Device and method for compensating disturbances in a rack force

Abstract

A device (200) for compensating for a disturbance in a rack force, the device comprising: a memory (210); and a processor (220) connected to the memory, wherein the processor obtains an optimally estimated value of a rack force for minimizing an error representing a difference between an actual value of the rack force and the optimally estimated value of the rack force, extracts a specific frequency component from the optimally estimated value of the rack force, and compensates for a disturbance in the actual value of the rack force reflected in the actual value of the rack force by means of the extracted specific frequency component.

Description

background

[0001] The present disclosure relates to an apparatus and method for compensating for a disturbance in a rack force. More specifically, the present disclosure relates to an apparatus and method for compensating for a disturbance in a rack force, the apparatus and method being capable of minimizing a delay in detecting an estimated value of a rack force, eliminating a disturbance reflected in the estimated value of the rack force, and thus increasing the degree of steering feel experienced by a driver.

[0002] Typically, power steering systems are designed and used to assist a driver in operating a steering wheel and provide driver comfort while driving a vehicle. The power steering systems developed and used are divided into hydraulic steering systems that utilize hydraulic power, motor-driven hydraulic steering systems that utilize hydraulic power and the electromotive power of an engine simultaneously, motor-driven steering systems that utilize only the electromotive power of the engine, and the like.

[0003] In recent years, steer-by-wire (SBW) systems have been developed and deployed. In SBW systems, a mechanical connecting device, such as a steering column, universal joint, or pinion shaft, between a steering wheel and a vehicle wheel is removed, and vehicle steering is achieved by controlling the drive of a motor connected to a rack using an electrical signal.

[0004] SBW systems are steering systems in which a vehicle's steering wheel and drive wheel are mechanically decoupled from each other. In SBW systems, a steering wheel rotation signal is received via an electronic control unit (ECU), and a steering assist motor (hereinafter referred to as the "steering motor") connected to the drive wheel is operated based on the received rotation signal, thereby steering the vehicle.

[0005] SBW systems lack a mechanical connection structure to an existing steering system. Thus, SB systems have the advantage of potentially increasing the degree of freedom in layout design, which varies with a steering system configuration, improving fuel efficiency, removing a disturbance input in the reverse direction from the vehicle wheel, and the like.

[0006] For controlling the lateral direction of the vehicle and controlling the degree of steering feel, it is very important to detect a lateral force (a force transmitted to a rack = a rack force) on an inner surface of a tire because the lateral force has a great influence on controlling the degree of steering feel as well as on the control of the vehicle.

[0007] Particularly since there is no physical connection between the steering rack and the driver in SBW systems, it is necessary to measure or estimate the steering rack force and communicate information about the road surface to the driver. Accordingly, in SBW systems, a lateral force of a steered front wheel is estimated and measured. The steering rack force can be determined, for example, by estimating the lateral force using a vehicle dynamics model or a steering system model.

[0008] In the case of a rack force value estimated in this way, a specific frequency signal may be amplified or a disturbance may occur due to various causes, such as the mechanism of the SBW system and the condition of a road surface. In the SBW system, the steering wheel reaction force is determined by the estimated rack force value, and therefore, the disturbance reduces the degree of steering feel felt by the driver.

[0009] Accordingly, a filter such as a low-pass filter, a notch filter, or a Kalman filter is used to remove the disturbance from the estimated value of the rack force.

[0010] However, the filter used in related art to eliminate noise has a drawback in that the higher the filter performance, the greater the delay, and the high delay thus reduces the responsiveness of the steering. For example, the Kalman filter is highly dependent on the degree of accuracy of the steering system model. Therefore, the Kalman filter has the disadvantage of being difficult to use for estimating the rack force.

[0011] Accordingly, it is necessary to develop a technology capable of minimizing a delay in detecting the estimated value of the rack force, eliminating the disturbance reflected in the estimated value of the rack force, and increasing the degree of steering feel experienced by the driver.

