Independent four-wheel steering device and control method therefor

Abstract

A control device for independent four-wheel steering, comprising: a load estimation module (130) configured to calculate an estimated load amount (T̂) by receiving a value detected and reported back by a sensor module arranged in a steering module (120); and a processor (110) configured to calculate an output value enabling an actual steering angle (θ) to follow a steering angle reference (θ_ref) received from an autonomous driving module, which is a higher-level control unit, based on the steering angle reference (θ_ref), a value returned by the sensor module, and a value input by the load estimation module (130), and outputting the output value to the steering module (120), characterized in that the load estimation module (130) also estimates a steering angle velocity, onto which a steering angle velocity error (ω error) is reflected, and a current value, onto which a current error is reflected.

Description

BACKGROUND

[0001] The present invention relates to a control device for an independent four-wheel steering system according to the preamble of claim 1 and to a control method for an independent four-wheel steering system according to the preamble of claim 7.

[0002] Exemplary embodiments of the present disclosure relate to an independent four-wheel steering device and a control method therefor, and in particular to an independent four-wheel steering device having a structure by which the independent four-wheel steering device can perform stable driving control by estimating and compensating for an accidental external load (or external force) or friction during the driving of a vehicle, and a control method therefor.

[0004] BACKGROUND DISCUSSION

[0003] In general, an independent four-wheel steering device of a vehicle (e.g., an autonomous vehicle) performs position control (i.e., position control for independent steering of four wheels) by receiving a position control reference from an autonomous driving module.

[0004] In order to properly perform position control, it is therefore necessary to implement suitable compensation output control via a random external load or friction.

[0005] In this case, a typical controller (e.g., a proportional-integral differential controller (PID controller)) of a typically used steering device does not have a compensation output function for an external load or friction.

[0006] Therefore, such a typical controller without a compensation function for external load or friction has only limited control performance.

[0007] Accordingly, for the use of the typical control unit in an autonomous vehicle, a function (or algorithm or device) capable of performing a compensating output control function for external load or friction must be added separately.

[0008] Furthermore, a function (or algorithm or device) must be added that enables a steering device to perform continuous position control through compensation output control for external load or friction, even in the event of a current sensor failure.

[0009] Background information for the present disclosure is disclosed in Korean patent KR 10 2 373 870 B1 (published on March 8, 2022, entitled “Road surface condition detection device of an electric steering device and control method therefor”).

[0010] A control device for a steering device is known from DE 10 2017 119 605 A1.

[0011] From DE 10 2017 108 692 A1, a control device for a steering system is known. The document discloses that a load (rack load) is estimated based on system information, such as vehicle speed, engine position, and engine speed (angular velocity). Current and / or future system states can be estimated based on the rack load and a mass model.

[0012] German patent DE 10 2021 130 555 A1 discloses a method for estimating the angular / velocity / acceleration capacity of a steering wheel for an autonomous driving system of a vehicle in real time. The method uses a modeled, state-based estimation of the steering motor capacity and the steering rack force under a variety of vehicle operating conditions.

[0013] From the generic patent US 2022 / 0 144 336 A1, a device and a method for a motor-driven power steering system are known. The device for controlling a motor-driven power steering system includes a steering angle position controller configured to control a steering angle by adjusting a gain value based on a steering angle error between a target steering angle input from an autonomous driving system and the actual steering angle. The device includes a current controller configured to compensate for a current error between a second command current output by the steering angle position controller and a sensor current.The device includes a noise estimator configured to estimate noise due to an external factor, pre-remove the estimated noise from a third command stream output by the current controller, and apply the noise-free third command stream to an MDPS.

[0014] US Patent 4,657,102 A discloses an all-wheel steering device for a vehicle. It discloses that the steering angle characteristic of the rear wheels relative to the steering angle of the front wheels is modified according to the vehicle speed. At very low vehicle speeds, the steering angle of the rear wheels is held at zero if the steering angle of the front wheels is less than a predetermined value, and reduced to less than zero if the steering angle of the front wheels exceeds the predetermined value. At very low vehicle speeds, the rear wheels are not turned until the front wheels have turned by at least a predetermined angle, and they are turned in the opposite direction to the front wheels when the front wheels have turned by an angle greater than the predetermined angle.

