CN112061229A - Friction compensation method of electric power steering system - Google Patents

Friction compensation method of electric power steering system Download PDF

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Publication number
CN112061229A
CN112061229A CN202010783010.2A CN202010783010A CN112061229A CN 112061229 A CN112061229 A CN 112061229A CN 202010783010 A CN202010783010 A CN 202010783010A CN 112061229 A CN112061229 A CN 112061229A
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friction compensation
signal
torque
compensation torque
electric power
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孟虎
蒋开洪
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Shanghai Tuowei Automotive Technology Co ltd
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Shanghai Tuowei Automotive Technology Co ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D5/00—Power-assisted or power-driven steering
    • B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
    • B62D5/0457—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear characterised by control features of the drive means as such
    • B62D5/046—Controlling the motor
    • B62D5/0463—Controlling the motor calculating assisting torque from the motor based on driver input

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Steering Control In Accordance With Driving Conditions (AREA)

Abstract

The invention relates to a friction compensation method of an electric power steering system, which comprises the following steps: collecting a steering wheel torque signal, a vehicle speed signal and a motor corner signal, and calculating a motor rotating speed signal according to the motor corner signal; obtaining static friction compensation torque by using a table look-up mode according to the steering wheel torque signal and the motor rotation angle signal; obtaining dynamic friction compensation torque by using a table look-up mode according to the vehicle speed signal and the motor rotating speed signal; when calculating the static friction compensation torque, when the change rates of the steering wheel torque signal and the motor rotation angle signal are both larger than respective first threshold values, switching to dynamic friction compensation torque calculation; when calculating the dynamic friction compensation torque, when the vehicle speed signal and the motor rotating speed signal are both smaller than respective second threshold values, switching to static friction compensation torque calculation; and adding the static friction compensation torque and the dynamic friction compensation torque to obtain the friction compensation torque. The invention can effectively restrain the torque fluctuation caused by the friction force change.

