A method for estimating and adjusting the friction to be adjusted, controlling the hysteresis of steering torque, and a corresponding power steering system.

Abstract

To provide a method for determining a friction to be adjusted in a power steering system or for modifying a hysteresis of a steering wheel torque applied to a steering wheel of the power steering system.SOLUTION: The method includes the steps of: determining a speed v, from a measurement of a speed v of a part of the power steering system and / or a measurement of the steering wheel torque T3; and determining the friction F to be adjusted on the basis of a modified LuGre model. The modified LuGre model determines the friction F to be adjusted as a function of a state of the system, and a time differential of the state is determined as a function of the state of the system, the speed v, a first gain, and a coulomb friction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to the field of power steering systems, particularly to a method for adjusting the friction in the steering wheel to improve the driver's feeling.

Summary of the Invention

Problems to be Solved by the Invention

[0002] It is known to adjust the mechanical friction between the components of a power steering system by estimating the friction based on the LuGre model in order to reduce the impact on the driver's feeling. Furthermore, the application of this method has revealed drawbacks such as torque loss that is sometimes very significant during certain cornering and excessive sensitivity to the road surface conditions. The more important the amount of friction to be compensated, the more serious all these drawbacks become.

[0003] Therefore, an object of the present invention is to propose a solution to all or part of these problems.

Means for Solving the Problems

[0004] For this purpose, the present invention relates to a method for determining the friction F to be adjusted in a power steering system, the method comprising a step of determining the speed v by measuring the speed v of a part of the power steering system and / or by measuring the steering torque applied to the steering wheel of the power steering system, and a step of determining the friction to be adjusted based on a modified LuGre model, the modified LuGre model determining the friction to be adjusted as a function of the state z of the system, and the time derivative JPEG0007832823000001.jpg62 of the state z of the system being a function of the speed v, a first gain σ0, a second gain β, and the Coulomb friction F c of the state JPEG0007832823000002.jpg1460 Determined according to an expression of the form, Here, JPEG0007832823000003.jpg1073 And, Here, sign(z) is the sign of quantity z, and sign(v) is the sign of quantity v. Here, JPEG0007832823000004.jpg1120 and JPEG0007832823000005.jpg527 If that is the case, JPEG0007832823000006.jpg29128 That is the case.

[0005] Under these conditions, the value of coefficient β can be adjusted such that, especially when the value of coefficient β is close to 1, the torque loss during certain cornering is not too significant after friction adjustment, and the sensitivity to the road surface condition is not too strong after friction adjustment.

[0006] According to one embodiment, the present invention includes, either alone or in a technically permissible combination, one or more of the following features:

[0007] According to one embodiment, the friction F to be adjusted is a function of the state z, JPEG0007832823000007.jpg417 It is determined by the formula.

[0008] According to one embodiment, the friction F to be adjusted is a function of the state z, JPEG0007832823000008.jpg428 It is determined by the formula.

[0009] Here, σ1 is a second gain representing micro-attenuation.

[0010] According to one embodiment, the friction F to be adjusted is a function of the state z, JPEG0007832823000009.jpg441 and is determined by the formula of.

[0011] Here, σ2 is a third gain representing the viscosity coefficient.

[0012] According to one embodiment, the speed is the angular velocity of the assist motor of the power steering system.

[0013] According to one embodiment, the speed is measured by an angular velocity sensor of the assist motor.

[0014] According to one embodiment, the speed is measured by an angular velocity sensor of the steering wheel.

[0015] According to one embodiment, the speed is the relative speed between two parts.

[0016] According to one embodiment, the Coulomb friction F c and / or the first gain σ0 and / or the second gain β vary according to one or more of the following variables: the longitudinal and lateral speeds of the vehicle, the lateral acceleration of the vehicle, the yaw rate of the vehicle, the steering angle or the power steering motor angle, the speed of the steering wheel or the power steering motor, the temperature of the power steering system, the external temperature, the steering torque, and the motor torque.

[0017] According to one embodiment, the step of determining the speed includes measuring a first speed v1 by an angular velocity sensor of the assist motor and estimating a second speed by measuring the steering torque, and the measurement of the steering torque is performed by a torque sensor, and the determined speed is the sum of the first speed and the second speed.