[0012] The background of the present disclosure is disclosed in KR 10 2018 0 007 393 A (published on January 23, 2018 and titled “Device for controlling a steering in a steer-by-wire system and method therefor”).

[0013] DE 10 2016 014 562 A1 discloses a device / method for compensating for a disturbance in a rack force, wherein a specific frequency component is extracted from the estimated value of the rack force, the extracted specific frequency component compensates for the actual value of the rack force and thus eliminates a disturbance reflected in the actual value of the rack force.

[0014] DE 10 2008 042 666 A1 discloses compensating for a disturbance in a rack force, inter alia, by means of a difference between an actual value of the rack force and an estimated value of the rack force, wherein a specific frequency component is extracted from the optimally estimated value of the rack force and the extracted specific frequency component compensates for the actual value of the rack force. Brief outline

[0015] An object of the present disclosure aimed at solving the above-mentioned problems is to provide an apparatus and a method for compensating for a disturbance in a rack force, the apparatus and the method being capable of minimizing a delay in detecting an estimated value of a rack force, eliminating a disturbance reflected in the estimated value of the rack force, and thus increasing the degree of steering feel experienced by a driver.

[0016] The above-mentioned object is achieved by a device and by a method for compensating a disturbance of a rack force with the features of claim 1 and with the features of claim 6, respectively. Advantageous further developments emerge from the subclaims. Brief description of the drawings Fig. 1 is a view showing an SBW system in which a rack force disturbance compensation device according to a first embodiment of the present disclosure may be used. Fig. 2 is a view used to describe a configuration of the rack force disturbance compensating apparatus according to the first embodiment of the present disclosure. Fig. 3 is a view used to describe an operation of the rack force disturbance compensating device according to the first embodiment of the present disclosure. Fig. 4 is a flowchart used to describe a method for compensating for a disturbance in a rack force according to a second embodiment of the present disclosure. Detailed description of the illustrated embodiments

[0017] The components described in the embodiments may be implemented by hardware components, e.g., by at least one digital signal processor (DSP), a processor, a controller, an application-specific integrated circuit (ASIC), a programmable logic element such as an FPGA, other electronic devices, or combinations thereof. At least some of the functions or processes described in the embodiments may be implemented by software, and the software may be recorded on a recording medium. The components, functions, and processes described in the embodiments may be implemented by a combination of hardware and software.

[0018] The method according to embodiments may be embodied as a computer-executable program and may be implemented on various recording media such as a magnetic storage medium, an optical reading medium, and a digital storage medium.

[0019] Various techniques described herein may be implemented as digital electronic circuits or as computer hardware, firmware, software, or combinations thereof. The techniques may be implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., a machine-readable storage medium (e.g., a computer-readable medium), or in a transmitted signal for processing by a data processing device or for controlling the operation of a data processing device, e.g., a programmable processor, a computer, or multiple computers.A computer program may be written in any form of programming language, including compiled or interpreted languages, and may be deployed in any form, including a stand-alone program or a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program may be designed to run on one computer or on multiple computers at one or more locations, distributed across multiple locations and interconnected by a communications network.

[0020] Processors suitable for executing a computer program include, for example, both general-purpose and special-purpose microprocessors, as well as one or more processors of any type of digital computer. Generally, a processor receives instructions and data from read-only memory or random access memory, or both. Elements of a computer may include at least one processor for executing instructions and one or more memories for storing instructions and data. Generally, a computer also includes, or is coupled to, one or more mass storage devices for storing data, such as magnetic, magneto-optical, or optical disks, for receiving data from, transferring data to, or both. Examples of information carriers suitable for embodying computer program instructions and data include semiconductor storage devices, such asMagnetic media such as hard disks, floppy disks, and magnetic tapes; optical media such as compact disk read-only memory (CD-ROM), digital video disks (DVDs), etc.; and magneto-optical media such as a floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, erasable programmable read-only memory (EPROM), and electrically erasable programmable read-only memory (EEPROM), as well as any other known computer-readable medium. A processor and memory may be supplemented by or integrated with dedicated logic circuitry.

