METHOD FOR CONTROLLING AN ASSISTANCE MOTOR OF A POWER STEERING SYSTEM COMPRISING AN ALGORITHM FOR COMPENSATING THE OSCILLATIONS OF A STEERING WHEEL LINKED TO THE PRESENCE OF AN IMBALANCE

Abstract

A method controls a power steering motor of a power steering system. The power steering system includes at least one steering wheel configured to receive a steering torque applied by a driver, the power steering motor being configured to apply a motor torque to a rack, at least one wheel connected to the rack, and at least one steering computer implementing a main control algorithm. The main control algorithm includes a step of determining a main engine torque according to at least the steering wheel torque, characterised in that the steering computer also includes an algorithm for compensating for an oscillation of the steering wheel implementing a step of determining a compensating engine torque such that the steering wheel torque is equal to a reference steering wheel torque.

Claims

1. A method for controlling an assistance motor of a power steering system, said power steering system comprising at least one steering wheel configured to receive a steering wheel torque applied by a driver, the assistance motor configured to apply a motor torque to a rack, at least one wheel connected to said rack, and at least one steering computer implementing a main control algorithm, the main control algorithm comprising a step of determining a main motor torque as a function of at least the steering wheel torque, wherein the steering computer also comprises a compensation algorithm for an oscillation of the steering wheel implementing a step of determining a compensation motor torque so that the steering wheel torque is equal to a reference steering wheel torque.

2. The method according to claim 1, comprising a summation step wherein the compensation motor torque is added to the main motor torque so as to determine the motor torque.

3. The method according to claim 1, wherein the reference steering wheel torque is equal to 0 Nm.

4. The method according to claim 1, wherein the step of determining a compensation motor torque comprises a phase of filtering the low frequencies by means of a high-pass filter.

5. The method according to claim 4, wherein the high-pass filter has a cut-off frequency of 10 Hz.

6. The method according to claim 1, wherein the step of determining a compensation motor torque comprises a phase of calculating a steering wheel torque error by subtracting the reference steering wheel torque and the steering wheel torque.

7. The method according to claim 6, wherein the step of determining a compensation motor torque comprises a compensation phase in which a controller determines the compensation motor torque depending on the steering wheel torque error.

8. The method according to claim 1, wherein an operating frequency of the compensation algorithm is selectable independently of an operating frequency of the main control algorithm.

9. The method according to claim 8, wherein the operating frequency of the compensation algorithm is less than 200 Hz.

10. A vehicle implementing a method according to claim 1.

Description

[0051] The invention will be better understood, thanks to the description below, which relates to an embodiment according to the present invention, given by way of non-limiting example and explained with reference to the appended diagrammatic drawings, in which:

[0052] FIG. 1 is a diagram representing the time as a function of a frequency of an oscillation of the steering wheel on which is illustrated an amplitude of the oscillation of the steering wheel, on a vehicle equipped with an imbalance carrying out a movement at approximately 110 km/h;

[0053] FIG. 2 is a diagram representing the time as a function of a frequency of an oscillation of the steering wheel on which is illustrated an amplitude of the oscillation of the steering wheel, on the vehicle of FIG. 1, said vehicle comprising a solution of the related art to decrease the amplitude of the steering wheel oscillation;

[0054] FIG. 3 is a schematic representation of a method according to the invention;

[0055] FIG. 4 is a representation of a detail of FIG. 3;

[0056] FIG. 5 is a diagram representing the time as a function of a frequency of an oscillation of the steering wheel on which is illustrated an amplitude of the oscillation of the steering wheel, on a vehicle equipped with an imbalance carrying out a movement at approximately 110 km/h;

[0057] FIG. 6 is a diagram representing the time as a function of a frequency of an oscillation of the steering wheel on which is illustrated an amplitude of the oscillation of the steering wheel, on the vehicle of FIG. 5, said vehicle comprising the method according to the invention to reduce the amplitude of the steering wheel oscillation;

[0058] FIG. 7 is a representation of the steering wheel torque as a function of time and as a function of frequency on the vehicle of FIG. 5;

[0059] FIG. 8 is a representation of the steering wheel torque and of the compensation torque as a function of time and as a function of frequency on the vehicle of FIG. 6;

[0060] FIG. 9 is a schematic representation of a power steering system.

