Method for supervising the operation of a power steering system

Abstract

A method (100) for monitoring the operation of a power steering system, the power steering system comprising a steering wheel, a servo motor and a monitoring module (M sur ), characterized in that the method comprises: - determining at least one temporary limit value (V lmaxt , V lmint ) step; ‑ estimating the effect of the auxiliary function (F) on the set point value of the parameter (C mc ) added value (V add ) step (3); ‑ According to the added value (V add ) corrects at least one temporary limit value (V lmaxt , V lmint ) in step (4).

Description

Technical Field

[0001] The present invention relates to the field of power steering systems for vehicles and more particularly to a method for supervising the operation of a power steering system. Background Art

[0002] The purpose of a vehicle's steering system is to allow the driver to monitor the vehicle's trajectory as a result of applying force to the steering wheel.

[0003] The vehicle's electric power steering system uses an assist motor controlled by a steering computer to reduce the force provided by the driver on the steering wheel to turn the wheels.

[0004] Under normal circumstances, the force applied by the driver on the steering wheel (also called steering wheel torque) results in a setpoint assist force (also called setpoint motor torque, to be applied by the assist motor) typically in the same direction as the direction of the steering wheel torque, in order to turn the wheels in the direction desired by the driver. The steering wheel torque and the setpoint motor torque are typically applied in the same direction.

[0005] For example, by determining that a positive direction corresponds to a "turn the wheels to the right" action, when the driver turns the steering wheel in the positive direction, he applies a positive steering wheel torque which results in a positive setpoint motor torque allowing to turn the vehicle's wheels to the right.

[0006] The power steering system plays a decisive role in the safety of the vehicle occupants through its effect on the vehicle's trajectory.

[0007] Therefore, regulations require that the correct operation of the power steering system is constantly monitored. That is, under normal circumstances the set point value of the parameter is consistent with the input signal. For example, the set point value may be a set point motor torque, and the input signal may be a steering wheel torque.

[0008] In normal situations, supervision of correct operation is performed by a monitoring module and a comparison module. The monitoring module is continuously operated and determines at least one limit value of a parameter set point value. The comparison module is continuously operated and compares the set point value of the parameter with at least one limit value.

[0009] When the electronic power steering system operates correctly, the set point value coincides with at least one limit value. Thus, it is possible to detect correct operation, whereas, conversely, a malfunction of the power steering system is detected.

[0010] For example, supervision of correct operation may include checking that the setpoint motor torque has a value consistent with the maximum and minimum limits determined by the supervision module from the steering wheel torque. The maximum and minimum limits allow ensuring that the setpoint motor torque and the steering wheel torque are in the same direction.

[0011] Furthermore, there are assistance functions integrated into the vehicle, such as driver assistance (ADAS), which allow occasional control of the power steering system in order, for example, to encourage the driver to correct his movements in dangerous situations (such as oversteering or understeering, or when crossing a white line), to control the vehicle to keep it between two white lines or to guide the vehicle during parking.

[0012] The assist function interferes with the normal regulation of the power steering system and thereby modifies at least the setpoint value of a parameter. The setpoint value then no longer corresponds to the input signal. For example, when the assist function is active, the setpoint motor torque may be in a different direction than the steering wheel torque.

[0013] Therefore, the auxiliary function interferes with the supervision module and determines the limit value which is inconsistent with the set point value.

[0014] One solution allowing the avoidance of inconsistencies is to weaken the supervision normally performed by the supervision module by modifying the limit values ​​of the parameters determined by the supervision module.

[0015] For example, one solution consists in modifying the maximum and minimum limit values ​​of the setpoint motor torque as a function of the steering wheel torque. This solution has the drawback of impairing the supervision performed by the supervision module without an auxiliary function.

[0016] Therefore, a compromise should be made between false detection of a power steering system malfunction and a reduction in the supervision performed. Summary of the invention

[0017] The present invention aims to overcome all or part of the above-mentioned drawbacks by ensuring a method for supervising the operation of a power steering system comprising a steering wheel, an auxiliary motor and a supervision module, characterized in that the method comprises:

[0018] - a step of determining at least one temporary limit value of a parameter;

[0019] - a step of estimating the additional value provided by the auxiliary function to the set point value of the parameter;

[0020] - A step of correcting at least one temporary limit value as a function of the additional value.

