Control device, electric power steering device, and control method

Abstract

To provide an electric power steering device comprising a control device capable of improving a steering feeling felt by a person steering a vehicle, and a control method.SOLUTION: A control device for controlling, as a control object, a part including at least a motor, comprises: a reaction force control section which generates input torque input to the control object and controls reaction force transmitted from a steering wheel to a person steering a vehicle; an assist control section which generates correction torque for correcting the input torque on the basis of output of the control object and a nominal model; and a state feedback section which feeds a state compensation value back to the input torque on the basis of the output of the control object. The assist control section is configured such that a transfer function of the control object is constrained by a transfer function of the nominal model in a frequency band where a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the control object and the nominal model is approximately 1. The state feedback section feeds back the state compensation value so as to bring an apparent transfer function of the control object close to the transfer function of the nominal model on the basis of the output of the control object.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a control device, an electric power steering device, and a control method. [Background technology]

[0002] BACKGROUND ART Electric power steering systems mounted on vehicles are known. For example, the electric power steering system described in Patent Document 1 includes a motor control device including a disturbance observer that estimates disturbance torque. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-183046 Summary of the Invention [Problem to be solved by the invention]

[0004] In the electric power steering system described above, there is a demand for an improvement in the steering feel felt by the driver operating the vehicle steering wheel. However, in the control system of the electric power steering system, the elements of stability, disturbance suppression characteristics, and responsiveness are in a trade-off relationship with each other. Therefore, it is difficult to adjust each element, which has been a problem in that it is difficult to improve the steering feel felt by the driver operating the vehicle steering wheel.

[0005] In view of the above circumstances, one of the objects of the present invention is to provide a control device that can improve the steering feel felt by the steerer, an electric power steering device equipped with such a control device, and a control method that can improve the steering feel felt by the steerer. [Means for solving the problem]

[0006] One aspect of the control device of the present invention is a control device that controls, as a controlled object, a portion of a steering mechanism including an input shaft connected to a steering wheel operated by a driver, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, the control device comprising: a reaction force control unit that generates an input torque input to the controlled object based on a torsion bar torque generated in the torsion bar and controls a reaction force transmitted from the steering wheel to the driver; an assist control unit that generates a correction torque that corrects the input torque based on an output of the controlled object and a nominal model; and a state feedback unit that feeds back a state compensation value to the input torque based on the output of the controlled object. The assist control unit is configured so that a transfer function of the controlled object is constrained to the transfer function of the nominal model in a frequency band where a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the controlled object and the nominal model is approximately 1. The state feedback unit feeds back the state compensation value based on the output of the controlled object so as to bring the apparent transfer function of the controlled object closer to the transfer function of the nominal model.

[0007] One aspect of the control device of the present invention is a control device that controls, as a controlled object, a portion of a steering mechanism including an input shaft connected to a steering wheel operated by a steerer, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, the control device comprising: a reaction force control unit that generates an input torque input to the controlled object based on a torsion bar torque generated in the torsion bar and controls a reaction force transmitted from the steering wheel to the steerer, an assist control unit that generates a correction torque that corrects the input torque based on an output of the controlled object and a nominal model, and a state feedback unit that feeds back, to the input torque, a state compensation value that compensates for at least a portion of an inertial force generated in the controlled object, a viscous force generated in the controlled object, and a frictional force generated in the controlled object. The assist control unit is configured so that a transfer function of the controlled object is constrained to a transfer function of the nominal model in a frequency band where a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the controlled object and the nominal model is approximately 1. The state feedback unit feeds back the state compensation value to the input torque after it has been corrected by the correction torque and before it is input to the controlled object.

[0008] One aspect of a power steering device of the present invention includes the above-described control device and the steering mechanism.

