Apparatus and method for controlling steer-by-wire system

Abstract

The present invention is characterized by comprising an inverter that supplies power to a synchronous motor that generates reaction torque, and a processor that controls the iron loss of the synchronous motor through the inverter to detect the point of unintentional reduction of the reaction torque generated by the synchronous motor and to improve the steering strangeness of the steering wheel that occurs at the point of unintentional reduction of the reaction torque.

Description

Technology Field

[0001] The present invention relates to a control device and method for an SBW system, and more specifically, to a control device and method for an SBW system capable of improving steering inconsistency caused by an unintended reduction in reaction torque. Background Technology

[0003] FIG. 1 is an example of a conventional Steer By Wire (SBW) system. As illustrated in FIG. 1, the SBW system is a system that eliminates the mechanical connection between the steering wheel (10) and the wheel (40). It receives rotation information of the steering wheel (10) through an ECU and, based on the received rotation information, operates a steering motor (30) connected to the driving wheel to steer the vehicle. This SBW system includes an actuator (20) to provide the driver with a steering sensation similar to that of a conventional mechanical steering system. The actuator (20) can generate a reaction torque in the opposite direction to the rotation direction of the steering wheel (10). However, since the actuator (20) generates the reaction torque through a synchronous motor, it reacts sensitively to disturbances acting on the synchronous motor. FIG. 2 is an example of a reaction torque generated through the actuator (20) according to the rotation of the steering wheel (10). As shown in FIG. 2, an unintended decrease in reaction torque may occur at a certain point during the rotation of the steering wheel (10), and if a decrease in reaction torque occurs, it may cause a steering strangeness such as looseness of the steering wheel (10) to the driver.

[0004] The background technology of the present invention is disclosed in the ‘method for controlling reaction force in an electronic steering system’ of Korean Registered Patent Publication No. 10-0505886 (July 26, 2005). The problem to be solved

[0006] The present invention was devised to solve the aforementioned problems, and an objective according to one aspect of the present invention is to provide a control device and method for an SBW system capable of improving steering inconsistency caused by a reduction in unintended reaction torque. means of solving the problem

[0008] A control device for an SBW system according to one aspect of the present invention comprises: an inverter that supplies power to a synchronous motor that generates a reaction torque; and a processor that controls the iron loss of the synchronous motor through the inverter to detect an unintentional decrease in the reaction torque generated by the synchronous motor and to improve the steering strangeness of the steering wheel that occurs at the time of the unintentional decrease in the reaction torque.

[0009] In the present invention, the synchronous motor is characterized as being a Surface Mounted Permanent Magnet Synchronous Motor (SPMSM).

[0010] In the present invention, the processor is characterized by detecting the point in time when reverse steering occurs by the steering wheel as the point in time when the reaction torque is unintentionally reduced.

[0011] The present invention further includes a steering angle sensor for measuring the steering angle of the steering wheel; and the processor is characterized by detecting the timing of the occurrence of the reverse steering based on the steering angle measured through the steering angle sensor.

[0012] In the present invention, the processor is characterized by applying a high-frequency d-axis current to the synchronous motor through the inverter to increase the iron loss of the synchronous motor.

[0013] The present invention further includes a steering angle sensor for measuring the steering angle of the steering wheel; and the processor calculates the angular velocity of the steering wheel based on the steering angle measured through the steering angle sensor, and calculates the value of the d-axis current to be applied to the synchronous motor based on the angular velocity of the steering wheel.

[0014] A control method for an SBW system according to one aspect of the present invention is characterized by comprising: a step in which a processor detects an unintentional decrease in reaction torque generated by a synchronous motor; and a step in which the processor controls the iron loss of the synchronous motor through an inverter that supplies power to the synchronous motor so as to improve the steering strangeness of the steering wheel occurring at the time of the unintentional decrease in reaction torque.

[0015] In the present invention, the synchronous motor is characterized as being a Surface Mounted Permanent Magnet Synchronous Motor (SPMSM).

[0016] In the detection step of the present invention, the processor is characterized by detecting the point in time when reverse steering occurs by the steering wheel as the point in time when the reaction torque is unintentionally reduced.

[0017] In the detection step of the present invention, the processor is characterized by detecting the timing of the occurrence of the reverse steering based on the steering angle of the steering wheel measured through the steering angle sensor.

[0018] In the control step of the present invention, the processor is characterized by applying a high-frequency d-axis current to the synchronous motor through the inverter to increase the iron loss of the synchronous motor.