[0021] The power steering system determines via a steering computer a setpoint value for a parameter which is dependent on at least one input signal or determines an assist function when an assist function is applied to the power steering system.

[0022] The supervision module determines during the determination step at least one temporary limit value, which corresponds to at least one limit value determined without application of the auxiliary function.

[0023] Therefore, the supervision module can operate identically whether the auxiliary function is activated or inactive.When the auxiliary function is inactive, there is no reduction in the supervision performed by the supervision module.

[0024] However, in order to take into account the influence of the auxiliary function on the set point value, the method estimates the additional value provided by the auxiliary function to the set point value. That is, the auxiliary function has an influence on the set point value. The set point value then corresponds to the sum of the additional value and the set point value determined without the application of the auxiliary function.

[0025] Finally, the method corrects at least one temporary limit value by the additional value in order to determine at least one limit value of the parameter.

[0026] The method according to the invention thus allows determining at least one limit value of a parameter taking into account the influence of the auxiliary function on the setpoint value, without having to modify the supervision when the auxiliary function is inactive.

[0027] When the set point value does not agree with the limit value, the power steering system will be declared faulty.

[0028] According to one feature of the invention, the determining step defines a temporary maximum limit value and a temporary minimum limit value of the parameter.

[0029] Therefore, without the assist function and when the power steering system operates correctly, the setpoint value of the parameter should be comprised between the temporary maximum limit value and the temporary minimum limit value.

[0030] According to one feature of the invention, the estimation step calculates the additional value using a first transformation function between the setpoint value and an auxiliary function of the auxiliary function.

[0031] The auxiliary function represents the influence of the auxiliary function on the steering computer.

[0032] A mathematical relationship is established between the setpoint value of the parameter and the auxiliary function of the auxiliary function.

[0033] According to one feature of the invention, the correction step adds an additional value to the temporary limit value of the parameter.

[0034] Therefore, the sum of the additional value and the temporary limit value is equal to the limit value of the parameter.

[0035] When the auxiliary function is inactive, the additional value is equal to 0 and the temporary limit value is equal to the limit value of the parameter.

[0036] The limit value of this parameter corresponds to the set point value when the power steering system is operating correctly and when the assist function is activated or deactivated.

[0037] According to one feature of the invention, the method comprises a step of calculating a complementary value provided by the auxiliary function to the modified input signal of the supervisory module.

[0038] The assist function may interfere with the power steering system by modifying a setpoint value of a parameter, but also by modifying at least one input signal of the steering computer, which in the following description is referred to as modified input signal.

[0039] In this case, the input signal of the supervisory module is also modified by the auxiliary function. The input signal of the supervisory module is equal to the modified input signal.

[0040] Auxiliary functions may affect more than one input signal.

[0041] The method calculates a supplementary value provided by the auxiliary function to the modified input signal. That is, the auxiliary function has an influence on the modified input signal.

[0042] According to one feature of the invention, the calculation step determines the complementary value using a second transformation function between the modified input signal and an auxiliary function of the auxiliary function.

[0043] Thus, a mathematical relationship is established between each modified input signal and the auxiliary function of the auxiliary function.

[0044] According to one feature of the invention, the first and / or second transformation function is identified based on a theoretical formula.

[0045] According to one feature of the invention, the first and / or second transformation function is identified empirically using at least one simulation and / or at least one experiment.

[0046] According to one feature of the invention, the method comprises the step of modifying the modified input signal according to the complementary value.

[0047] The method takes into account the influence of the auxiliary function on the modified input signal by defining the input signal of the supervisory module as a combination of the complementary value and the modified input signal.

[0048] Therefore, the input signal of the supervisory module is not affected by the auxiliary function, whether the auxiliary function is activated or inactivated.

[0049] The supervisory module determines a temporary limit value which is not influenced by the auxiliary function based on such an input signal which is not influenced by the auxiliary function.

[0050] According to a feature of the invention, the modifying step subtracts the complementary value from the modified input signal.

[0051] Thus, the input signal is a subtraction of the complementary value and the modified input signal in order to remove the effect of the auxiliary function from the modified input signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The invention will be better understood from the following description of embodiments of the invention, by way of non-limiting example and explained with reference to the accompanying schematic drawings, in which:

[0053] - Figure 1 is a schematic diagram of the normal operation of the power steering system.

[0054] - Figure 2 is a graph showing the relationship between the maximum and minimum limit values ​​of the motor torque and the steering wheel torque in normal operation.

