A method designed to subordinate the position of a vehicle steering rack to a position setpoint based on dynamic constraints imposed on the movement of the vehicle

Abstract

A method (1) for controlling an assist motor (12) of a power steering system (100), the power steering system (100) applying a motor torque (C) to a rack (S). M ) and at least one steering computer (20), and the method (1) comprises: S ) to the position set point (T X ), and the method (1) is designed to servo-control the assist motor (12) to a motor torque set point (T CM ) according to the motor torque (C M ) to the rack (S), and the method (1) comprises a steering step (3) in which the steering computer (20) applies a position set point (T X ) and rack (S) position (X S ) according to the speed set point (T VS ) and a servo control step (2) in which the steering computer (20) determines the maximum speed threshold (SV S ) below the speed limit set point (T VSL ) and the steering computer (20) issues a limiting step (4) to set a speed limit set point (T VSL ) and rack (S) speed (V S ) according to the motor torque set point (T CM and a control step (5) of determining the

Description

Technical Field

[0001] The present invention relates to the field of power steering systems, and more particularly to a method designed to servo-control the position of a rack to a position set point.

Background Art

[0002] The purpose of a vehicle's steering system is to enable the driver to control the vehicle's trajectory by applying force to the steering wheel.

[0003] Generally, a steering system includes several elements, including a steering wheel connected to a steering column, a rack, and two wheels respectively connected to tie rods. The rack is the part that enables the steering wheel to be connected to the wheels via the steering column and the tie rods, that is, the rack converts the force exerted by the driver on the steering wheel into the rotation of the vehicle's wheels. More specifically, the rack moves linearly between a neutral position where the moving vehicle travels on a straight track and a straight position, that is, a left straight position where the vehicle travels on a curved track to the right and a left curved track respectively. Next, the position of the rack is defined as the distance (in millimeters) from the center of the rack to the neutral position.

[0004] The electric power steering system of a vehicle uses an assist motor controlled by a steering computer, and in particular reduces the effort exerted by the driver on the steering wheel to rotate the vehicle's wheels. Based on the force applied to the steering wheel, that is, the steering torque, the assist motor applies an auxiliary force, that is, a motor torque, to the rack to rotate the steering wheel.

[0005] The power steering system may also be provided with driving assistance functions such as a parking assistance function ("city park") or a lane keeping assistance function ("lane keeping"). This function automatically controls the trajectory of the vehicle (hereinafter referred to as the actual trajectory). In other words, the driving assistance function determines a reference trajectory and requires that the actual trajectory of the vehicle remains close to the reference trajectory.

[0006] The actual trajectory of the vehicle is forced by the driving assistance function by servo - controlling the position of the rack to a position set point that depends on the reference trajectory. In this way, the actual trajectory of the vehicle is brought closer to the reference trajectory.

[0007] A method 1' shown in FIG. 1 that enables such servo - control to be executed is known, which a steering computer determines a motor torque set point T X and the rack position X S according to a position servo - control step 2' for determining the motor torque set point T CM and a steering step 3 in which an assist motor exerts a motor torque C on the rack S according to the motor torque set point T CM and a motor torque C M on the rack S.

[0008] Such a method 1' has a closed - loop control of the position X S of the rack S. That is, this method corrects the position X S of the rack S by the motor torque C X of the assist motor as long as the position X M of the rack S is not equal to the position set point T S . In this way, method 1' enables the actual trajectory of the vehicle to be maintained by controlling the position X X of the rack S near the reference trajectory indicated by the position set point T S .

Summary of the Invention

Problems to be Solved by the Invention

[0009] The dynamic response of the steering system directly depends on fluctuations in the structure of the environment of the steering system, particularly fluctuations in the load and condition of the vehicle's traffic surface. The dynamic response of the vehicle depends on the kinematic constraints imposed on the vehicle.

[0010] In the above method 1’, it is possible to observe a sudden and rapid movement of the rack S depending on the structure of the environment of the steering system. This reduces the driver's sense and the vehicle's safety. This method cannot manage changes in the structure of the environment without changing at least one parameter.