[0018] According to these conditions, the sum of the first speed and the second speed enables consideration of both the low pressure of the driver on the steering wheel due to the second speed and the low pressure that rises from the rolling surface and directly biases the rack by the first speed.

[0019] According to one embodiment, the friction F to be adjusted is determined from an intermediate friction coefficient, the intermediate friction coefficient w is determined based on the modified LuGre model and the speed v, and the friction F to be adjusted is determined according to the step of calculating the product of the intermediate friction coefficient and the difference between the estimated dynamic friction and the desired dynamic friction, and the estimated dynamic friction is estimated from at least the intermediate friction coefficient.

[0020] According to one embodiment, the desired dynamic friction is determined from a mapping defined during the development stage.

[0021] According to one embodiment, the estimation of the second speed comprises the steps of measuring the steering torque using the torque sensor configured to measure the steering torque between the steering wheel and the rack of the electric power steering; differentiating the measured value of the steering torque with respect to time; and multiplying the time differentiation by a stiffness coefficient to obtain the second speed called the torque speed.

[0022] The present invention also relates to a method for adjusting the friction to be adjusted in a power steering system or correcting the hysteresis of the steering torque applied to the steering wheel of the power steering system, the method comprising estimating the friction to be adjusted using a method according to any of the above implementation methods; and controlling an auxiliary motor to apply a target steering torque for adjusting the friction to be adjusted estimated in the previous step.

[0023] According to one embodiment, the step of controlling the auxiliary motor A step of determining a target handle torque from the difference between an estimated value of the friction to be adjusted and an estimated value of the rack force or "estimated rack force" representing the set of forces that hinder movement, The method includes the step of controlling the auxiliary motor in a closed loop based on the target handle torque and the measured handle torque.

[0024] According to one embodiment, the target handle torque is determined from a correspondence table, also called a mapping, which establishes a correspondence between a set of values ​​representing the difference between the estimated friction to be adjusted and the estimated rack force, and a corresponding set of values ​​representing the target handle torque.

[0025] Under these conditions, the hysteresis of the rack force estimate will present a controlled and desired hysteresis that also influences the hysteresis at the target torque generation level.

[0026] The present invention also relates to a method for controlling the hysteresis of a handle torque by correcting the hysteresis of a target handle torque by adding friction determined according to the method of the present invention, as described in one embodiment described above, wherein the method is: The steps include determining the friction to be adjusted using a method for determining the friction to be adjusted according to the present invention, according to one of the embodiments described above, The first step is to determine the target handle torque by adding the friction to be adjusted to the first target handle torque, and the first target handle torque is determined from the angle of the handle, The method includes the step of controlling the auxiliary motor in a closed loop based on the target handle torque and the measured handle torque.

[0027] According to one embodiment, the target handle torque is determined from a correspondence table or mapping that establishes a correspondence between a set of values ​​representing the difference between the angles of the handle and a corresponding set of values ​​representing the target handle torque.

[0028] The present invention also relates to a power steering system configured to implement a method for determining the friction to be adjusted according to one of the embodiments described above, or a method for adjusting the friction according to one of the embodiments described above, or a method for controlling the hysteresis of the steering torque by correcting the hysteresis of the target steering torque according to one of the methods described above.

[0029] Furthermore, the present invention relates to a vehicle equipped with a power steering system configured to carry out one of the methods according to the present invention in accordance with one of the embodiments described above. [Brief explanation of the drawing]

[0030] For a good understanding thereof, examples and / or embodiments of the present invention will be described with reference to the accompanying drawings, which each represent an example or embodiment of the apparatus and / or method according to the present invention as a non-limiting example. The same reference numerals in the drawings indicate similar elements or elements having similar functions. [Figure 1] This is a schematic diagram of a steering device to which the present invention is applied. [Figure 2] This is a graphical representation of the curve of the alpha function value according to the state of the power steering system to which the present invention is applied. [Figure 3] This is a representative diagram of a friction estimation method according to an embodiment of the present invention. [Figure 4] This is a representative diagram of a friction adjustment method according to one embodiment of the present invention. [Modes for carrying out the invention]

[0031] Figure 1 shows a steering device equipped with power steering that enables the implementation of the estimation and adjustment methods of the present invention. In a manner known in itself, and as seen in Figure 1, the power steering device 1 includes a steering wheel 3 that allows a driver to steer the power steering device 1 by applying a force called steering torque T3 to the steering wheel 3. The steering wheel 3 is preferably mounted on a steering column 4 and guided to rotate on a vehicle 2 and engages on a steering rack 6 by a steering pinion 5. The steering rack 6 is guided to move in parallel within a steering casing 7 fixed to the vehicle 2.

