Improves perception of road contours by varying gains based on vehicle speed and steering wheel torque

Abstract

The invention relates to a power steering system for a motor vehicle, comprising a steering wheel and an auxiliary electric motor controlled by a closed-loop regulation system, said regulation system determining the motor torque of the auxiliary electric motor as a function of a measured steering wheel torque by calculating, by means of at least one "setpoint monitoring" branch, a component of the motor torque, called "variable motor torque", by subtracting a set steering wheel torque from RFe corresponding to the sum of the measured steering wheel torque and the motor torque, characterised in that the variable motor torque is multiplied by a gain determined by a three-dimensional mapping as a function of the vehicle speed and the measured steering wheel torque.

Description

Technical Field

[0001] The invention relates to the field of power steering for motor vehicles and more particularly to a closed-loop regulation system for the torque of an assisting electric machine as a function of the torque applied by the driver to the steering wheel. Background Art

[0002] A power steering system for a motor vehicle comprises a steering wheel on which the driver applies a force, referred to as "applied steering wheel torque", in order to manipulate the rack so that it can steer the wheels of the vehicle. An electric auxiliary motor, controlled by a regulating system, allows assisting the driver in turning the wheels of the vehicle with his intention, by providing an auxiliary motor torque that reduces the applied steering wheel torque. This is referred to as the steering wheel torque felt by the driver.

[0003] Ultimately, the steering wheel torque felt by the driver is the same as the applied steering wheel torque. The steering wheel torque can be measured by means of a torque sensor, so in the following description we will discuss around the measured steering wheel torque.

[0004] like Figure 3 As shown, the control system 1 of the power steering system determines, in particular, the steering wheel torque C measured based on the vm To determine the auxiliary motor torque C m , which is called "motor torque".

[0005] Therefore, the motor torque C m The measured steering wheel torque C vm has an impact, and vice versa.

[0006] Furthermore, increasingly efficient regulation systems 1 integrate various electronic devices and software functions (not shown) making it possible to adjust the measured steering wheel torque C vm , in order to best meet the driver's expectations. For example, this feature allows for improved:

[0007] - stability, that is to say the convergence of the control system with respect to disturbances (such as rapid changes in the direction of rotation of the steering wheel),

[0008] - the feeling of the mechanical behavior of the power steering system, such as dynamic dry friction, viscosity, the feeling of disengagement (that is to say the threshold of force that the driver must overcome to trigger the steering system to move), or the inertia of the power steering system,

[0009] - steering comfort, that is to say the damping of the steering wheel when it is not held by the driver, and the steering wheel return which makes it possible to bring the steering wheel back to the centre position (that is to say the steering wheel position in which the vehicle is travelling in a straight line).

[0010] Typically, the closed-loop regulation system 1 includes:

[0011] - Setpoint monitoring branch 2, by subtracting the setpoint steering wheel torque C from RFe vc (We hope that the driver will feel the steering wheel torque, which is obtained by measuring the steering wheel torque C vm and motor torque C m The deviation motor torque TOL is calculated by applying the first auxiliary law A based on RFe.

[0012] - Proportional branch Kp, based on the measured steering wheel torque C vm and the setpoint steering wheel torque C vc The difference between the proportional motor torque C mp ,

[0013] - Derive branch Kd, based on the measured steering wheel torque C vm The time derivative of the motor torque C is estimated md .

[0014] Motor torque C m is the sum of the components of each branch 2, Kp, and Kd, that is, the derived motor torque C md , deviation motor torque TOL and proportional motor torque C mp sum.

[0015] The study of each branch shows that the contribution of the setpoint monitoring branch 2 in determining the motor torque C m In order to monitor the set point steering wheel torque C vc The contribution of the proportional branch Kp and the derived branch Kd allows for their parts to track dynamic changes and stabilize the regulation system in order to reach the setpoint steering wheel torque C more quickly. vc , that is to say, shorten the time to establish steady state.

[0016] The control system 1 controls the measured steering wheel torque C vm , and thus control the steering wheel torque felt by the driver, reducing feedback of information related to the road profile.

[0017] A set of intrinsic physical properties of the surface on which the vehicle moves is called road profile, such as, for example, the grip, or the height and depth of the road's deformations related to the presence of grooves, pavements, potholes, cobblestones or speed bumps.

[0018] Therefore, in certain situations, the regulating system 1 gives the driver a rather false driving sensation, which may be dangerous, unpleasant or even counterintuitive.