[0009] One aspect of the control method of the present invention is a control method for controlling, as a controlled object, a portion of a steering mechanism including an input shaft connected to a steering wheel operated by a helmsman, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, the control method including: generating an input torque input to the controlled object based on a torsion bar torque acting on the torsion bar to control a reaction force transmitted from the steering wheel to the helmsman; generating a correction torque for correcting the input torque based on an output of the controlled object and a nominal model; and feeding back a state compensation value to the input torque based on the output of the controlled object. Generating the correction torque includes constraining a transfer function of the controlled object to a transfer function of the nominal model in a frequency band where a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the controlled object and the nominal model is approximately 1. Feeding back the state compensation value to the input torque includes feeding back the state compensation value based on the output of the controlled object so as to bring an apparent transfer function of the controlled object closer to the transfer function of the nominal model.

[0010] One aspect of the control method of the present invention is a control method for controlling, as a controlled object, a portion of a steering mechanism including an input shaft connected to a steering wheel operated by a helmsman, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, the control method including: generating an input torque input to the controlled object based on a torsion bar torque acting on the torsion bar, controlling a reaction force transmitted from the steering wheel to the helmsman, generating a correction torque that corrects the input torque based on an output of the controlled object and a nominal model, and feeding back, to the input torque, a state compensation value that compensates for at least a portion of an inertial force acting on the controlled object, a viscous force acting on the controlled object, and a frictional force acting on the controlled object. Generating the correction torque includes constraining a transfer function of the controlled object to a transfer function of the nominal model in a frequency band where a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the controlled object and the nominal model is approximately 1. Feeding back the state compensation value to the input torque includes feeding back the state compensation value to the input torque after it has been corrected by the correction torque and before it is input to the controlled object. [Effects of the Invention]

[0011] According to one aspect of the present invention, it is possible to improve the steering feel felt by a driver operating the steering wheel of a vehicle equipped with an electric power steering device. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram schematically illustrating an electric power steering device according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing the configuration of the control device according to an embodiment. [Figure 3] FIG. 3 is a functional block diagram illustrating functions of a processor in a control device according to an embodiment. [Figure 4]FIG. 4 is a graph illustrating the gain characteristic of the complementary sensitivity function and the gain characteristic of the reciprocal of the modeling error between the transfer function of the controlled object and the transfer function of the nominal model. [Figure 5] FIG. 5 is a graph showing an example of the measurement results of the steering angle and the torsion torque when the model following control is not applied. [Figure 6] FIG. 6 is a graph showing an example of the measurement results of the steering angle and the torsion torque when the model following control is applied. [Figure 7] FIG. 7 is a graph showing another example of the measurement results of the steering angle and the torsion torque when the model following control is not applied. [Figure 8] FIG. 8 is a graph showing another example of the measurement results of the steering angle and the torsion torque when the model following control is applied. [Figure 9] FIG. 9 is a graph showing yet another example of the measurement results of the steering angle and the torsion torque when the model following control is not applied. [Figure 10] FIG. 10 is a graph showing yet another example of the measurement results of the steering angle and the torsion torque when the model following control is applied. [Figure 11] FIG. 11 is a graph showing yet another example of the measurement results of the steering angle and the torsion torque when the model following control is not applied. [Figure 12] FIG. 12 is a graph showing yet another example of the measurement results of the steering angle and the torsion torque when the model following control is applied. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of a control device, an electric power steering device, and a control method according to the present disclosure will be described with reference to the accompanying drawings. However, more detailed explanations than necessary may be omitted. For example, detailed explanations of already well-known matters and redundant explanations of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following explanation and to facilitate understanding by those skilled in the art.

[0014] The following embodiments are merely examples, and the control device, electric power steering device, and control method according to the present disclosure are not limited to the following embodiments. For example, the numerical values, steps, and order of steps shown in the following embodiments are merely examples, and various modifications are possible as long as no technical contradictions occur. The embodiments and examples described below are merely examples, and various combinations are possible as long as no technical contradictions occur.

[0015] An electric power steering device 1000 of this embodiment shown in FIG. 1 is mounted on a vehicle. As shown in FIG. 1, the electric power steering device 1000 includes a steering mechanism 530 and a control device 100. The steering mechanism 530 includes a steering mechanism section 520 and an assist mechanism section 540. The electric power steering device 1000 controls the assist mechanism section 540 using the control device 100, thereby controlling the steering torque T generated in the steering mechanism section 520 when a driver of the vehicle steers a steering wheel 521. h The assist torque reduces the burden on the driver when the driver operates the steering wheel 521. The driver of the vehicle is the person who steers the steering wheel 521 of the vehicle.

