System and method for electric power steering

Abstract

An electric power steering system and an electric power steering method are introduced, comprising: a reaction force generating unit including a reaction force motor connected to a steering wheel and providing a steering reaction force to the steering wheel; a steering force generating unit including a steering motor connected to a driving wheel of a vehicle and providing a steering force to the wheel of the vehicle; and a controller that inputs the vehicle speed and the wheel angle into an on-center control function to determine a self-aligning torque, inputs the speed of the steering motor and the torque of the steering motor into an off-center control function to determine a rack-force torque, inputs the self-aligning torque and the rack-force torque into a blending function to determine a blending torque, determines a target torque from the blending torque, and inputs a command torque, which is the difference between the target torque and the steering wheel input torque, to the steering motor.

Description

Technology Field

[0001] The present disclosure relates to an electric power steering system and an electric power steering method that improve the driver's steering feel through a smooth transition between on-center and off-center. Background Technology

[0003] The Steer-by-Wire (SBW) system is a technology that controls a vehicle's steering force using electronic signals instead of mechanical connections. In this system, the steering wheel and steering components are not physically connected; instead, electric devices, such as reaction motors, perform steering via electrical signals. This enables precise steering control and improves the freedom of vehicle design. A key feature of the SBW system is that it electronically replicates the steering sensation felt by the driver, allowing the steering feel to be changed in real time according to driving conditions.

[0004] However, conventional SBW systems had limitations in providing a natural driving experience because their steering feel generation methods were designed separately for on-center and off-center states. While consistent steering feel is required during straight-line driving in the on-center state, a sensitive and immediate response is demanded in the off-center state. Existing technology had the problem of being unable to consistently adjust steering force because it treated these two states separately. As a result, the feedback felt by the driver became inconsistent, which could lead to an unstable steering feel.

[0005] In conventional technology, a problem occurred in that the transition of steering feel between on-center and off-center was not smooth. For example, when the vehicle's lateral acceleration changed, the steering feel did not transition naturally, causing the driver to feel uncomfortable or resulting in reduced maneuverability. Furthermore, the target torque was not well defined in the on-center and off-center states, affecting the vehicle's driving performance and safety. These problems not only degraded the driver's experience but also affected the accuracy of vehicle control.

[0006] A technical approach is required to effectively generate steering feel in SBW systems and enable drivers to receive natural and intuitive feedback. In particular, methods are needed to seamlessly transition steering feel between on-center and off-center states and to adjust target torque according to various driving conditions. This allows drivers to maintain a consistent steering feel in different driving situations, thereby improving the accuracy and safety of vehicle control. This approach can play a crucial role in more efficiently incorporating driver feedback and optimizing the performance of the vehicle's steering system.

[0007] The matters described as background technology above are intended only to enhance understanding of the background of the present disclosure and do not constitute prior art already known to those skilled in the art. The problem to be solved

[0009] The present disclosure is proposed to solve these problems and aims to provide an electric power steering system and an electric power steering method that facilitate the transition of steering feel between on-center and off-center and provide a steering response tailored to driving conditions.

[0010] The technical problems to be solved in this disclosure are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which this invention belongs from the description below. means of solving the problem

[0012] An electric power steering system according to the present disclosure for achieving the above objective may include: a reaction force generating unit comprising a reaction force motor connected to a steering wheel and providing a steering reaction force to the steering wheel; a steering force generating unit comprising a steering motor connected to a driving wheel of a vehicle and providing a steering force to the driving wheel of the vehicle; and a controller that inputs the speed of the vehicle and the angle of the driving wheel into an on-center control function to determine a self-aligning torque, inputs the speed of the steering motor and the torque of the steering motor into an off-center control function to determine a rack-force torque, inputs the self-aligning torque and the rack-force torque into a blending function to determine a blending torque, determines a target torque from the blending torque, and inputs a command torque, which is the difference between the target torque and the steering wheel input torque, to the steering motor.

[0013] In the electric steering system according to the present disclosure, the on-center control function of the controller may be the following formula.

[0014]

[0015]

[0016]

[0017] In the electric steering system according to the present disclosure, the off-center control function of the controller may be the following formula.

[0018]

[0019]

[0020]

[0021]

[0022] In the electric steering system according to the present disclosure, the blending function of the controller may be the following formula.

[0023]

[0024]

[0025]

[0026] The electric power steering system according to the present disclosure comprises the weighting coefficient ( ) is a value greater than or equal to 0 and less than or equal to 1, and the controller, when the lateral acceleration of the vehicle decreases, the weighting coefficient ( Control ) to approach 0, and when the lateral acceleration of the vehicle increases, the weighting coefficient ( ) can be controlled to get closer to 1.