[0011] An object of the present invention is to overcome all or part of the above-mentioned drawbacks by proposing a method for servo-controlling the position of a rack while keeping the speed and / or acceleration of the rack below a predetermined threshold regardless of changes in the structure of the environment of a power steering system.

Means for Solving the Problem

[0012] The subject of the present invention is a method for controlling an assist motor of a power steering system, the power steering system comprising an assist motor configured to apply a motor torque to a rack and at least one steering computer, the method being designed to servo-control the position of the rack to a position setpoint, the method comprising: a steering step in which the assist motor exerts a motor torque on the rack according to a motor torque setpoint; the method comprising: a servo-control step in which the steering computer determines a speed setpoint of the rack according to the position setpoint and the position of the rack; a limiting step in which the steering computer issues a limiting speed setpoint below a maximum speed threshold; and a control step in which the steering computer determines the motor torque setpoint according to the limiting speed setpoint and the speed of the rack.

[0013] The control method according to the present invention includes two closed-loop controls nested one inside the other, i.e., in a cascade manner.

[0014] The first closed-loop control is executed by a servo control step. In fact, the servo control step determines the magnitude, here the speed setpoint, such that the position of the rack becomes equal to the position setpoint. By taking into account the current position of the rack, the servo control step integrates the feedback of the power steering system.

[0015] The servo control step corrects the speed setpoint such that the position of the rack is required to be substantially equal to the position setpoint. Thus, the method according to the invention makes it possible to maintain the actual trajectory of the vehicle by controlling the position of the rack near the reference trajectory indicated by the position setpoint.

[0016] The second closed-loop adjustment is executed by a control stage. In fact, the control step determines the magnitude, here the motor torque setpoint, such that the speed of the rack becomes equal to the limit speed setpoint. By taking into account the current speed of the rack, the control step integrates the feedback of the power steering system.

[0017] The control step corrects the motor torque setpoint such that the speed of the rack is required to be equal to the limit speed setpoint in a sensitive state. Thus, the method according to the invention makes it possible to maintain the speed of the rack near the limit speed setpoint.

[0018] The limiting step requires that the limit speed setpoint be equal to the speed setpoint when the speed setpoint is lower than the maximum speed threshold and 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 boundary corresponding to the maximum speed threshold on the speed setpoint of the rack.

[0019] In this way, it is known that the limit speed setpoint of the rack is renewable and adjustable.

[0020] The method according to the present invention ensures that the rack makes a continuous, predictable, and gradual movement so as to maintain the driver's perception and vehicle safety by requiring that the rack speed becomes equal to the limit speed setpoint.

[0021] According to a feature of the present invention, the servo control step includes a comparison phase for calculating a displacement based on the position of the rack and the position setpoint, and a correction phase for determining the speed setpoint so as to reduce the displacement.

[0022] In the comparison phase, the displacement is calculated, for example, by subtracting the position of the rack from the position setpoint.

[0023] In the correction phase, the speed setpoint is determined based on the displacement according to a predetermined mathematical relationship.

[0024] Therefore, the servo control step is a closed-loop control.

[0025] According to a feature of the present invention, the control step includes a deviation phase for calculating a speed deviation according to the speed of the rack and the limit speed setpoint, and a compensation phase for determining the motor torque setpoint so as to reduce the speed deviation.

[0026] In the deviation phase, the displacement is calculated, for example, by subtracting the speed of the rack from the limit speed setpoint.

[0027] In the compensation phase, the motor torque setpoint is determined based on the speed deviation according to a predetermined mathematical relationship.

[0028] Therefore, the control stage is a closed-loop adjustment.

[0029] According to a feature of the present invention, the limiting step determines the maximum speed threshold of the rack according to at least one kinematic constraint imposed on the vehicle.

[0030] Therefore, the limiting step makes it possible to adapt the method to the dynamic response of the steering system by taking into account at least one kinematic constraint. This method not only adapts to different vehicles but also to changes in the state of the vehicle's traffic surface.

[0031] The speed setpoint of the rack adapts to at least one kinematic constraint.

[0032] The method according to the invention can be installed on different vehicles without modification, since changes in vehicle weight, and more generally changes in kinematic constraints, are automatically taken into account during the limiting step.

[0033] According to a feature of the invention, the limiting step determines a limiting speed setpoint according to a maximum acceleration threshold.

