A method for controlling a power steering system making it possible to limit the physical supply current supplied to the power steering motor in the event of a mechanical shock between the rack and the mechanical end stop.

Abstract

A control method (50) for a power steering system (1) of a vehicle (2), intended to limit a physical supply current (CA) of at least one assist motor (12) upon an impact (X) between at least one rack (6) and at least one mechanical stop (B), includes a determining step (E1) in which at least one steering computer (20) determines a setpoint torque (Cc) of the at least one assist motor (12), and a driving step (E2) in which the at least one steering computer (20) determines a setpoint supply current (CM) of the at least one assist motor (12). The control method (50) is characterized by further including a detecting step (E3) in which the at least one steering computer (20) detects an impact (X) between the at least one rack (6) and the at least one mechanical stop (B), and a protecting step (E5) in which the at least one steering computer (20) issues a protection signal (SP) to the driving step (E2) when the impact (X) is detected, such that the setpoint supply current (CM) determined by the driving step (E2) is less than a maximum setpoint supply current.

Description

[Technical field]

[0001] The present invention relates to the field of power steering systems for vehicles, and more particularly to a control method for limiting the physical supply current of an assist motor in the event of an impact between a rack and a mechanical stop. [Background technology]

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

[0003] Generally, a steering system comprises several elements, including the above-mentioned steering wheel connected to a steering column, a rack, and two wheels each connected to a tie rod. The rack is the part that allows the steering wheel to be connected to the wheels via the steering column through the tie rods, i.e. it converts the forces applied by the driver to the steering wheel into the rotation of the wheels of the vehicle.

[0004] The rack is translatable between two mechanical stops which define first and second extreme positions of the rack.

[0005] The electric power steering system of a vehicle uses an assist motor driven by a steering computer to reduce the effort applied by the driver to the steering wheel to turn the wheels of the vehicle. In particular, based on the force applied to the steering wheel, i.e. the steering wheel torque, the steering computer determines an assist torque, hereafter called setpoint torque. The steering computer then determines a setpoint supply current of the assist motor based on the setpoint torque. From the setpoint supply current and the constraints applied to the assist motor, the assist motor consumes a physical supply current. In other words, the physical supply current is the actual current flowing through the assist motor. The physical supply current is not controllable since the constraints are not controllable. Only the setpoint supply current, which is a digital signal, is controllable.

[0006] Finally, the assist motor applies an assist force, i.e., a motor torque, to the rack, which then undergoes a translational movement to rotate the wheel.

[0007] For proper operation, the motor torque is substantially equal to the setpoint torque and the physical supply current is substantially equal to the setpoint supply current.

[0008] In the remainder of this specification, the term "torque" refers to a digital or analog signal representing torque, except in the case of a motor torque which actually corresponds to a physical torque.

[0009] When the rack approaches a mechanical stop, the additional steering wheel torque from the driver causes the rack to contact said mechanical stop. When said additional steering wheel torque is high, the setpoint torque is also high, increasing or maintaining the approach speed of the rack until a mechanical shock with a stop occurs. The mechanical shock exposes the power steering system to an overcurrent phenomenon, i.e. a sudden increase in the physical supply current of the assist motor beyond the maximum physical supply current, degrading the steering computer and / or interfering with the monitoring of the correct operation of the assist motor.

[0010] More specifically, the overcurrent phenomenon occurs firstly as a result of large fluctuations in rack speed and secondly as a result of increased steering wheel torque.

[0011] Upon strong fluctuations in the rack speed, corresponding to a deceleration of the rack speed during an impact, the result is a sudden drop in the back EMF at the terminals of the assist motor, which is perceived as an uncompensated voltage disturbance that ultimately increases the physical supply current.

[0012] Solutions are known which make it possible to counter the consequences of strong rack speed variations by predicting and eliminating these voltage disturbances by modifying the control parameters of the steering computer. The parameters which make it possible to control the performance, stability and robustness of the steering computer are called steering computer control parameters.

[0013] In the case of a closed loop servo control, the set control parameter may be a gain, such as a proportional, integral or derivative gain. Summary of the Invention [Problem to be solved by the invention]

[0014] However, this solution has undesirable side effects, such as reducing the robustness and stability margins of the steering system.

[0015] The consequence of the increase in steering wheel torque is related to the mechanical shock: indeed, when the rack is connected to the steering wheel by a steering column, a sudden stop of the rack will cause a significant steering wheel torque and therefore an increase in the setpoint torque, which will induce an increase in the setpoint supply current and, finally, an increase in the physical supply current of the assist motor.