[0027] In the electric steering system according to the present disclosure, the command torque initially input to the steering motor may be the steering wheel input torque.

[0028] The electric power steering system according to the present disclosure can determine the self-aligning torque through the on-center control function when the lateral acceleration of the vehicle is less than or equal to a preset value during driving of the vehicle, and determine the rack force torque through the off-center control function when the lateral acceleration of the vehicle exceeds the preset value.

[0029] The electric steering system according to the present disclosure can determine the steering wheel input torque by the sum of the torque generated by the driver's operation of the steering wheel and the torque by the reaction motor, and transmit the determined steering wheel input torque to the controller.

[0030] The electric power steering system according to the present disclosure comprises a controller that determines the target torque from the blending torque according to a target table, wherein the target torque increases non-linearly as the blending torque increases, and the target torque may increase as the speed of the vehicle increases at a constant blending torque.

[0031] The electric steering system according to the present disclosure comprises, wherein the steering force generating unit includes a wheel angle sensor, and the controller can input the angle of the driving wheel determined by the wheel angle sensor into the on-center control function.

[0032] An electric steering method according to the present disclosure comprises: determining a self-aligning torque by inputting the speed of a vehicle and the angle of a driving wheel into an on-center control function in a controller; determining a rack-force torque by inputting the speed of a steering motor that provides steering force to the driving wheel of the vehicle and the torque of the steering motor into an off-center control function in the controller; determining a blending torque by inputting the self-aligning torque and the rack-force torque into a blending function in the controller; determining a target torque from the blending torque in the controller; determining a command torque through the difference between the target torque and the steering wheel input torque in the controller; and controlling the steering motor based on the command torque in the controller.

[0033] In the electric steering method according to the present disclosure, when determining the self-aligning torque, the on-center control function of the controller may be the following formula.

[0034]

[0035]

[0036]

[0037] In the electric steering method according to the present disclosure, when determining the rack force torque, the off-center control function of the controller may be the following formula.

[0038]

[0039]

[0040]

[0041]

[0042] In the electric steering method according to the present disclosure, when determining the blending torque, the blending function of the controller may be the following formula.

[0043]

[0044]

[0045]

[0046] The electric steering method according to the present disclosure, when determining the blending torque, the weighting coefficient ( ) is a value greater than or equal to 0 and less than or equal to 1, and the controller, when the lateral acceleration of the vehicle decreases, the weighting coefficient ( Control ) to approach 0, and when the lateral acceleration of the vehicle increases, the weighting coefficient ( ) can be controlled to get closer to 1.

[0047] In the electric steering method according to the present disclosure, when the command torque is input to the steering motor, the controller may determine the steering wheel input torque as the command torque that is initially input to the steering motor.

[0048] In the electric steering method according to the present disclosure, when determining the self-aligning torque or determining the rack force torque, the controller can determine the self-aligning torque through the on-center control function when the lateral acceleration of the vehicle during driving is less than or equal to a preset value, and determine the rack force torque through the off-center control function when the lateral acceleration exceeds a preset value.

[0049] In the electric steering method according to the present disclosure, when determining the command torque, the controller can determine the steering wheel input torque as the sum of the torque generated by the driver's operation of the steering wheel and the torque provided by a reaction motor connected to the steering wheel and providing a steering reaction force to the steering wheel.

[0050] In the electric steering method according to the present disclosure, when determining the target torque, the controller determines the target torque from the blending torque according to a target table, wherein the target torque increases non-linearly as the blending torque increases, and the target torque can increase as the speed of the vehicle increases at a constant blending torque.

[0051] In the electric steering method according to the present disclosure, when determining the self-alignment torque, the driving wheel of the vehicle is connected to a wheel angle sensor, and the controller can input the angle of the driving wheel determined by the wheel angle sensor into the on-center control function. Effects of the invention

[0053] According to the electric power steering system and electric power steering method of the present disclosure, the steering feel of the driver can be improved naturally and intuitively by providing appropriate feedback in on-center and off-center states, and driving stability and operability can be improved by making the transition of steering feel smooth.

[0054] The effects obtainable from the present disclosure are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present disclosure belongs from the description below. Brief explanation of the drawing

[0056] FIG. 1 is a diagram showing the configuration of an electric steering system of the present disclosure according to one embodiment. FIG. 2 is a block diagram of a controller of an electric steering system shown in FIG. 1 of the present disclosure according to one embodiment. FIG. 3 is a graph showing a graph for obtaining the target torque of a controller of an electric power steering system illustrated in FIG. 1 of the present disclosure according to one embodiment. FIG. 4 is a flowchart showing the flowchart of an electric steering method of the present disclosure according to one embodiment. Specific details for implementing the invention

[0057] In describing the embodiments disclosed in this specification, detailed descriptions of related prior art are omitted if it is determined that such detailed descriptions may obscure the essence of the embodiments disclosed in this specification. Furthermore, the attached drawings are intended only to facilitate understanding of the embodiments disclosed in this specification, and the technical concept disclosed in this specification is not limited by the attached drawings; it should be understood that they include all modifications, equivalents, and substitutions that fall within the spirit and technical scope of this disclosure. The disclosure below is not intended to limit this disclosure to the described form or specific field, and it is considered that various alternative modes and modifications to this disclosure are possible, whether explicitly stated or implied in this specification. Those skilled in the art will recognize that the form and details of this disclosure may change.