Description

Friction compensation method of electric power steering system
Technical Field
The invention relates to the technical field of friction compensation control of an electric power steering system, in particular to a friction compensation method of the electric power steering system.
Background
In the development history of automobiles, steering systems go through four stages of development: the original mechanical steering system is developed into a hydraulic power steering system, and then an electric control hydraulic power steering system and an electric power steering system are developed. In order to solve the problem that a steering operation burden on a driver is too heavy when a vehicle equipped with a mechanical steering system is parked and driven at a low speed, the hydraulic power steering system was first adopted in a car by GM corporation in the united states in the 50 th century. However, since the hydraulic power steering system cannot achieve both the steering convenience at low speed and the steering stability at high speed, an electronically controlled hydraulic power steering system having a vehicle speed sensing function was introduced in 1983 by Koyo corporation of japan. The novel steering system can provide gradually reduced steering power with the rise of the vehicle speed, but the electric control hydraulic power-assisted steering system has a complex structure and higher manufacturing cost, can not overcome many defects of the hydraulic system, and is a transition product between hydraulic power-assisted steering and electric power-assisted steering. In 1988, Suzuki corporation, japan first provided a steering column assist type electric power steering system developed by Koyo corporation on a sedan Cervo. In 1990, Honda, japan also adopted a rack assist type electric power steering system developed autonomously in a sport car NSX, and thus, the history of application of electric power steering to automobiles was revealed.
The electric power steering system can obviously improve the dynamic performance and the static performance of the automobile, improve the comfort and the safety of a driver in driving, reduce the environmental pollution and the like. Therefore, once the technology is put forward, many automobile parts companies in the world develop and research the technology, the electric power steering in future steering systems will become the mainstream of the steering systems, and compared with other steering systems, the system has the advantages of light steering, good controllability and reduced oil consumption. However, the electric power steering system cannot be separated from a mechanical structure, the friction force between the mechanical structures can influence the stability and the accuracy of the electric power steering system, and the introduction of friction compensation for overcoming the adverse effect has very important significance.
Disclosure of Invention
The invention aims to provide a friction compensation method of an electric power steering system, which effectively inhibits torque fluctuation caused by friction force change.
The technical scheme adopted by the invention for solving the technical problems is as follows: provided is a friction compensation method of an electric power steering system, including the steps of:
(1) collecting a steering wheel torque signal, a vehicle speed signal and a motor corner signal, and calculating a motor rotating speed signal according to the motor corner signal;
(2) obtaining static friction compensation torque by using a table look-up mode according to the steering wheel torque signal and the motor rotation angle signal; obtaining dynamic friction compensation torque by using a table look-up mode according to the vehicle speed signal and the motor rotating speed signal; when calculating the static friction compensation torque, when the change rates of the steering wheel torque signal and the motor rotation angle signal are both larger than respective first threshold values, switching to dynamic friction compensation torque calculation; when calculating the dynamic friction compensation torque, when the vehicle speed signal and the motor rotating speed signal are both smaller than respective second threshold values, switching to static friction compensation torque calculation;
(3) and adding the static friction compensation torque and the dynamic friction compensation torque to obtain the friction compensation torque.
The step (1) comprises the following steps after collecting the steering wheel torque signal: and performing first-order low-pass filtering processing on the steering wheel torque signal to reserve a low-frequency part.
In the step (2), the abscissa when the static friction compensation torque is obtained in a table look-up mode is obtained from a steering wheel torque signal, and the ordinate is obtained from a motor corner signal, wherein the abscissa is
Figure BDA0002620921240000021
The ordinate is
Figure BDA0002620921240000022
n is the sample time, FSWT (n) is the steering wheel torque at the nth sample time, and SWAMot (n) is the motor rotational angle at the nth sample time.
And (3) in the step (2), the abscissa when the dynamic friction compensation torque is obtained in a table look-up mode is a vehicle speed signal, and the ordinate is a motor rotating speed signal.
And (4) filtering the friction compensation torque obtained in the step (3) through a third-order band elimination filter to improve the stability.
The friction compensation torque obtained in step (3) is also processed by a limit value to avoid the steering being too light.
And (4) setting the change rate of the friction torque after the friction compensation torque obtained in the step (3).
Advantageous effects
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects: the invention fully considers the difference between static friction and dynamic friction to realize the switching of the static friction and the dynamic friction, the friction force is changed from the static friction to the dynamic friction in the process of the steering wheel from static to rotating, and the friction force is changed from the dynamic friction to the static friction in the process of the steering wheel from rotating to static. The invention can effectively inhibit torque fluctuation caused by friction force change, better overcome the adverse effect caused by mechanical friction and reduce steering hysteresis, thereby enabling the electric power steering system to be more stable and comfortable.
Drawings
FIG. 1 is a schematic view of an electric power steering system in an embodiment of the present invention;
FIG. 2 is a flow chart of an embodiment of the present invention;
FIG. 3 is a computational block diagram of an embodiment of the present invention;
FIG. 4 is a schematic diagram of friction compensation torque filtering in an embodiment of the present invention;
FIG. 5 is a schematic diagram of an output torque limit in an embodiment of the present invention.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