[0021] The processor may execute an operating system (OS) and one or more software applications running on the OS. The processor device may also access, store, manipulate, process, and create data in response to the execution of the software. For simplicity, the description of a processor device is used in the singular; however, one of ordinary skill in the art will recognize that a processor device may include multiple processing elements and / or multiple types of processing elements. For example, a processor device may include multiple processors or a processor and a controller. Furthermore, various processing configurations are possible, such as parallel processors.

[0022] Non-transferable, computer-readable media can be any available media that can be accessed by a computer and can include both computer storage media and transmission media.

[0023] This specification contains details of a number of specific embodiments, but it should be understood that the details do not limit any invention or what may be claimed in the specification, but rather describe features of the specific embodiments. Features described in the specification in connection with individual embodiments may be implemented in combination in a single embodiment. In contrast, various features described in the specification in connection with a single embodiment may be implemented in multiple embodiments individually or in any suitable subcombination.Furthermore, the features may operate in a particular combination and be initially described as a claimed combination, but one or more features may, in some cases, be excluded from the claimed combination, and the claimed combination may be changed into a sub-combination or a variation of a sub-combination.

[0024] Although the operations in the drawings are described in a particular order, this should not be understood to mean that the operations must be performed in that order or in the correct order to achieve the desired results, or that all operations must be performed. In a particular case, multitasking and parallel processing may be advantageous. Furthermore, it should not be understood that separation of various device components in the embodiments described above is required in all embodiments, and it should be understood that the program components and devices described above may be integrated into a single software product or packaged into multiple software products.

[0025] It is to be understood that the embodiments disclosed herein are for illustrative purposes only and are not intended to limit the scope of the invention. It will be apparent to one skilled in the art that various modifications to the embodiments may be made without violating the spirit and scope of the claims and their equivalents.

[0026] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that a person skilled in the art can readily practice the present disclosure. However, the present disclosure may be embodied in many different forms and is not limited to the embodiments described herein.

[0027] In the following description of the embodiments of the present disclosure, a detailed description of known functions and configurations will be omitted if doing so might obscure the subject matter of the present disclosure. Parts not related to the description of the present disclosure in the drawings are omitted, and like parts are denoted by like reference numerals.

[0028] In the present disclosure, the individual components are distinguished from one another to clarify the individual features. However, this does not necessarily mean that the components are separate. That is, a plurality of components may be integrated into a single hardware or software unit, or a single component may be distributed across a plurality of hardware or software units. Unless otherwise stated, such integrated or distributed embodiments are also within the scope of the present disclosure.

[0029] In the present disclosure, the components described in the various embodiments are not necessarily essential components, and some may be optional components. Accordingly, embodiments consisting of a subset of the components described in an embodiment are also within the scope of the present disclosure. Furthermore, embodiments that include further components in addition to the components described in the various embodiments are also included within the scope of the present disclosure.

[0030] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that a person skilled in the art can readily practice the present disclosure. However, the present disclosure may be embodied in many different forms and is not limited to the embodiments described herein.

[0031] In the following description of the embodiments of the present disclosure, a detailed description of known functions and configurations will be omitted if doing so might obscure the subject matter of the present disclosure. Parts not related to the description of the present disclosure in the drawings are omitted, and like parts are denoted by like reference numerals.

[0032] Whenever this disclosure refers to a component being "linked," "coupled," or "connected" to another component, this may refer not only to a direct connection relationship, but also to an indirect connection relationship via an intervening component. When a component is referred to as "comprising" or "with" another component, this may refer to the inclusion of another component, not its exclusion, unless expressly described to the contrary.

[0033] In this disclosure, the terms "first," "second," etc., are used only to distinguish between the individual components and do not limit the order or importance of the components, etc., unless expressly stated otherwise. Thus, throughout this disclosure, a first component in one exemplary embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one exemplary embodiment may be referred to as a first component.