[0061] The invention concerns a method 10 for controlling an assistance motor 12 of a power steering system 1 of a vehicle 2, and more particularly of a motor vehicle 2 intended for the transport of persons.

[0062] In a manner known per se, and as can be seen in FIG. 9, said power steering system 1 comprises a steering wheel 3 which allows a driver to manoeuvre said power steering system 1 by exerting a force, called «steering torque» T3, on said steering wheel 3.

[0063] Said steering wheel 3 is preferably mounted on a steering column 4, guided in rotation on the vehicle 2, and which meshes, by means of a steering pinion 5, on a rack 6, which is itself guided in translation in a steering casing 7 fixed to said vehicle 2.

[0064] Preferably, the ends of said rack 6 are each connected to a connection tie-rod 8, 9 connected to the steering knuckle of a wheel 100, 11 (respectively a left wheel 100 and a right wheel 11), so that the longitudinal displacement in translation of the rack 6 makes it possible to carry out a lateral rotation and therefore to modify the steering angle (yaw angle) of the wheels 100, 11.

[0065] The wheels 100, 11 can moreover preferably also be driving wheels.

[0066] The power steering system 1 also comprises the assistance motor 12 intended to supply an assistance force T12, and more particularly a motor torque T12, to assist the operation of said power steering system 1.

[0067] The assistance motor 12 will preferably be an electric motor, with two directions of operation, and preferably a rotary electric motor, of the brushless type. The assistance motor 12 can come into engagement, if necessary via a reducer of the gear reducer type, or on the steering column 4 itself, to form a so-called «single pinion» mechanism, either directly on the rack 6, for example by means of a second pinion 13 separate from the steering pinion 5 which allows the steering column 4 to mesh with the rack 6, so as to form a so-called «double pinion» mechanism, as illustrated in FIG. 9, or even by means of a ball screw which cooperates with a corresponding thread of said rack 6, at a distance from said steering pinion 5.

[0068] The power steering system 1 also comprises a steering computer 20 which receives information from a steering wheel torque T3 sensor 23 and transmits to the assistance motor 12 the motor torque T12 to be applied.

[0069] FIG. 3 represents a method 10 for controlling the assistance motor 12 carried out by the steering computer 20 which implements a main control algorithm 51 and a compensation algorithm 61.

[0070] The main control algorithm 51 comprises a step of determining a main motor torque T12P as a function of the steering wheel torque T3. The main control algorithm 51 therefore receives the steering wheel torque T3 as input and determines the main motor torque T12P. The main control algorithm 51 comprises a plurality of functions allowing, for example, a detection of good maintenance of the steering wheel 3 by the driver, or even a detection of an oversteer or an understeer. The purpose of the main motor torque T12P is to reduce the force required by the driver to turn the steering wheel 3. In other words, the main motor torque T12P reduces the steering wheel torque T3 exerted by the driver on the steering wheel 3.

[0071] The object of the compensation algorithm 61 for an oscillation of the steering wheel 3 is to reduce an oscillation induced in the steering wheel 3 by an imbalance present on a wheel 100, 11.

[0072] The compensation algorithm 61 is more precisely represented in FIG. 4. The compensation algorithm 61 implements a step 62 of determining a compensation motor torque T12C so that the steering wheel torque T3 is equal to a reference steering wheel torqueT3.sub.ref. In other words, the compensation algorithm 61 receives the steering wheel torque T3 as input and the reference steering wheel torque T3.sub.ref and determines the compensation motor torque T12C.

[0073] For this, the step 62 of determining a compensation motor torque T12C comprises a phase 63 of calculating a steering wheel torque error ΔT3 by subtracting the reference steering wheel torque T3.sub.ref and the steering wheel torque T3. The reference steering wheel torque T3.sub.ref is selected equal to 0 Nm so as to completely suppress the amplitude A of oscillation of the steering wheel 3. Indeed, the reference motor torque T3.sub.ref is the value at which the method imposes the steering wheel torque T3.