[0058] The present disclosure is described with reference to specific embodiments. However, as understood by those skilled in the art to which the present disclosure pertains, the various embodiments disclosed herein may be modified or otherwise implemented in various other ways without departing from the spirit and scope of the present disclosure. Accordingly, the following description should be considered illustrative and is intended to teach those skilled in the art to the manner in which various embodiments are made and used. It will be understood that the forms of the disclosure shown and described herein are to be taken as representative embodiments. Equivalent elements, or materials, processes, or steps may be substituted for those representatively exemplified and described in the present disclosure. Expressions used in describing the present disclosure, such as "including," "comprising," "incorporating," "consisting of," "have," "is," etc., should be interpreted as allowing items, components, or elements not explicitly described to be indicated in a non-exclusive manner, i.e., to be indicated. In addition, references to the singular should be interpreted as including those related to the plural.

[0059] Furthermore, the various embodiments disclosed herein should be accepted as illustrative and descriptive and should not be interpreted as limiting the content of the disclosure. All references to joining (e.g., attached, affixed, coupled, connected, etc.) are used solely to aid in understanding the disclosure and are not intended to limit the location, orientation, or use of the configuration or the methods disclosed herein. Accordingly, where joining references exist, they should be interpreted broadly. Moreover, in such joining references, it is not assumed that two or more elements are directly connected to each other. Additionally, all numeric terms, e.g., "first," "second," "third," "primary," "secondary," "major," or any other general or numeric terms, are to be taken solely as identifiers to aid in understanding the various components, forms, variations, or modifications of the present disclosure and are not to imply any limitation to any component, form, variation, or modification, or to any order or preference thereof. That is, while such expressions may be used to describe various components, the components are not limited by such expressions. Such expressions are used solely for the purpose of distinguishing one component from another.

[0060] The suffixes "module" and "part" used for components in the following description are assigned or used interchangeably solely for the ease of drafting the specification, and do not inherently possess distinct meanings or roles.

[0061] When it is stated that one component is "connected" or "connected" to another component, it should be understood that while it may be directly connected or connected to that other component, there may also be other components in between. On the other hand, when it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0062] Furthermore, the terms "Unit" or "Control Unit" included in the name are merely terms widely used to name controllers that control specific vehicle functions, and do not refer to generic function units.

[0063] A controller may include a communication device that communicates with other controllers or sensors to control the function it is responsible for, a memory that stores an operating system, logic instructions, and input / output information, and one or more processors that perform judgments, calculations, decisions, etc., necessary for controlling the function it is responsible for.

[0064] Any number of components or various components in any configuration described herein may be included within the disclosure described herein. Components may include any combination of features described herein and may be arranged in any configuration among the various configurations described herein. Concepts regarding the structure and arrangement of the components of the disclosure, as well as their use and operation, may be applied to any number of embodiments in any combination, as well as to specific embodiments discussed herein. Embodiments including those having various features of various arrangements are described below with reference to the drawings.

[0066] FIG. 1 is a diagram showing the configuration of an electric power steering system according to one embodiment of the present disclosure, FIG. 2 is a diagram showing the block diagram of the controller of the electric power steering system shown in FIG. 1 according to one embodiment of the present disclosure, FIG. 3 is a diagram showing a graph for obtaining the target torque of the controller of the electric power steering system shown in FIG. 1 according to one embodiment of the present disclosure, and FIG. 4 is a diagram showing the flowchart of an electric power steering method according to one embodiment of the present disclosure.

[0067] Hereinafter, various embodiments disclosed in this specification will be described in detail with reference to the attached drawings. Identical or similar components are given the same reference number regardless of the drawing symbols, and redundant descriptions thereof will be omitted.

[0069] Steer-by-Wire (SBW) systems are a technology that controls a vehicle's steering force using electronic signals instead of mechanical connections, enhancing precise steering control and design freedom. However, existing SBW systems have limitations in how they generate steering feel between on-center and off-center states; consequently, steering force adjustment between the two states is inconsistent, and unstable feedback control can cause driver discomfort. In particular, the transition in steering feel with changes in lateral acceleration is unnatural, and the lack of defined target torque has impacted driving performance and safety. Therefore, a technical approach is required to smooth the transition in steering feel between on-center and off-center states and to adjust target torque according to driving conditions. Through this, drivers can maintain a consistent steering feel while improving the vehicle's control performance and safety.