[0034] In this disclosure, the individual components are distinguished from one another to clarify their individual features. However, this does not necessarily mean that the components are separate. That is, a plurality of components may be integrated into a single hardware or software unit, or a single component may be distributed across a plurality of hardware or software units. Unless otherwise stated, such integrated or distributed embodiments are also within the scope of this disclosure.

[0035] In the present disclosure, the components described in the various embodiments are not necessarily essential components, and some may be optional components. Accordingly, embodiments consisting of a subset of the components described in an embodiment are also within the scope of the present disclosure. Furthermore, exemplary embodiments that include additional components in addition to the components described in the various embodiments are also within the scope of the present disclosure.

[0036] An apparatus and method for compensating for disturbance in a rack force according to first and second embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. For clarity and simplicity of description, the thicknesses of lines, the sizes of constituent elements, and the like in the drawings may be shown in an inexact ratio. Moreover, a term defined in consideration of its meaning in the present disclosure will be used below, which may vary depending on the intention of the user or manager or according to the custom of the art. Therefore, the term should be defined in the context of the present description.

[0037] A feature of the present disclosure described in the present specification may, for example, be implemented in the form of a method, a process, an apparatus, a software program, a data stream, or a signal. The feature, although described in the form of a single embodiment (e.g., only in the form of a method), may also be implemented in another embodiment (e.g., in the form of an apparatus or a program). The apparatus may be implemented in the form of suitable hardware, software, firmware, or the like. The method may, for example, be implemented in a device such as a computer, a microprocessor, or a processor, which generally refers to a processing device such as an integrated circuit or a programmable logic device.Examples of a device also include a computer and a communications device, such as a mobile phone or a portable / personal information terminal (a personal digital assistant (“PDA”)), that facilitates the communication of information between end users.

[0038] Fig. 1 is a view showing an SBW system in which a rack force disturbance compensation device according to a first embodiment of the present disclosure may be used.

[0039] With reference to Fig. 1, the SBW system in which the device for compensating for disturbance in a rack force according to the first embodiment of the present disclosure can be used may include a steering wheel 11, a steering column 12 supporting the steering wheel 11, a reaction force motor 130 driven by an electronic control unit (ECU) 140, a detection unit 110 arranged on one side of the steering column 12, the reaction force motor 130, or a rack 20 and receiving steering-related information and rack position information, the ECU 140 generating a control signal for a steering reaction force torque and a steering assist force through an electric assist current control map based on vehicle speed information, and one or more steering motors or drive actuators 150 each steering left and right wheels 18 of a vehicle with the control signal from the ECU 140.

[0040] In the SBW system, a steering torque sensor 14, a steering angle sensor 13, and the like mounted on the reaction force motor 130 and the steering column 12 can be expressed as steering feedback actuators (SFAs), which constitute a high-level terminal of the SBW system; the steering motor or drive actuator 150 or the like for driving the steering rack 20 can be expressed as a road wheel actuator (RWA), which constitutes a low-level terminal of the SBW system.

[0041] In an SBW system 1 having a rack and pinion component, a steering torque occurring by rotation of the steering wheel 11 can be transmitted to the rack 20 via a rack and pinion mechanism, and the steering assist force occurring in the drive actuator 150 can be transmitted to the left and right wheels 18 via a tie rod 19 and the rack 20.

[0042] At this time, the detection unit 110 may include at least one of the steering angle sensor 13 that detects a change in rotation of the steering column 12 that changes according to a driver's operation of the steering wheel 11; the steering torque sensor 14 that is installed on either side of the reaction force motor 130 and the steering column 12 and measures the steering torque applied to the steering column 12 or the reaction force torque output from the reaction force motor 130; a vehicle speed sensor 15 that measures a speed of the vehicle; a rack position sensor 16 that is arranged on the steering rack 20 and obtains the rack position information; and a motor torque sensor 17 that measures the torque of the drive actuator 150. Alternatively, the detection unit 110 may also obtain detection information from the above-mentioned sensors.

[0043] When the drive actuator 150 is actuated, the rack 20 is moved. When the left and right wheels 18 are moved, a friction force Ffric of the SBW system and a rack force transmitted from the left and right wheels 18 are exerted.