Embodiments of the present invention relate to a friction compensation method of an electric power steering system. As shown in FIG. 1, when the driver turns the steering wheel, the angle and torque integrated sensor sends sensor signals such as period, pulse width and the like to the ECU, and the ECU can obtain the turning angle and torque of the driver through calculation. The speed signal is sent to the ECU through the CAN network, the motor angle is obtained through a rotor position signal, and the motor rotating speed is obtained through motor angle derivation. The ECU calculates the current friction compensation torque by using a friction compensation method, the torque signal is converted into a current signal through calculation, corresponding current is applied to the power-assisted motor through an electric and electronic driving circuit embedded in the ECU to control the motor to rotate, the torque output by the motor is reduced and increased through a speed reduction mechanism, and then the wheels are controlled to steer through a mechanical steering gear.
As shown in fig. 2, the present embodiment designs a friction compensation enabling switch, and when the switch is enabled, the system can perform friction compensation; otherwise, the system has no friction compensation. When the friction compensation switch is enabled, the system firstly filters a steering wheel torque signal to remove a high-frequency jitter part, and then calculates a dynamic friction compensation torque and a static friction compensation torque by combining other input signals, so that the friction compensation torque is obtained, and the friction compensation torque needs to be filtered by a third-order band elimination filter to keep the stability of the system. The friction compensation torque is limited through the limiting value module, and the over-light steering caused by the overlarge friction compensation torque is avoided. In order to ensure better hand feeling and comfort of a driver, the friction compensation torque needs to be kept slowly ascending and slowly descending, so that the change rate of the friction torque can be calibrated in a preset mode. The friction compensation torque is used as a part of the steering assistance and acts on the steering assistance together with other torques, the design is independent, other functions are not influenced, and a host factory can independently select whether to open the function according to requirements.
As shown in fig. 3, the friction compensation method of the electric power steering system according to the present embodiment may also automatically identify the mutual switching between the dynamic friction and the static friction according to the actual operating conditions, and compensate for the abrupt torque change caused by the change of the dynamic friction and the static friction. In order to overcome the problem of input torque jitter, the steering wheel torque needs to be filtered, and the low-pass filter can filter the high-frequency part of the input torque signal and only keep the low-frequency part of the input torque signal. The low-pass filter used in this embodiment is a first-order low-pass filter, and its transfer function is:
Figure BDA0002620921240000041
wherein the content of the first and second substances,
Figure BDA0002620921240000042
fcis the cut-off frequency.
The first-order backward method is adopted to carry out Z transformation,
Figure BDA0002620921240000043
where T is the sampling period.
Substituting to obtain:
Figure BDA0002620921240000044
simplifying to obtain:
Figure BDA0002620921240000045
then convert to discrete domain transfer function: y (z) (T + tau) -Y (z)-1) τ ═ X (z) T, then
Figure BDA0002620921240000046
Handle
Figure BDA0002620921240000047
T＝1/fsWherein f issIs the sampling frequency, and is obtained by substituting:
Figure BDA0002620921240000048
simplifying to obtain:
Figure BDA0002620921240000049
order to
Figure BDA00026209212400000410
The discrete domain transfer function of the first order low pass filter is then:
Figure BDA00026209212400000411
static friction compensation torque fcstaticIs obtained by looking up table 1, wherein the table is looked upThe horizontal and vertical coordinates of 1 are derived from the filtered steering wheel torque signal and the motor rotation angle signal respectively. The abscissa derivation formula is:
Figure BDA00026209212400000412
the ordinate derivation formula is:
Figure BDA00026209212400000413
where FSWT (n) is the filtered rear steering wheel torque at sample time n and SWAMot (n) is the motor rotational angle at sample time n. When the torque of the steering wheel and the angle change rate of the motor both exceed the respective set threshold values, the system is switched to dynamic friction compensation torque calculation. Dynamic friction compensation torque fcdynamicThe vehicle speed is obtained by looking up a table 2, wherein the horizontal and vertical coordinates of the looked-up table 2 are the vehicle speed and the motor rotating speed respectively, and the motor rotating speed is obtained by deducing the motor rotating angle. When the vehicle speed and the motor rotating speed are both smaller than the respective set threshold values, the system is switched to static friction compensation torque calculation. Relation of dynamic friction compensation torque with vehicle speed and motor speed: the larger the vehicle speed, the smaller the dynamic friction compensation torque, and the larger the motor rotating speed, the smaller the dynamic friction compensation torque.
As shown in fig. 4, the friction compensation torque needs to be filtered by a third-order band-stop filter to improve the stability of the system. The transfer function of a third order band-stop filter is:
Figure BDA0002620921240000051
wherein, ω isnIs the natural angular frequency of the third-order band-stop filter, zeta is the damping coefficient of the third-order band-stop filter, p1、p2And p3The pole of the third-order band-stop filter.
Simplifying to obtain:
Figure BDA0002620921240000052
order to
Figure BDA0002620921240000053
The transfer function of the third order band-stop filterThe method comprises the following steps:
Figure BDA0002620921240000054
the Z-transform is performed using a bilinear transform,
Figure BDA0002620921240000055
where T is the sampling period.
Substituting discrete domain transfer functions of H(s) and Y(s):
Figure BDA0002620921240000056
h (z), Y (z) are multiplied by (1+ z) at the same time-1)3Obtaining:
Figure BDA0002620921240000057
is simple and easy to obtain
Figure BDA0002620921240000061
H (z) and Y (z) are simultaneously divided by
Figure BDA0002620921240000062
Then:
Figure BDA0002620921240000071
then the process of the first step is carried out,
Figure BDA0002620921240000072
order:
Figure BDA0002620921240000081
Figure BDA0002620921240000082
then the discrete domain derivation function is
Figure BDA0002620921240000083
Then G (z) ═ m0-m1z-1-m2z-2+m3z-3+n1G(z-1)-n2G(z-2)+n3G(z-3)。
As shown in fig. 5, the friction compensation torque needs to be subjected to limit processing by a limit module, and the maximum value and the minimum value of the friction compensation torque can be calibrated, so that the over-light steering caused by the over-large friction compensation is avoided.
The invention fully considers the difference between static friction and dynamic friction to realize the switching of the static friction and the dynamic friction, wherein the friction is changed from the static friction to the dynamic friction in the process of the steering wheel from static to rotating, and the friction is changed from the dynamic friction to the static friction in the process of the steering wheel from rotating to static. The invention can effectively inhibit torque fluctuation caused by friction force change, better overcome the adverse effect caused by mechanical friction and reduce steering hysteresis, thereby enabling the electric power steering system to be more stable and comfortable.