[0074] Furthermore, the step 62 of determining a compensation motor torque T12C comprises a phase 64 of filtering the low frequencies by means of a high-pass filter.

[0075] The filtering step 64 receives the steering wheel torque error ΔT3 as input and determines a filtered steering wheel torque error ΔT3f. The high pass filter has a cut-off frequency of 10 Hz. In other words, only frequencies of the steering wheel torque error ΔT3 greater than 10 Hz pass to the next phase. Thus, the compensation algorithm 61 is only applied to the frequencies of the steering wheel torque T3 greater than 10 Hz, and therefore only to the oscillations of the steering wheel 3 associated with the imbalance.

[0076] The step 62 of determining a compensation motor torque T12C finally comprises a compensation phase 65 in which a controller determines the compensation motor torque T12C as a function of the filtered steering wheel torque error ΔT3f. The controller is parameterized with a plurality of parameters selected judiciously so that the compensation algorithm 61 is robust and stable.

[0077] The compensation algorithm 61 is positioned in parallel with the main control algorithm 51. Thus, an operating frequency of the compensation algorithm 61 can be selected independently of an operating frequency of the main control algorithm 51 The operating frequency of the compensation algorithm 61 is less than 100 Hz.

[0078] The compensation algorithm 61 is a regulation of the steering wheel torque T3 in closed loop. Indeed, in the method 10 according to the invention, it can be considered that the compensation algorithm 61 is applied to a general system G comprising the main control algorithm 51 and the assistance motor 21. A reaction of the general system G is compared with a reference value so as to correct the compensation algorithm 61.

[0079] The method also comprises a summation step 52 in which the compensation motor torque T12C is added to the main motor torque T12P so as to determine the motor torque T12. Thus, the motor torque T12 comprises a part linked to the main control algorithm 51 and a part linked to the compensation algorithm 61.

[0080] FIG. 5 represents the results in the form of a graph of a test carried out on a vehicle 2 exhibiting an imbalance and moving at about 110 km/h, when the vehicle 2 does not comprise a method 10 according to the invention. Analogously to FIG. 1, the diagram of FIG. 5 represents the time T as a function of the frequency F as well as a substantially vertical line R corresponding to a high oscillation amplitude A at 14.5 Hz.

[0081] FIG. 6 represents the results in the form of a graph of the test carried out on the vehicle 2 of FIG. 5, when the vehicle 2 comprises a method 10 according to the invention. On the graph of FIG. 6, the high amplitude R line A visible in FIG. 5 has completely disappeared. Thus, the method 10 according to the invention therefore makes it possible to suppress any amplitude A of oscillation of the steering wheel 3 when a wheel 100, 11 has an imbalance. The driver is no longer aware that the wheel has an imbalance.

[0082] This result is confirmed in FIGS. 7 and 8.

[0083] FIG. 7a illustrates the steering wheel torque T3 felt by the driver during the previous test in which the method 10 according to the invention is not activated. FIG. 7a shows perfectly the oscillation of the steering wheel torque T3 which is perceptible to the driver. This is confirmed by a frequency analysis of the steering wheel torque T3 and which is represented in FIG. 7b. FIG. 7b shows a frequency peak at 14.5 Hz.

[0084] FIGS. 8a and 8b are similar to FIGS. 7a and 7b when the method 10 according to the invention is activated on the vehicle. The steering wheel torque T3 no longer exhibits oscillation, which is confirmed by the frequency analysis. In addition, FIG. 8c illustrates the compensation motor torque T12C determined by the compensation algorithm 61.

[0085] The compensation motor torque T12C has a visible oscillation. This is confirmed by the frequency analysis carried out in FIG. 8d.

[0086] Of course, the invention is not limited to the embodiments described and represented in the appended 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 thereby departing from the scope of protection of the invention.