[0034] Therefore, the speed setpoint is limited, but the maximum acceleration of the rack is also limited.

[0035] By limiting the speed and acceleration, it is possible to accurately define the dynamics of the movement of the rack.

[0036] According to a feature of the invention, the maximum acceleration threshold is determined according to at least one kinematic constraint exerted on the vehicle.

[0037] Therefore, the dynamics of the vehicle can be adapted according to at least one kinematic constraint. This method not only adapts to different vehicles but also to changes in the state of the vehicle's traffic surface.

[0038] According to a feature of the invention, the position of the rack is obtained by any of mathematical calculations using a position sensor, measurement of the angle of the steering wheel, and measurement of the angle of the shaft of the assist motor.

[0039] Therefore, this method is not restricted by the method for determining the position of the rack. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be better understood from the following description of some embodiments of the present invention, given by way of non-limiting example and described with reference to the accompanying schematic drawings.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0041] The present invention relates to a method 1 for managing an assist motor 12 of a power steering system 100 for a vehicle 21, and more particularly to a motor vehicle 21 intended for the transportation of people.

[0042] In a manner known per se, as shown in FIG. 7, the power steering system 100 comprises a steering wheel 30, which enables a driver to steer the power steering system 100 by applying a force to the steering wheel 30.

[0043] The handle 30 is preferably attached to the steering column 40, guided to rotate on the vehicle 21, and meshes with a rack S guided to translate within a steering casing 7 fixed to the vehicle 21 by a steering pinion 50.

[0044] Preferably, each end of the steering rack S is connected to steering tie rods 8, 9 connected to the steering knuckles of the steering wheels 10, 11 (left wheel 10 and right wheel 11, respectively), thereby enabling the translational longitudinal movement of the rack S to change the steering angle (yaw angle) of the steering wheels.

[0045] Furthermore, the steering wheels 10, 11 may preferably also be drive wheels.

[0046] The power steering system 100 also includes an assist motor 12 intended to provide a motor torque C to assist in the operation of the power steering system 100. M to provide a motor torque C to assist in the operation of the power steering system 100.

[0047] The assist motor 12 is preferably an electric motor having two operating directions and is preferably a brushless type rotary electric motor. The assist motor 12 meshes with the steering column 40 itself, optionally via a gear reduction type reducer, to form a so-called "single pinion" mechanism, or, as shown in FIG. 7, to form a so-called "double pinion" mechanism, for example, by a second pinion 13 separate from the steering pinion 50 that enables the steering column 40 to mesh with the rack S, or otherwise, at a location remote from the steering pinion 50, it can mesh directly on the rack S by a ball screw that cooperates with the corresponding thread of the rack S.

[0048] The steering system further includes a steering computer 20 that implements Method 1 according to the present invention. More specifically, the steering computer 20 uses either the position sensor, the angle measurement θ3 of the steering wheel 30 performed by the angle sensor 23, or a mathematical calculation using the angle measurement θ12 of the shaft 24 of the assist motor 12 to obtain the position X of the rack S S and receives information thereof.

[0049] As shown in FIG. 2, the steering system 100 includes Control Method 1.

[0050] Method 1 for controlling the assist motor 12 of the power steering system 100 includes a servo control step 2 in which the steering computer 20 determines a speed setpoint T X for the rack S according to the position setpoint T S and the position X of the rack S VS .

[0051] Specifically, the servo control step 2 has a comparison phase in which a position deviation is calculated based on the position X of the rack S S and the position setpoint T X .

[0052] The comparison phase calculates the position deviation by subtracting the position X of the rack S X from the position setpoint T S .

[0053] Then, the servo control step 2 includes a correction phase in which the speed setpoint T VS is determined to reduce the calculated position deviation. Therefore, the servo control step 2 is a first closed-loop control for determining the speed setpoint T S such that the position X of the rack S X equals the position setpoint T VS .

[0054] Next, Method 1 according to the present invention includes a limiting step in which the steering computer issues a limiting speed setpoint T VSL .

