METHOD FOR SUPERVISING THE OPERATION OF A POWER STEERING SYSTEM

Abstract

Method for monitoring the operation of a power steering system including a steering wheel, a servo motor and a monitoring module, characterized in that said method involves a step of determining at least one temporary limit value of a parameter, a step of estimating an additional value which an assistance functionality contributes to a setpoint value of the parameter, and a step of correcting the at least one temporary limit value by the additional value.

Claims

1. A method for supervising the operation of a power steering system comprising a steering wheel, an assist motor and a supervising module wherein it comprises: a step of determining at least one temporary limit value of a parameter; a step of estimating an additional value provided by an assistance functionality to a setpoint value of the parameter; a step of correcting the at least one temporary limit value by the additional value.

2. The method according to claim 1, wherein the determination step defines a temporary maximum limit value and a temporary minimum limit value of the parameter.

3. The method according to claim 1, wherein the estimation step calculates the additional value using a first transfer function between the setpoint value and an assistance function of the assistance functionality.

4. The method according to claim 1, wherein the correction step adds the additional value to a temporary limit value of the parameter.

5. The method according to claim 1 comprising a step of calculating a supplementary value provided by the assistance functionality to a modified input signal of the supervising module.

6. The method according to claim 5, wherein the calculation step determines the supplementary value using a second transfer function between the modified input signal and the assistance function of the assistance functionality.

7. The method according to claim 5, comprising a step of modifying the modified input signal by the supplementary value.

8. The method according to claim 7, wherein the modification step subtracts the supplementary value from the modified input signal.

Description

[0052] 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 schematic drawings, in which:

[0053] FIG. 1 is a schematic representation of a normal operation of a power steering system;

[0054] FIG. 2 is a curve representing a maximum limit value and a minimum limit value of a motor torque as a function of a steering wheel torque in normal operation;

[0055] FIG. 3 is a representation of an operating point of an assistance functionality;

[0056] FIG. 4 is a schematic representation of an assisted operation of a power steering;

[0057] FIG. 5 is a schematic representation of the method according to the invention;

[0058] In a normal operation of a power steering, a regulation loop regulates an applied motor torque C.sub.ma depending on a steering wheel torque C.sub.v exerted by a driver on a steering wheel of a vehicle in order to determine a trajectory of said vehicle. As shown in FIG. 1, a steering computer CD determines a setpoint motor torque C.sub.mc, which is equal, in the absence of failure, to the applied motor torque C.sub.ma on a mechanical system SM comprising at least one assist motor, in order to assist the driver in his intention to turn. The regulation loop influences the steering wheel torque C.sub.v the applied motor torque C.sub.ma and vice versa.

[0059] Legislation require ensuring the safety of the driver and the integrity of the vehicle in the case of failure of the steering computer CD, that is to say when the setpoint motor torque C.sub.mc becomes inconsistent relative to the steering wheel torque C.sub.v. Thus, for example, it is determined that the applied motor torque C.sub.ma should always, in normal operation, have a value related to the exerted steering wheel torque C.sub.v.

[0060] This condition is checked by a supervising module M.sub.sur and by a comparison module MCP.

[0061] The interlock type supervising module M.sub.sur receives an input signal corresponding to the exerted steering wheel torque C.sub.v and determines a maximum limit value V.sub.lmax and a minimum limit value V.sub.lmin of a motor torque C.sub.m according to monitoring curves represented in FIG. 2. The maximum limit value V.sub.lmax is substantially equal to 0 when the steering wheel torque C.sub.v is negative, then increases linearly to an asymptote. The minimum limit value V.sub.lmin is equal to a negative constant on certain negative values of the steering wheel torque C.sub.v, then increases linearly so as to be substantially equal to 0 when the steering wheel torque C.sub.v is positive.

[0062] Of course, FIG. 2 represents an example which is in no way limiting of a monitoring curve, other forms of monitoring curves can be considered.

[0063] Thus, the supervising module M.sub.sur bounds the value of the motor torque C.sub.m between the maximum limit value V.sub.lmax and the minimum limit value V.sub.lmin. Furthermore, in the embodiment of FIG. 2, the maximum limit value V.sub.lmax being substantially equal to 0 when the steering wheel torque C.sub.v is negative and the minimum limit value V.sub.lmin being substantially equal to 0 when the steering wheel torque C.sub.v is positive, the supervising module M.sub.sur establishes that the steering wheel torque C.sub.v and the motor torque C.sub.m are in the same direction.

[0064] The comparison module MCP receives the maximum limit value V.sub.lmax, the minimum limit value V.sub.lmin and the setpoint motor torque C.sub.mc as input. The comparison module MCP compares the setpoint motor torque C.sub.mc with the maximum V.sub.lmax and minimum V.sub.lmin limit values and transmits the applied motor torque C.sub.ma.

[0065] The applied motor torque C.sub.ma is equal to the setpoint motor torque C.sub.mc as long as the setpoint motor torque C.sub.mc is comprised between the maximum V.sub.lmaxt and minimum V.sub.lmint limit values.

