A method designed to control the position of a vehicle's rack and pinion to a position setpoint based on kinematic constraints imposed on the vehicle's movement.
The process enslaves the rack position using nested closed-loop regulations to limit speed and acceleration, addressing sudden rack movements and ensuring stable vehicle trajectory and enhanced safety.
Patent Information
- Application Number
- FR2020000254
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2020-01-13
- Publication Date
- 2025-04-25
- Estimated Expiration
- 2040-01-13
AI Technical Summary
Existing power steering systems struggle to maintain vehicle trajectory stability and driver comfort by managing sudden and rapid rack movements due to environmental variations without modifying system parameters.
A process that enslaves the rack position to a set position using a nested closed-loop regulation, limiting rack speed and acceleration to predefined thresholds, adapting to kinematic constraints and environmental changes.
Ensures smooth, predictable rack movements, maintaining vehicle trajectory and enhancing driver comfort and safety by controlling rack speed and acceleration within defined limits.
Smart Images
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Abstract
Description
Title of the invention: Method designed to control a position of a rack of a vehicle to a position setpoint as a function of kinematic constraints imposed on a movement of the vehicle.
[0001] The invention relates to the field of power steering systems and more particularly to a method designed to control a position of a rack to a position setpoint.
[0002] A vehicle steering system has the purpose of allowing a driver to control a trajectory of the vehicle by exerting force on a steering wheel.
[0003] Generally, a steering system comprises several elements including said steering wheel connected to a steering column, a rack, and two wheels each connected to a connecting rod. The rack is the part enabling the steering wheel to be connected, via the steering column, to the wheels, via the connecting rods; that is to say that the rack transforms the forces exerted by the driver on the steering wheel into a rotation of the vehicle's wheels.
[0004] More precisely, the rack performs a rectilinear movement between a neutral position in which the moving vehicle performs a rectilinear trajectory, and a right position, respectively a left position, in which the vehicle performs a curved trajectory to the right, respectively to the left. We subsequently define that a position of the rack is the length, measured in millimeters, of the center of the rack relative to the neutral position.
[0005] An electric power steering system of a vehicle uses an assistance motor, controlled by a steering computer, in particular to reduce the efforts required by the driver on the steering wheel to turn the wheels of the vehicle. Depending on the efforts exerted on the steering wheel, i.e. the steering wheel torque, the assistance motor exerts an assistance effort, i.e. a driving torque, on the rack so as to turn the wheels.
[0006] The power steering system may also include a driving assistance function, such as a parking assistance function (“city park”) or a function for assisting the vehicle in its lane (“lane keeping”). This function automatically controls the trajectory, hereinafter called the actual trajectory, of the vehicle. In other words, the driving assistance function determines a reference trajectory and requires that the actual trajectory of the vehicle remains in the vicinity of the reference trajectory.
[0007] The actual trajectory of the vehicle is imposed by the driving assistance function by slaving the position of the rack to a position setpoint which is dependent of the reference trajectory. In this way, the actual trajectory of the vehicle is maintained in the vicinity of the reference trajectory.
[0008] There is a known method 1', represented in figure 1, allowing to carry out such a control which comprises:
[0009] - A servo-control step in position 2' in which the steering computer determines an engine torque setpoint TCM as a function of the position setpoint Tx, and the rack position Xs; - A maneuvering step 3 in which the assistance motor exerts a motor torque CM on the rack S according to the motor torque setpoint TCM-
[0010] Such a method 1' has a closed-loop regulation on the position Xs of the rack S. In other words, the method modifies the position Xs of the rack S by means of the motor torque CM of the assistance motor as long as the position Xs of the rack S is not equal to the position setpoint Tx. Thus, the method 1' makes it possible to maintain the actual trajectory of the vehicle by means of the control of the position Xs of the rack S, in the vicinity of the reference trajectory indicated by the position setpoint Tx.
[0011] A dynamic reaction of the steering system depends directly on variations in a structure of the environment of said steering system, in particular the weight and a state of the vehicle's driving surface. The dynamic reaction of the vehicle depends on the kinematic constraints exerted on the vehicle.
[0012] With the method 1' above and depending on the structure of the steering system environment, a sudden and rapid movement of the rack S may be observed. This degrades a driver's feeling and the safety of the vehicle. This method cannot handle variations in the structure of the environment without modification of at least one parameter.
