WO2021141436A1

WO2021141436A1 - Electric power steering system

Info

Publication number: WO2021141436A1
Application number: PCT/KR2021/000241
Authority: WO
Inventors: 이정일; 손중락; 방희성
Original assignee: 이래에이엠에스 주식회사
Priority date: 2020-01-08
Filing date: 2021-01-08
Publication date: 2021-07-15
Also published as: KR102156259B1

Abstract

A method for controlling friction compensation torque of an electric power steering system comprises the steps of: performing variable band-pass filtering with respect to differentiated input steering torque; integrating the variable band-pass filtered steering torque; performing amplification with respect to the integrated steering torque by using a basic amplification gain, so as to generate basic friction torque; calculating phase control friction torque by applying a phase lead to the basic friction torque obtained by the amplification; and performing low-pass filtering with respect to the phase control friction torque by using a cutoff frequency for each vehicle speed.

Description

electric power steering system

The present invention relates to an electric power steering system for a vehicle.

An electric power steering (EPS) system is a steering system that uses electric power to steer auxiliary power, and FIG. 1 shows the structure of a general EPS system. Torsion of the torsion bar 2 is formed through the steering angle applied to the steering wheel 1 by the driver, and the torque and angle sensor (TAS) 3 measures this to steer the driver desired. A steering torque is generated to The steering angle and steering torque together with the vehicle speed are the main inputs to the EPS logic 4 for determining the optimal steering assistance force. The optimal steering assistance force should be generated based on inputs such as steering angle, steering angular speed, and steering torque applied by the driver at the corresponding vehicle speed. The determined steering assist force is transmitted to the motor driver 5 and converted into an actually required steering current. When the motor 6 is driven by this steering current, it is converted into a required force through a power transmission medium such as a worm wheel or a worm gear, and by driving the steering mechanism 7, the steering wheel 8 is driven to perform steering.

Steering assistance is the sum of several outputs. The EPS control system uses the control logic to create a light and comfortable steering feel during low-speed driving and a heavy and stable steering feel for high-speed driving. In addition, the EPS system controls the motor to achieve quick steering in an emergency or a situation requiring sudden steering.

2 is a diagram showing the configuration and operation flow of control logic in a general EPS system. EPS control includes friction logic. Due to the effect of friction generated when each steering part is operated, a situation may arise where the motor cannot generate the necessary amount of auxiliary torque/steering force, and also a situation where the responsiveness is insufficient due to the disturbance caused by the friction of the tire, resulting in a steering feel. and a decrease in steering performance, a friction logic is required. For example, when such friction and disturbance occur in a situation where urgent steering is required at high speed driving, the motor may not be able to generate the necessary steering assistance power. Steering may be difficult as it does not operate.

The problem of reduced responsiveness due to internal mechanical friction or external disturbance is not limited to sudden steering, etc., but also affects general cornering and steering operations. Mechanical friction and disturbance during driving vary depending on the vehicle condition and various driving situations, but since they have a slight effect on creating an appropriate auxiliary steering force, it can lead to a decrease in steering feel and major fine performance degradation. Mechanical friction and disturbance during driving also affect on-center operation during straight-line driving and affect other overall steering performance. Several types of logic have been developed that can compensate for the appropriate auxiliary steering force by overcoming the problems caused by such internal and external friction.

A basic way to find out whether the driver has made a sudden steering or how fast the responsiveness is steering is to sense and use the frequency change of the steering torque input by the driver. In order to determine the additional steering assistance force required by the internal and external friction forces, it is necessary to analyze the steering torque component input by the driver. Considering the direction in which the driver intends to steer in the frequency change of the steering torque input by the driver, it can be seen in which direction the driver attempted to steer while demanding a certain degree of responsiveness. The frequency change range that the driver can give is inevitably limited, and steering at a frequency of 10 Hz or higher generally does not occur no matter how fast the steering is. Most drivers' steering is observed around 4 to 5 Hz. However, it is not desirable to control the frequency band reflecting the driver's will to be absolutely limited to the corresponding band, and it is desirable to control the frequency band to be limited within an appropriate range in consideration of the tunable range and steering stability and responsiveness.

By observing a specific frequency band when the frequency of the steering torque is changed, it is possible to know what type of steering intention the driver has. In general, if the accumulated value of magnitude information at each frequency within a frequency band that can be input by the driver is large, it is determined that the driver's input has proceeded in a form requiring sudden steering or high responsiveness. If the accumulated value is decreased, it may be determined that the steering operation is not a type of steering operation requiring high responsiveness. This frequency characteristic is because the higher the driver's attempt to steer, the higher the magnitude of the component at the relatively high frequency. It can be seen that the larger the size of this component, the greater the steering response is required. At this time, the steering assistance torque suitable for this in the EPS system should be output at an appropriate time and with an appropriate size.