[0044] The ECU 140 may measure an actual value of the rack force and, based on the measured actual value of the rack force, perform vehicle control or control of the reaction force motor 130 to generate a steer-by-wire (SBW) steering reaction force.

[0045] The measured actual value of the rack force reflects a disturbance, and the disturbance may reduce the degree of steering feel experienced by the driver. Accordingly, the ECU 140 may include a rack force disturbance compensation device 200 that eliminates the disturbance reflected in the actual value of the rack force. The rack force disturbance compensation device 200 is described with reference to Fig. 2 described in detail.

[0046] Fig. 2 is a view used to describe a configuration of the rack force disturbance compensation device 200 according to the first embodiment of the present disclosure. Fig. 3 is a view used to describe an operation of the rack force disturbance compensation device 200 according to the first embodiment of the present disclosure.

[0047] Referring to Fig. 2, the rack force disturbance compensation device 200 according to the first embodiment of the present disclosure includes a memory 210 and a processor 220.

[0048] The memory 210 is configured to store data related to the operation of the rack force disturbance compensation device 200. Specifically, an application (a program or an applet) or the like may be stored in the memory 210. The application obtains an optimally estimated value of the rack force by applying an optimization algorithm to an error representing a difference between the actual rack force value and the estimated rack force value. Subsequently, the disturbance reflected in the actual rack force value can be removed by compensating for the subtraction of a specific frequency component of the optimally estimated rack force value from the actual rack force value. Stored pieces of information may be selected by the processor 220 as needed.Memory 210 stores various types of data generated during execution of an operating system or an application (a program or an applet) for controlling device 200 to compensate for a disturbance in a rack force. Memory 210 refers here to both a non-volatile storage device that retains the stored information even though it is not supplied with electrical power, and a volatile storage device that requires electrical power to retain the stored information. Furthermore, memory 210 can perform a function of temporarily or permanently storing data processed by processor 220.Examples of memory 210 here may include a magnetic storage medium and a flash storage medium, as well as a volatile storage device that requires electrical power to retain the stored information. The scope of the present disclosure is not limited thereto.

[0049] The processor 220 can determine the estimated value of the rack force to minimize the error representing the difference between the actual value of the rack force and the estimated value of the rack force, can extract the specific frequency component from the optimally estimated value of the rack force, and can remove the disturbance reflected in the actual value of the rack force by compensating for the specific frequency component from the actual value of the rack force. The actual value of the rack force, as a value resulting from a measurement of a rack force acting on the rack, can include a target value and the disturbance (noise). The disturbance (noise) has the specific frequency component.Therefore, the processor 220 can remove the disturbance reflected in the actual value of the rack force by performing an arithmetic operation in which the specific frequency component corresponding to the disturbance is subtracted from the actual value of the rack force.

[0050] Processor 220 may perform the optimization such that the actual value of the rack force and the estimated value of the rack force match. Optimization here may mean minimizing the error representing the difference between the actual value of the rack force and the estimated value of the rack force. Therefore, processor 220 may perform the optimization such that the difference between the actual value of the rack force and the estimated value of the rack force is zero.

[0051] The operation of the processor 220 will be described with reference to Fig. 3 described.

[0052] Processor 220 may optimize the estimated rack force value by inputting the error, which represents the difference between the actual rack force value and the estimated rack force value, into an optimization module 224. Processor 220 may then extract a vibration component from the optimally estimated rack force value and subtract the extracted vibration component from the actual rack force value in a compensating manner, thereby removing the disturbance reflected in the actual rack force value. The estimated rack force value may be configured as the sum of a linear component and the vibration component, and the vibration component may be a signal with the form of sin and cos.

[0053] With reference to Fig. 3, the processor 220 may input the actual rack force value and the estimated rack force value from the optimization module 224 into a first arithmetic operation module 222 and calculate the error representing the difference between the actual rack force value and the estimated rack force value.