[0015] Various embodiments relate to an independent four-wheel steering device with a structure by which the independent four-wheel steering device can perform stable driving control by estimating and compensating for a random external load (or external force) or friction during the driving of a vehicle, and to a control method for this.

[0016] The aforementioned problem is solved by a device according to claim 1 and a method according to claim 7. Advantageous embodiments are described in the dependent claims.

[0017] According to one embodiment, an independent four-wheel steering device comprises: a load estimation module configured to calculate an estimated load amount by receiving a value detected and fed back from a sensor module located in a steering module; and a processor configured to calculate an output value to enable an actual steering angle to follow a steering angle reference received from an autonomous driving module, which is a higher-level control unit, based on the steering angle reference, a value fed back from the sensor module, and a value input from the load estimation module, and outputting the output value to the steering module.

[0018] The load estimation module also estimates a steering angle velocity, which is the basis for a steering angle velocity error, and a current value, which is the basis for a current error.

[0019] The value returned by the sensor module to the load estimation module can include the actual steering angle and steering angle speed.

[0020] The processor can establish a steering angle velocity reference value by using an actual steering angle velocity reported back by the sensor module or a steering angle velocity estimated by the load estimation module to calculate the output value to be sent to the steering module.

[0021] The processor can establish a current reference value using an actual current value reported back by the sensor module or a current value estimated by the load estimation module to calculate the output value to be sent to the steering module.

[0022] The processor can set a steering angle velocity reference value and a current reference value where the error between a reference value and an actual value is 0.

[0023] The processor can calculate the output value to be sent to the steering module using the following equation 1: u=−K1*Theta_error−K2*Omega_error−K3*Current_error−Omega_ref*Kb+Current_ref*R−Current_ref*L where K t denotes a motor constant, R an electrical resistance, L an inductance, and Kb a torque constant due to counter-electromotive force.

[0024] According to another embodiment, a control method of an independent four-wheel steering device may comprise: calculating, by a load estimation module, an estimated load amount detected and returned by a sensor module arranged in a steering module; and calculating, by a processor, an output value to enable an actual steering angle to follow a steering angle reference received from an autonomous driving module, which is a higher-level controller, based on the steering angle reference, a value returned by the sensor module, and a value input by the load estimation module, and outputting the output value to the steering module.

[0025] After the value detected by the sensor module has been reported back, the load estimation module can also estimate a steering angle velocity, which is the cause of a steering angle velocity error, and a current value, which is the cause of a current error.

[0026] The value returned by the sensor module to the load estimation module can include the actual steering angle and steering angle speed.

[0027] The processor can establish a steering angle velocity reference value using an actual steering angle velocity reported back by the sensor module or a steering angle velocity estimated by the load estimation module to calculate the output value to be sent to the steering module.

[0028] The processor can establish a current reference value using an actual current value reported back by the sensor module or a current value estimated by the load estimation module to calculate the output value to be sent to the steering module.

[0029] When setting a steering angle velocity reference value or a current reference value, the processor can adjust the steering angle velocity setpoint and the current reference value so that the error between a reference value and an actual value is 0.

[0030] The processor can calculate the output value to be sent to the steering module using the following equation 1: u=−K1*Theta_error−K2*Omega_error−K3*Current_error−Omega_ref*Kb+Current_ref*R−Current_ref*L where K t denotes a motor constant, R an electrical resistance, L an inductance, and Kb a torque constant due to a counter-electromotive force.

[0031] According to one aspect of the present disclosure, it is possible to perform stable vehicle control by estimating and compensating for a random external load (or external force) or friction during the movement of a vehicle, and a control method for doing so.

[0032] Furthermore, according to one aspect of the present disclosure, it is possible to estimate and compensate for an external load (or external force) or friction even if a current sensor of a steering device has failed.