[0013] The invention aims to remedy all or part of the aforementioned drawbacks by proposing a method of controlling the position of the rack in which the speed and / or acceleration of the rack remain below a determined threshold regardless of changes in the structure of the environment of the power steering system.
[0014] The subject of the invention is a method for controlling an assistance motor of a power steering system, said power steering system comprising the assistance motor configured to apply a motor torque to a rack, and at least one steering computer, said method being designed to slave a position of the rack to a position setpoint, said method comprising:
[0015] - a maneuvering step in which the assistance motor exerts a motor torque on the rack according to a motor torque setpoint;
[0016] characterized in that the method also comprises:
[0017] - a control step in which the steering computer determines a speed setpoint for the rack as a function of the position setpoint and the position of the rack; - a limitation step in which the steering computer issues a limited speed instruction which is less than or equal to a maximum speed threshold; - a control step in which the steering computer determines the engine torque setpoint as a function of the limited speed setpoint and a rack speed.
[0018] The control method according to the invention comprises two closed-loop regulations nested within each other, i.e. in cascade.
[0019] The first closed-loop regulation is carried out by the servo-control step. Indeed, the servo-control step determines a quantity, here the speed setpoint, so that the position of the rack is equal to the position setpoint. By taking into account the actual position of the rack, the servo-control step integrates a reaction, or feedback in English, from the power steering system.
[0020] The servo-control step modifies the speed setpoint so as to require that the position of the rack be substantially equal to the position setpoint. Thus, the method according to the invention makes it possible to maintain an actual trajectory of the vehicle by means of controlling the position of the rack, in the vicinity of the reference trajectory indicated by the position setpoint.
[0021] The second closed-loop regulation is carried out by the control step. Indeed, the control step determines a quantity, here the engine torque setpoint, so that the rack speed is equal to the limited speed setpoint. By taking into account the actual rack speed, the control step integrates a reaction from the power steering system.
[0022] The control step modifies the engine torque setpoint so as to require that the rack speed be substantially equal to the limited speed setpoint. Thus, the method according to the invention makes it possible to maintain the rack speed in the vicinity of the limited speed setpoint.
[0023] The limiting step requires that the limited speed setpoint be equal to the speed setpoint when the speed setpoint is less than the maximum speed threshold and be equal to the maximum speed threshold when the speed setpoint is greater than or equal to the maximum setpoint threshold. In other words, the limiting step imposes a maximum limit corresponding to the maximum speed threshold at the rack speed setpoint.
[0024] Thus, the limited speed setpoint of the rack is known, reproducible and adjustable.
[0025] The method according to the invention ensures, by requiring that the rack speed be equal to a limited speed setpoint, that the rack performs a continuous, predictable and gradual movement so as to preserve the driver's feeling and the safety of the vehicle.
[0026] According to a characteristic of the invention, the servo-control step comprises a comparison phase in which a position deviation is calculated as a function of the position of the rack and the position setpoint, then a correction phase in which the speed setpoint is determined so as to reduce the position deviation.
[0027] The comparison phase calculates a position deviation, for example by subtracting the position of the rack from the position setpoint.
[0028] The correction phase determines a speed setpoint as a function of the position deviation by means of a predetermined mathematical relationship.
[0029] Thus, the control step is a closed-loop regulation.
[0030] According to a characteristic of the invention, the control step comprises a deviation phase in which a speed deviation is calculated as a function of the speed of the rack and the limited speed setpoint, then a compensation phase in which the engine torque setpoint is determined so as to reduce the speed deviation.
[0031] The deviation phase calculates a position deviation, for example by subtracting the rack speed from the limited speed setpoint.
[0032] The compensation phase determines the engine torque setpoint as a function of the speed difference by means of a predetermined mathematical relationship.
[0033] Thus, the control step is a closed-loop regulation.
[0034] According to a characteristic of the invention, the limitation step determines the maximum speed threshold of the rack as a function of at least one kinematic constraint exerted on the vehicle.
[0035] Thus, the limitation step makes it possible to adapt the method to a dynamic reaction of the steering system by taking into account at least one kinematic constraint. The method adapts to different vehicles but also to changes in the state of the vehicle's traffic surface.