However, the biggest problem in developing such a friction torque compensation logic is the relationship with the damping control logic of the existing EPS system or the performance degradation part due to a trade-off relationship. In fact, existing friction control logics have this limitation or try to compensate or overcome this limitation in a partial way.

Friction compensation torque is generated only above or below the specific speed (RPM) value of the steering motor, so that in the build-up section where a large initial torque is required or in emergency steering operation, step waveform, trapezoidal waveform, etc. A form of compensating for insufficient auxiliary power by outputting a compensation torque of the waveform of This auxiliary force is controlled so that the torque felt during the initial start does not change abruptly. In addition, since the initial starting torque is smaller than when there is no compensation logic, the driver can steer without difficulty by compensating for the problem of lack of responsiveness when steering. At this time, since the motor speed has a linear relationship when the steering angular speed and the reduction ratio are considered, the value of a specific steering angular speed can be used as an upper and lower limit value for outputting the compensation torque. This compensation torque, which is output only above or below a certain speed, inevitably brings about a sudden change in torque, and this characteristic may basically cause vibration or a sense of steering heterogeneity.

A method of turning the output on/off based on a value of a specific steering angular speed or motor speed has a basic limitation that it may cause a sudden change in torque. In addition, the effect of such a sudden torque change may be amplified or deteriorated by ambient disturbance caused by a change in vehicle speed. This method has greater limitations in terms of steering stability. The friction compensation torque basically has a form in which it is output as a specific value based on the upper and lower limits of a specific motor or steering angular velocity value. However, this type of operation results in a decrease in the performance of the damping logic operating for yaw stability and steering stability of the vehicle. This is because the friction compensation logic is operated to reduce insufficient responsiveness in the steering direction or to reduce the starting torque that varies greatly in the initial stage, while the damping logic is operated to control abrupt steering in the opposite direction and to provide a stable steering feel. . Due to the reasons of such operation direction and characteristics, the previously developed friction compensation logic takes an action to quickly or slowly accumulate the accumulated values in a specific frequency band section, or if the damping logic is above a specific value, it is associated with the friction compensation logic. The output value is set to be small or large according to this damping value. 3 and 4 show an example thereof.

3 and 4 basically show a sudden change in the friction compensation torque, which implies the possibility of causing vibration or a sense of difference in steering, as mentioned above. In addition, it can be seen that the compensation torque of the friction logic is different from the torque direction of the logic such as damping and cancels each other, and the overlapping operation area is large. Even if it operates in the form of correlating its compensation torque above and below a specific damping torque value and reducing it, the underlying performance degradation factor is not solved. Also, since damping still exists at a time point when damping is most required, that is, a section or region in which the damping torque is maximum, a decrease in damping performance also exists. And it can be understood that this corresponds to an attempt to compensate for the trade-off situation in the form of yielding performance values according to mutually set values as well as reducing the friction compensation torque.

(Patent Document 1) Patent Publication No. 10-2010-0114995 (Published date: October 27, 2010)

The problem to be solved by the present invention is an electric power steering that has a flexible structure that can satisfy various steering performance and responsiveness while preventing performance degradation due to a relationship or trade-off relationship with damping control logic and can be operated flexibly It is to provide the friction compensation torque logic of the system.

A friction compensation torque control method of an electric power steering system according to an embodiment of the present invention includes performing variable bandpass filtering on a differentiated input steering torque, integrating the variable bandpass filtered steering torque, and the integrated generating a basic friction torque by performing amplification on the steering torque using a basic amplified gain, calculating a phase controlled friction torque by applying a phase lead to the basic friction torque obtained by the amplification, and the phase controlled friction and performing low-pass filtering on the torque using a cutoff frequency for each vehicle speed.

The bandpass filtering may variably operate according to a value of F2 at a given vehicle speed.

The phase leading may be variably performed through a combination of poles and zeros tuned for each vehicle speed.

In the friction compensation torque control method according to another embodiment of the present invention, a limit value given for each vehicle speed is applied to the phase control friction torque on which the low-pass filtering is performed, and a gain value for the torque increase for each vehicle speed is applied to further adjust the size. It may further include the step of

In the step of performing the basic amplification, the basic amplification gain may be set differently depending on whether the operation is returning to the steering wheel center or moving away from the steering wheel center.