[0033] Furthermore, according to one aspect of the present disclosure, it is possible to estimate and compensate for load or friction by receiving a feedback steering angle, steering angle velocity and current value, or a steering angle velocity, current value and load and friction by only providing feedback of a steering angle, thereby enabling stable driving control of an independent four-wheel steering device. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is an example diagram showing a schematic configuration of an independent four-wheel steering device according to an embodiment of the present disclosure; Fig. Figure 2 is an example diagram illustrating equations applied to a load estimation model used when calculating an estimated load amount by the load estimation module in Fig. 1 is used; Fig. 3 is a flowchart illustrating a control method for an independent four-wheel steering device according to an embodiment of the present disclosure; and Fig. Figure 4 is an example diagram showing state diagrams before and after application of the control method of an independent four-wheel steering device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS SHOWN

[0034] The components described in the exemplary embodiments can be implemented by hardware components, such as 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 exemplary embodiments can be implemented by software, and the software can be recorded on a recording medium. The components, functions, and processes described in the exemplary embodiments can be implemented by a combination of hardware and software.

[0035] The method according to the exemplary embodiments can be embodied as a computer-executable program and can be implemented on various recording media such as a magnetic storage medium, an optical reading medium and a digital storage medium.

[0036] Several of the techniques described here can be implemented as digital electronic circuits or as computer hardware, firmware, software, or combinations thereof. The techniques can be implemented as a computer program product, that is, as a computer program tangibly embodied in an information carrier, such as 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, such as a programmable processor, a computer, or multiple computers.A computer program can be written in any form of a programming language, including compiled or interpreted languages, and can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computer environment. A computer program can be executed on one computer or on multiple computers at one location or distributed across multiple locations and interconnected via a communication network.

[0037] Processors suitable for executing a computer program include, for example, both general-purpose and specialized 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 one or more mass storage devices for storing data, such as magnetic, magneto-optical, or optical disks, or is coupled to them to receive data from them, to transmit data to them, or both. Examples of information carriers suitable for embodying computer program instructions and data include semiconductor storage devices, such as...Magnetic media such as hard disks, floppy disks, and magnetic tapes; optical media such as compact disc read-only storage (CD-ROM), digital video discs (DVD), etc.; and magneto-optical media such as optical floppy disks, read-only memory (ROM), random access memory (RAM), flash memory, erasable programmable ROM (EPROM), and electrically erasable programmable ROM (EEPROM), as well as any other known computer-readable medium. A processor and memory can be supplemented by or integrated into a special logic circuit.

[0038] The processor can execute an operating system (OS) and one or more software applications that run on the OS. The processor unit can also access, store, manipulate, process, and create data in response to software execution. For simplicity, the description of a processor unit is used in the singular; however, a person skilled in the art will recognize that a processor unit can contain multiple processing elements and / or multiple types of processing elements. For example, a processor unit can comprise multiple processors or a processor and a controller. Furthermore, various processing configurations are possible, such as parallel processors.

[0039] Non-transferable, computer-readable media can be any available media that a computer can access, and can include both computer storage media and transmission media.

[0040] This specification contains details of a number of specific embodiments, but it should be understood that these details do not limit the invention or what may be claimed in the specification, but rather describe features of the specific exemplary embodiment. Features described in the description in connection with individual embodiments may be implemented as a combination in a single embodiment. Conversely, various features described in the description in connection with a single embodiment may be implemented individually or in a suitable subcombination in several embodiments.Furthermore, the features can act in a specific combination and initially be described as the claimed combination, but one or more features can be excluded from the claimed combination in some cases, and the claimed combination can be changed into a subcombination or a modification of a subcombination.

[0041] Even though the processes in the drawings are described in a specific order, this should not be interpreted as meaning that the processes must be performed in that order or in the correct order to achieve the desired results, or that all processes must be performed. In certain cases, multitasking and parallel processing may be advantageous. Furthermore, it should not be interpreted as meaning that the separation of different device components in the example implementations described above is necessary in all example implementations. It should be understood that the program components and devices described above can be integrated into a single software product or packaged into multiple software products.

[0042] It goes without saying that the embodiments disclosed here serve only for illustration and are not intended to limit the scope of the invention. It will be clear to a person skilled in the art that various modifications of the embodiments can be made without infringing the spirit and scope of the claims and their equivalents.

[0043] The following sections describe in detail embodiments of the present disclosure with reference to the accompanying drawings, so that a person skilled in the art can readily implement the present disclosure. However, the present disclosure can be realized in many different forms and is not limited to the embodiments described here.

[0044] In the following description of embodiments of the present disclosure, a detailed description of known functions and configurations is omitted if this could render the subject matter of the present disclosure unclear. Parts that do not relate to the description of the present disclosure in the drawings are omitted, and identical parts are designated by similar reference numerals.