[0066] As soon as the setpoint motor torque C.sub.mc exceeds a limit value V.sub.lmax, V.sub.lmin, the steering computer CD is declared faulty and the applied motor torque C.sub.ma is limited to the maximum V.sub.lmaxt or minimum V.sub.lmint limit values.

[0067] In assisted operation, an assistance function F is occasionally exerted on the power steering system and more particularly on the steering computer CD as shown in FIG. 4. The assistance functionality F determines an operating point P.sub.fa corresponding to an assistance steering wheel torque C.sub.va and an assistance setpoint motor torque C.sub.mca, different from a normal operating point P corresponding to the operating point exerted in a normal situation.

[0068] In assisted operation, the steering wheel torque C.sub.v is equal to the assistance steering wheel torque C.sub.va and the setpoint motor torque C.sub.mc is equal to the assistance setpoint motor torque C.sub.mca.

[0069] In the absence of a method according to the invention, the supervising module M.sub.sur receives the value of the assistance steering wheel torque C.sub.va and determines maximum V.sub.lmax and minimum V.sub.lmin limit values associated to this assistance steering wheel torque C.sub.va so as to guarantee that the motor torque applied to a value consistent with the assistance steering wheel torque C.sub.va. However, the assistance setpoint motor torque C.sub.mca determined by the assistance function F is not comprised between the monitoring curves of the supervising module M.sub.sur as shown in FIG. 3. Thus the comparison module MCP detects a false failure of the steering computer CD and transmits an applied motor torque C.sub.ma equal to the minimum limit value V.sub.lmin.

[0070] In the method according to the invention 100 as represented in FIG. 5, the supervising module M.sub.sur is not affected by an activation of the assistance functionality F.

[0071] In the method according to the invention 100, a calculation step 1 determines a supplementary value V.sub.supp provided by the assistance functionality F to the assistance steering wheel torque C.sub.va relative to the steering wheel torque C.sub.v being exerted in normal situation. The supplementary value V.sub.supp is calculated thanks to a second transfer function H2 between the assistance steering wheel torque C.sub.va and an assistance function Fa of the assistance functionality F.

[0072] The assistance steering wheel torque C.sub.va exerted by the assistance functionality F is therefore equal to the sum of the steering wheel torque C.sub.v exerted in normal situation and the supplementary value V.sub.supp.

[0073] During a modification step 2, the method subtracts the supplementary value V.sub.supp from the assistance steering wheel torque C.sub.va. Thus, the modification step 2 emits a signal corresponding to the steering wheel torque C.sub.v in the absence of an assistance functionality F.

[0074] The steering wheel torque C.sub.v is the input signal of the supervising module M.sub.sur. Thus, the signal received by the supervising module M.sub.sur always corresponds to the steering wheel torque C.sub.v whether the assistance function F is active or inactive. The supervising module M.sub.sur determines, during a determination step, thanks to the monitoring curves, a temporary maximum limit value V.sub.lmaxt and a temporary minimum limit value V.sub.lmint associated to this steering wheel torque C.sub.v. The operation of the supervising module M.sub.sur is not influenced by the assistance functionality F.

[0075] Furthermore, the method also determines an additional value V.sub.add provided by the assistance functionality F to the assistance setpoint motor torque C.sub.mca during an estimation step 3. The estimation step 3 implements a first transfer function H1 between the assistance setpoint motor value C.sub.mca and the assistance function Fa of the assistance functionality F.

[0076] The assistance setpoint motor torque C.sub.mca exerted by the assistance functionality F is therefore equal to the sum of the setpoint motor torque C.sub.mc exerted in a normal situation and the additional value V.sub.add.

[0077] The influence of the assistance functionality F on the assistance setpoint motor torque C.sub.mca is taken into account by the supervising module M.sub.sur during a step 4 of correcting the temporary maximum limit value V.sub.lmaxt and the temporary minimum limit value V.sub.lmint. During the correction step 4, the additional value V.sub.add is added to each of the maximum V.sub.lmaxt and minimum V.sub.lmint temporary limit values so as to obtain maximum V.sub.lmax and minimum V.sub.lmin limit values taking into account the influence of the assistance functionality F.

[0078] Thus, the influence of the assistance functionality F is subtracted upstream of the supervising module M.sub.sur and the influence of the assistance functionality F is added downstream of the supervising module M.sub.sur such that the supervising module M.sub.sur is not influenced by the assistance functionality but that the maximum limit value V.sub.lmax and the minimum limit value V.sub.lmin take into account the influence of the assistance functionality F.

[0079] Finally, the comparison module MCP compares the assistance setpoint motor value C.sub.mca with the maximum limit value V.sub.lmax and the minimum limit value V.sub.lmin. The comparison module MCP is not influenced by the activation of the assistance functionality F.

[0080] 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 departing from the protection field of the invention.