[0016] There are solutions that make it possible to reduce the mechanical shock between the rack and the mechanical stop by reducing the setpoint torque when approaching said stop. This solution, although effective, requires knowledge of the steering wheel angle and is not applicable to all steering systems. [Means for solving the problem]

[0017] The object of the present invention is to remedy all or part of the above mentioned drawbacks, in particular in the absence of a steering wheel angle, by proposing a control method for a power steering system of a vehicle, comprising at least one steering computer, at least one steering wheel and at least one assist motor consuming a physical supply current and providing a motor torque to at least one rack, the movement of said at least one rack being limited by at least one mechanical stop, intended to limit said physical supply current of said at least one assist motor in the event of an impact between said at least one rack and said at least one mechanical stop.

[0018] The control method includes a determining step in which the at least one steering computer determines a set point torque for the at least one assist motor, and a driving step in which the at least one steering computer determines a set point supply current for the at least one assist motor.

[0019] The control method is characterized in that it also includes a detection step in which the at least one steering computer detects an impact between the at least one rack and the at least one mechanical stop, and a protection step in which, when an impact is detected, a protection signal is issued to the drive step such that the setpoint supply current determined by the drive step is less than a maximum setpoint supply current.

[0020] The detection step makes it possible to detect impact situations in which the rack undergoes a significant deceleration, i.e. a deceleration greater than a determined threshold value. For this purpose, the detection step performs a comparison of a parameter representative of the acceleration of the rack with a predetermined threshold value of said parameter.

[0021] The predefined threshold depends on the parameters, but also on the technology of the suspension, such as its material, and on the deceleration gain or gear ratio of the power steering system. The predefined threshold is chosen so that it is much higher than any other operating condition of the rack, such as during disturbances arising from maneuvers controlled by the driver or from the road on which the vehicle is traveling.

[0022] There are several ways to ensure that the physical supply current does not exceed the maximum physical supply current. The method according to the invention makes it possible to do so by limiting the setpoint supply current to the maximum setpoint supply current.

[0023] The protection step issues a protection signal when an impact is detected, in other words the set point torque is replaced and / or supplemented by the protection signal such that the set point supply current of the assist motor determined by the drive step is less than the maximum set point supply current.

[0024] Thus, the consequences of large variations in rack speed leading to a sudden drop in the back EMF and of an increase in steering wheel torque are indirectly compensated for by a reduction in the setpoint supply current, allowing a reduction in the physical supply current flowing through the assist motor. Overcurrent phenomena are thus avoided.

[0025] According to one feature of the invention, the protection signal corresponds to a limit set point torque.

[0026] There are several ways to ensure that the set point supply current does not exceed the maximum set point supply current. One solution is to replace the set point torque delivered to the drive step when an impact is detected with a limit set point torque. The limit set point torque is a predefined value of the set point torque.

[0027] The limit setpoint torque therefore makes it possible to deceive the steering computer during the driving step in order to accelerate reaching the normal setpoint supply current without exceeding the maximum setpoint supply current.

[0028] According to one feature of the invention, the guard signal corresponds to at least one control parameter of the driving step.

[0029] When an impact is detected, the protection step communicates its control parameters to the drive step.

[0030] Thus, for limited periods of time and in certain circumstances of impact, the consequences of large fluctuations in the rack speed are damped by modifying at least one control parameter of the steering computer. In this way, it is possible to accelerate the reaching of the normal physical supply current without exceeding the maximum physical supply current.

[0031] The modification of the control parameters is performed in a very limited time manner so that there are no edge effects perceptible to the driver of the vehicle.

[0032] According to one feature of the invention, the detecting step generates an impact signal when an impact is detected.

[0033] Thus, the shock signal indicates an impact situation of the rack against the machine stop.

[0034] The shock signal may be emitted when an impact is detected, or conversely, may be shut off when an impact is detected.

[0035] According to one feature of the invention, the protection signal is dependent on the shock signal.

[0036] Thus, a protection signal limiting the set point supply current of the assist motor is issued only when an impact is detected.

[0037] According to one feature of the invention, the control method includes a timing step of issuing an application signal to the protection step in response to the shock signal.

[0038] The timing step determines how the issuance of a protection signal should be performed when an impact is detected.

[0039] Indeed, if the protection signal is emitted erratically, for example following a fault, this may reduce the safety of the method.