[0045] 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 to say, a plurality of components can be integrated into a hardware or software unit, or a single component can be distributed across a plurality of hardware or software units. Unless otherwise stated, such integrated or distributed embodiments also fall within the scope of this disclosure.

[0046] 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 one embodiment also fall within the scope of the present disclosure. Furthermore, embodiments containing additional components beyond those described in the various embodiments are also included within the scope of the present disclosure.

[0047] The following sections describe in detail embodiments of the present disclosure with reference to the accompanying drawings, so that a person skilled in the art can readily implement the present disclosure. However, the present disclosure can be realized in many different forms and is not limited to the embodiments described here.

[0048] In the following description of embodiments of the present disclosure, a detailed description of known functions and configurations is omitted if this could render the subject matter of the present disclosure unclear. Parts that do not relate to the description of the present disclosure in the drawings are omitted, and identical parts are designated by similar reference numbers.

[0049] When the present disclosure refers to a component that is "linked," "coupled," or "connected" to another component, this can mean not only a direct but also an indirect connection via an intervening component. When a component is described as "encompassing" or "having" another component, this can mean the inclusion of another component, not its exclusion, unless expressly stated otherwise.

[0050] In this disclosure, the terms "first", "second", etc. are used only to distinguish between the individual components and do not restrict the order or meaning of the components, etc., unless expressly stated otherwise. Thus, within the scope of 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.

[0051] In this disclosure, 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 multitude of components can be integrated into a hardware or software unit, or a single component can be distributed across a multitude of hardware or software units. Unless otherwise stated, such integrated or distributed embodiments also fall within the scope of this disclosure.

[0052] 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 one embodiment also fall within the scope of the present disclosure. Furthermore, exemplary embodiments that include additional components beyond those described in the various embodiments are also included within the scope of the present disclosure.

[0053] An independent four-wheel steering device and a control method therefor according to an embodiment of the present disclosure are described below with reference to the accompanying drawings.

[0054] Fig. Figure 1 is an example diagram showing a schematic configuration of an independent four-wheel steering device according to an embodiment of the present disclosure.

[0055] As in Fig. As shown in Figure 1, the independent four-wheel steering device according to the present embodiment comprises a processor 110, a steering module (i.e. an independent four-wheel steering module) 120 and a load estimation module 130.

[0056] The load estimation module 130 receives an actual steering angle θ, an actual steering angular velocity ω and an actual current value i, which are fed back from a sensor module (not shown) located in the steering module 120, estimates a steering angular velocity onto which a steering angular velocity error (or ω error) is reflected and a current value onto which a current error is reflected, and calculates an estimated load amount T̂.

[0057] Here, the sensor module (not shown) records the current steering angle θ, the current steering angle velocity ω and the current i.

[0058] The processor 110 receives a steering angle reference θ_ref (or a steering angle command) from an autonomous driving module (not shown), which is a higher-level control unit, receives the actual steering angle θ, which is detected by the sensor module (not shown) located in the steering module 120, and performs position control so that the actual steering angle θ follows the steering angle reference θ_ref.

[0059] In addition, the processor 110 sets a steering angle velocity reference ω_ref, using the actual steering angle velocity ω detected by the sensor module (not shown) located in the steering module 120, or the steering angle velocity estimated by the load estimation module 130.

[0060] In addition, the processor 110 sets a current reference i_ref using the actual current value i detected by the sensor module (not shown) located in the steering module 120, or a current value estimated by the load estimation module 130.

[0061] Furthermore, the processor 110 can output a value u(V). in ) calculate the amount of the load T̂ output by the load estimation module 130 that is reflected, as described in the following equation 1, and the output value u(V in ), onto which the estimated load amount T̂ is reflected, enter into the steering module 120. u=−K1*Theta_error−K2*Omega_error−K3*Current_error−Omega_ref*Kb+Current_ref*R−Current_ref*L

[0062] In this context, Kt represents a motor constant, J represents a moment of inertia, B represents a damping coefficient, R represents an electrical resistance, L represents an inductance, and Kb represents a torque constant due to a counter-electromotive force.