[0070] To solve these problems, the present disclosure proposes an electric power steering system and an electric power steering method that facilitate the transition of steering feel between on-center and off-center and provide a steering response tailored to driving conditions.

[0072] Specifically, the electric steering system of the present disclosure will be described with reference to FIG. 1.

[0073] In one embodiment, the electric power steering system may be composed of a reaction force generating unit (300), a steering force generating unit (500), and a controller (700). As shown in FIG. 1, the reaction force generating unit (300) may be mechanically connected to the steering wheel (100) of the vehicle, and the steering force generating unit (500) may be mechanically connected to the driving wheel (900) of the vehicle. Additionally, the reaction force generating unit (300) and the steering force generating unit (500) are each connected to communicate with the controller (700), so that the controller (700) can control electric power steering between the reaction force generating unit (300) and the steering force generating unit (500).

[0074] In one embodiment, the reaction force generating unit (300) may include a reaction force motor (320), and the reaction force motor (320) is connected to the steering wheel (100) and can provide steering reaction force to the steering wheel (100). In addition, the steering force generating unit (500) may include a steering motor (520), and the steering motor (520) is connected to the driving wheel (900) of the vehicle and can provide steering force to the driving wheel (900) of the vehicle.

[0075] In one embodiment, the controller (700) derives a self-aligning torque and a rack force torque, and can derive a blending torque by blending the derived self-aligning torque and the rack force torque. The controller (700) determines a target torque through the blending torque and can input a command torque, which is the difference between the steering wheel (100) torque determined by the reaction force generating unit (300) and the target torque, to the steering motor (520).

[0076] In one embodiment, the self-aligning torque can be determined by inputting the vehicle speed and the angle of the driving wheel (900) into the on-center control function (720), and the rack-force torque can be determined by inputting the speed of the steering motor (520) and the torque of the steering motor (520) into the off-center control function (740). Additionally, the self-aligning torque and the rack-force torque can be input into the blending function (760) to determine the blending torque, and the blending torque can be input into the target table (780) to determine the target torque. The command torque can be defined as the difference between the target torque and the steering wheel (100) input torque, and the command torque can be input to the steering motor (520). Subsequently, feedback control can be performed by inputting the torque and speed of the steering motor (520), to which the command torque has been input, back into the off-center control function (740).

[0077] In one embodiment, a target table (780) may be used as described above to obtain the target torque, but this table (780) can be tuned in various ways as a tuned value. In addition, the user can set the desired level of target torque by tuning with formulas such as functions or graphs in addition to the table (780). However, for the sake of understanding, the target table (780) is used as an example for the following explanation, and FIG. 3 can be understood as illustrating an example of a graph that can be formed according to the target table (780).

[0078] In one embodiment, unlike as illustrated in FIG. 1, the reaction force generating unit (300) and the steering force generating unit (500) may be physically connected to each other. In this case, the reaction force generating unit (300) can detect the force of the driver steering the steering wheel (100), receive the steering angle of the driver's steering wheel (100) as input, convert it into an electrical signal, and transmit it to the steering force generating unit (500) which adjusts the wheel angle of the vehicle.

[0079] In one embodiment, the SBW system may be a system that controls the steering wheel (100) without physical connections between devices, unlike conventional steering systems. That is, instead of conventional mechanical link or pinion systems, reaction force and steering force can be generated by electrical control. For example, the steering wheel (100) may be connected to the electric steering system of the present disclosure through a steering column. In the SBW system, since the connection is made electrically without physical links, the torque generated by the steering wheel (100) is transmitted to the reaction force generating unit (300), allowing the reaction force to be physically felt.

[0080] In one embodiment, the reaction force generating unit (300) may include a reaction force motor (320). Accordingly, when power is supplied to the reaction force motor (320), the rotor of the reaction force motor (320) rotates and can apply torque to the steering column. This torque can be converted into a force felt by the driver at the steering wheel (100). Additionally, the reaction force generating unit (300) can transmit an appropriate reaction force to the driver in response to an external force, such as a force transmitted from the road to the driving wheel (900) through the electric steering system of the present disclosure.

[0081] In one embodiment, the steering force generating unit (500) can be implemented in various ways, such as a rack and pinion method. Accordingly, the pinion gear can be connected to the rotor of the steering motor (520) of the steering force generating unit (500). Thus, power is supplied to the steering motor (520), and as the rotor of the steering motor (520) rotates, the rack is moved, thereby allowing the vehicle driving wheel (900) to be steered.