[0019] The setpoint monitoring branch 2 mainly reduces the increase of information related to small road deformations, that is to say low frequencies, mainly between 0 and 5 Hz, such as low-altitude sidewalks. In contrast, the frequency of particles on the road is about 50 Hz, while the frequency of pebbles is between 5 and 30 Hz, depending on the size of the pebbles.

[0020] Automobile manufacturers need to measure the steering wheel torque C vm , and thus the steering wheel torque sensed is needed to allow the driver to obtain information about the road profile, in particular about low-frequency deformations. Therefore, the measured steering wheel torque C vm The driver must be allowed to judge the vehicle's course at all times without compromising all functions of the regulation system. Summary of the invention

[0021] The object of the present invention is to remedy all or part of the above-mentioned drawbacks by proposing a power steering system for a motor vehicle, the system comprising an auxiliary motor controlled by a steering wheel and a closed-loop regulation system, the regulation system determining the motor torque of the auxiliary motor based on the measured steering wheel torque in the following way: with the aid of at least one "set point monitoring branch", the set point monitoring branch calculates a component of the motor torque of the auxiliary motor, called "deviation motor torque", by subtracting the set point steering wheel torque from RFe corresponding to the sum of the measured steering wheel torque and the motor torque of the auxiliary motor, the set point steering wheel torque being defined as the steering wheel torque that we want the driver to feel, characterised in that the deviation motor torque is multiplied by a gain determined by a three-dimensional mapping specifically based on the vehicle speed and the measured steering wheel torque.

[0022] The torque of the auxiliary motor is called “motor torque” and corresponds to the torque applied by the auxiliary motor to the rack of the power steering system in order to help the driver to turn the wheels of the vehicle as he intends.

[0023] The measured steering wheel torque is defined as the torque corresponding to the force applied by the driver to the power steering system steering wheel, which is the same as the steering wheel torque felt by the driver.

[0024] The setpoint steering wheel torque is the steering wheel torque that the driver wants to feel. The setpoint steering wheel torque is determined by applying the first assist law according to RFe, that is to say the sum of the motor torque and the measured steering wheel torque.

[0025] According to the invention, the setpoint monitoring branch multiplies the deviation motor torque by a gain determined by a three-dimensional mapping as a function of the vehicle speed and the measured steering wheel torque.

[0026] Therefore, the component of the motor torque determined by the setpoint monitoring branch is variable.

[0027] Preferably, the gain is between 0 and 1 comprised.

[0028] Thus, the value of the component of the setpoint monitoring branch can be reduced when calculating the motor torque, that is, the determined motor torque will be lower than the motor torque applied in the absence of the present invention. The reduction of the motor torque can improve the driving experience by reducing the assistance provided to the driver when the driver intends to turn or hold the wheels of the vehicle. As a result, the measured steering wheel torque, that is to say the steering wheel torque felt by the driver, will be greater.

[0029] In particular, the driver will feel low-frequency road deformations better.

[0030] Advantageously, the gain is determined by a three-dimensional mapping using a plurality of input parameters, here at least two input parameters, namely the vehicle speed and the measured steering wheel torque.

[0031] Therefore, the gains are adjusted according to parameters that accurately and completely characterize the life situation of the vehicle.

[0032] According to a feature of the invention, the gain is variable as a function of the longitudinal speed of the vehicle.

[0033] According to a feature of the invention, the gain is variable as a function of the absolute value of the measured steering wheel torque.

[0034] According to a feature of the invention, the three-dimensional mapping comprises at least one improved perception zone, in which the gain is strictly less than 1, and at least one auxiliary zone, in which the gain is strictly equal to 1.

[0035] Therefore, in at least one improved feeling area, a motor torque that is lower than the motor torque determined without the present invention can improve the feeling of the road contour, while in at least one auxiliary area, the motor torque is the same as the motor torque determined without the present invention to help the driver turn the wheels of the vehicle as he intends.

[0036] According to a feature of the invention, the first assistance region extends beyond a predetermined steering wheel torque threshold.

[0037] When the measured steering wheel torque is greater than the predetermined steering wheel torque, the driver intends to turn the wheels of the vehicle to execute a curved path. Therefore, the power steering system must therefore have maximum performance, that is to say the same motor torque as determined without the present invention, to assist the driver's intention.

