Perception of a road profile by the varying a gain as a function of a vehicle speed and steering wheel torque

Abstract

A power-steering system for a motor vehicle includes a steering wheel and an assistance motor controlled by a closed-loop regulation system, the regulation system determining a motor torque of the assistance motor as a function of a measured steering-wheel torque, using at least one “setpoint monitoring” arm calculating a component of the motor torque, referred to as “variant motor torque”, by subtracting a set steering-wheel torque from the RFe corresponding to the sum of the measured steering-wheel torque and the motor torque, wherein the variant motor torque is multiplied by a gain determined by a three-dimensional map as a function of a vehicle speed and the measured steering-wheel torque.

Claims

1. A power steering system for a motor vehicle comprising a steering wheel and an assist motor controlled by a closed loop regulation system, said regulation system determining a motor torque of the assist motor as a function of a measured steering wheel torque, by means of at least one setpoint monitoring branch calculating a deviation motor torque that is a component of the motor torque of the assist motor, the deviation motor toque being calculated by subtracting a setpoint steering wheel torque, defined as a steering wheel torque that a driver is desired to feel, from a sum of the measured steering wheel torque and the motor torque of the motor assistance, wherein the deviation motor torque is multiplied by a gain determined by a three-dimensional mapping depending in particular on a vehicle speed and the measured steering wheel torque.

2. The power steering system according to claim 1, wherein the three-dimensional mapping comprises at least one area of improving the feeling in which the gain is strictly less than 1 and at least one assistance area in which the gain is strictly equal to 1.

3. The power steering system according to claim 2, wherein a first assistance area extends beyond a predetermined steering wheel torque threshold.

4. The power steering system according to claim 3, wherein the predetermined steering wheel torque threshold is equal to or lower than a torque measurement range of a measured steering wheel torque sensor.

5. The power steering system according to claim 3, wherein a first area of improving the feeling extends from a predetermined vehicle speed threshold and of a zero-measured steering wheel torque up to the predetermined steering wheel torque threshold.

6. The power steering system according to claim 5, wherein the predetermined speed threshold is equal to or less than 80 km/h.

7. The power steering system according to claim 5, wherein a second assistance area extends between a zero vehicle speed up to the predetermined vehicle speed threshold and extends between a low speed steering wheel torque threshold, lower than the predetermined steering wheel torque threshold, up to the predetermined steering wheel torque threshold.

8. The power steering system according to claim 7, wherein the low speed steering wheel torque threshold is equal to or less than 1 Nm.

9. The power steering system according to claim 7, wherein a second area of improving the feeling extends from a zero vehicle speed up to the predetermined vehicle speed threshold and extends from a zero measured steering wheel torque up to the low speed steering wheel torque threshold.

Description

(1) The invention will be better understood thanks to the following description, 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:

(2) FIG. 1 is a representation of a three-dimensional mapping of a gain as a function of vehicle speed and of a measured steering wheel torque according to the invention,

(3) FIG. 2 is a representation of a setpoint monitoring branch according to the invention,

(4) FIG. 3 is a representation of a regulation system known in the related art and already described.

(5) FIG. 1 represents a three-dimensional mapping 3 of a gain G as a function of a longitudinal vehicle speed V.sub.v and of a measured steering wheel torque C.sub.vm according to the invention. The longitudinal vehicle speed V.sub.v is expressed in kilometers per hour and the measured steering wheel torque C.sub.vm is the absolute value of the measured steering wheel torque C.sub.vm expressed in Newton meters.

(6) The three-dimensional mapping 3 comprises 2 areas of improving the feeling 5, 7 in which the gain G is strictly less than 1 and 2 assistance areas 4, 6 in which the gain G is strictly equal to 1.

(7) The numerical values below as well as the three-dimensional mapping are given by way of example, and refer to an embodiment of the invention as represented in FIG. 1.

(8) A first assistance area 4 extends beyond a predetermined steering wheel torque threshold C.sub.vp equal to 2 Nm.

(9) A first area of improving the feeling 5 extends from a predetermined vehicle speed threshold V.sub.vp, equal to 25 km/h, and of a zero-measured steering wheel torque C.sub.vm up to the predetermined steering wheel torque threshold C.sub.vp.

(10) The gain is substantially equal to 0 when the measured steering wheel torque C.sub.vm is substantially equal to 0 and the vehicle speed V.sub.v is greater than an ascent vehicle speed threshold V.sub.vr, equal to 60 km/h, greater than the predetermined vehicle speed threshold V.sub.vp.

(11) The gain G varies linearly between 0 and 1 between a measured steering wheel torque C.sub.vm and the predetermined steering wheel torque threshold C.sub.vp, when the vehicle speed V.sub.v is greater than the ascent vehicle speed threshold V.sub.vr.