[0032] Preferably, the ends of the steering rack 6 are connected to steering tie rods 8 and 9, respectively, which are connected to the steering knuckles of the steered wheels 10 and 11 (the left wheel 10 and the right wheel 11, respectively), thereby allowing the steering angle (yaw angle) of the steered wheels to be corrected by the longitudinal displacement of the rack 6 during parallel movement. The steered wheels 10 and 11 may more preferably be drive wheels.

[0033] Furthermore, the power steering device 1 includes a motor 12 configured to assist in the operation of the power steering device 1. The motor 12 is preferably an electric motor having two operating directions, and is preferably a brushless type rotary electric motor.

[0034] The power steering system 1 further includes a steering torque sensor 14 specially positioned within the power steering system 1, for example on the steering column 4, for measuring the steering torque T3, and the primary objective is to truly exclusively provide a measurement of the steering torque T3, regardless of the measurement technique used by the steering torque sensor 14. Furthermore, the power steering system 1 includes an engine speed sensor 24 for measuring the rotational speed of the engine 12.

[0035] Finally, the power steering system 1 also includes a calculation control unit 20 configured to perform estimation and adjustment methods based on data from sensors 14 and 24.

[0036] As shown in Figure 3, according to one embodiment, a method 100 for estimating the friction to be adjusted includes the step of measuring a first speed v1 by a speed sensor 24 of the electric motor 12 of the vehicle power steering system 1. The estimation method 100 includes the step of determining a second speed v2, which includes a substep of measuring the steering torque T3 and a substep of the time derivative of the measured value of the steering torque T3 to which a differential gain is applied. The estimation method includes the step of calculating the sum v of the first and second speeds v1 and v2, represented by the reference sign Σ. Next, a speed v called the steering speed is obtained. The next step in the estimation method 100, represented by the box LM, consists of simulating a simplified one-dimensional (one-mass) steering model and the friction with a modified LuGre model LM, the sole input speed being the steering speed v obtained in the previous step. Thus, an estimate of the friction to be adjusted by the power steering 1 is obtained.

[0037] Under these conditions, the sum of the first and second speeds allows for the consideration of both the low pressure exerted on the steering wheel by the driver due to the second speed and the low pressure exerted by the first speed that rises from the rolling surface and directly biases the rack.

[0038] The modified LuGre model LM allows for the determination of the friction F to be tuned as a function of the system state, and the time derivative of the state z. JPEG0007832823000010.jpg62 shows the state z, the velocity v, the first gain σ0, and the Coulomb friction F. c As a function of, JPEG0007832823000011.jpg1460 Determined according to an expression of the form, Here, The filename is JPEG0007832823000012.jpg1073. Here, sign(z) is the sign of quantity z, and sign(v) is the sign of quantity v. Here, JPEG0007832823000013.jpg1120 and JPEG0007832823000014.jpg527 If that is the case, JPEG0007832823000015.jpg29128 That is the case.

[0039] Figure 2 shows the expansion of the function α(z) as a function of state z, using a diagram, and in particular the specific value -z max -z ba , z ba , and z max This indicates.

[0040] Under these conditions, the value of coefficient β can be adjusted such that, especially when the value of coefficient β is close to 1, the torque loss during certain cornering is not too significant after friction adjustment, and the sensitivity to the road surface condition is not too strong after friction adjustment.

[0041] In particular, the friction F to be adjusted is a function of the state z, JPEG0007832823000016.jpg417 It is determined by the formula.

[0042] For more details, the friction F to be adjusted is expressed as a function of the state z. JPEG0007832823000017.jpg428 It is directly determined by the formula.

[0043] Here, σ1 is a second gain representing micro-attenuation.