[0054] Once the error is calculated, processor 220 may input the calculated error to optimization module 224, and optimization module 224 may optimize the estimated value of the rack force in the direction of optimizing the error. At this point, optimization module 224 may execute the optimization algorithm in the direction of error minimization and determine the optimal estimated value of the rack force.

[0055] The optimization module 224 can divide the optimally estimated value of the rack force into the linear component and the vibration component, and estimate the linear component and the vibration component. Here, the vibration component can be a signal with the form of sin and cos. A linear value, a sin value, and a cos value can vary in real time, and the optimization can be performed in the direction of increasing the degree of estimation.

[0056] The optimization module 224 may be configured to execute the optimization algorithm and estimate an optimized value of the rack force (the estimated value of the rack force) by applying the optimization algorithm to the error.

[0057] To this end, processor 220 may define an objective function based on the error and apply the optimization algorithm to a gradient of the objective function. At this point, processor 220 may apply various optimization algorithms, such as a conjugate gradient and an accelerated Nesterov gradient (NAG).

[0058] For example, the processor 220 may define the error as in the following equation 1. error=x0+x1∗sin(2∗pi∗f∗t)+x2∗cos(2∗pi∗f∗t) where x0, x1 and x2 are optimization parameters, f is a frequency and t is a time.

[0059] From equation 1 it can be seen that the error is composed of x0, i.e. the linear component, and x1 * sin(2 * pi * f * t) * x2 * cos(2 * pi * f * t) , i.e. the oscillation component.

[0060] The processor 220 may define an objective function (f(x)) as in the following equation 2 based on the error. f(x)=12∗e2 where e represents the error.

[0061] When solving Equation 2, the objective function can be configured as the sum of sin and cos. Since the objective function is configured as the sum of sin and cos, two values ​​of sin and cos can be adjusted respectively, and thus a phase of the estimated value of the rack force can be adjusted as desired.

[0062] The optimization may consist of minimizing the objective function because the error is minimized at a value to minimize the objective function.

[0063] Accordingly, the optimization processor 220 may define the gradient of the objective function as in the following equation 3. Gradient=g=∇f(x)=12∂e2∂x=e∂e∂x

[0064] If the gradient of the objective function is defined as in Equation 3, the processor 220 may perform the optimization using various optimization algorithms, such as a Polak-Ribier max conjugate gradient and a Nesterov accelerated gradient (NAG).

[0065] The maximum conjugate Polak-Ribier gradient can be defined as follows: β=min(0,max(gkT∗(gk−gk−1)gk−1Tgk−1,1)) where β represents a weighted value for a moment effect, g a gradient and k a step.

[0066] Processor 220 may perform an update using the Nesterov Accelerated Gradient (NAG) algorithm. The NAG algorithm may be defined as in Equation 5 below. vk=βvk−1−α∇f(xk+βvk−1)xk=xk−1+vk where v is a moment, x is an optimization parameter and α is a step size.

[0067] In Equation 4, the value of β is limited from 0 to 1. Therefore, convergence can be ensured, and the step size can be updated in a decreasing direction. That is, a tuning parameter can be limited to a step size. If the tuning parameter actually applies to the vehicle, this limitation can provide a high degree of convenience.

[0068] When the optimal estimated value of the rack force is obtained by the optimization module 224, the processor 220 may divide the optimal estimated value of the rack force into the linear component and the vibration component and input the vibration component to a second arithmetic operation module 226.

[0069] The second arithmetic operation module 226 may perform an arithmetic operation of subtracting the input vibration component from the actual value of the rack force and output the result. That is, the second arithmetic operation module 226 may perform the arithmetic operation of subtracting the vibration component from the actual value of the rack force, thus removing the disturbance from the actual value of the rack force.

[0070] Fig. 4 is a flowchart used to describe a method for compensating for a disturbance in a rack force according to a second embodiment of the present disclosure.

[0071] With reference to Fig.4, the processor 220 calculates the error, which represents the difference between the actual value of the rack force and the estimated value of the rack force (S402), and defines the objective function based on the calculated error (S404). At this point, the error can be composed of the linear component and the vibration component, and the objective function can be created based on the error. For example, the objective function can be defined as the square of the error. The objective function is created based on the error. Therefore, the objective function can be formed from the sum of sin and cos.