The basic amplification gain may be a value tuned according to a steering angular velocity.

A friction compensation torque control system of an electric power steering system according to an embodiment of the present invention is a variable band-pass filter for performing band-pass filtering on a differentiated input steering torque, and integrating the steering torque that has passed through the variable band-pass filter. An integrator, an amplifier for generating a basic friction torque that amplifies the integrated steering torque using a basic amplification gain, and a variable for calculating a phase control friction torque by applying a phase lead to the basic friction torque obtained by the amplifier a phase lead controller, and a low-pass filter for performing low-pass filtering on the phase control friction torque by using a cutoff frequency for each vehicle speed.

The variable bandpass filter may variably operate according to a value of F2 at a given vehicle speed.

The variable phase lead controller may variably apply the phase lead through a combination of a pole and a zero point tuned for each vehicle speed.

In the friction compensation torque control system according to another embodiment of the present invention, a limit value given for each vehicle speed is applied to the phase control friction compensation torque that has passed through the low-pass filter, and a gain value for the torque increase for each vehicle speed is applied to further increase the size. It may further include a size adjuster to adjust.

The basic amplification gain may be set differently depending on whether the operation is returning to the steering wheel center or moving away from the steering wheel center.

According to the present invention, by applying the variable bandpass filtering by the variable bandpass filter and the phase leading by the phase leading controller, the friction compensation torque can be flexibly created while overcoming problems such as deterioration of damping performance and steering resistance. It can provide a natural steering feel to the driver in situations such as general steering and sudden steering.

1 is a view showing the structure of a general EPS system.

2 is a diagram illustrating a configuration and an operation flow of a control logic in an existing EPS system.

3 is a view showing a basic form of a friction compensation torque output of a conventional friction compensation logic.

4 is a view showing a modified form of a conventional friction compensation logic.

5 shows an example of an ideal operation form according to damping performance attenuation by friction logic during a release operation of a steering wheel in friction compensation logic.

6 and 7 are block diagrams illustrating a friction compensation torque control method according to an embodiment of the present invention.

8 shows various examples of a phase leading operation according to a pole and a zero point in the friction compensation torque control method according to an embodiment of the present invention.

9 shows a comparison of the phase lead response according to the pole and the zero point in the friction compensation torque control method according to the embodiment of the present invention.

10 is a view showing an operation form of a friction compensation torque to which phase control is not applied and an operation form of a friction compensation torque to which a phase control concept according to an embodiment of the present invention is applied.

11 is a view showing a frequency region of interest among the phase leading operation types in the friction compensation torque control method according to an embodiment of the present invention.

12 is a view showing a compensation torque by applying a phase lead in a friction compensation torque control method according to an embodiment of the present invention.

13 is a diagram illustrating a change in friction compensation torque according to a frequency change of a bandpass filter in a friction compensation torque control method according to an embodiment of the present invention.

14 is a diagram illustrating an operation form according to frequency selection of a bandpass filter in a friction compensation torque control method according to an embodiment of the present invention.

15 is a diagram illustrating an operation form according to frequency selection of a bandpass filter in a band of interest in a friction compensation torque control method according to an embodiment of the present invention.

16 is a view showing a change in the friction compensation torque according to a change in the F2 value of the bandpass filter in the friction compensation torque control method according to an embodiment of the present invention.

17 shows an example of an interpolation table based on a steering angular velocity and a steering wheel center in a friction compensation torque control method according to an embodiment of the present invention.

18 is a view showing the operation forms of the damping torque and the friction compensation torque when the phase control is not applied, and the operation forms of the damping torque and the friction compensation torque to which the phase control concept according to the embodiment of the present invention is applied.

19 is a diagram comparatively showing an operation at the time of restoration to the center when the phase lead is applied according to an embodiment of the present invention.

20 is a view comparatively showing steering torque according to the presence or absence of friction logic during sudden steering.

21 is a view comparatively showing steering torque according to the presence or absence of friction logic during on-center driving.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

It is characterized by applying the phase control method to the compensation torque control logic based on the basic steering angular speed or the motor speed. The addition of the phase control method can solve the problem of performance degradation of the damping logic. Hereinafter, an example for explaining such a situation in an actual vehicle will be described, and a problem in the case where the damping performance is deteriorated through an operation when the steering wheel is released at a specific speed will be described.