(12) Below the ascent vehicle speed threshold V.sub.vr, when the measured steering wheel torque C.sub.vm is substantially equal to 0, the gain G linearly varies.

(13) The gain G varies linearly between 0 and 1 between a measured steering wheel torque C.sub.vm and the predetermined steering wheel torque threshold C.sub.vp.

(14) A second assistance area 6 extends between a zero vehicle speed V.sub.v up to the predetermined vehicle speed threshold V.sub.vp and extends between a low-speed steering wheel torque threshold C.sub.vbv, equal to 0.5 Nm, below the predetermined steering wheel torque threshold C.sub.vp, up to the predetermined steering wheel torque threshold C.sub.vp.

(15) A second area of improving the feeling 7 extends from a zero vehicle speed V.sub.v up to the predetermined vehicle speed threshold V.sub.vp and extends from a zero-measured steering wheel torque C.sub.vm up to the low speed steering wheel torque threshold C.sub.vbv.

(16) FIG. 2 represents a setpoint monitoring branch 2 of a regulation system according to the invention.

(17) In a first step, the setpoint monitoring branch determines a deviation motor torque TOL by subtracting, from a signal corresponding to the sum of the measured steering wheel torque and the motor torque RFe, a setpoint steering wheel torque signal C.sub.vc.

(18) In a second step C, the setpoint monitoring branch determines the gain G using the three-dimensional mapping 3 as represented in FIG. 1. Thus, the second step C receives as input the vehicle speed V.sub.v and the absolute value D of the measured steering wheel torque C.sub.vm.

(19) Finally, the setpoint monitoring branch 2′ performs a step B of multiplying the deviation motor torque TOL and the gain G determining a variable deviation motor torque TOL.sub.v.

(20) The gain G varying from 0 to 1, the value of the variable deviation motor torque is lower than the deviation motor torque TOL.

(21) The setpoint monitoring branch 2′ thus calculates the variable deviation motor torque TOL.sub.v corresponding to a fraction of a motor torque C.sub.m of an assist motor of an electric power steering. As in the related art represented in FIG. 3, the motor torque C.sub.m is the sum of the variable deviation motor torque TOL.sub.v, a proportional motor torque C.sub.mp and a derived motor torque C.sub.md.

(22) Thus, the weight of the setpoint monitoring branch 2′ in the setpoint monitoring varies as a function of the vehicle life conditions characterized by the measured steering wheel torque C.sub.vm and by the vehicle speed V.sub.v.

(23) When the vehicle makes many turns, that is to say when the measured steering wheel torque C.sub.vm is large, and more particularly greater than the predetermined steering wheel torque C.sub.vp, the vehicle is in the first assistance area 4. In this case, the gain G is equal to 1. Thus, the deviation motor torque TOL is equal to the variable deviation motor torque TOL.sub.v. The part taken in the calculation of the motor torque C.sub.m by the setpoint monitoring branch 2′ is maximum. This means that the assistance provided by the driver assist motor to turn the vehicle wheels is maximum. Priority is given to helping to turn the wheels of the vehicle rather than improving the driver feeling of road deformations.

(24) When the vehicle goes substantially in a straight line, that is to say when the measured steering wheel torque C.sub.vm is substantially equal to 0, the assistance provided by the assist motor to turn the wheels of the vehicle is not a priority relative to improving the feeling of the road profile. In fact, the driver will prefer to know where the wheels of his vehicle are, rather than having assistance in maneuvering the wheels of the vehicle. Thus, the gain G multiplying the deviation motor torque TOL is equal to 0, and therefore the variable deviation motor torque TOL.sub.v is equal to 0. In this life situation of the vehicle, the participation of the setpoint monitoring branch 2′ in the calculation of the motor torque C.sub.m is inhibited.

(25) However, the setpoint monitoring branch 2′ is inhibited, that is to say that the gain G is equal to 0, only when the vehicle reaches a speed V.sub.v greater than the ascent vehicle speed threshold V.sub.vr. In fact, when the vehicle speed V.sub.v is lower than the ascent vehicle speed threshold V.sub.vr, the setpoint branch makes it possible to reduce the feeling by the driver of the vibrations and mechanical friction of the power steering system.

(26) When the driver maneuvers the vehicle to perform a parking operation, the vehicle is in the second assistance area 6. The gain G is maximum to facilitate the maneuvering of the vehicle and limit the feeling by the driver of the vibrations and mechanical friction of the power steering system.

(27) Finally, the three-dimensional mapping 3 varies the gain G linearly between the assistance areas 4, 6 and the gain equal to 0 so as not to make sudden variations in the gain which can disturb the feeling of the driver.

(28) The three-dimensional mapping 3 could not vary the gain G linearly between the assistance areas 4, 6 and the gain equal to 0.

(29) 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.