[0072] When step S404 is executed, the processor 220 performs the optimization in such a manner that a value of the objective function is a minimum value (S406) and estimates the optimized value of the rack force (the estimated value of the rack force) (S408).

[0073] Since minimizing the value of the objective function involves minimizing the error, optimization may involve minimizing an objective function. Accordingly, the optimization processor 220 may apply the optimization algorithm to the gradient of the objective function. When the optimization algorithm is applied to the gradient of the objective function, the processor 220 may obtain the optimal estimated value of the rack force. The optimal estimated value of the rack force may be composed of the linear component and the vibration component.

[0074] When step S408 is executed, the processor 220 extracts the vibration component from the optimally estimated value of the rack force (S410) and performs the arithmetic operation of subtracting the extracted vibration component from the actual value of the rack force (S412). Then, the disturbance reflected in the actual value of the rack force can be removed.

[0075] The rack force disturbance compensation device according to one aspect of the present disclosure and the rack force disturbance compensation method according to another aspect of the present disclosure use the optimization algorithm in this way. Accordingly, a delay is reduced more than when an existing filter is used. Furthermore, the disturbance in a desired frequency band is reduced more effectively than when the existing filter is used. Thus, the delay in the estimated value of the rack force can be minimized while simultaneously eliminating the disturbance in a desired frequency range. As a result, the steering feel can be improved.

Claims

[1] A device (200) for compensating for a disturbance in a rack force, the device comprising: a memory (210); and a processor (220) connected to the memory, wherein the processor obtains an optimally estimated value of a rack force for minimizing an error representing a difference between an actual value of the rack force and the optimally estimated value of the rack force, extracts a specific frequency component from the optimally estimated value of the rack force, and compensates for a disturbance in the actual value of the rack force reflected in the actual value of the rack force by means of the extracted specific frequency component. [2] The apparatus of claim 1, wherein the processor executes an optimization algorithm in the direction of minimizing the error and thus obtaining the optimal estimated value of the rack force. [3] The apparatus of claim 2, wherein the processor defines an objective function based on the error, applies the optimization algorithm to a gradient of the objective function, and thus obtains the optimal estimated value of the rack force. [4] The apparatus according to any one of claims 1 to 3, wherein the optimal estimated value of the rack force has a linear component and a vibration component, and wherein the specific frequency component is a vibration component included in the optimal estimated value of the rack force. [5] The apparatus of claim 4, wherein the processor performs an arithmetic operation of subtracting the vibration component from the actual value of the rack force and thus compensating for the disturbance in the actual value of the rack force. [6] A method for compensating for a disturbance in a rack force, the method comprising Calculating (S402) by a processor an error representing a difference between an actual value of a rack force and an estimated value of the rack force; Obtaining (S408) an optimally estimated value of the rack force by the processor to minimize the error; and Compensating (S412) by the processor for a disturbance reflected in the actual value of the rack force by performing an arithmetic operation of subtracting a specific frequency component included in the optimally estimated value of the rack force from the actual value of the rack force. [7] The method of claim 6, wherein, upon obtaining the optimal estimated value of the rack force by the processor, the processor executes an optimization algorithm in the direction of minimizing the error and thus obtaining the optimal estimated value of the rack force. [8] The method of claim 7, wherein, when the processor obtains the optimal estimated value of the rack force, the processor defines an objective function based on the error, applies the optimization algorithm to a gradient of the objective function, and thus obtains the optimal estimated value of the rack force. [9] A method according to any one of claims 6 to 8, wherein the optimally estimated value of the rack force includes a linear component and a vibration component, and wherein the specific frequency component is a vibration component included in the optimally estimated value of the rack force. [10] The method of claim 9, wherein the processor performs an arithmetic operation in which the vibration component is subtracted from the actual value of the rack force, thus compensating for the disturbance in the actual value of the rack force.

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