5 shows an example of an ideal operation form according to damping performance attenuation by friction logic during a release operation of a steering wheel. In FIG. 5 , 'YDT_monitor' denotes a damping torque, 'inputSWA' denotes a steering angle, and 'limit_Friction-tq_monitor' denotes a friction compensation torque. 5 shows that the friction compensation torque is not output only above and below a specific motor speed or steering angular velocity value, and the reason for using this type is because it responds more flexibly in terms of the sense of heterogeneity of steering, including vibration. to be. It shows relatively better characteristics in terms of steering feel.

By using a signal (limit_Friction_tq_monitor) whose size changes naturally, the shape that causes vibration or a sense of heterogeneity in steering torque can be relatively reduced, but the characteristic output in proportion to the speed is maintained. When the damping magnitude YDT_monitor is output large during the release operation in which the steering angle inputSWA is released, the friction compensation magnitude is also output large in the vicinity of the corresponding operation section. This is because the motor and steering angular velocities increased in the corresponding section. The damping torque (YDT_monitor) was activated to naturally and slowly return the steering wheel, but the friction torque works and offsets this part, thereby reducing the performance of yaw damping and causing the steering wheel to become unnatural (car does not follow the behavior of , and returns rapidly and quickly (as tuned). These operating characteristics make the driver feel the instability of the vehicle during restoration. Even if this friction torque value is momentarily reduced in the maximum section or a specific section of the damping torque as in the past, as in this example, it is simply applying a small size that causes performance degradation in the damping operation section that is controlled to be restored naturally as in this example. There is still a point that degrades the performance of the damping logic in .

Steering restoration has intrinsic limitations that make it difficult to achieve stable damping control. That is, in an important section in which the damping logic operates and controls to have the most stable restoration or stability, the influence of the friction logic may be minimized or may not be necessary. The initial torque section requiring high steering torque occurs in the initial torque generation section in both the general steering and sudden steering situations, and then moves away from the effective operating section of the friction logic in the operation. That is, it can be said that the time point at which the damping torque logic operates as the maximum size and the main effective operation period of the friction compensation logic are different from each other.

The friction torque logic has as a basic criterion that the necessary compensation torque is output while minimizing the delay so that the compensation-response is not insufficient at the timing when the responsiveness is required. The friction torque disappears quickly after output, and it is necessary to limit and minimize the operation of the friction logic in the section with the maximum damping magnitude. In order to achieve this, in the embodiment of the present invention, the operation section of the friction logic is developed in the form of phase control to secure such operation characteristics. In conclusion, friction compensation logic is the best when two forms are combined: an operation method that induces a natural change rather than an abrupt change and minimizes performance degradation during operation based on correlation with other logic such as the existing damping logic. performance is obtained.

The embodiment of the present invention shows a structure and an output form of a friction compensation torque having characteristics of a natural compensation torque change in consideration of various main input and control situations. In addition, more importantly, we present a new approach and flexible control method that overcomes tradeoffs or limitations with major steering stability-related control logic such as damping. In addition, the actual vehicle performance test results for demonstrating these methods are presented below to prove the effectiveness of the method of the present invention.

6 and 7 are block diagrams illustrating a friction compensation torque control method and system according to an embodiment of the present invention. Referring to FIG. 6 , the steering torque is differentiated by the differentiator 11 , and the variable BPF 10 performs variable bandpass filtering on the differentiated input steering torque. The variable bandpass filter 10 changes the differentiated input steering torque according to the f2 value using the f2 frequency table 20 at a given vehicle speed. Thereby, the steering torque component required at a given vehicle speed can be flexibly adjusted and selected according to the intended purpose. The integrator 30 integrates the steering torque band that has passed through the variable bandpass filter 10 . The variable bandpass filter 10 is a filter that passes a band between the lower limit frequency f1 and the upper limit frequency f2, and when f1 is fixed and f2 is increased, a bandpass result having a relatively high frequency component is obtained. In steering, the high frequency component is related to the responsiveness, and the responsiveness is improved by increasing f2. That is, the upper limit frequency becomes a tuning parameter that can increase or decrease the responsiveness by raising or lowering the frequency in relation to the vehicle speed. In the embodiment of the present invention, the responsiveness is improved by slightly increasing f2. However, it is not possible to increase f2 blindly, and it is desirable that the value that can be raised according to the vehicle speed is determined in advance in the tuning stage. Since an increase in responsiveness causes a decrease in stability, a tuning factor that can achieve fine responsiveness improvement in a range that does not cause stability problems by adjusting the maximum and minimum values of f2 that can be raised in advance for each vehicle speed will secure

The determiner 40 determines whether the operation is returning to the steering wheel center or moving away from the steering wheel center with respect to the integrated steering torque component. For example, this determination may be made using a steering angle and a steering torque. When the steering angle is divided into an on-center area, a transition area, and an off-center area, whether the steering angle is moving away from or closer to the center can be known as an angle. In this case, the steering torque may also be considered, and the above determination may be made using the steering angle and the steering torque.