[0038] According to a feature of the invention, the predetermined steering wheel torque threshold value is equal to or smaller than a measuring range of the measured steering wheel torque sensor.

[0039] According to a feature of the invention, the predetermined steering wheel torque threshold is, for example, equal to or less than 5 Nm, preferably equal to or less than 3 Nm, or even equal to or less than 2 Nm.

[0040] According to a feature of the invention, the first improved sensing region extends from a predetermined vehicle speed threshold and a measured steering wheel torque to a predetermined steering wheel torque threshold.

[0041] When the measured steering wheel torque is lower than the predetermined steering wheel torque, the driver wants to keep the path roughly straight. Therefore, the power steering system must enhance the feeling of the road contour rather than assisting the driver to turn the wheel.

[0042] Thus, the gain varies between 0 and 1 when the vehicle speed is greater than a predetermined vehicle speed threshold and the measured steering wheel torque is less than a predetermined steering wheel torque.

[0043] Preferably, the gain varies linearly between 0 and 1 between a measured zero steering wheel torque and a predetermined steering wheel torque threshold.

[0044] According to a feature of the invention, the gain is substantially equal to 0 when the measured steering wheel torque is substantially equal to 0 and the vehicle speed is greater than an uphill vehicle speed threshold, i.e., a speed threshold when the need to feel the contour or uphill road exceeds the need to reduce the mechanical friction feel of the power steering system, which speed threshold is higher than a predetermined vehicle speed threshold.

[0045] This improves the sense of the road contour as much as possible when the vehicle is moving in a substantially straight line, with a low measured steering wheel torque and at a relatively high speed (that is, a speed greater than an uphill vehicle speed threshold).

[0046] Below the uphill vehicle speed threshold, when the measured steering wheel torque is substantially equal to zero, the gain varies linearly or preferably non-linearly between zero vehicle speed and the uphill vehicle speed threshold. In fact, when the vehicle speed becomes lower than the uphill vehicle speed threshold, the power steering system must be more effective so that the driver does not feel the drawbacks of the mechanical behavior of the steering system (such as friction) and the steering comfort related to the steering wheel restoration is improved. A compromise must be found between the driver's pleasure and safety, which is related to the feeling of the road contour and the steering comfort.

[0047] According to a feature of the invention, the predetermined speed threshold is equal to or lower than 80 km / h, preferably equal to or lower than 60 km / h, or even equal to or lower than 25 km / h.

[0048] According to a feature of the invention, the second assistance region extends between zero vehicle speed to a predetermined vehicle speed threshold and between a low speed steering wheel torque threshold (below a predetermined steering wheel torque threshold) to a predetermined steering wheel torque threshold.

[0049] When the vehicle speed is between 0 and a predetermined vehicle speed threshold and the measured steering wheel torque is between a low speed steering wheel torque threshold and a predetermined steering wheel torque threshold, the vehicle is in a parked or maneuvered state. Therefore, the power steering system must assist the driver in turning the vehicle's wheels, which is why the gain is equal to 1.

[0050] According to a feature of the invention, the low-speed steering wheel torque threshold is equal to or less than 1 Nm, or equal to or less than 0.5 Nm, or even equal to or less than 0.25 Nm.

[0051] In accordance with a feature of the invention, the second improved sensing region extends from zero vehicle speed to a predetermined vehicle speed threshold and from the measured steering wheel torque to a low speed steering wheel torque threshold.

[0052] The power steering system thus improves the driver's sense of the road contour at very low speeds. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The invention will be better understood through the following description, which relates to embodiments according to the invention, which are given by way of non-limiting examples and are illustrated with reference to the accompanying schematic drawings, in which:

[0054] - Figure 1 is a representation of a three-dimensional mapping of the gain according to the invention as a function of the vehicle speed and the measured steering wheel torque,

[0055] - Figure 2 is a representation of the setpoint monitoring branch according to the invention,

[0056] - Figure 3 is a representation of a regulation system that is known and has been described in the related art. DETAILED DESCRIPTION

[0057] Figure 1 The longitudinal vehicle speed V v and the measured steering wheel torque C vm 3. Three-dimensional mapping of the gain G. Longitudinal vehicle speed V v Expressed in kilometers per hour, the steering wheel torque C is measured vm is the measured steering wheel torque C vm The absolute value of , expressed in Newton meters.

[0058] The three-dimensional map 3 comprises two improved perception areas 5, 7, in which the gain G is strictly less than 1, and two auxiliary areas 4, 6, in which the gain G is strictly equal to 1.