[0040] According to one feature of the invention, the guarding step issues the guard signal when the application signal is present.

[0041] According to one feature of the invention, the timing step includes an application time corresponding to a period during which the protection signal is issued after detection of an impact.

[0042] The application time is the period during which a protection signal is issued after an impact signal is detected.

[0043] The application time therefore ensures that when an impact is detected, a protection signal is issued long enough to avoid an overcurrent event, but does not exceed a certain period that may compromise the safety of the method.

[0044] According to one feature of the invention, the timing step includes an exclusion time corresponding to a period during which the protection signal cannot be issued after detection of an impact.

[0045] The exception time is a period during which a guard signal cannot be emitted. The exception time is subject to the application time.

[0046] The exclusion time therefore limits the number of times a guard signal is issued during a certain period of time, thus ensuring the security of the method.

[0047] According to one aspect of the present invention, the detection step detects the impact based on the acceleration of the assist motor.

[0048] The acceleration of the assist motor is obtained by differentiating the speed of the assist motor, which is easily measurable data. Acceleration has faster dynamics than speed. Therefore, it is practical to detect impacts by an acceleration threshold.

[0049] The invention also relates to a power steering system of a vehicle making it possible to implement the control method according to the invention.

[0050] The invention will be better understood thanks to the following description of an embodiment according to the invention, given as a non-limiting example and illustrated with reference to the attached schematic drawings, in which: [Brief description of the drawings]

[0051] [Figure 1] FIG. 1 is a schematic diagram of a power steering system. [Diagram 2] FIG. 2 is a schematic diagram of the method according to the present invention. [Diagram 3] FIG. 3 is a graph showing the speed of the steering motor during an impact. [Figure 4] FIG. 4 is a graph showing the acceleration of the steering motor when a shock occurs. [Diagram 5] FIG. 5 is a graph showing the steering wheel angle at the time of impact. [Figure 6]FIG. 6 is a graph showing the setpoint torque and motor torque of the steering motor during an impact in the absence of the method according to the invention. [Figure 7] FIG. 7 is a graph illustrating the physical supply current and the maximum physical supply current of the steering motor during an impact in the absence of the method according to the invention. [Figure 8] FIG. 8 is a graph showing the setpoint torque and motor torque of the steering motor during an impact in the presence of the method according to the invention. [Figure 9] FIG. 9 is a graph representing the physical supply current and the maximum physical supply current of the steering motor during an impact in the presence of the method according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] The invention relates to a method for managing a power steering system 1 for a vehicle 2, more particularly for a motor vehicle 2 intended for the transportation of people.

[0053] In a manner known per se, as shown in Fig. 1, the power steering system 1 comprises a steering wheel 3. The steering wheel 3 enables a driver to steer the power steering system 1 by applying a force called "steering wheel torque" T3 to the steering wheel 3. The steering wheel torque T3 is measured by a torque sensor 23.

[0054] The steering wheel 3 is preferably mounted on a steering column 4, is guided for rotation on the vehicle 2, meshes with a rack 6 by means of a steering pinion 5 and is itself guided for translation in a steering casing 7 fixed to the vehicle 2.

[0055] Preferably, each end of said rack 6 is connected to a tie rod 8, 9 connected to the steering knuckles of the steered wheels 10, 11, so that the translational longitudinal displacement of the rack 6 makes it possible to change the steering angle of the steered wheels. The amplitude of the displacement of the rack 6 is limited by two mechanical stops B located at the right and left ends of the steering casing 7, respectively.

[0056] Furthermore, the steered wheels 10, 11 may preferably be drive wheels.

[0057] The power steering system 1 also comprises an assist motor 12 intended to provide a motor torque T12 to assist the operation of said power steering system 1.

[0058] The assist motor 12 is preferably an electric motor having two directions of operation of a brush or brushless type, preferably a rotary electric motor.

[0059] The assist motor 12 may be engaged with the steering column 4 itself, if necessary via a gear reducer type reducer, forming a so-called "single pinion" mechanism, or may be engaged directly with the steering rack 6, for example by means of a second pinion 13 separate from the steering pinion 5 which enables the steering column 4 to mesh with the rack 6, forming a so-called "double pinion" mechanism as shown in FIG. 1, or by means of a ball screw cooperating with a corresponding thread of the rack 6 remote from the steering pinion 5.

[0060] The power steering system 1 also includes a steering computer 20 which receives a steering wheel torque T3 from a torque sensor 23 and determines a setpoint supply current CM for the assist motor 12.