[0082] In one embodiment, in the case of a conventional mechanical steering system, the movement of the rack gear is sequentially transmitted to the steering claw and steering wheel (100) through the pinion gear, allowing the driver to feel the reaction force. However, in an SBW system as disclosed herein, since there is no physical connection, this can be implemented virtually. To this end, the reaction force generating unit (300) can transmit the steering wheel (100) input torque, which is determined by the sum of the torque generated by the driver's operation and the torque by the reaction force motor (320), to the controller (700). Additionally, the steering force generating unit (500) includes a wheel angle sensor (540) and can transmit the angle of the driving wheel (900) determined by the wheel angle sensor (540) to the controller (700).

[0083] In one embodiment, the reaction force generating unit (300) is connected to the steering wheel (100) and may include a reaction force motor (320) that receives the steering angle of the steering wheel (100) and provides a steering reaction force to the steering wheel (100). For example, the reaction force generating unit (300) may be a Steering Force Actuator (SFA) configured to electronically control the steering of the vehicle in a Steer-By-Wire (SBW) system. Accordingly, the reaction force generating unit (300) can generate a reaction force when the driver steers. This helps the driver intuitively feel the road surface condition or the vehicle's motion state. For example, it can serve to naturally transmit the vehicle's inertia on irregular surfaces or curves of the road. The reaction force generated by this reaction force generating unit (300) may be generated by the reaction force motor (320).

[0084] In one embodiment, the reaction force generating unit (300) can not only simply transmit a signal for the driver to operate the steering wheel (100), but also generate a reaction force so that the driver can receive appropriate steering feedback according to the road surface condition. For example, the driver can naturally feel the road condition by providing more reaction force when the vehicle turns a curve or less reaction force when driving in a straight line.

[0085] In one embodiment, the reaction force generating unit (300) uses parts that are simplified compared to a conventional mechanical steering system, thereby achieving vehicle weight reduction, and since it can be electronically controlled, more freedom can be given in designing the vehicle's steering system. In addition, the steering angle can be controlled very precisely and accurately through an electronically controlled steering system compared to a mechanical steering system, thereby providing safe vehicle driving to the driver.

[0087] In one embodiment, the steering force generating unit (500) may include a steering motor (520) that is connected to the driving wheel (900) of the vehicle and provides steering force to the driving wheel (900) of the vehicle. For example, the steering force generating unit (500) may be a Road Wheel Actuator (RWA) that performs the role of adjusting the wheel angle in an SBW system. The steering force generating unit (500) replaces the steering mechanism found in conventional steering systems to electronically control the angle of the driving wheel (900) of the vehicle, and through this process, can accurately adjust the steering direction of the vehicle.

[0088] In one embodiment, the steering force generating unit (500) can set the angle of the vehicle's driving wheel (900) based on steering angle information transmitted from the reaction force generating unit (300) to the controller (700) by the driver. This control is performed electronically by receiving a control signal from the controller (700), and can accurately set the target angle of the driving wheel (900) so that the vehicle can drive in the desired direction. In this case, the steering force generating unit (500) can control the position of the driving wheel (900) using a steering motor (520) and adjust the angle of the driving wheel (900) by detecting changes in real time. Therefore, in addition to the described steering motor (520), additional components such as a servo motor or a sensing sensor may be added to the steering force generating unit (500) as needed.

[0089] In one embodiment, the steering force generating unit (500) electronically adjusts the wheel angle, unlike a conventional mechanical steering system, so it can correct position errors in real time and enable precise position control. Specifically, the controller can monitor the wheel angle and status of the vehicle in real time and transmit this information to the steering force generating unit (500) to perform feedback control. In addition, unlike a conventional steering system, the steering force generating unit (500) does not affect the wheel angle according to the force of the steering wheel (100) or the condition of the road surface, so it can provide the driver with a constant and predictable steering sensation.

[0090] In one embodiment, since the steering force generating unit (500) is electronically controlled, precise and rapid control is possible, and, like the reaction force generating unit (300), more freedom can be given to the design of the vehicle. In addition, there is an advantage that it can provide the driver with a predictable and consistent steering sensation by being relatively less affected by external shocks or the environment and minimizing vibrations or shaking.

[0092] Next, the controller (700) of the present disclosure will be described with reference to FIG. 2.

[0093] In one embodiment, the controller (700) can determine the self-alignment torque through the on-center control function (720), and the on-center control function (720) may be as follows.

[0094]

[0095]

[0096]

[0098] In one embodiment, the controller (700) can determine the rack post torque through the off-center control function (740), and the off-center control function (740) may be as follows.