[0063] That is, the processor 110 sets the steering angular velocity reference ω_ref and the current reference i_ref, by which there is no error between an intended reference value (i.e., a reference value) and an actual value, using a value (e.g., the estimated magnitude of the load T̂, an estimated steering angular velocity, or an estimated current value) output by the load estimation module 130, and calculates the input value u(V). in ) of the steering module 120 by applying the steering angle velocity reference ω_ref and the current reference i_ref set above in Equation 1.

[0064] As a reference, equation 1 is set such that each state error (e.g. a theta error, an omega error or a current error) is multiplied by each value of the motor constants K1 to K3 and a compensation output, taking into account system model properties of the steering module 120, is added to a reference value (e.g. ω_ref, i_ref) of each state variable.

[0065] Here, values ​​of the motor constants K1 to K3 are derived by tuning or properties of a system model, taking into account an intended bandwidth, sensitivity, etc.

[0066] The steering module 120 controls an actual vehicle (i.e., an engine) using the applied value u(V). in ).

[0067] The load estimation module 130 calculates and outputs the estimated load amount T̂ by applying a control current of the vehicle (i.e., the engine) to the steering module 120 from the processor 110, or a voltage value u(V) corresponding to the control current. in ) receives and receives the actual steering angle θ, the actual steering angle velocity ω and the actual current i detected by the sensor module (not shown).

[0068] A method for calculating the estimated load amount T̂̂ using the load estimation module 130 is described in Fig. 2 shown in more detail.

[0069] A symbol “^” in the estimated load amount T̂ indicates an estimated value.

[0070] Fig. Figure 2 is an example diagram illustrating equations applied to a load estimation model used to calculate the estimated load magnitude T̂ by the load estimation module in Fig. 1 is used.

[0071] The in Fig. However, equation 2 shown is only intended to show that the calculation of the estimated load amount T̂ is possible; it is not intended to restrict the calculation of the estimated load amount T̂.

[0072] With reference to Fig. 2 The load estimation model according to the present disclosure is expressed as Ẋ=AX+Bu and Y=CX, where A is a state parameter, B is an input parameter, u is an input, X is a state variable, Y is an output, and C is the relationship between the state variable and the output.

[0073] In Fig. 2. A symbol “^” (hat) indicates an estimated value, a symbol “~” (tilde) indicates a difference (i.e., an error) between an actual value and a reference value.

[0074] Furthermore, L1 to L4 are gain values ​​for estimating the respective state variables. The gain values ​​L1 to L4 are adjusted by tuning or determined according to the characteristics of a model that is controlled taking into account an intended bandwidth or tracking power (e.g., the sensitivity of a response to external disturbances or noise).

[0075] Furthermore, Kt represents a motor constant, J a moment of inertia, B a damping coefficient, R an electrical resistance, L an inductance, and Kb a torque constant due to counter-electromotive force.

[0076] The estimated load amount T̂ can therefore be compared with the one in Fig. The equation shown in point 2 can be calculated using another equation.

[0077] Here, a value of the estimated load magnitude T̂, calculated by the load estimation module 130, directly indicates the external load (or external force) or friction. As in Fig. As shown in Figure 2, a differentiated value T̂=L4w can be derived by differentiating the estimated load amount T̂, and an estimated value of the external load (or external force) or friction can be derived by integrating the differentiated value T̂.

[0078] If a current sensor (not shown) of the sensor module (not shown) has failed, the load estimation module 130 replaces a current error with a steering angle from the equation l^˙=−RLl^−KbLω^+1Lvin+L3l¯↔θ¯ in Fig. 2. If the gain L3 is used here as a previously tuned value or a value calculated according to the steering angle, it is possible to estimate the current value. Consequently, position control is possible even if the current sensor has failed.

[0079] This means that the present embodiment can estimate the external load or friction as described above and perform continuous position control (i.e. steering control) even when the current sensor has failed.

[0080] As described above, according to the present embodiment, the processor 110 can estimate the external load or friction by receiving a steering angle, steering angle velocity, and current value fed back by the sensor module (not shown) of the steering module 120, or it can estimate a steering angle velocity, current value, and load and friction values ​​by receiving only a steering angle fed back by the sensor module (not shown) of the steering module 120. Furthermore, according to the present embodiment, even in a case where the current sensor has failed, if a steering angle and steering angle velocity are fed back, a current value, an external load (or external force), or a friction value can be estimated.