The amplifier 50 generates basic friction torque by amplifying the integrated steering torque using the basic amplification gain. The amplifier 50 generates a necessary basic friction compensation torque by amplifying the steering torque by the values tuned in the interpolation gain tables 61 and 62 according to the steering angular velocity according to the determination result of the determiner 40 . The first interpolation gain table 61 includes gain data according to the steering angular velocity when the steering wheel is restored to the center, and the second interpolation gain table 62 includes the gain data according to the steering angular velocity when the steering wheel moves away from the center. Includes gain data. The steering angle is differentiated by the differentiator 12 to obtain the steering angular velocity, and the first and second interpolation tables use the obtained steering angular velocity. The amplifier 50 performs basic amplification by selectively using the gains of the first or second interpolation gain tables 61 and 62 according to the determination result of the determiner 40 .

A variable phase lead controller 80 calculates a phase-controlled friction compensation torque by applying a phase lead to the basic friction compensation torque obtained by the amplifier 50 . The variable phase lead controller 80 is a phase lead through the combination of poles and zeros of the pole / zero table 70 tuned for each vehicle speed with respect to the basic friction compensation torque obtained by the amplifier 50 . make it happen The phase lead controller itself is a known control equation. The variable phase lead controller 80 may use such a previously known control equation, and applies an application applied to each vehicle speed of steering. For example, at P20, that is, pole 20, Z0.3, that is, a response with zero point 0.3 and a response zero point with P30, the phase of P30 appears larger in the same frequency band, for example, a band below 10 Hz. That is, P30 appears first at the same frequency because the phase is ahead. In a physical sense, it means appearing first in a larger size. This combination of poles and zeros is used in the form of an interpolation table for each vehicle speed.

The variable low-pass filter (LPF) 100 performs low-pass filtering with respect to the phase control friction compensation torque by using a cutoff frequency given for each vehicle speed. Since the component passing through the variable phase lead controller 80 may include a vibration component and the like, a variable low-pass filter (LPF) using the cut-off frequency of the cut-off frequency table 90 including the cut-off frequency given for each vehicle speed as a torque component. ) (100).

The size adjuster 120 additionally adjusts the size by applying a limit value given for each vehicle speed to the phase control friction compensation torque that has passed through the variable low-pass filter 100 and applying a gain value for the torque increase for each vehicle speed. The size adjuster 120 applies the torque limit value given for each vehicle speed of the torque limit value table 121 to the torque component made after filtering, and adjusts the torque increase amount for the torque increase until the limit value is given for each vehicle speed of the gain table 122 . By applying the increment control gain, the torque magnitude is adjusted and limited for each vehicle speed. It is to set a limit value at the corresponding vehicle speed, and also to set the slope for each vehicle speed, so that when the vehicle reaches the limit value, the shifting slope is different. This results in a single tuning factor that controls the rate at which the final compensation torque is produced. It is common to put a limit on the output in the control logic and have this gradient speed control. For example, at low speed, it can be accumulated slowly to the limit value, and at high speed, it can be accumulated quickly. The gain tables 121 and 122 may be used to simply change the final amplification for each vehicle speed, or may be used to adjust the torque increase speed reaching a limit value.

The summer 130 adds up the friction compensation torque component determined as above with the existing steering logic torque components, for example, assist torque, return torque, damping torque, and other logic-based torque components. The final torque signal output from the summer 130 is processed as a stable final torque through a notch filter 140 and is output as a torque command to the motor 200 accordingly.

The above-described variable bandpass filter 10, integrator 30, determiner 40, amplifier 50, variable phase lead controller 80, variable low-pass filter 100, magnitude adjuster 120, summer 130 and notch filter 140 may be implemented in a microprocessor, memory, and related hardware and software, as is known in the art.