[0055] Speed setpoint T VS is adjusted by the kinematic constraints of the speed and acceleration exerted on the vehicle 21. For this purpose, the speed setpoint T VS is limited by the maximum speed threshold SV S and its derivative with respect to time, i.e. its acceleration, is limited by the maximum acceleration threshold SA S The maximum speed threshold SV S and the maximum acceleration threshold SA S depend on at least one kinematic constraint.

[0056] The method 1 also includes a control step 5 in which the steering computer 20 determines the motor torque setpoint T VSL according to the limited speed setpoint T S and the speed V of the rack S CM There is also a control step 5 in which the steering computer 20 determines the motor torque setpoint T

[0057] The control step has a deviation phase in which the speed deviation is calculated by subtracting the speed V of the rack S from the limited speed setpoint T VSL from the speed V of the rack S S There is also a compensation phase in which the motor torque setpoint is determined so as to reduce the speed deviation.

[0058] The control step also includes a compensation phase in which the motor torque setpoint is determined so as to reduce the speed deviation.

[0059] Control step 5 corresponds to a second closed-loop control arranged in parallel with the first control loop. In fact, control step 5 uses the limited speed setpoint T VSL which is the output of the first control loop, as an input, and uses the speed V of the rack S S measured simultaneously with the position X of the rack S S to determine the motor torque setpoint T CM There is also a control step 5 in which the steering computer 20 determines the motor torque setpoint T

[0060] Control step 5 modifies the motor torque setpoint T S so that the speed V of the rack S VSL is substantially equal to the limited speed setpoint T CM There is also a control step 5 in which the steering computer 20 determines the motor torque setpoint T

[0061] Finally, Method 1 includes a maneuvering step 3 in which the assist motor 12 exerts a motor torque C CM on the rack S according to the motor torque setpoint T M .

[0062] Method 1 is designed such that, while keeping the speed V of the rack S lower than a threshold value by steps of Limit 4 and Control 5, the position X of the rack S S is servo-controlled to the position setpoint T S by the servo control step 2 X .

[0063] Thus, Method 1 according to the present invention, on the one hand, maintains the actual trajectory of the vehicle 21 close to the reference trajectory indicated by the position setpoint T S by controlling the position X of the rack S, and on the other hand, enables the speed V of the rack S X to be maintained close to the speed limit setpoint T S . VSL

[0064] Figure 3 shows the position X of the rack S S , the maximum speed threshold SV S and the maximum acceleration threshold SA S as a function of time t

[0065] In Figure 3, the speed setpoint T VS has a value higher than the maximum speed threshold SV S and has a time derivative higher than the maximum acceleration threshold SA S . Thus, the limiting step 4 determines that the speed limit setpoint T VSL is constrained on the one hand by the maximum speed threshold SV S and on the other hand by the maximum acceleration threshold SA S .

[0066] In Figure 3, the maximum acceleration threshold SA S is constant and equal to the value A max over a first duration I and has the value -A max ​is equal to, and is equal to 0 over a second duration II included between a first duration I and a third duration III. Thus, the maximum speed threshold S VS is a straight line having a constant gradient coefficient over the durations of the first I and the third III, and is 0 over the third duration III.

[0067] Finally, the position X of the rack S progresses slowly over the first duration I and the third duration III, and progresses more rapidly over the second duration II.

[0068] Figures 4 to 6 show the response of the rack S controlled by the method 1 according to the present invention.

[0069] Specifically, in the response shown in Figure 4, the maximum speed threshold SV S is selected to be equal to 70 mm / S, and the maximum acceleration threshold SA S has no determined value. In addition, the method imposes a position setpoint T X in the form of a slope.

[0070] Figure 4 shows that the position X of the rack S S follows a slightly offset position setpoint T X , while the speed V of the rack S follows the restricted speed setpoint T VSL except for the adjustment overrun. The motor torque setpoint T CM automatically decreases when the speed V of the rack S exceeds the restricted speed setpoint T VSL . Thus, the method 1 according to the present invention ensures that, except for adjustment errors, the speed V of the rack S S does not exceed the restricted speed setpoint T VSL .

[0071] In the response shown in Figure 5, the maximum speed threshold SV S is selected to be equal to 20 mm / S, and the maximum acceleration threshold SA S is not determined. Further, the method has a position setpoint T Ximpose.