[0016] The steering mechanism 520 has a handle 521, a steering shaft 522, universal joints 523A, 523B, an input shaft 524a, an output shaft 524b, a rack and pinion mechanism 525, a rack shaft 526, left and right ball joints 552A, 552B, tie rods 527A, 527B, knuckles 528A, 528B, and left and right steering wheels 529A, 529B. That is, the steering mechanism 530 has a handle 521, a steering shaft 522, universal joints 523A, 523B, an input shaft 524a, an output shaft 524b, a rack and pinion mechanism 525, a rack shaft 526, left and right ball joints 552A, 552B, tie rods 527A, 527B, knuckles 528A, 528B, and left and right steering wheels 529A, 529B.

[0017] The steering shaft 522 extends from the steering wheel 521 operated by the driver. One end of the input shaft 524a is connected to the end of the steering shaft 522 opposite to the end connected to the steering wheel 521 via universal joints 523A and 523B. Thus, the steering wheel 521 is connected to the input shaft 524a via the universal joints 523A and 523B and the steering shaft 522. The output shaft 524b is connected to the input shaft 524a via a torsion bar 546, which will be described later. More specifically, one end of the output shaft 524b is connected to the other end of the input shaft 524a via the torsion bar 546. The other end of the output shaft 524b is connected to the rack shaft 526 via a rack-and-pinion mechanism 525.

[0018] The input shaft 524a and the output shaft 524b are arranged coaxially. The input shaft 524a and the output shaft 524b are rotatable around the same central axis. The input shaft 524a and the output shaft 524b are rotatable relative to each other within a range in which a torsion bar 546 (described later) can twist.

[0019] The auxiliary mechanism 540 includes a steering torque sensor 541, a steering angle sensor 542, a motor 543, a reduction gear mechanism 544, an inverter 545, and a torsion bar 546. That is, the steering mechanism 530 includes the steering torque sensor 541, the steering angle sensor 542, the motor 543, the reduction gear mechanism 544, the inverter 545, and the torsion bar 546. The torsion bar 546 connects the input shaft 524a and the output shaft 524b. The torsion bar 546 is disposed coaxially with the input shaft 524a and the output shaft 524b. In the following description, a virtual axis passing through the common central axis of the input shaft 524a, the output shaft 524b, and the torsion bar 546 is referred to as the rotation axis R. The torsion bar 546 can twist around the rotation axis R.

[0020] The steering torque sensor 541 detects the amount of twist of the torsion bar 546 around the rotation axis R, thereby detecting the steering torque T h Detects the steering torque T h is the torsion bar torque generated in torsion bar 546, and is a torsion moment about rotation axis R. Steering angle sensor 542 can detect the rotation angle θa of input shaft 524a about rotation axis R. Rotation angle θa of input shaft 524a is equal to the steering angle of steering wheel 521. In other words, steering angle sensor 542 can detect the steering angle of steering wheel 521 by detecting the rotation angle θa of input shaft 524a. It is possible to detect the rotation angle θb of output shaft 524b based on steering torque sensor 541 and steering angle sensor 542.

[0021] In accordance with a motor drive signal input from the control device 100, the inverter 545 converts DC power into three-phase AC power, which is a pseudo-sine wave of U-phase, V-phase, and W-phase, and supplies the power to the motor 543. The motor 543 is connected to the output shaft 524b via a speed reducer 544. The three-phase AC power is supplied to the motor 543 from the inverter 545. The motor 543 is, for example, an interior permanent magnet synchronous motor (IPMSM), a surface permanent magnet synchronous motor (SPMSM), or a switched reluctance motor (SRM). When the three-phase AC power is supplied from the inverter 545 to the motor 543, the steering torque T h The motor 543 transmits the generated auxiliary torque to the output shaft 524b via the reduction mechanism 544.