[0099]

[0100]

[0101]

[0102]

[0103] In one embodiment, the rack force torque can be defined as the torque applied to the rotation axis of the pinion driven part by the rack force applied to the rack gear.

[0105] In one embodiment, the controller (700) can calculate a blending torque to obtain a target torque by inputting the self-aligning torque calculated through the on-center control function (720) and the rack force torque calculated through the off-center control function (740) into the blending function (760). The blending function (760) may be as follows.

[0106]

[0107]

[0108]

[0109] In one embodiment, weighting coefficients ( ) is a value greater than or equal to 0 and less than or equal to 1; it approaches 0 when the vehicle's lateral acceleration decreases and may approach 1 when the vehicle's lateral acceleration increases. For example, the weighting coefficient ( ) can change to 0 when the lateral acceleration is 1 m / s² or less, and to 1 when it exceeds 1 m / s². This can be controlled by the controller (700). That is, when the vehicle changes direction quickly or makes a sharp turn while driving on a curve, the weighting coefficient ( ) can be 1. Also, weight coefficients ( ) can change within 0.5 seconds. For example, if the lateral acceleration suddenly increases as the vehicle enters a curve, the weighting coefficient ( ) must change quickly from 0 to 1, and this time can be set to take 0.5 seconds. However, 0.5 seconds is merely an example, and it can be tuned to change faster or slower than 0.5 seconds to suit various environments. By tuning in this way, the weight coefficients ( Since ) changes gradually, even if a rapid change in acceleration occurs, the weighting coefficient ( You can prevent ) from changing suddenly.

[0110] In one embodiment, the command torque initially input to the steering motor (520) may be the steering wheel (100) input torque. Specifically, the steering wheel (100) input torque is input to the steering motor (520), and the steering motor (520) characteristic values, such as the torque and speed of the steering motor (520) output based on this, are sequentially input to the on-center control function (720), the off-center control function (740), the blending function (760), and the target table (780) to derive the target torque. Then, the difference between the target torque and the steering wheel (100) input torque can be calculated and input to the steering motor (520) as a new command torque.

[0111] In one embodiment, the controller (700) can determine the self-aligning torque through the on-center control function (720) when the lateral acceleration of the vehicle during driving is less than or equal to a preset value, and can determine the rack-force torque through the off-center control function (740) when the lateral acceleration of the vehicle exceeds a preset value. For example, if the lateral acceleration of the vehicle is less than or equal to 1 m / s², it is determined that it is on-center and the self-aligning torque is determined, and if the lateral acceleration of the vehicle exceeds 1 m / s², it is determined that it is off-center and the rack-force torque is determined.

[0112] In one embodiment, the reaction force generating unit (300) can transmit the steering wheel (100) input torque to the controller (700). At this time, the steering wheel (100) input torque can be determined as the sum of the torque generated by the driver's operation and the torque generated by the reaction force motor (320). Specifically, the torque generated by the driver's force acts in the direction of rotating the steering wheel (100), and the torque generated by the reaction force motor (320) can generate torque in the opposite direction to the driver's force. For example, when the driver turns the steering wheel (100) to the left, the driver's hand applies force in the left direction, and this force can generate torque on the steering wheel (100). In this case, the reaction force motor (320) can generate torque by acting in the opposite direction, to the right.

[0113] In one embodiment, the steering force generating unit (500) may include a wheel angle sensor (540), and the wheel angle sensor (540) may sense the current angle of the vehicle's driving wheel (900). The controller (700) may input the angle of the wheel determined by the wheel angle sensor (540) into the on-center control function (720).

[0115] Referring to Fig. 3, the method for obtaining the target torque will be explained.

[0116] In one embodiment, the target table (780) of the controller (700) may be as shown in the graph in FIG. 3. In the graph in FIG. 3, the X-axis may be the blending torque and the Y-axis may be the target torque. Accordingly, as the blending torque increases, the target torque may also show a tendency to increase, and when the blending torque exceeds a certain level, the rate of increase may slow down. Additionally, the target torque may show a tendency to increase as the vehicle speed increases. However, this is merely an exemplary table, and various forms of target tables, functions, graphs, etc., may be applied depending on the actual applied model or environment.

[0118] Next, the electric steering method of the present disclosure will be described with reference to FIG. 4. However, in the electric steering method, any content that overlaps with the electric steering system mentioned above will be replaced by the content of the electric steering system.

[0119] In one embodiment, the electric steering method of the present disclosure may be composed of a step of determining a self-aligning torque (S110), a step of determining a rack force torque (S120), a step of determining a blending torque (S130), a step of determining a target torque (S140), a step of determining a command torque (S150), and a step of controlling a steering motor based on the command torque (S160).