[0019] In the control step of the present invention, the processor calculates the angular velocity of the steering wheel based on the steering angle of the steering wheel measured through the steering angle sensor, and calculates the value of the d-axis current to be applied to the synchronous motor based on the angular velocity of the steering wheel. Effects of the invention

[0021] According to one aspect of the present invention, when an unintended reduction in reaction torque occurs in an SBW system, the steering disparity of the steering wheel can be improved by controlling the iron loss of the synchronous motor. Brief explanation of the drawing

[0023] Figures 1 and 2 are exemplary diagrams for explaining an SBW system. FIG. 3 is a block diagram illustrating a control device of an SBW system according to an embodiment of the present invention. FIGS. 4 and FIGS. 5 are illustrative diagrams for explaining a control device of an SBW system according to an embodiment of the invention. FIG. 6 is a flowchart illustrating a control method for an SBW system according to an embodiment of the present invention. Specific details for implementing the invention

[0024] Hereinafter, a control device and method of an SBW system according to an embodiment of the present invention will be described in detail with reference to the attached drawings. In this process, the thickness of lines or the size of components shown in the drawings may be exaggerated for clarity and convenience of explanation. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intention or convention of the user or operator. Therefore, the definitions of these terms should be based on the content throughout this specification.

[0025] FIG. 3 is a block diagram illustrating a control device of an SBW system according to an embodiment of the present invention, and FIG. 4 and FIG. 5 are illustrative diagrams illustrating a control device of an SBW system according to an embodiment of the invention.

[0026] Referring to FIG. 3, a control device of an SBW system according to one embodiment of the present invention may include a synchronous motor (100), an inverter (200), a steering angle sensor (300), and a processor (400).

[0027] The synchronous motor (100) receives power from the inverter (200) and can generate a reaction torque in the opposite direction to the rotation direction of the steering wheel (10). According to one embodiment, the synchronous motor (100) may be a surface-mounted permanent magnet synchronous motor (SPMSM).

[0028] The inverter (200) can supply power to the synchronous motor (100). The inverter (200) can vary the magnitude and frequency of the power input from the outside and output the power with varied magnitude and frequency to the synchronous motor (100).

[0029] The steering angle sensor (300) can measure the steering angle of the steering wheel (10). According to one embodiment, the steering angle sensor (300) is provided in the steering column and can measure the steering angle of the steering wheel (10) by detecting the steering angle of the steering column.

[0030] The processor (400) can detect the point of unintentional decrease in the reaction torque generated by the synchronous motor (100) and control the core loss of the synchronous motor (100) through the inverter (200) to improve the steering strangeness of the steering wheel (10) that occurs at the point of unintentional decrease in the reaction torque.

[0031] The processor (400) can detect the point in time when reverse steering occurs by the steering wheel (10) as the point in time when the reaction torque is unintentionally reduced. The present invention is based on the fact that a momentary reduction in reaction torque occurs at the point in time when an act of changing the rotation direction of the steering wheel (10) occurs, or at the point in time when an act of rotating the steering wheel (10) that is stopped on-center occurs, and thus the point in time when an act of changing the rotation direction of the steering wheel (10) occurs, or at the point in time when an act of rotating the steering wheel (10) that is stopped on-center occurs, etc., can be considered as the point in time when reverse steering occurs.

[0032] The processor (400) can detect the timing of reverse steering based on the steering angle measured through the steering angle sensor (300). The processor (400) can detect whether the steering wheel (10) is rotated and the direction of rotation based on the steering angle measured through the steering angle sensor (300), and can detect the timing of reverse steering based on whether the steering wheel (10) is rotated and the direction of rotation.

[0033] The processor (400) can apply a high-frequency d-axis current to the synchronous motor (100) through the inverter (200) to increase the iron loss of the synchronous motor (100). The steering sensation felt by the driver is determined by the reaction torque generated by the synchronous motor (100) and the frictional force generated when the steering wheel (10) rotates. The frictional force generated when the steering wheel (10) rotates can be divided into mechanical frictional force and magnetic frictional force. Mechanical frictional force is a frictional force determined by the mechanical characteristics of the synchronous motor (100) and cannot be controlled externally. On the other hand, magnetic frictional force is a frictional force generated by the iron loss of the synchronous motor (100) and can be controlled by the degree of saturation of the magnetic circuit of the synchronous motor (100) and the frequency of the alternating magnetic field. The iron loss of the synchronous motor (100) can be calculated through the following mathematical formula 1.