[0022] The control device 100 controls a control object 560 of the steering mechanism 530, which has at least an input shaft 524a, an output shaft 524b, and a motor 543. In this embodiment, the control object 560 has a steering wheel 521, universal joints 523A and 523B, an input shaft 524a, an output shaft 524b, a torsion bar 546, a motor 543, and a reduction mechanism 544. Because the control object 560 includes the input shaft 524a and the output shaft 524b that are rotatable relative to each other via the torsion bar 546, the motion of the control object 560 cannot be described by a simple equation of motion for a single-inertia system. The control object 560 changes between a single-inertia system and a two-inertia system depending on how tightly the helmsman grips the steering wheel 521. The tighter the helmsman grips the steering wheel 521, the closer the control object 560 becomes to a single-inertia system. The more the helmsman grips the steering wheel 521, the closer the controlled object 560 becomes to a two-inertia system.

[0023] The control device 100 is electrically connected to the inverter 545. The control device 100 generates a motor drive signal based on detection signals detected by the steering torque sensor 541, the steering angle sensor 542, the vehicle speed sensor 300 mounted on the vehicle, and outputs the generated signal to the inverter 545. The control device 100 controls the rotation of the motor 543 via the inverter 545, thereby controlling the controlled object 560. More specifically, the control device 100 controls the switching operations of a plurality of switching elements included in the inverter 545. Specifically, the control device 100 generates control signals for controlling the switching operations of each switching element and outputs the control signals to the inverter 545. Each switching element is, for example, a MOSFET. In the following description, the control signal for controlling the switching operation of each switching element is referred to as a "gate control signal."

[0024] The control device 100 calculates the steering torque T h The control device 100 generates a torque command value based on the above and controls the torque and rotational speed of the motor 543 by, for example, vector control. Vector control is a method of decomposing the current flowing through the motor 543 into a current component that contributes to torque generation and a current component that contributes to magnetic flux generation, and independently controlling each of the mutually orthogonal current components. The control device 100 is not limited to vector control and may also perform other closed-loop control. The rotational speed of the motor 543 is expressed, for example, in rotations per minute [rpm] or rotations per second [rps].

[0025] The control device 100 receives the steering torque T directly from the steering torque sensor 541. h Alternatively, the control device 100 may input the steering torque T h The value of the steering angle of the steering wheel 521 may be input directly to the control device 100 from the steering angle sensor 542, or the control device 100 may calculate the value of the steering angle from the output value of the steering angle sensor 542.

[0026] The control device 100 and the motor 543 are modularized and manufactured and sold as a motor module. The motor module includes the motor 543 and the control device 100, and is suitable for use in the electric power steering device 1000. The control device 100 can also be manufactured and sold as a control device for controlling the electric power steering device 1000, independent of the motor 543.

[0027] 2 shows a typical example of the configuration of the control device 100 in this embodiment. The control device 100 includes, for example, a power supply circuit 111, an angle sensor 112, an input circuit 113, a communication I / F 114, a drive circuit 115, a ROM 116, and a processor 200. The control device 100 can be realized as a printed circuit board (PCB) on which these electronic components are mounted.

[0028] A vehicle speed sensor 300, a steering torque sensor 541, and a steering angle sensor 542 mounted on the vehicle are communicably connected to the processor 200. The vehicle speed is transmitted from the vehicle speed sensor 300 to the processor 200. The steering torque sensor 541 transmits the steering torque T h The steering angle is transmitted to the processor 200 from the steering angle sensor 542.

[0029] The processor 200 is a semiconductor integrated circuit, also referred to as a central processing unit (CPU) or microprocessor. The processor 200 sequentially executes a computer program, which is stored in the ROM 116 and contains instructions for controlling the motor drive, to perform desired processing. In addition to or instead of the processor 200, the control device 100 may include a field programmable gate array (FPGA) equipped with a CPU, a graphics processing unit (GPU), an application specific integrated circuit (ASIC), an application specific standard product (ASSP), or a combination of two or more circuits selected from these circuits. The processor 200 sets a current command value based on the actual current value and the rotation angle of the rotor of the motor 543, generates a pulse width modulation (PWM) signal, and outputs the PWM signal to the drive circuit 115.

[0030] The power supply circuit 111 is connected to an external power supply (not shown). The power supply circuit 111 generates a DC voltage required for each component of the control device 100. The DC voltage generated by the power supply circuit 111 is, for example, 3V or 5V.