[0044] More specifically, the friction F to be adjusted is a function of the state z, JPEG0007832823000018.jpg441 It is determined by the formula.

[0045] Here, σ² is a third gain representing the viscosity coefficient.

[0046] In a particular example, the speed v may be the angular velocity of the auxiliary motor 12 of the power steering system 1, as measured by the angular velocity sensor of the auxiliary motor 12, instead of being the sum of the first speed and the second speed according to the previous example.

[0047] In another example, the speed is the relative speed between the two parts of the power steering system 1.

[0048] According to the embodiment, method 100 can obtain an estimate of the intermediate friction ratio w of the power steering 1, and from this estimate, for example, referring to Figure 4, an estimate of the friction to be adjusted is calculated according to step 150 described later.

[0049] The friction F to be adjusted is determined from the intermediate friction ratio w according to step 150, which includes calculating the product of the intermediate friction ratio w and the difference E3 between the estimated kinetic friction FRI and the desired kinetic friction FRC, wherein the estimated kinetic friction FRI is estimated from at least the intermediate friction ratio w during step E1, and the desired kinetic friction FRC is obtained during step E2, for example, from the adjusted mapping during the development stage.

[0050] The estimated dynamic friction is estimated, for example, according to one of the methods described in one of the following patent documents: FR3070957B1, FR3095515A1, or FR3018917B1.

[0051] As shown in Figure 4, the present invention also relates to a method 200 for adjusting the friction F to be adjusted in a power steering system 1, or for correcting the hysteresis of the steering torque T3 applied to the steering wheel 3 of the power steering system 1, wherein the method is Using method 100 according to one of the embodiments described above, the steps include: estimating the friction F to be adjusted; The process includes controlling the auxiliary motor 12 to apply a target handle torque Cc that compensates for the friction F to be adjusted, which was estimated in the previous step.

[0052] In particular, the step of controlling the auxiliary motor 12 is: The estimated value of the friction F to be adjusted, and the rack representing the set of forces that hinder movement. Power Step E5 involves determining the target steering torque Cc from the difference with the estimated RFE, Based on the target handle torque Cc and the measured handle torque T3, the adjustment The system includes step E6 for closed-loop BF control of the auxiliary motor 12.

[0053] For example, the target handle torque is determined from a correspondence table, also called a mapping, which establishes a correspondence between a set of values ​​representing the difference between an estimated friction F to be adjusted and an estimated rack force RFE, and a corresponding set of values ​​representing the target handle torque Cc.

[0054] Under these conditions, the hysteresis of the rack force estimate will present a controlled and desired hysteresis, which will also affect the hysteresis at the target torque generation level.

[0055] For example, if electric power steering is desired to have a friction of 400N and a feel of 300N, the friction estimator FRI identifies the steering as 400N, and the desired friction value input is 300N. Therefore, the difference is 100N, and the determined estimate of all forces opposing movement is 400N, from which 100N is subtracted to make the friction correspond to the desired value of 300N.

[0056] The present invention also relates to a method for controlling the hysteresis of a handle torque T3 by correcting the hysteresis of a target handle torque Cc by applying friction determined according to a method according to the present invention, according to one of the embodiments described above, the method being: A step of determining the friction F to be adjusted using the method according to any one of claims 1 to 4, A step of determining a first target handle torque Cc determined from the handle angle by adding a friction F to be adjusted to the first target handle torque Cc, The method includes the step of controlling the auxiliary motor 12 in a closed loop BF based on the target handle torque Cc and the measured handle torque T3.

[0057] For example, the target handle torque is determined from a correspondence table or mapping that establishes a correspondence between a set of values ​​representing the difference between the angles of the handle and a corresponding set of values ​​representing the target handle torque Cc.

[0058] The present invention also relates to a power steering system configured to implement a method 100 according to the present invention for determining the friction F to be adjusted, or a method 200 according to the present invention for adjusting the friction F to be adjusted, or a method according to the present invention for controlling the hysteresis of the steering torque T3 by correcting the hysteresis of the target steering torque Cc.

[0059] The present invention also relates to a vehicle equipped with a power steering system configured to adjust friction to be adjusted by carrying out method 100 according to the present invention.