Claims (7)

1. A method of friction compensation in an electric power steering system, comprising the steps of:
(1) collecting a steering wheel torque signal, a vehicle speed signal and a motor corner signal, and calculating a motor rotating speed signal according to the motor corner signal;
(2) obtaining static friction compensation torque by using a table look-up mode according to the steering wheel torque signal and the motor rotation angle signal; obtaining dynamic friction compensation torque by using a table look-up mode according to the vehicle speed signal and the motor rotating speed signal; when calculating the static friction compensation torque, when the change rates of the steering wheel torque signal and the motor rotation angle signal are both larger than respective first threshold values, switching to dynamic friction compensation torque calculation; when calculating the dynamic friction compensation torque, when the vehicle speed signal and the motor rotating speed signal are both smaller than respective second threshold values, switching to static friction compensation torque calculation;
(3) and adding the static friction compensation torque and the dynamic friction compensation torque to obtain the friction compensation torque.
2. The friction compensation method of an electric power steering system according to claim 1, wherein the step (1) of collecting the steering wheel torque signal comprises: and performing first-order low-pass filtering processing on the steering wheel torque signal to reserve a low-frequency part.
3. The friction compensation method of an electric power steering system according to claim 1, wherein the abscissa of the static friction compensation torque obtained in step (2) by using the table lookup is obtained from the steering wheel torque signal, and the ordinate is obtained from the motor rotation angle signal, wherein the abscissa is
Figure FDA0002620921230000011
The ordinate is
Figure FDA0002620921230000012
n is the sample time, FSWT (n) is the steering wheel torque at the nth sample time, and SWAMot (n) is the motor rotational angle at the nth sample time.
4. The friction compensation method of an electric power steering system according to claim 1, wherein the abscissa of the dynamic friction compensation torque obtained in step (2) by using a table lookup is a vehicle speed signal, and the ordinate is a motor speed signal.
5. The friction compensation method of an electric power steering system according to claim 1, wherein the friction compensation torque obtained in step (3) is further filtered by a third-order band-stop filter to improve stability.
6. A friction compensation method of an electric power steering system according to claim 1, characterized in that the friction compensation torque obtained in step (3) is also processed by a limit value to avoid an excessively light steering.
7. The friction compensation method of an electric power steering system according to claim 1, characterized by further comprising the step of setting a friction torque change rate after the friction compensation torque obtained in the step (3).
CN202010783010.2A 2020-08-06 2020-08-06 Friction compensation method of electric power steering system Pending CN112061229A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113581281A (en) * 2021-08-30 2021-11-02 中汽创智科技有限公司 Vehicle steering control method, device, equipment and storage medium
CN115158442A (en) * 2022-08-16 2022-10-11 中国第一汽车股份有限公司 Method and device for determining power-assisted torque, storage medium and processor

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CN105383555A (en) * 2014-09-02 2016-03-09 现代摩比斯株式会社 Friction compensation control apparatus and method of mdps system
CN107054448A (en) * 2016-12-28 2017-08-18 海特汽车科技（苏州）有限公司 A kind of steering friction compensation method based on torque signals
CN107097846A (en) * 2017-05-13 2017-08-29 浙江仕善汽车科技股份有限公司 A kind of determination method of automobile electric booster steering system friciton compensation moment of torsion

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CN102105341A (en) * 2009-01-28 2011-06-22 日本精工株式会社 Electric power steering device
CN104995083A (en) * 2013-03-29 2015-10-21 日立汽车***转向器株式会社 Power steering device, and control device used for same
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Cited By (4)

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Publication number Priority date Publication date Assignee Title
CN113581281A (en) * 2021-08-30 2021-11-02 中汽创智科技有限公司 Vehicle steering control method, device, equipment and storage medium
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CN115158442A (en) * 2022-08-16 2022-10-11 中国第一汽车股份有限公司 Method and device for determining power-assisted torque, storage medium and processor
CN115158442B (en) * 2022-08-16 2024-05-17 中国第一汽车股份有限公司 Method and device for determining boosting moment, storage medium and processor

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Application publication date: 20201211