[0059] The following numerical values ​​and three-dimensional mappings are given by way of example and refer to Figure 1 The embodiment of the present invention is shown.

[0060] The first assistance zone 4 extends beyond a predetermined steering wheel torque threshold C equal to 2 Nm. vp .

[0061] The first improvement feeling area 5 is from a predetermined vehicle speed threshold V equal to 25 km / h vp and the measured zero steering wheel torque C vm Extends to a predetermined steering wheel torque threshold C vp .

[0062] When the steering wheel torque C vm is essentially equal to 0 and the vehicle speed V v The uphill vehicle speed threshold V is greater than or equal to 60 km / h vr , greater than a predetermined vehicle speed threshold V vp , the gain is essentially equal to 0.

[0063] When the vehicle speed V v Greater than the uphill vehicle speed threshold V vr When the steering wheel torque C is measured vm and a predetermined steering wheel torque threshold C vp The gain G varies linearly between 0 and 1.

[0064] At the uphill vehicle speed threshold V vr Below, when the steering wheel torque C is measured vm When it is basically equal to 0, the gain G changes linearly.

[0065] Gain G is the value of the steering wheel torque C vm and a predetermined steering wheel torque threshold C vp It varies linearly between 0 and 1.

[0066] The second assistance zone 6 is at zero vehicle speed V v to a predetermined vehicle speed threshold V vp and below a predetermined steering wheel torque threshold C vp The low speed steering wheel torque threshold C vbv (equal to 0.5Nm) to the predetermined steering wheel torque threshold C vp Extend between.

[0067] The second improvement feeling area 7 starts from zero vehicle speed Vv Extends to a predetermined vehicle speed threshold V vp , and from the measured zero steering wheel torque C vm Extended to the low-speed steering wheel torque threshold C vbv .

[0068] Figure 2 The set point monitoring branch 2 of the regulating system according to the invention is shown.

[0069] In a first step, the setpoint monitoring branch performs the control by subtracting the setpoint steering wheel torque signal C from the signal RFe corresponding to the sum of the measured steering wheel torque and the motor torque. vc To determine the deviation motor torque TOL.

[0070] In the second step C, if Figure 1 As shown, the setpoint monitoring branch determines the gain G using the three-dimensional map 3. Thus, the second step C receives the vehicle speed V v and the measured steering wheel torque C vm The absolute value D is taken as input.

[0071] Finally, the set point monitoring branch 2′ executes step B, which compares the deviation motor torque TOL with the variable deviation motor torque TOL v Multiply by the gain G.

[0072] The gain G varies between 0 and 1, and the value of the variable deviation motor torque is smaller than the deviation motor torque TOL.

[0073] Therefore, the setpoint monitoring branch 2 ′ calculates the motor torque C corresponding to the auxiliary motor of the electric power steering m Variable deviation motor torque TOL of a part v .like Figure 3 In the related art shown in FIG. , the motor torque C m is the variable deviation motor torque TOL v , proportional motor torque C mp And the derived motor torque C md sum.

[0074] Therefore, the weight of the setpoint monitoring branch 2′ in the setpoint monitoring is determined by the steering wheel torque C vm and vehicle speed V v The characterization varies depending on the vehicle usage conditions.

[0075] When the vehicle turns multiple times, that is, when the steering wheel torque C vm is greater than the predetermined steering wheel torque C vpWhen , the vehicle is in the first assist area 4. In this case, the gain G is equal to 1. Therefore, the deviation motor torque TOL is equal to the variable deviation motor torque TOL v The motor torque C calculated by the setpoint monitoring branch 2' m The adopted parts are the largest. This means that the assistance provided by the auxiliary motor to the driver in turning the vehicle's wheels is the largest possible. Priority is given to helping turn the wheels rather than improving the driver's feeling of road deformations.

[0076] When the vehicle is traveling substantially in a straight line, that is, when the steering wheel torque C vm When the gain G is substantially equal to 0, the assistance provided by the auxiliary motor to turn the vehicle's wheels is not a priority relative to improving the feeling of the road contour. In fact, the driver will be more interested in knowing where the wheels of his vehicle are rather than enjoying assistance in steering the wheels of the vehicle. Therefore, the gain G multiplied by the deviation motor torque TOL is equal to 0, and the variable deviation motor torque TOL v = 0. In this use condition of the vehicle, the setpoint monitoring branch 2 ′ is prohibited from participating in the motor torque C m 's calculation.