Claims

1. A method (100) for determining the friction (F) to be adjusted in a power steering system (1), A step of determining the speed (v) by measuring a portion of the speed (v) of the power steering system and / or measuring the steering torque (T3) applied to the steering wheel (3) of the power steering system (1), The process comprises the step of determining the friction (F) to be adjusted based on a modified LuGr model (LM), The modified LuGr model (LM) determines the friction (F) to be adjusted as a function of the state (z) of the power steering system, and the time derivative of the state (z) ( ) is the state (z), speed (v), first gain (σ0), second gain (β), and Coulomb friction (F) of the power steering system. ｃ ) as a function of, Determined according to an expression of the form, Here, And, Here, sign(z) is the sign of quantity z, and sign(v) is the sign of quantity v. and If that is the case, The way of doing so.

2. In the method according to claim 1 (100), The aforementioned Coulomb friction F ｃ and / or the first gain σ0 and / or the second gain β vary according to one or more of the following variables: longitudinal speed of the vehicle, lateral acceleration of the vehicle, yaw rate of the vehicle, steering angle or power steering motor angle, steering speed or power steering motor speed, temperature of the power steering system, external temperature, steering torque, and motor torque.

3. In the method according to claim 1 (100), The step of determining the speed includes measuring a first speed (v1) by an angular velocity sensor (24) of an auxiliary motor (12) and estimating a second speed (v2) by measuring the handle torque (T3), wherein the measurement of the handle torque is performed by a torque sensor (14), and the determined speed (v) is the sum of the first speed (v1) and the second speed (v2).

4. In the method (100) according to any one of claims 1 to 3, A method wherein the friction (F) to be adjusted is determined from the intermediate friction rate (w) (150), the intermediate friction rate (w) is determined based on the modified LuGr model (LM) and the velocity (v), and the friction (F) to be adjusted is determined according to the step (150) of calculating the product of the intermediate friction rate (w) and the difference between the estimated kinetic friction (FRI) and the desired kinetic friction (FRC), the estimated kinetic friction (FRI) is estimated from at least the intermediate friction rate (w).

5. In the method according to claim 3 (100), The estimation of the second velocity (v2) is as follows: The steps include: measuring the steering torque (T3) using the torque sensor (14) configured to measure the steering torque (T3) between the steering wheel (3) and the rack (6) of the electric power steering (1); The steps include: taking the time derivative of the measured value of the handle torque (T3); A method comprising the step of multiplying the aforementioned time derivative by a stiffness coefficient to obtain the second velocity (v2), called the torque velocity.

6. A method (200) for adjusting the friction (F) to be adjusted in a power steering system (1), A step of estimating the friction (F) to be adjusted using the method (100) according to any one of claims 1 to 5, A method comprising the steps of controlling an auxiliary motor (12) to apply a target handle torque (Cc) to adjust the friction (F) to be adjusted, which was estimated in the previous step.

7. In the method (200) of claim 6, The step of controlling the auxiliary motor (12) is as follows: Step (E5) of determining the target handle torque (Cc) from the difference between the estimated value of the friction (F) to be adjusted and the estimated value of the rack force (RFE) which represents the set of forces that hinder movement, A method comprising the step (E6) of performing closed-loop control (BF) of the auxiliary motor (12) based on the target handle torque (Cc) and the measured handle torque (T3).

8. A method for controlling the hysteresis of a handle torque (T3) by correcting the hysteresis of a target handle torque (Cc) by adding friction determined according to the method of any one of claims 1 to 5 to a first target handle torque, A step of determining the friction (F) to be adjusted using the method (100) according to any one of claims 1 to 5, The first target handle torque (Cc) is determined by adding the friction to be adjusted (F) to the first target handle torque (Cc), and the first target handle torque is determined from the angle of the handle. A method comprising the step of performing closed-loop control (BF) of an auxiliary motor (12) based on the target handle torque (Cc) and the measured handle torque (T3).

9. A power steering system (1) configured to perform a method (100) for determining the friction (F) to be adjusted according to any one of claims 1 to 5, a method (200) for adjusting the friction (F) according to claim 6, or the method according to claim 8.

10. A vehicle comprising the power steering system (1) according to claim 9.

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