[0036] The rack speed setpoint is adapted to at least one kinematic constraint.
[0037] The method according to the invention can be installed on different vehicles without modification thereof because changes in vehicle weight, and more generally changes in kinematic constraints, are automatically taken into account during the limitation step.
[0038] According to a characteristic of the invention, the limitation step determines the limited speed setpoint as a function of a maximum acceleration threshold;
[0039] Thus, the speed setpoint is limited but also the maximum acceleration of the rack.
[0040] It is possible to define exactly a dynamics of the rack movement by limiting the speed and the acceleration.
[0041] According to a characteristic of the invention, the maximum acceleration threshold is determined as a function of at least one kinematic constraint exerted on the vehicle.
[0042] Thus, the dynamics of the vehicle are adapted according to at least one kinematic constraint. The method adapts to different vehicles but also to changes in the state of the vehicle's traffic surface.
[0043] According to a characteristic of the invention, the position of the rack is obtained by a choice of: a position sensor, an angular measurement of a steering wheel, a mathematical calculation using an angular measurement of a shaft of the assistance motor.
[0044] Thus the method is not constrained by a method of determining the position of the rack.
[0045] 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:
[0046] [fig. 1] is a schematic representation of a method for controlling an engine state-of-the-art assistance;
[0047] [fig.2] is a schematic representation of a method for controlling an engine assistance according to the invention;
[0048] [fig.3] is a schematic representation of a rack position, a threshold maximum speed and a maximum acceleration threshold, as a function of time;
[0049] [fig.4] is a representation of a response of the rack to an instruction of position according to a first embodiment;
[0050] [fig.5] is a representation of a response of the rack to an instruction of position according to a second embodiment;
[0051] [fig.6] is a representation of a response of the rack to an instruction of position according to a third embodiment;
[0052] [fig.7] is a schematic representation of a vehicle steering system.
[0053] The invention relates to a method 1 for managing an assistance motor 12 of a power steering system 100 for a vehicle 21, and more particularly for a motor vehicle 21 intended for the transport of people.
[0054] In a manner known per se, and as can be seen in Figure 7, said system of power steering 100 comprises a steering wheel 30 which allows a driver to maneuver said power steering system 100 by exerting force on said steering wheel 30.
[0055] Said steering wheel 30 is preferably mounted on a steering column 40, guided in rotation on the vehicle 21, and which meshes, by means of a steering pinion 50, on a rack S, which is itself guided in translation in a steering casing 7 fixed to said vehicle 21.
[0056] Preferably, the ends of said steering rack S 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 S makes it possible to modify the steering angle (yaw angle) of the steered wheels.
[0057] The steered wheels 10, 11 may also preferably be driving wheels.
[0058] The power steering system 100 also comprises the assistance motor 12 intended to provide a motor torque CM, to assist the maneuvering of said power steering system 100.
[0059] The assistance motor 12 will preferably be an electric motor, with two operating directions, and preferably a rotary electric motor, of the brushless type.
[0060] The assistance motor 12 can engage, if necessary by means of a gear reducer type reducer, either on the steering column 40 itself, to form a so-called “single pinion” mechanism, or directly on the rack S, by means for example of a second pinion 13 separate from the steering pinion 50 which allows the steering column 40 to mesh with the rack S, so as to form a so-called “double pinion” mechanism, as illustrated in FIG. 7, or even by means of a ball screw which cooperates with a corresponding thread of said rack S, at a distance from said steering pinion 50.
[0061] The steering system further comprises a steering computer 20 which implements the method 1 according to the invention. More precisely, the steering computer 20 receives the information of a position Xs of the rack S either by means of a position sensor, or by an angular measurement 03 of the steering wheel 30 which is carried out by an angle sensor 23, or by a mathematical calculation using an angular measurement 012 of a shaft 24 of the assistance motor 12.
[0062] The steering system 100 comprises the control method 1, as shown in FIG. 2.
[0063] The method 1 for controlling the assistance motor 12 of the power steering system 100 comprises a servo-control step 2 in which the steering computer 20 determines a speed setpoint TVs of the rack S as a function of a speed setpoint position Tx and position Xs of rack S.
[0064] More precisely, the control step 2 comprises a comparison phase in which a position deviation is calculated as a function of the position Xs of the rack S and the position setpoint Tx.