[0072] Figure 5 shows the position X of the rack S S merging into the position setting point T along the slope X while the speed V of the rack S S follows the restricted speed setting point T except for the adjustment overrun VSL . The response of the position X of the rack S S is independent of the track to be traveled. Subject to the maximum speed threshold SV S , the rack S reaches the desired position T X . Thus, the method 1 according to the present invention ensures that even when the distance to be traveled is significant, the speed V of the rack S does not exceed the restricted speed setting point T VSL .

[0073] In the response shown in Figure 6, the maximum speed threshold SV S is selected to be equal to 20 mm / S, and the maximum acceleration threshold SA S is selected to be equal to 156 mm / S 2 . Further, the method imposes a position setting point T in the form of steps X .

[0074] Figure 6 shows the position X of the rack S S merging into the position setting point T along the curve X while the speed V of the rack S S follows the restricted speed setting point T except for the adjustment overrun VSL . Except for the adjustment error, while subject to the constraints of the maximum speed threshold SV S and the maximum acceleration threshold SA S , the rack S reaches the desired position T X . Thus, the method 1 according to the present invention ensures that even when the distance to be traveled is significant, the speed V of the rack S S does not exceed the restricted speed setting point T VSL , and that the acceleration of the rack remains lower than the maximum acceleration until the end of the movement.

[0075] Of course, the present invention is not limited to the embodiments described and represented in the accompanying drawings. In particular, with respect to the structure of various elements or by substitution of technical equivalents, modifications are still possible without departing from the scope of protection of the present invention.

Claims

1. A method (1) for controlling an assist motor (12) of a power steering system (100), comprising: The power steering system (100) includes an assist motor (12) configured to apply a motor torque (C Ｍ ) to a rack (S), and at least one steering computer (20), and the method (1) is designed to servo-control the position (X Ｓ ) of the rack (S) to a position setpoint (T Ｘ ), and the method (1) is The assist motor (12) includes a control step (3) of applying a motor torque (C ＣＭ ), in accordance with a motor torque setting point (T Ｍ ), to the rack (S). The method (1) is such that the steering computer (20) determines the setpoint (T Ｘ ), and according to the position (X Ｓ ) of the rack (S), determines the speed setpoint (T ＶＳ ) of the rack (S) in a servo control step (2); The steering computer (20) issues a restricted speed set point (T Ｓ ), which is below the maximum speed threshold (SV ＶＳＬ ), in a restricted step (4); The steering computer (20) further has a control step (5) for determining the motor torque setpoint (T ＶＳＬ ), according to the speed limit setpoint (T Ｓ ) and the speed (V ＣＭ ) of the rack (S).

2. In the method (1) according to Claim 1, The servo control step (2) is the position (X Ｓ ) of the rack (S) and the position set point (T Ｘ ) and a comparison phase for calculating a displacement based thereon, and a correction phase for determining the speed set point (T ＶＳ ) so as to reduce the displacement.

3. In the method (1) according to Claim 1 or 2, The control step (5) calculates a speed deviation according to the speed (V Ｓ ) of the rack (S) and the setpoint of the limiting speed (T ＶＳＬ ), and includes a deviation phase for calculating the speed deviation and a compensation phase for determining the motor torque setpoint (T ＣＭ ) so as to reduce the speed deviation.

4. In the method (1) according to any one of Claims 1 to 3, The limitation step (4) determines the maximum speed threshold (SV Ｓ ) of the rack (S) in accordance with at least one kinematic constraint exerted on the vehicle (21).

5. In the method (1) according to any one of Claims 1 to 4, The limiting step (4) is a method for determining the limiting speed setpoint (T Ｓ ), according to a maximum acceleration threshold value (SA ＶＳＬ ).

6. In the method (1) according to Claim 5, The maximum acceleration threshold value (SA Ｓ ) is a method determined in accordance with at least one kinematic constraint exerted on the vehicle (21).

7. In the method (1) according to any one of Claims 1 to 6, The position (X Ｓ ) of the rack (S) is obtained by any of mathematical calculations using a position sensor, an angle measurement (θ3) of the handle (30), and an angle measurement (θ12) of the shaft (24) of the assist motor (12).

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