[0061] Furthermore, the rotation speed of the assist motor 12 JPEG0007602547000001.jpg48 is determined by the motor speed 24 or position sensor.

[0062] The control method 50 according to the invention implemented by the steering computer 20 is explained in more detail in FIG.

[0063] The control method 50 includes a determination step E1 in which the steering computer 20 determines a setpoint torque Cc. The setpoint torque Cc corresponds to the assist torque and thus to the motor torque T12 that would normally have to be provided by the assist motor 12.

[0064] The control method 50 includes an operating step E2 in which the steering computer 20 determines a setpoint supply current CM for the assist motor 12 .

[0065] Due to the setpoint supply current CM and the constraints imposed on the assist motor 12, the assist motor 12 consumes a physical supply current CA. If the physical supply current CA of the assist motor 12 is greater than the maximum physical supply current CAmax, the steering computer 20 is degraded and / or disturbed.

[0066] The control method 50 includes a detection step E3 in which the steering computer 20 detects an impact X between the rack 6 and the mechanical stop B. For this purpose, the detection step E3 detects the rotation speed of the assist motor 12. Absolute value of acceleration of the assist motor 12 from differentiation of JPEG0007602547000002.jpg48 JPEG0007602547000003.jpg510. The detection step E3 includes a phase P1 for calculating the absolute value of the acceleration of the assist motor 12. JPEG0007602547000004.jpg610 includes a tracking phase P2 in which the absolute value of the acceleration of the assist motor 12 is compared with a predetermined threshold value. When JPEG0007602547000005.jpg 610 exceeds a predefined threshold, the method 50 according to the invention considers that an impact X has occurred between the rack 6 and the machine stop B. A detection step E3 then generates an impact signal S.

[0067] The control method 50 also includes a timing step E4 for issuing the application signal SA from the shock signal S so as to ensure the safety of the control method 50. More specifically, when an impact X is detected by the detection step E3, in other words when the shock signal S is issued, the timing step E4 issues the application signal SA for an application time Ta. The application time Ta is less than 50 ms, preferably less than 10 ms. Furthermore, the timing step E4 prevents the issuance of the application signal SA for an exclusion time Te after the end of the application time Ta. The exclusion time is less than 10 s, preferably less than 5 s.

[0068] The control method 50 includes a protection step E5 which receives the setpoint torque Cc and the application signal SA and issues a protection signal SP and the setpoint torque Cc to the drive step E2 when the application signal SA is issued. In the absence of the application signal SA, the protection step E5 only delivers the setpoint torque Cc without interfering with the decision step E1.

[0069] The protection signal SP includes a setpoint torque C3 limited to a predetermined value and control parameters of the drive step E2.

[0070] 3 to 9 show some parameters of the steering system 1 during an impact occurring at 0.5 s.

[0071] FIG. 3 shows the rotation speed of the assist motor 12. JPEG0007602547000006.jpg48 as a function of time T. Upon impact X, the rotational speed JPEG0007602547000007.jpg48 is significantly reduced. In fact, the rack 6 is stopped from moving by the stop B. And the rotation speed JPEG0007602547000008.jpg48 bounces before stabilizing at about 0.52s. The bounce is related to the nature of the mechanical stop, i.e. its elasticity.

[0072] FIG. 4 shows the acceleration of the assist motor 12. JPEG0007602547000009.jpg48 as a function of time T. This is the rotation speed JPEG0007602547000010.jpg48 is the derivative. Therefore, the acceleration JPEG0007602547000011.jpg48 drops significantly to a minimum before rising again around 0.52s, bouncing back and stabilizing.

[0073] Figure 5 shows the steering wheel angle θ3 of the steering wheel 3 as a function of time T. Before the impact X, the steering wheel angle θ3 increases as the driver turns the steering wheel 3. Upon impact, the elasticity of stop B allows the driver to turn the steering wheel further and the steering wheel angle θ3 increases a little further to a maximum elastic value before stabilising at the maximum rotation value of 540°.

[0074] Fig. 6 shows the motor torque T12 and the setpoint torque Cc as a function of time T when the control method 50 according to the invention is not present in the steering computer 20. In Fig. 6, the assist motor 12 should achieve a motor torque T12 equal to 5.2 Nm, which corresponds to the setpoint torque Cc. However, the motor torque T12 provided by the assist motor 12 increases and then decreases before stabilizing at the setpoint torque Cc. This phenomenon is associated with the impact X.