[0065] The comparison phase calculates the position deviation by subtracting the position Xs of the rack S from the position setpoint Tx.
[0066] Then the servo-control step 2 comprises a correction phase in which the speed setpoint TVs is determined so as to reduce the calculated position deviation.
[0067] The control step 2 is therefore a first closed-loop regulation which determines the speed setpoint TVs so that the position Xs of the rack S is equal to the position setpoint Tx.
[0068] The method 1 according to the invention then comprises a limitation step in which the steering computer issues a limited speed instruction TVsl-
[0069] The speed setpoint TVs is conditioned by kinematic constraints of speed and acceleration acting on the vehicle 21. For this, the speed setpoint TVs is limited by a maximum speed threshold SVs and its derivative with respect to time, in other words its acceleration, is limited by a maximum acceleration threshold SAs. The maximum speed threshold SVs and the maximum acceleration threshold SAs depend on at least one kinematic constraint.
[0070] The method 1 also comprises a control step 5 in which the steering computer 20 determines an engine torque setpoint TCM as a function of the limited speed setpoint TVsl and a speed Vs of the rack S.
[0071] The control step comprises a deviation phase in which a speed deviation is calculated by subtracting the speed Vs of the rack S from the limited speed setpoint TVsl-
[0072] The control step also includes a compensation phase in which the engine torque setpoint is determined so as to reduce the speed difference.
[0073] Control step 5 corresponds to a second closed-loop regulation positioned in parallel with the first regulation loop. Indeed, control step 5 determines the engine torque setpoint TCM by using as input the limited speed setpoint Tvsi which is the output of the first control loop, and by using the speed Vs of the rack S which is measured at the same time as the position Xs of the rack S.
[0074] Control step 5 modifies the engine torque setpoint TCm so as to require that the speed Vs of the rack S is substantially equal to the limited speed setpoint TVsl-
[0075] Finally, the method 1 comprises a maneuvering step 3 in which the assistance motor 12 exerts the motor torque CM on the rack S as a function of the engine torque setpoint TCm-
[0076] Method 1 is designed to control a position Xs of the rack S to a position setpoint Tx, which is achieved by the control step 2, while maintaining a speed Vs of the rack S at a value lower than a threshold, which is achieved by the limitation step 4 and control step 5.
[0077] Thus, the method 1 according to the invention makes it possible, on the one hand, to maintain a real trajectory of the vehicle 21 by means of controlling the position Xs of the rack S, in the vicinity of the reference trajectory indicated by the position setpoint Tx, and on the other hand to maintain the speed Vs of the rack S in the vicinity of the limited speed setpoint TVsl-
[0078] Figure 3 illustrates the position Xs of the rack S, the maximum speed threshold SV s and the maximum acceleration threshold SAs as a function of time t.
[0079] In Figure 3, the speed setpoint TVs has a value greater than the maximum speed threshold SVs and a derivative with respect to time greater than the maximum acceleration threshold SAs. Thus, the limitation step 4 determines that the limited speed setpoint TVsl is constrained on the one hand by the maximum speed threshold SVs and on the other hand by the maximum acceleration threshold SAs.
[0080] In Figure 3, the maximum acceleration threshold SAs is constant and equal to the value Amax over a first duration I, equal to the value -Amax over a third duration III and equal to zero over a second duration II between the first duration I and the third duration III. Thus, the maximum speed threshold SVs is a straight line with a constant directing coefficient over the first I and third III durations, and zero over the third duration III.
[0081] Finally, the position Xs of the rack evolves slowly over the first duration I and the third duration III then more quickly over the second duration II.
[0082] Figures 4 to 6 illustrate a response of a rack S controlled with method 1 according to the invention.
[0083] More precisely, in the response illustrated in Figure 4, the maximum speed threshold SVs is chosen equal to 70mm / s, and there is no determined value for the maximum acceleration threshold SAs. In addition, the method imposes a position setpoint Tx, in the form of a ramp.
[0084] Figure 4 shows that the position Xs of the rack S follows the position setpoint Tx with a slight offset while the speed Vs of the rack follows the limited speed setpoint TVsl with the exception of regulation overruns. The engine torque setpoint TCm automatically decreases when the speed Vs of the rack exceeds the limited speed setpoint TVsl. Thus, the method 1 according to the invention guarantees that the speed Vs of the rack S does not exceed the limited speed setpoint TVsl with the exception of regulation errors.