[0034]

[0035] Here, W is the iron loss, and k h is the hysteresis loss coefficient, and k e is the eddy current loss coefficient, and k a is an ideal eddy current loss coefficient, f is the frequency of the magnetic field according to the rotational speed of the synchronous motor (100), and B m is the magnetic flux density of the iron core due to the permanent magnet provided in the synchronous motor (100). f and B m Since the value changes according to the magnitude and frequency of the current applied to the synchronous motor (100), the iron loss can be controlled by varying the magnitude and frequency of the current applied to the synchronous motor (100).

[0036] Typically, the current applied to the synchronous motor (100) can be controlled by varying the q-axis current and / or d-axis current applied to the synchronous motor (100). However, in the case of a surface-mounted permanent magnet synchronous motor, there is a problem in that varying the q-axis current changes the reaction torque generated by the synchronous motor (100). The following Equation 2 is a formula for calculating the reaction torque generated by a surface-mounted permanent magnet synchronous motor.

[0037]

[0038] Here, T is the reaction torque, p is the pole pair, and is the magnetic flux linkage, is the q-axis current. According to the above mathematical formula 2, the reaction torque generated in a surface-mounted permanent magnet synchronous motor is determined by the q-axis current and is independent of the d-axis current.

[0039] As such, in the case of a surface-mounted permanent magnet synchronous motor, varying the q-axis current changes the reaction torque generated in the synchronous motor (100), so it is not desirable to vary the q-axis current to control iron loss. Therefore, the processor (400) can vary only the d-axis current applied to the synchronous motor (100) through the inverter (200) to control the iron loss of the synchronous motor (100).

[0040] The processor (400) can calculate the angular velocity of the steering wheel (10) based on the steering angle of the steering wheel (10) measured through the steering angle sensor (300), and calculate the value of the d-axis current to be applied to the synchronous motor (100) based on the angular velocity of the steering wheel (10). According to another embodiment, the processor (400) may also calculate the angular velocity of the steering wheel (10) through a separate sensor. The following Equation 3 is an equation representing the relationship between iron loss and magnetic friction force.

[0041]

[0042] Here, W is the iron loss, and T f is magnetic friction, and is the angular velocity of the steering wheel (10). According to the above mathematical formula 3, the magnetic friction force is proportional to the iron loss and inversely proportional to the angular velocity of the steering wheel (10). The processor (400) can determine the value of the iron loss by considering the angular velocity of the steering wheel (10). FIG. 4 is an example of the magnetic friction force according to the angular velocity of the steering wheel (10) and the d-axis current. As shown in FIG. 4, the processor (400) can generate a constant magnetic friction force by varying the magnitude of the d-axis current according to the angular velocity of the steering wheel (10).

[0043] According to one embodiment, the value of the additional magnetic friction force to be generated to compensate for the reduced reaction torque at the point of unintentional reduction of the reaction torque may be determined in advance through experiment or simulation, and the processor (400) may calculate the value of the iron loss to be compensated based on the angular velocity of the steering wheel (10) at that point and the value of the magnetic friction force calculated in advance, generate a d-axis current command according to the calculated value of the iron loss, and generate additional magnetic friction force by outputting the generated d-axis current command to the inverter (200). At this time, the frequency of the d-axis current may be fixed to a specific value in advance.

[0044] FIG. 5 is an example of the reaction torque of a synchronous motor according to the d-axis current and electrical angle. As shown in FIG. 5, it can be seen that even if the magnitude of the d-axis current applied to the synchronous motor (100) is varied, the torque ripple of the synchronous motor (100) remains almost constant. Thus, the present invention can change only the magnetic friction force of the synchronous motor (100) without changing the torque ripple by varying the d-axis current applied to the synchronous motor (100).

[0045] As described above, the present invention can control the magnetic friction force of a synchronous motor by varying the d-axis current applied to the synchronous motor to vary the iron loss of the synchronous motor when an unintended reduction in reaction torque occurs in an SBW system, and thereby compensates for the reduction in reaction torque and improves the steering feel of the steering wheel.

[0047] FIG. 6 is a flowchart illustrating a control method for an SBW system according to an embodiment of the present invention.

[0048] Hereinafter, with reference to FIG. 6, we will examine a control method of an SBW system according to an embodiment of the present invention.

[0049] First, the processor (400) can detect the point of unintentional decrease in the reaction torque generated by the synchronous motor (100) (S601). According to one embodiment, the processor (400) can detect the point of occurrence of reverse steering by the steering wheel (10) as the point of unintentional decrease in the reaction torque. According to one embodiment, the processor (400) can detect the point of occurrence of reverse steering based on the steering angle measured through the steering angle sensor (300).