[0075] Fig. 7 shows the physical supply current CA of the assist motor 12 as a function of time T when the control method 50 according to the invention is not present in the steering computer 20. The physical supply current CA has a curve substantially similar to that of the motor torque T12 shown in Fig. 6. In other words, after an impact X, the physical supply current CA increases sharply above the maximum physical supply current CAmax before stabilizing and then decreasing. When increasing, the physical supply current CA passes through a maximum value above the maximum physical supply current CAmax, which corresponds to an overcurrent phenomenon in the power steering system 1.

[0076] Fig. 8 shows the motor torque T12 as a function of time T when the control method 50 according to the invention is present in the steering computer 20. In this case, the assist motor 12 should execute a motor torque T12 having a profile required by the limit set torque C3 issued by the protection step E5. In this way, the motor torque T12 provided by the assist motor 12 increases very slightly and then decreases before increasing again to stabilize at the limit set torque C3. Fig. 8 also shows the application time Ta of the protection signal SP and the subsequent exclusion time Te during which the protection signal SP cannot be issued.

[0077] 9 shows the physical supply current CA of the assist motor 12 as a function of time T when the control method 50 according to the invention is present in the steering computer 20. The physical supply current CA has a curve substantially similar to that of the motor torque T12. In other words, after an impact X, the physical supply current CA increases very slightly but then decreases sharply thanks to an almost simultaneous reduction in the setpoint supply current CM. In this way, there is almost no overrun of the maximum physical supply current CAmax and no overcurrent phenomenon appears.

[0078] The control method 50 according to the invention therefore makes it possible to avoid the occurrence of overcurrent phenomena without requiring knowledge of the steering wheel angle θ 3 of the steering wheel 3 .

[0079] Of course, the invention is not limited to the embodiments described and shown in the attached drawings: modifications remain possible, in particular with regard to the configuration of the various elements or by substitution by technical equivalents, without departing from the scope of protection of the invention.

Claims

1. at least one steering computer (20), at least one steering wheel (3), at least one assist motor (12) consuming a physical supply current (CA) and providing a motor torque (T12) to at least one rack (6), the movement of said at least one rack (6) being limited by at least one mechanical stop (B), A method (50) for controlling a power steering system (1) of a vehicle (2), comprising: said control method (50) being intended to limit said physical supply current (CA) of said at least one assist motor (12) upon an impact (X) between said at least one rack (6) and said at least one mechanical stop (B); The control method (50) comprises: a determining step (E1) in which the at least one steering computer (20) determines a setpoint torque (Cc) of the at least one assist motor (12); and a driving step (E2) in which the at least one steering computer (20) determines a setpoint supply current (CM) of the at least one assist motor (12), The control method (50) comprises: a detection step (E3) in which said at least one steering computer (20) detects an impact (X) between said at least one rack (6) and said at least one mechanical stop (B); a protection step (E5) of issuing a protection signal (SP) to the driving step (E2) when an impact (X) is detected, so that the set value supply current (CM) determined by the driving step (E2) is less than a maximum set value supply current; The control method (50), further comprising:

2. 2. The control method (50) of claim 1, wherein said protection signal (SP) corresponds to a limit set point torque (C3).

3. 3. Control method (50) according to claim 1 or 2, wherein said protection signal (SP) corresponds to at least one control parameter of said actuation step (E2).

4. 4. A control method (50) according to any one of claims 1 to 3, wherein said detection step (E2) generates an impact signal (S) when an impact (X) is detected.

5. 5. Control method (50) according to claim 4, wherein said protection signal (SP) is dependent on said shock signal (S).

6. A control method (50) according to claim 4 or 5, comprising a timing step (E4) of issuing an application signal (SA) to said protection step (E5) upon receipt of said shock signal (S).

7. 7. Control method (50) according to claim 6, wherein said timing step (E5) comprises an application time (Ta) corresponding to the period during which said protection signal (SP) is issued after detection of an impact (X).

8. Control method (50) according to claim 6 or 7, wherein said timing step (E5) includes an exclusion time (Te) corresponding to a period during which said protection signal (SP) cannot be emitted after detection of an impact (X).

9. The detection step (E3) is a step of detecting the acceleration ( 9. The control method (50) according to claim 1, further comprising detecting an impact (X) by:

10. A power steering system (1) of a vehicle (2) making it possible to implement a control method (50) according to any one of claims 1 to 9.

Images