[0085] In the response illustrated in Figure 5, the maximum speed threshold SVs is chosen equal at 20mm / s, and there is no determined value for the maximum acceleration threshold SAs. In addition, the method imposes a position setpoint Tx, in the form of a step.
[0086] Figure 5 shows that the position Xs of the rack S reaches the position setpoint Tx along a slope, while the speed Vs of the rack S follows the limited speed setpoint TVsl except for regulation overruns. The response of the position Xs of the rack S is independent of the trajectory to be traveled. The rack S reaches the desired position Tx while respecting the constraint of the maximum speed threshold SVs. Thus, the method 1 according to the invention guarantees that the speed Vs of the rack does not exceed the limited speed setpoint TVsl even when the distance to be traveled is significant.
[0087] In the response illustrated in Figure 6, the maximum speed threshold SVs is chosen equal to 20mm / s, and the maximum acceleration threshold SAs is chosen equal to 156mm / s2. In addition, the method imposes a position setpoint Tx, in the form of a step.
[0088] Figure 6 shows that the position Xs of the rack S reaches the position setpoint Tx following a curve, while the speed Vs of the rack S follows the limited speed setpoint TVsl, except for regulation overruns. The rack S reaches the desired position Tx while respecting the constraint of the maximum speed threshold SVs and the maximum acceleration threshold SAs, except for regulation errors. Thus, the method 1 according to the invention guarantees that the speed Vs of the rack S does not exceed the limited speed setpoint TVsl even when the distance to be covered is significant, and that the acceleration of the rack remains lower than the maximum acceleration until the completion of the movement.
[0089] Of course, the invention is not limited to the embodiments described and shown in the attached figures. Modifications remain possible, in particular from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.
Claims
Claims
1. Method (1) for controlling an assist motor (12) of a power steering system (100), said power steering system (100) comprising the assist motor (12) configured to apply a motor torque (CM) to a rack (S), and at least one steering computer (20), said method (1) being designed to control a position (Xs) of the rack (S) to a position setpoint (Tx), said method (1) comprising: - an operating step (3) in which the assist motor (12) exerts a motor torque (CM) on the rack (S) as a function of a motor torque setpoint (TCM); characterized in that the method (1) also comprises: - a control step (2) in which the steering computer (20) determines a speed setpoint (TVs) of the rack (S) as a function of the position setpoint (Tx) and the position (Xs) of the rack (S);- a limitation step (4) in which the steering computer (20) issues a limited speed instruction (TVsl) which is less than or equal to a maximum speed threshold (SVs); - a control step (5) in which the steering computer (20) determines the engine torque instruction (TCM) as a function of the limited speed instruction (TVsl) and a speed (Vs) of the rack (S).;
2. Method (1) according to claim 1, in which the servo-control step (2) comprises a comparison phase in which a position deviation is calculated as a function of the position (Xs) of the rack (S) and the position setpoint (Tx), then a correction phase in which the speed setpoint (TVs) is determined so as to reduce the position deviation.
3. Method (1) according to any one of the preceding claims, in which the control step (5) comprises a deviation phase in which a speed deviation is calculated as a function of the speed (Vs) of the rack (S) and the limited speed setpoint (TVsl), then a phase of
4.
5.
6.
7. compensation in which the engine torque setpoint (TCM) is determined so as to reduce the speed deviation. Method (1) according to any one of the preceding claims, in which the limiting step (4) determines the maximum speed threshold (SVs) of the rack (S) as a function of at least one kinematic constraint exerted on the vehicle (21). Method (1) according to any one of the preceding claims, in which the limiting step (4) determines the limited speed setpoint (Tvsl) as a function of a maximum acceleration threshold (SAs); Method (1) according to claim 5, in which the maximum acceleration threshold (SAs) is determined as a function of at least one kinematic constraint exerted on the vehicle (21). Method (1) according to any one of the preceding claims, in which the position (Xs) of the rack (S) is obtained by either: a position sensor, an angular measurement (03) of a steering wheel (30), a mathematical calculation using an angular measurement (012) of a shaft (24) of the assistance motor (12).