[0081] That is, according to the present embodiment, as in Fig. As shown in Figure 1, even in a case where the current sensor (not shown) has failed, the processor 110 estimates a steering angle velocity, a current value, and load and friction values ​​by receiving only a returned steering angle, and calculates the voltage value u(V). in ), which corresponds to a control current of a vehicle (i.e., a motor) to be applied to the steering module 120, based on the given equation 1.

[0082] Accordingly, the steering module 120 can also provide stable position control based on the voltage value u(V) even in a case where the current sensor (not shown) has failed. in ) perform, which corresponds to the control current of a vehicle (i.e., a motor) calculated by processor 110.

[0083] Fig. Figure 3 is a flowchart showing a control method for an independent four-wheel steering device according to an embodiment of the present disclosure.

[0084] Referring to Fig. 3. When a vehicle is driving autonomously in S101, an actual steering angle θ, an actual steering angle velocity ω and an actual current i, which are detected by the sensor module (not shown) located in the steering module 120, are returned to the load estimation module 130 in S102.

[0085] The load estimation module 130 calculates an estimated load amount T̂ by estimating a load amount and estimates a steering angular velocity and a current value in the process of calculating the estimated load amount T̂ in S103.

[0086] The processor 110 sets a steering angle velocity reference ω_ref and a current reference i_ref using a preset equation, based on a steering angle reference θ_ref input from the autonomous driving module (not shown), which is a higher-level controller, a value reported back from the sensor module (not shown), and a value estimated by the load estimation module 130 in S104.

[0087] Furthermore, the processor 110 calculates a control current of a vehicle (i.e., a motor) to be applied to the steering module 120, or a voltage value u(V). in), which corresponds to the control current, from the value (e.g. a steering angle error, a steering angle velocity error, a current error, a steering angle velocity reference or a current reference) estimated by the load estimation module 130 using the present equation, as in Equation 1, and gives the calculated control current or voltage value u(V in ) to the steering module 120 in S105.

[0088] Accordingly, even in a case where the current sensor (not shown) has failed, the steering module 120 can perform stable position control based on the control current of a vehicle (i.e., a motor), which is achieved by compensating for the external load (or external force) or friction by the processor 110 or the voltage value u(V) corresponding to the control current. in ) is calculated.

[0089] Fig. Figure 4 is an example diagram showing state diagrams before and after application of the control method of an independent four-wheel steering device according to an embodiment of the present disclosure.

[0090] Referring to (a) of Fig. 4, when an external load (or external force) is applied (as in the lower block of the Fig. 4(a) shown), before the control method of an independent four-wheel steering device according to an embodiment of the present disclosure is applied, it can be seen that an actual steering angle is above or below a specified steering angle (in the upper block of the Fig. 4(a) shown), depending on the direction in which the external load acts.

[0091] Referring to (b) of Fig. 4, when an external load (or external force) is applied (as in the lower block of the Fig. 4(b) shown), after the control method of an independent four-wheel steering device according to an embodiment of the present disclosure has been applied, it can be seen that an actual steering angle is identical to an instructed steering angle (in the upper block of the Fig. 4(b) shown), while it does not extend above or below these, regardless of the direction in which the external load acts.

[0092] As described above, according to the present embodiment, optimized position control can be performed regardless of changes in external force (or load), friction, or similar factors, thereby maximizing the path-tracking performance of the independent four-wheel steering system. Even in the event of a current sensor failure, position control can be performed continuously, thus improving stability.

[0093] Even if a random external load acts during autonomous driving, compensation can be performed in response to the external load, thus enabling more robust position control of autonomous driving.

[0094] Furthermore, an electric steering device of an autonomous vehicle must be robust against noise or external disturbances in the steering angle position control and continuously maintain the steering force even if the current sensor or similar component has failed. Accordingly, the present embodiment can optimize the position control performance of a vehicle's independent four-wheel steering device in response to an external load, thereby enabling autonomous driving to be carried out continuously without turning the steering wheel, even in cases where, for example, an external load or friction has occurred, or a driver inadvertently manipulates the steering wheel during autonomous driving.