[0120] In one embodiment, in the step of determining the self-aligning torque (S110), the controller (700) can determine the self-aligning torque by inputting the vehicle speed and the angle of the driving wheel (900) into the on-center control function (720). Then, in the step of determining the rack force torque (S120), the controller (700) can determine the rack force torque by inputting the speed of the steering motor (520) and the torque of the steering motor (520) into the off-center control function (740), and in the step of determining the blending torque (S130), the controller (700) can determine the blending torque by inputting the self-aligning torque and the rack force torque into the blending function (760). In the step of determining the target torque (S140), the controller (700) can determine the target torque by inputting the blending torque into the target table (780); in the step of determining the command torque (S150), the controller can determine the command torque through the difference between the target torque and the steering wheel input torque; and in the step of controlling the steering motor based on the command torque (S160), the controller (700) can control the steering motor (520) based on the command torque.

[0121] In one embodiment, in the step (S110) of determining the self-alignment torque, the on-center control function (720) of the controller (700) may be as follows.

[0122]

[0123]

[0124]

[0126] In one embodiment, in the step (S120) of determining the rack post torque, the off-center control function (740) of the controller (700) may be as follows.

[0127]

[0128]

[0129]

[0130]

[0132] In one embodiment, in the step (S130) of determining the blending torque, the blending function (760) of the controller (700) may be as follows.

[0133]

[0134]

[0135]

[0136] In one embodiment, in the step (S130) of determining the blending torque, the weighting coefficient ( ) is a value greater than or equal to 0 and less than or equal to 1, and may approach 0 when the vehicle's lateral acceleration decreases and approach 1 when the vehicle's lateral acceleration increases.

[0137] In one embodiment, the command torque initially input to the steering motor (520) in the step of determining the command torque (S150) may be the steering wheel (100) input torque. Specifically, the steering wheel (100) input torque is input to the steering motor (520), and the steering motor (520) characteristic values ​​such as the torque and speed of the steering motor (520) output based thereon are input to the on-center control function (720) to determine the self-aligning torque (S110); the rack force torque is input to the off-center control function (740) to determine the rack force torque (S120); the blending torque is determined through the blending function (760) (S130); and the target torque is determined by sequentially inputting to the target table (780) (S140). The process can then proceed to the step of calculating the difference between the target torque and the steering wheel input torque and determining it as a new command torque (S150), and the step of controlling the steering motor based on the command torque (S160).

[0138] In one embodiment, the controller (700) can determine the self-alignment torque through the on-center control function (720) in the step (S110) of determining the self-alignment torque when the lateral acceleration of the vehicle during driving is less than or equal to a preset value, and can determine the rack-force torque through the off-center control function (740) when the lateral acceleration of the vehicle during driving exceeds a preset value. For example, the controller (700) can determine the self-alignment torque through the on-center control function (720) in the step (S110) of determining the self-alignment torque when the lateral acceleration of the vehicle is less than or equal to 1 m / s² and determine the rack-force torque through the off-center control function (740) in the step (S120) of determining the rack-force torque when the lateral acceleration of the vehicle is greater than or equal to 1 m / s² and determine the rack-force torque when determining the off-center state.

[0139] In one embodiment, in the step (S150) of determining the command torque, the controller (700) can determine the steering wheel (100) input torque as the sum of the torque generated by the driver's operation and the torque from the reaction motor (320) which is connected to the steering wheel (100), receives the steering angle of the steering wheel (100), and provides a steering reaction force to the steering wheel (100).

[0140] In one embodiment, in the step (S140) of determining the target torque, the target torque in the target table (780) may increase non-linearly as the blending torque increases, and the target torque may increase as the vehicle speed increases at a constant blending torque value.

[0141] In one embodiment, in the step (S110) of determining the self-alignment torque, the driving wheel (900) of the vehicle is connected to a wheel angle sensor, and the controller (700) can input the angle of the driving wheel (900) determined by the wheel angle sensor into the on-center control function (720).

[0143] Although specific embodiments of the present disclosure have been illustrated and described, it is obvious to those skilled in the art that the present disclosure may be modified and changed in various ways without departing from the technical spirit of the present disclosure as provided by the following claims. Explanation of the symbols

[0146] 100 : Steering wheel 300 : Reaction force generating part 320 : Reaction motor 500 : Steering force generating unit 520 : Steering motor 540 : Wheel angle sensor 700 : Controller 720 : On-center control function 740 : Off-center control function 760 : Blending function 780 : Target Table 900 : Driving wheel