[0055] - Figure 3 Representation of the operating point of the auxiliary function.

[0056] - Figure 4 is a schematic diagram of the auxiliary operation of the power steering.

[0057] - Figure 5 is a schematic diagram of the method according to the present invention. DETAILED DESCRIPTION

[0058] In normal operation of the power steering, the control circuit is based on the steering wheel torque C applied by the driver to the steering wheel of the vehicle. v To adjust the applied motor torque C ma , in order to determine the trajectory of the vehicle. Figure 1 As shown in FIG. 1 , the steering computer CD determines the set point motor torque C mc , the set point motor torque C mc In the absence of faults, it is equal to the motor torque C applied to the mechanical system SM including at least one auxiliary motor ma , in order to assist the driver to turn according to his intention. The regulation loop makes the steering wheel torque Cv to the applied motor torque C ma Influence and vice versa.

[0059] The regulations require that in the event of a failure in the steering computer CD, that is, at the set point motor torque C mc Relative to the steering wheel torque C v To ensure the driver's safety and the integrity of the vehicle when the torque C is inconsistent. ma The applied steering wheel torque C v The associated value.

[0060] This situation is monitored by the monitoring module M sur and is checked by comparing the module MCP.

[0061] "Interlock" type monitoring module M surReceives the steering wheel torque C corresponding to the applied v The input signal, and according to Figure 2 The monitoring curve shown determines the motor torque C m The maximum limit value V lmax and the minimum limit value V lmin When the steering wheel torque C v When it is negative, the maximum limit value V lmax It is basically equal to 0, and then increases linearly to the asymptote. Minimum limit value V lmin At some negative values ​​of the steering wheel torque Cv, it is equal to a negative constant value and then increases linearly. v When positive, it is basically equal to 0.

[0062] certainly, Figure 2 The examples of monitoring curves are not intended to be limiting, and other forms of monitoring curves may be considered.

[0063] Therefore, the supervision module M sur The motor torque C m The value is limited to the maximum limit value V lmax and the minimum limit value V lmin In addition, Figure 2 In the embodiment, when the steering wheel torque C v When it is negative, the maximum limit value V lmax is basically equal to 0, and when the steering wheel torque C v When it is positive, the minimum limit value V lmin Basically equal to 0, supervision module M sur Establish the steering wheel torque C v and motor torque C m In the same direction.

[0064] The comparison module MCP receives the maximum limit value V lmax , minimum limit value V lmin and set point motor torque C mc The comparison module MCP takes the setpoint motor torque C mc With maximum V lmax and minimum V lmin The limit value is compared and the applied motor torque C is transmitted ma .

[0065] As long as the set point motor torque C mc Included in the maximum V lmaxt and minimum V lmint If the applied motor torque C ma Equal to the set point motor torque C mc .

[0066] Once the set point motor torque Cmc Exceeding the limit value V lmax 、V lmin , the steering computer CD is declared faulty and the applied motor torque C ma is limited to a maximum V lmaxt or minimum V lmint Limit value.

[0067] In auxiliary operations, such as Figure 4 As shown, the assistance function F is occasionally applied to the power steering system and in particular to the steering computer CD. The assistance function F determines the torque corresponding to the assistance steering wheel torque C va and auxiliary setpoint motor torque C mca The operating point P fa , the operating point P fa Different from the normal operating point P which corresponds to the operating point applied under normal circumstances.

[0068] In assist operation, the steering wheel torque C v Equal to the auxiliary steering wheel torque C va , and the set point motor torque C mc Equal to the auxiliary set point motor torque C mca .

[0069] Without the method according to the invention, the supervisory module M sur Receive auxiliary steering wheel torque C va The value of the auxiliary steering wheel torque C is determined va The associated maximum V lmax and minimum V lmin limit value in order to ensure that the motor torque is applied to the auxiliary steering wheel torque C va However, if Figure 3 As shown, the auxiliary setpoint motor torque C is determined by the auxiliary function F. mca Not included in the supervision module M sur The comparison module MCP thus detects a fault in the steering computer CD and transmits a signal equal to the minimum limit value V lmin The applied motor torque C ma .

[0070] In such Figure 5 In the method 100 according to the present invention, the supervisory module M sur Not affected by activation of auxiliary function F.