[0077] However, only when the vehicle reaches a speed greater than the uphill vehicle speed threshold V vr Speed ​​V v The set point monitoring branch 2′ is disabled only when the vehicle speed V v Below the uphill vehicle speed threshold V vr When the set point branch is used, it can reduce the driver's perception of vibration and mechanical friction in the power steering system.

[0078] When the driver is maneuvering the vehicle for a parking maneuver, the vehicle is in the second assist zone 6. The gain G is maximum to facilitate maneuvering of the vehicle and to limit the driver's feeling of vibration and mechanical friction of the power steering system.

[0079] Finally, the three-dimensional map 3 varies the gain G linearly between the assistance zones 4 , 6 and a gain equal to 0, in order to avoid abrupt gain changes which could disturb the driver's perception.

[0080] The three-dimensional mapping 3 does not allow the gain G to be varied linearly between the auxiliary areas 4, 6 and a gain equal to zero.

[0081] Of course, the invention is not limited to the embodiments described and represented in the accompanying drawings. Modifications are still possible, in particular from the point of view of the composition of the various elements or of the replacement by technical equivalents, without thereby departing from the scope of protection of the invention.

Claims

1. A power steering system for a motor vehicle, comprising a steering wheel and an auxiliary motor controlled by a closed-loop regulation system, wherein the regulation system is based on a measured steering wheel torque (C vm ) The motor torque (C) of the auxiliary motor is determined by m ): by means of at least one "setpoint monitoring" branch (2'), by means of the steering wheel torque measured and the motor torque of the auxiliary motor (C m ) minus the setpoint steering wheel torque (C vc ) calculates the deviation motor torque (TOL), the set point steering wheel torque (C vc ) is defined as the steering wheel torque that the driver is expected to feel, characterized in that The deviation motor torque (TOL) is multiplied by the vehicle speed (V v ) and the measured steering wheel torque (C vm ) The gain (G) determined by the three-dimensional mapping (3) is used to obtain the variable deviation motor torque (TOL V ), the variable deviation motor torque (TOL V ) is the motor torque of the auxiliary motor (C m )’s weight.

2. The power steering system according to claim 1, wherein the three-dimensional mapping (3) comprises at least one improved feeling area (5, 7) and at least one auxiliary area (4, 6), in which the gain (G) is strictly less than 1 and in which the gain (G) is strictly equal to 1.

3. The power steering system according to claim 2, wherein the first assistance region (4) extends beyond a predetermined steering wheel torque threshold (C vp ).

4. The power steering system according to claim 3, wherein the predetermined steering wheel torque threshold (C vp ) is below the measuring range of the sensor of the measured steering wheel torque.

5. The power steering system according to claim 3 , wherein the first improved feeling region (5) is from a predetermined vehicle speed threshold (V vp ) extends to a speed greater than the predetermined vehicle speed threshold (V vp ) of the vehicle speed (V v ), and from the measured zero steering wheel torque (C vm ) extends to the predetermined steering wheel torque threshold (C vp ).

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

7. The power steering system according to claim 5, wherein the predetermined vehicle speed threshold (V vp ) is equal to or less than 60km / h.

8. The power steering system according to claim 5, wherein the predetermined vehicle speed threshold (V vp ) is equal to or less than 25km / h.

9. The power steering system according to claim 5, wherein the second assist region (6) is at zero vehicle speed (V v ) to the predetermined vehicle speed threshold (V vp ) and extends between and below the predetermined steering wheel torque threshold (C vp ) of the low speed steering wheel torque threshold (C vbv ) to the predetermined steering wheel torque threshold (C vp ) 10. The power steering system according to claim 9, wherein the low speed steering wheel torque threshold (C vbv ) is equal to or less than 1Nm.

11. The power steering system according to claim 9, wherein the low speed steering wheel torque threshold (C vbv ) is equal to or less than 0.5Nm.

12. The power steering system according to claim 9, wherein the low speed steering wheel torque threshold (C vbv ) is equal to or less than 0.25Nm.

13. The power steering system according to any one of claims 9 to 12, wherein the second improved feeling region (7) is from zero vehicle speed (V v ) extends to the predetermined vehicle speed threshold (V vp ), and from the measured zero steering wheel torque (C vm ) extends to the low speed steering wheel torque threshold (C vbv ).

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