Claims

Claim 1 An electric power steering system comprising: a reaction force generating unit including a reaction force motor connected to a steering wheel and providing a steering reaction force to the steering wheel; a steering force generating unit including a steering motor connected to a driving wheel of a vehicle and providing a steering force to the driving wheel of the vehicle; and a controller that inputs the speed of the vehicle and the angle of the driving wheel into an on-center control function to determine a self-aligning torque, inputs the speed of the steering motor and the torque of the steering motor into an off-center control function to determine a rack force torque, inputs the self-aligning torque and the rack force torque into a blending function to determine a blending torque, determines a target torque from the blending torque, and inputs a command torque, which is the difference between the target torque and the steering wheel input torque, to the steering motor. Claim 2 An electric steering system according to claim 1, wherein the on-center control function of the controller is the following formula. Claim 3 An electric steering system according to claim 1, wherein the off-center control function of the controller is the following formula. Claim 4 An electric steering system according to claim 1, wherein the blending function of the controller is the following formula. Claim 5 In claim 4, the weighting coefficient ( ) is a value greater than or equal to 0 and less than or equal to 1, and the controller, when the lateral acceleration of the vehicle decreases, the weighting coefficient ( Control ) to approach 0, and when the lateral acceleration of the vehicle increases, the weighting coefficient ( An electric power steering system that controls ) to approach 1. Claim 6 An electric power steering system according to claim 1, wherein the command torque initially input to the steering motor is the steering wheel input torque. Claim 7 An electric power steering system according to claim 1, wherein the controller determines the self-aligning torque through the on-center control function when the lateral acceleration of the vehicle is less than or equal to a preset value during driving of the vehicle, and determines the rack force torque through the off-center control function when the lateral acceleration of the vehicle exceeds the preset value. Claim 8 An electric power steering system according to claim 1, wherein the reaction force generating unit determines the steering wheel input torque as the sum of the torque generated by the driver's operation of the steering wheel and the torque by the reaction force motor, and transmits the determined steering wheel input torque to the controller. Claim 9 An electric power steering system according to claim 1, wherein the controller determines the target torque from the blending torque according to the target table, wherein the target torque increases non-linearly as the blending torque increases, and the target torque increases as the speed of the vehicle increases at a constant blending torque. Claim 10 An electric steering system according to claim 1, wherein the steering force generating unit includes a wheel angle sensor, and the controller inputs the angle of the driving wheel determined by the wheel angle sensor into the on-center control function. Claim 11 An electric steering method comprising: determining a self-aligning torque by inputting the speed of a vehicle and the angle of a driving wheel into an on-center control function in the controller; determining a rack-force torque by inputting the speed of a steering motor providing steering force to the driving wheel of the vehicle and the torque of the steering motor into an off-center control function in the controller; determining a blending torque by inputting the self-aligning torque and the rack-force torque into a blending function in the controller; determining a target torque from the blending torque in the controller; determining a command torque through the difference between the target torque and the steering wheel input torque in the controller; and controlling the steering motor based on the command torque in the controller. Claim 12 An electric steering method according to claim 11, wherein when determining the self-aligning torque, the on-center control function of the controller is the following formula. Claim 13 An electric steering method according to claim 11, wherein when determining the rack force torque, the off-center control function of the controller is the following formula. Claim 14 An electric steering method according to claim 11, wherein when determining the blending torque, the blending function of the controller is the following formula. Claim 15 In claim 14, when determining the blending torque, the weighting coefficient ( ) is a value greater than or equal to 0 and less than or equal to 1, and the controller, when the lateral acceleration of the vehicle decreases, the weighting coefficient ( Control ) to approach 0, and when the lateral acceleration of the vehicle increases, the weighting coefficient ( An electric steering method that controls ) to approach 1. Claim 16 An electric steering method according to claim 11, wherein when the command torque is input to the steering motor, the controller determines the steering wheel input torque as the command torque initially input to the steering motor. Claim 17 An electric steering method according to claim 11, wherein when determining the self-aligning torque or when determining the rack force torque, the controller determines the self-aligning torque through the on-center control function when the lateral acceleration of the vehicle during driving is less than or equal to a preset value, and determines the rack force torque through the off-center control function when the lateral acceleration exceeds a preset value. Claim 18 An electric steering method according to claim 17, wherein when determining the command torque, the controller determines the steering wheel input torque as the sum of the torque generated by the driver's operation of the steering wheel and the torque from a reaction motor connected to the steering wheel and providing a steering reaction force to the steering wheel. Claim 19 An electric steering method according to claim 11, wherein when determining the target torque, the controller determines the target torque from the blending torque according to a target table, wherein the target torque increases non-linearly as the blending torque increases, and the target torque increases as the speed of the vehicle increases at a constant blending torque. Claim 20 An electric steering method according to claim 11, wherein when determining the self-alignment torque, the driving wheel of the vehicle is connected to a wheel angle sensor, and the controller inputs the angle of the driving wheel determined by the wheel angle sensor into the on-center control function.

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