Claims

[1] A control device for independent four-wheel steering, comprising: a load estimation module (130) configured to calculate an estimated load amount (T̂) by receiving a value detected and reported back by a sensor module arranged in a steering module (120); and a processor (110) configured to calculate an output value that allows an actual steering angle (θ) to follow a steering angle reference (θ_ref) received from an autonomous driving module, which is a higher-level control unit, based on the steering angle reference (θ_ref), a value returned by the sensor module, and a value input by the load estimation module (130), and to output the output value to the steering module (120). characterized by, that the load estimation module (130) also estimates a steering angular velocity onto which a steering angular velocity error (ω error) is reflected, and a current value onto which a current error is reflected. [2] Control device according to claim 1, wherein the value returned by the sensor module to the load estimation module (130) comprises the actual steering angle (θ) and an actual steering angle velocity (ω). [3] Control device according to one of claims 1 to 2, characterized by , that the processor (110) establishes a steering angle velocity reference (ω_ref) using an actual steering angle velocity (ω) reported by the sensor module or a steering angle velocity estimated by the load estimation module (130) to calculate the output value to be output to the steering module (120). [4] Control device according to any one of claims 1 to 3, characterized by, that the processor (110) establishes a current reference value using an actual current value returned by the sensor module or a current value estimated by the load estimation module (130) to calculate the output value to be sent to the steering module (120). [5] Control device according to claim 3 or 4, characterized by , that the processor (110) sets a steering angle velocity reference value and an actual reference value where the error between a reference value and an actual value is 0. [6] Control device according to any one of claims 1 to 5, characterized by , that the processor (110) calculates the output value to be sent to the steering module (120) using the following equation 1: u=−K1*Theta_error−K2*Omega_error−K3*Current_error−Omega_ref*Kb+Current_ref*R−Current_ref*L, where K 1-3specifies a motor constant, R specifies an electrical resistance, L specifies an inductance, Kb specifies a torque constant due to counter-electromotive force, Theta_error specifies a steering angle error, Omega_error specifies a steering angle velocity error, Current_error specifies a current error, Omega_ref specifies a steering angle velocity reference, and Current_ref specifies a current reference. [7] Control method for an independent four-wheel steering device, the control method comprising: Calculate, by a load estimation module (130), an estimated load amount (T̂) which is detected and returned by a sensor module arranged in a steering module (120); and Calculate, by a processor (110), an output value to enable an actual steering angle (θ) to follow a steering angle reference (θ_ref) received from an autonomous driving module, which is a higher-level control unit, based on the steering angle reference (θ_ref), a value returned by the sensor module and a value input by the load estimation module (130), and output the output value to the steering module (120), characterized by , that, after the value detected by the sensor module has been returned, the load estimation module (130) also estimates a steering angular velocity onto which a steering angular velocity error (ω error) is reflected, and a current value onto which a current error is reflected. [8] The control method according to claim 7, wherein the value returned by the sensor module to the load estimation module (130) is the actual steering angle (θ) and includes an actual steering angle velocity (ω). [9] The control method according to one of claims 7 to 8, characterized by , that the processor (110) establishes a steering angle velocity reference value using an actual steering angle velocity returned by the sensor module or a steering angle velocity estimated by the load estimation module (130) in order to calculate the output value to be output to the steering module (120). [10] The control method according to any one of claims 7 to 9, characterized by , that the processor (110) establishes a current reference value using an actual current value returned by the sensor module or a current value estimated by the load estimation module (130) to calculate the output value to be sent to the steering module (120). [11] The control method according to claim 9 or 10, characterized by, that when setting a steering angle velocity reference value or an actual reference value, the processor (110) sets the steering angle velocity reference value and the actual reference value where the error between a reference value and an actual value is 0. [12] The control method according to any one of claims 7 to 11, characterized by , that the processor (110) calculates the output value to be sent to the steering module (120) using the following equation 1: u=−K1*Theta_error−K2*Omega_error−K3*Current_error−Omega_ref*Kb+Current_ref*R−Current_ref*L, where K tTheta_error specifies a motor constant, R specifies an electrical resistance, L specifies an inductance, Kb specifies a torque constant due to the counter-electromotive force, Theta_error specifies a steering angle error, Omega_error specifies a steering angle velocity error, Current_error specifies a current error, Omega_ref specifies a steering angle velocity reference, and Current_ref specifies a current reference.

Images