[0050] Next, the processor (400) can control the iron loss of the synchronous motor (100) through the inverter (200) to improve the steering strangeness of the steering wheel (10) that occurs at the point of unintentional reduction of the reaction torque (S603). According to one embodiment, the processor (400) can apply a high-frequency d-axis current to the synchronous motor (100) through the inverter (200) to increase the iron loss of the synchronous motor (100).

[0052] As described above, the control device and method of an SBW system according to one embodiment of the present invention can improve the steering dissonance of the steering wheel by controlling the iron loss of the synchronous motor when an unintended reduction in reaction torque occurs in the SBW system.

[0053] The implementations described herein may be implemented, for example, as methods or processes, devices, software programs, data streams, or signals. Even if discussed only in the context of a single form of implementation (e.g., discussed only as a method), the implementation of the discussed features may also be implemented in other forms (e.g., devices or programs). Devices may be implemented in appropriate hardware, software, and firmware, etc. Methods may be implemented in devices such as processors, which generally refer to processing devices including, for example, computers, microprocessors, integrated circuits, or programmable logic devices. Processors also include communication devices such as computers, cell phones, portable / personal digital assistants ("PDAs"), and other devices that facilitate the communication of information between end-users.

[0054] Although the present invention has been described with reference to the embodiments illustrated in the drawings, this is merely illustrative and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the claims below. Explanation of the symbols

[0056] 10: Steering wheel 20: Actuator 30: Steering motor 40: Wheel 100: Synchronous motor 200: Inverter 300: Steering angle sensor 400: Processor

Claims

Claim 1 A control device for an SBW system characterized by comprising: an inverter that supplies power to a synchronous motor that generates reaction torque; and a processor that detects an unintentional decrease in the reaction torque generated by the synchronous motor and controls the iron loss of the synchronous motor through the inverter to improve the steering strangeness of the steering wheel occurring at the time of the unintentional decrease in the reaction torque. Claim 2 A control device for an SBW system according to claim 1, characterized in that the synchronous motor is a Surface Mounted Permanent Magnet Synchronous Motor (SPMSM). Claim 3 A control device for an SBW system according to claim 1, wherein the processor detects the point in time when reverse steering occurs by the steering wheel as the point in time when the reaction torque is unintentionally reduced. Claim 4 A control device for an SBW system according to claim 3, further comprising a steering angle sensor for measuring the steering angle of the steering wheel; wherein the processor detects the timing of the occurrence of the reverse steering based on the steering angle measured through the steering angle sensor. Claim 5 A control device for an SBW system according to claim 1, wherein the processor applies a high-frequency d-axis current to the synchronous motor through the inverter to increase the iron loss of the synchronous motor. Claim 6 A control device for an SBW system according to claim 5, further comprising a steering angle sensor for measuring the steering angle of the steering wheel; wherein the processor calculates the angular velocity of the steering wheel based on the steering angle measured through the steering angle sensor, and calculates the value of the d-axis current to be applied to the synchronous motor based on the angular velocity of the steering wheel. Claim 7 A control method for an SBW system characterized by comprising: a step of a processor detecting an unintentional decrease in reaction torque generated by a synchronous motor; and a step of the processor controlling the iron loss of the synchronous motor through an inverter that supplies power to the synchronous motor so as to improve the steering strangeness of the steering wheel occurring at the time of the unintentional decrease in reaction torque. Claim 8 A control method for an SBW system according to claim 7, characterized in that the synchronous motor is a Surface Mounted Permanent Magnet Synchronous Motor (SPMSM). Claim 9 A control method for an SBW system according to claim 7, wherein, in the detection step, the processor detects the point in time when reverse steering occurs by the steering wheel as the point in time when the reaction torque is unintentionally reduced. Claim 10 A control method for an SBW system according to claim 9, wherein, in the detection step, the processor detects the timing of the occurrence of the reverse steering based on the steering angle of the steering wheel measured through a steering angle sensor. Claim 11 A control method for an SBW system according to claim 7, wherein, in the controlling step, the processor applies a high-frequency d-axis current to the synchronous motor through the inverter to increase the iron loss of the synchronous motor. Claim 12 A control method for an SBW system according to claim 11, wherein, in the controlling step, the processor calculates the angular velocity of the steering wheel based on the steering angle of the steering wheel measured through a steering angle sensor, and calculates the value of the d-axis current to be applied to the synchronous motor based on the angular velocity of the steering wheel.

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