied motor torque are eliminated. The low-pass filter Moy makes it possible to obtain a sort of "average" motor torque.
[0137] The parameter representing the average motor torque exerted at the previous instant Pfc is obtained by multiplying the target value of the setpoint torque at the instant The previous filtered value, or the measurement of the parameter representing the engine torque exerted at the previous instant, Cmot, is filtered, with a gain Ks hereafter referred to as the "static gain". The static gain Ks depends on the vehicle speed V.
[0138] Finally, the process 100, 200 includes a safety 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, the second intermediate value Ckd of the setpoint torque, 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 motor 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 safe setpoint torque. In other words, the safety step ES ensures that the requested setpoint torque, corresponding to the target value Ctgs of the setpoint torque, is within a defined range around the parameter representing the average motor torque exerted at a previous instant Pfi, Pc. Therefore, there cannot be a significant and sudden deviation from the requested setpoint torque. Thus, errors related to a malfunction of the controller implementing at least the first step are eliminated.
[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 representing the average motor 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 representing the average motor torque exerted at the previous instant Pfi.
[0141] The method also includes 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, the limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint torque, and the parameter representing the average motor torque exerted at the previous instant Pfc. More specifically, 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 motor 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 safety step ES to be carried out by a safety controller AFS receiving, in particular, as input the temporary value Ctg of the setpoint torque of the controller in the AFC position. Thus, the safety 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 faults than that of the AFC position controller. The securing of the motor's setpoint torque is thus ensured.
[0144] In the embodiment illustrated in [Fig.4], the process 200 includes 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 safety step consists more precisely of limiting the first intermediate value Ckp of the setpoint pair by the limit value Bkpb Bkpu of the first intermediate value Ckp of the setpoint pair, and limiting the second intermediate value Ckd of the setpoint pair by the limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint pair. Thus, the target value Ckps of the first intermediate value Ckp of the setpoint pair is at most or at least equal to the limit value Bkpb Bkpu of the first intermediate value Ckp of the setpoint pair, and the target value Ckds of the second intermediate value Ckd of the setpoint pair is at most or at least equal to the limit value Bkdb Bkdu of the second intermediate value Ckd of the setpoint pair.
[0146] Next, the safety 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, and 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 evident that modifications and changes can 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 embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than a restrictive sense.
[0148] It is also evident that all the characteristics described with reference to a process 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 process.
Claims
Demands
1. Method of securing (100, 200) a setpoint 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 carried out by at least one controller (20) and comprising: - A first determination step (EDI) in which at least a first intermediate value (Ckp) of the setpoint torque is determined as a function of at least one parameter representing a setpoint angular position (Ptg) of the device (6) and at least one parameter representing the angular position (Pc) of the device (6);- A second determination step (ED2) in which a limit value (Bkpb Bkpu) of 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 motor 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 motor torque exerted at the previous instant (Pfi, Pfe).
2. A securing method (100, 200) according to claim 1, wherein the parameter representing the average motor torque exerted at the previous instant (Pfi) 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) of the device (6).
3. A securing method (100, 200) according to claim 1, wherein the parameter representing the average motor torque exerted at time The previous (Pfc) is determined based on the target value (Ctgs) of the setpoint 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. mot / * Safety method (100, 200) according to claim 3, wherein the representative parameter of the average motor 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 representative parameter of the motor torque exerted at the previous instant (Cmot).
5. A securing method (100, 200) according to any one of the preceding claims, wherein the first determination step (EDI) determines at least one first intermediate value (Ckp) of the setpoint torque also as a function of the speed (V) of the vehicle (2).
6. A securing method (100, 200) according to any one of the preceding claims, wherein the second determination step (ED2) determines the limit value (Bkpi, Bkpu) of at least one first intermediate value (Ckp) of the setpoint torque as a function of the vehicle speed (V) (2).
7. A safety 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 at least a first intermediate value (Ckp) of the setpoint torque and the parameter representing the average motor 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 at least a first intermediate value (Ckp) of the setpoint torque and the parameter representing the average motor torque exerted at the previous instant (Pfl, Pfc); the securing 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. A 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. A safety method (200) according to any one of claims 1 to 6, comprising: - A first safety step (ESI) in which at least one target value (Ckps) of at least one first intermediate value (Ckp) of the setpoint torque is determined as a function of at least one first intermediate value (Ckp) of the setpoint torque and the limit value (Bkpb Bkpu) of at least one first intermediate value (Ckp) of the setpoint torque; the safety step (ES) determining the target value (Ctgs) of the setpoint torque as a function of at least the target value (Ckps) of at least one first intermediate value (Ckp) of the setpoint torque and the parameter representing the average motor torque exerted at the previous instant (Pfl, P
10. fc / * A securing method (100, 200) according to any one of the preceding claims, wherein the first determination step (EDI) also determines a second intermediate value (Ckd) of the setpoint torque as a function of at least one parameter representing a setpoint speed (Vctg) of said device (6) and a parameter representing 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 representing the setpoint speed (Vrtg) of said device (6) and the parameter representing the speed (Vc) of said device (6).
11. Vehicle (2) comprising a power steering system (1) of the mechanically linkless type implementing a securing method (100, 200) according to any one of the preceding claims.