Due to various demands or intentions, the operation form of the friction compensation torque may be various. The purpose may be that the friction compensation torque is output quickly and cancelled quickly, and a performance in the form of relatively slow and slow offsetting may be preferred. Furthermore, a form that outputs a little later and decreases rapidly may be preferred. What is important is whether it can be tuned and operated according to changes caused by various factors and intended operation. Friction compensation torque having various phase control characteristics using differences in frequency response and various characteristics according to combinations of poles and zeros as shown in FIGS. 8 and 9 in consideration of the characteristics of vehicle speed and input steering torque can create Through this, it is possible to minimize factors that degrade performance such as damping while securing the intended operation or to have a relationship with the intended operation. Equation 1 shows a transfer function for phase leading. The combination of the pole and zero points of the transfer function designed in this way is changed according to the situation according to the characteristics of the vehicle speed and the input steering torque, thereby outputting a friction compensation torque having a phase control characteristic.

where y is the output, μ is the input, α _d is the zero-phase gain characteristic, and T _d is the pole-center frequency.

As can be seen in FIG. 8 , it can be seen that the phase and gain in the frequency domain of interest can be controlled in various ways through the combination of the pole and the zero point. Also, as can be seen in FIG. 9 , it can be seen that desired responsiveness can be tuned in various forms. In order to control using the combination of poles and zeros of the phase lead controller 80, an interpolation table of poles and zeros according to vehicle speed needs to be implemented.

10 shows the operation form of the friction compensation torque based on the phase control according to the embodiment of the present invention, and shows the results measured in a real vehicle running at 60 kph on an asphalt road. Fig. 10 (a) shows the operation form of the friction compensation torque to which the phase control concept is not applied, and Fig. 10 (b) shows the operation form of the friction compensation torque to which the phase control concept is applied. In FIG. 10 , 'YDT_Monitor' indicates damping torque logic, 'RealControl_inputSWA' indicates a steering angle, and 'limit_friction_tq_monitor' indicates friction compensation torque.

As when releasing the steering wheel in FIG. 5 , FIG. 10 shows the interrelated action with damping. In (a) of FIG. 10 , only the basic control concept is applied so that the friction compensation torque is large above a specific value according to the steering angular speed or the motor speed. In fact, due to this, the friction compensation torque is also maximized within the maximizing operation section of the damping torque to cancel it. At this time, during sudden steering, the initial starting torque is reduced due to the effect of the friction compensation torque, so that the driver obtains a smooth steering feel during steering. However, at the next timing, the damping performance is greatly reduced, so that the driver does not feel a stable steering feeling and receives an unstable steering feeling. On the other hand, Fig. 10 (b) shows the result of applying the phase control concept, and it can be easily seen that the shape of the friction compensation torque is much different. That is, the tuning values that determine the magnitude at a specific motor speed or steering angular speed are the same, but completely different operating characteristics are obtained by applying the phase control. The friction compensation torque rises rapidly in the initial sudden steering driving section, operates quickly to lower the initial torque that may be burdened on the driver, and then falls rapidly. Due to this, it is possible to create a friction compensation torque output with a flexible structure that can cope with a wide variety of situations.

11 shows the frequency response characteristics at various pole/zero combinations in a relatively low/high frequency band based on a band of about 10 Hz, which is a pole during operation for a relatively low frequency input and a high frequency input. It indicates that various properties can be obtained through various combinations of and zero. That is, for example, it is possible not to operate sensitively in steering at a relatively normal speed, and to react quickly when a more abrupt steering speed occurs to prevent a lack of responsiveness from occurring and then to decrease rapidly. Of course, even when steering in a low frequency band, it is possible to finely adjust the compensation torque through fine adjustment to achieve smoother steering. This fine adjustment is not a form in which the driver holds the wheel and steers, but as in the example described above, even in the release operation of the steering wheel, the friction compensation torque with this phase control induces a more natural restoration and operates according to the intended purpose. Tuning can also be made more flexible.

Basically, it is not a friction compensation torque that operates only above/below a specific motor speed or steering angular speed. In the case of compensation torque to which this phase control concept is applied, it responds less during low-frequency steering, which means that it does not create unnecessary damping inhibitory components. That is, the higher the frequency, the faster the steering response and the less response when steering in a relatively low frequency band, thereby significantly reducing the problem caused by deterioration of damping performance. As described above, this is a more efficient and flexible operation form in that it does not create vibrations or other steering differences because it does not make sudden changes while reflecting the intention to operate only during sudden steering in a basically step-shaped waveform such as a square or trapezoid, as described above. can It can be seen that the compensation torque is much smaller in the method in which the phase lead of the 'B' part is applied compared to the 'A' part of FIG. 12 . This is less responsive to steering at relatively low frequencies. However, since it shows a waveform that naturally increases and decreases more flexibly, there is no sense of heterogeneity due to sudden change. This is because, as described above, the phase characteristics are different depending on the frequency characteristics, so it is possible to operate in a section different from the maximum damping operation section, and the gain characteristics for low and high frequencies can also be applied differently. This operation characteristic can create various types of friction compensation torque desired while minimizing the degradation of damping performance, and thus the response characteristic can be made more flexible.