[0071] In the method 100 according to the invention, the calculation step 1 determines the auxiliary steering wheel torque C from the auxiliary function F. va The steering wheel torque C provided is relative to the normal applied vThe supplementary value V supp Based on the auxiliary steering wheel torque C va and the auxiliary function Fa of the auxiliary function F, calculate the supplementary value V supp .

[0072] Therefore, the assist steering wheel torque C applied by the assist function F va Equal to the steering wheel torque C applied under normal conditions v With the supplement value V supp sum.

[0073] During modification step 2, the method is modified from the auxiliary steering wheel torque C va Subtract the supplement value V supp Therefore, in the absence of the auxiliary function F, the modified step 2 emits a torque corresponding to the steering wheel torque C v signal.

[0074] Steering wheel torque C v It is the supervision module M sur Therefore, whether the auxiliary function F is activated or inactivated, the monitoring module M sur The received signal always corresponds to the steering wheel torque C v . Supervision module M sur During the determination step, the steering wheel torque C is determined according to the monitoring curve. v The associated temporary maximum limit value V lmaxt and the temporary minimum limit value V lmint . Supervision module M sur The operation is not affected by auxiliary function F.

[0075] Furthermore, the method also determines during the estimation step 3 the direction from the auxiliary function F to the auxiliary setpoint motor torque C mca Provided added value V add . Estimate step 3 at the auxiliary set point motor value C mca A first transformation function H1 is implemented between the auxiliary function Fa and the auxiliary function F.

[0076] Therefore, the auxiliary setpoint motor torque C applied by the auxiliary function F mca Equal to the set point motor torque C applied under normal conditions mc With added value V add sum.

[0077] After correcting the temporary maximum limit value V lmaxt and the temporary minimum limit value V lmint During step 4, the supervision module M sur Considering the auxiliary function F for the auxiliary setpoint motor torque C mcaDuring correction step 4, the additional value V add Add to maximum V lmaxt and minimum V lmint Each of the temporary limit values ​​in order to obtain the maximum V taking into account the influence of the auxiliary function F lmax and minimum V lmin Limit value.

[0078] Therefore, the influence of auxiliary function F is supervised by the module M sur The positive subtraction is performed, and the influence of the auxiliary function F is supervised by the module M sur The reverse addition makes the supervision module M sur Not affected by auxiliary functions, but the maximum limit value V lmax and the minimum limit value V lmin Consider the impact of the auxiliary function F.

[0079] Finally, the comparison module MCP compares the auxiliary setpoint motor value C mca With the maximum limit value V lmax and the minimum limit value V lmin Comparison. The comparison module MCP is not affected by the activation of the auxiliary function F.

[0080] Of course, the invention is not limited to the embodiments described and represented in the accompanying drawings. Modifications are still possible, notably from a structural point of view of the various elements or by replacement by technical equivalents, without departing from the scope of protection of the invention.

Claims

1. A method (100) for supervising the operation of a power steering system, the power steering system comprising a steering wheel, an auxiliary motor and a supervision module (M sur ), the method comprising: - determining at least one temporary limit value (V lmaxt , V lmint ) - Estimation of the set point value (C) of the parameter to be determined by the auxiliary function (F) mc ) provides added value (V add ) estimation step; - calculation by the auxiliary function (F) to the supervisory module (M sur ) of the modified input signal (C va ) provides a complementary value (V supp ) calculation steps; and - According to the added value (V add ) to correct at least one temporary limit value (V lmaxt , V lmint ) correction steps.

2. The method (100) according to claim 1, wherein: The determining step defines a temporary maximum limit value (V lmaxt ) and the temporary minimum limit value (V lmint ).

3. The method (100) according to claim 1, wherein: The estimation step uses the set point value (C mc ) and the auxiliary function (F) to calculate the additional value (V add ).

4. The method (100) according to claim 1, wherein: The correction step adds the additional value (V add ) is added to the at least one temporary limit value of the parameter (V lmaxt , V lmint ).

5. The method (100) according to claim 1, wherein: The calculating step uses the modified input signal (C va ) and the auxiliary function (F) to determine the supplementary value (V supp ).

6. The method (100) according to any one of claims 1 to 5, comprising: supp ) to modify the modified input signal (C va ) modification steps.

7. The method (100) according to claim 6, wherein: The modifying step is performed from the modified input signal (C va ) minus the supplementary value (V supp ).

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