As shown in FIG. 13, even if all the tuning values are the same, the size of the friction compensation torque is reduced only by changing the value of the second frequency F2 (band frequency of the bandpass filter, F1<F2) of the bandpass filter for the steering torque. Able to know. As shown in FIGS. 14 and 15 , when the F2 value is small, the integral value of the steering torque is very large and fluctuates greatly, whereas when the value is relatively small, the difference or magnitude is small, which means that when the F2 value is small, the driver's This is because the magnitude in the continuous integration of the operating frequency components during sudden steering increases. This provides a method to flexibly tune the control characteristics by finely adjusting the size of the source stage in applying various control methods according to the accumulated torque passing through the bandpass filter.

Referring to FIG. 16 , it can be seen that the magnitude of the friction compensation torque decreases as the value of F2 (F2>F1) increases at the main frequencies of F1 to F2 of the bandpass filter.

As described above, if it is determined that the fine steering feel or performance value is not reached by combining the band-pass filter whose F2 value changes according to the vehicle speed and the phase lead controller, which also changes the combination of poles and zeros according to the vehicle speed, the band-pass filter By adjusting the F2 value, this subtle difference can be overcome. For example, the combination of the phase leading pole and zero point at a specific vehicle speed and the various gain values determined according to the vehicle speed in the interpolation table at this time approximate the desired performance value or operating characteristic, but increase or decrease the gain or increase or decrease the gain or increase or decrease the pole and It is conceivable that changing the zero combination will produce a larger change. In this case, it is possible to fine-tune the friction compensation torque by changing the F2 value of the bandpass filter without changing the combination of the pole and the zero point or various gain values.

Moreover, there is a structural relationship between the frequency selection that determines the passband of the bandpass filter and the pole and zero values that determine the frequency characteristic of the phase lead controller at the same vehicle speed. For example, if the F2 value of the bandpass filter is reduced from '4' to '3', the processing for the bands above 4 Hz in the phase leading frequency characteristic of the combined pole and zero combination is eliminated or minimized, so different steering and operating characteristics this can be obtained. The frequency bands targeted by the phase leading controller of the bandpass filter may be matched with each other, or the band of the bandpass filter may be overlapped with the main effective band of the phase leading controller. Alternatively, operating characteristics such as ignoring a specific band or making it more amplified may be correlated.

As an additional method, by applying the gain interpolation table for two areas when the steering wheel returns to the center and when the steering wheel moves away from the center for the steering torque signals determined through the variable bandpass filter, the initial starting torque and sudden steering It is possible to create a basic amount of auxiliary torque to satisfy the required responsiveness. By configuring a separate interpolation table for the shape of returning to the center and moving away from the center based on the zero center of the steering wheel, the steering feel and motion when moving away from the sensor and returning to the center can be made more flexible. It can be implemented in the intended form.

Such an interpolation table may take various forms with the steering angular velocity and the steering torque or the steering torque change value as an axis for the steering torque after passing through the bandpass filter. 17 shows one form of such an interpolation table. This operation can be called a more flexible structure because the gain can be varied in a specific section or value for a specific steering torque, a steering torque change (differential), or a steering angular velocity. The example shown in FIG. 17 is a structure having a separate gain table different from the steering torque and the steering angular velocity.

18 shows the results of comparing the damping torque and the friction compensation torque obtained from the data measured in the actual vehicle as an area ratio. Fig. 18 (a) shows the result when the phase control is not applied, and Fig. 18 (b) shows the result when the phase control concept according to the present invention is applied. In both cases, the output form of the damping torque is similar, other tuning values are the same, and there is only a difference in the presence or absence of the phase lead controller. In (b) of FIG. 18 , the friction compensation torque is output faster than in (a) of FIG. 18 , and after rapidly rising, it also decreases rapidly on the contrary. It can be seen as a form that operates quickly only in the section where responsiveness is required and then disappears quickly to minimize deterioration of damping performance. In the damping maximization section and in the main section, the area that can degrade the damping performance is minimized. However, in the section to create the initial starting torque or the auxiliary torque required for sudden steering, it is quickly supported and then attenuated according to the tuned value, so that the steering response is not impaired.

The friction compensation torque logic to which the phase control concept is applied is configured in a very flexible and dynamic form. As in the example described above, it can rise rapidly and then disappear quickly, operating to minimize the impact on other logic such as damping. The control method used is variable phase lead, which is closely related to and paired with the variable bandpass filter (10). The desired characteristic is achieved by the combination of the pole value and the zero value that are set to change according to the vehicle speed of the phase lead designed to advance the phase and various input conditions. That is, through the combination of the pole value and the zero value, the friction compensation torque can be outputted and reacted more quickly and attenuated more quickly. Conversely, it can also be made to output and respond more slowly and decay more slowly. You can also make it decay a little slower when it reacts faster but decays.

19 is a comparison of the restoration operation when the steering wheel described in FIG. 5 is released through the steering angle. When the phase lead is applied, the movement of the steering angle is relatively natural, but when it is not, an inflection point occurs and a sharp change in the inclination appears, indicating that the movement of the steering angle is not natural. This is also a phenomenon that occurs when the effective damping control section and the friction operation area overlap and cancel each other.

FIG. 20 comparatively shows waveforms of steering torque measured in the actual vehicle when the friction torque compensation logic according to the embodiment of the present invention is turned on/off during sudden steering, and all other conditions are the same. When the steering wheel is moved away from the center or restored to the center, it can be observed that the initial starting torque and the steering torque required within a specific section are formed smaller than the off state in the on state of the friction logic.

21 shows a comparison of driving data during on-center steering in the actual vehicle waveform at 60 kph, and even in this case, the steering required in the on state compared to the off state both when moving away from the center and returning to the center. It can be seen that the torque naturally rises and moves to the target torque as it is formed low rather than rapidly rising.

Although the embodiment of the present invention has been described above, the scope of the present invention is not limited thereto, and it is easily changed by a person skilled in the art from the embodiment of the present invention and recognized as equivalent. including all changes and modifications to the scope of

The present invention relates to an electric power steering system that can be applied as a steering device for a vehicle, and thus has industrial applicability.

Claims

A friction compensation torque control method for an electric power steering system, comprising:

performing variable bandpass filtering on the differentiated input steering torque;

integrating the variable bandpass filtered steering torque;

generating a basic friction torque by amplifying the integrated steering torque using a basic amplification gain;

calculating a phase control friction torque by applying a phase lead to the basic friction torque obtained by the amplification; and

performing low-pass filtering on the phase control friction torque using a cutoff frequency for each vehicle speed

A friction compensation torque control method comprising a.
In claim 1,

The bandpass filtering is a friction compensation torque control method that variably operates according to an F2 value at a given vehicle speed.
In claim 1,

The phase lead is a friction compensation torque control method that is variably performed through a combination of poles and zeros tuned for each vehicle speed.
In claim 1,

and applying a limit value given for each vehicle speed to the phase control friction torque on which the low-pass filtering has been performed and further adjusting the magnitude by applying a gain value for the torque increase for each vehicle speed.
In claim 1,

In the step of performing the basic amplification, the basic amplification gain is set differently depending on whether the operation is returning to the steering wheel center or moving away from the steering wheel center.
In claim 5,

The basic amplification gain is a value tuned according to the steering angular speed.
A friction compensation torque control system for an electric power steering system, comprising:

a variable bandpass filter that performs bandpass filtering on the differential input steering torque;

an integrator for integrating the steering torque that has passed through the variable bandpass filter;

an amplifier for generating a basic friction torque that amplifies the integrated steering torque by using a basic amplification gain;

a variable phase lead controller for calculating a phase control friction torque by applying a phase lead to the basic friction torque obtained by the amplifier; and

A low-pass filter that performs low-pass filtering on the phase control friction torque by using a cutoff frequency for each vehicle speed

A friction compensation torque control system comprising a.
In claim 7,

The variable bandpass filter is a friction compensation torque control system that variably operates according to a value of F2 at a given vehicle speed.
In claim 7,

The variable phase lead controller is a friction compensation torque control system that variably applies a phase lead through a combination of a pole and a zero point tuned for each vehicle speed.
In claim 7,

The friction compensation torque control system further comprising a magnitude adjuster for additionally adjusting the magnitude by applying a limit value given for each vehicle speed to the phase control friction compensation torque that has passed through the low-pass filter and applying a gain value for the torque increase for each vehicle speed.
In claim 7,

The basic amplification gain is set differently depending on whether the operation is returning to the steering wheel center or moving away from the steering wheel center.
In claim 7,

The basic amplification gain is a value tuned according to the steering angular velocity.