[0031] Angle sensor 112 detects the rotation angle of the rotor of motor 543 and outputs the detected rotation angle to processor 200. Angle sensor 112 may be a resolver, a Hall element such as a Hall IC, or an MR sensor having a magnetic resistance element. Processor 200 can calculate angular velocity ω [rad / s] of motor 543 based on the electrical angle θm of motor 543 obtained based on angle sensor 112. Note that control device 100 may include, instead of angle sensor 112, a velocity sensor capable of detecting the rotation angular velocity of motor 543 and an acceleration sensor capable of detecting the rotation angular acceleration of motor 543.

[0032] A motor current value detected by a current sensor (not shown) is input to the input circuit 113. In the following description, the motor current value detected by the current sensor (not shown) will be referred to as the "actual current value." The input circuit 113 converts the level of the input actual current value to an input level for the processor 200 as necessary, and outputs the actual current value to the processor 200. A typical example of the input circuit 113 is an analog-to-digital conversion circuit.

[0033] The communication I / F 114 is, for example, an input / output interface for transmitting and receiving data in accordance with an in-vehicle control area network (CAN).

[0034] The drive circuit 115 is typically a gate driver or a pre-driver. The drive circuit 115 generates a gate control signal in accordance with the PWM signal and applies the gate control signal to the gates of multiple switching elements of the inverter 545. For example, when the motor 543 to be driven is a motor that can be driven at a low voltage, the drive circuit 115 may not necessarily be required as a gate driver. In this case, the gate driver function of the drive circuit 115 may be implemented in the processor 200.

[0035] The ROM 116 is electrically connected to the processor 200. The ROM 116 is, for example, a writable memory, a rewritable memory, or a read-only memory. An example of a writable memory is a PROM (Programmable Read Only Memory). An example of a rewritable memory is a flash memory or an EEPROM (Electrically Erasable Programmable Read Only Memory). The ROM 116 stores a control program including a group of instructions for causing the processor 200 to control motor drive. For example, the control program stored in the ROM 116 is temporarily loaded into a RAM (not shown) at boot time.

[0036] FIG. 3 shows an example of functional blocks of the processor 200 of this embodiment. The processor 200, which is a computer, sequentially executes processes or tasks required to control the motor 543 using each functional block. Each functional block of the processor 200 shown in FIG. 3 may be implemented in the processor 200 as software such as firmware, as hardware, or as both software and hardware. The processing of each functional block in the processor 200 is typically written in a computer program on a software module basis and stored in the ROM 116. However, when an FPGA or the like is used, all or part of these functional blocks may be implemented as a hardware accelerator. Furthermore, the control method of the control device 100 of this embodiment may be implemented in a computer and executed by causing the computer to perform desired operations.

[0037] The processor 200 has a reaction force control unit 210, an assist control unit 230, a state feedback unit 280, a subtractor SU1, an adder AD1, and an adder AD2. That is, the control device 100 is equipped with the reaction force control unit 210, the assist control unit 230, the state feedback unit 280, the subtractor SU1, the adder AD1, and the adder AD2. In other words, the processor 200 of the control device 100 is equipped with functions corresponding to the reaction force control unit 210, the assist control unit 230, the state feedback unit 280, the subtractor SU1, the adder AD1, and the adder AD2.

[0038] The reaction force control unit 210 receives the steering torque T detected by the steering torque sensor 541. h The reaction force control unit 210 receives the input torque T r is the steering torque T h , i.e., generated based on the torsion bar torque generated in the torsion bar 546. r is the target torque of the motor 543 and is the torque command value. rand controls the torque of the motor 543, thereby controlling the reaction force transmitted to the helm from the steering wheel 521. The reaction force control unit 210 generates the steering torque T h By applying phase compensation to the input torque T r The steering frequency is the frequency of the steering angle that changes based on the operation of the steering wheel 521 by the driver. The steering speed is the speed of the steering angle that changes based on the operation of the steering wheel 521 by the driver. The reaction force control unit 210 illustrated in FIG. 3 has a base assist calculation unit 211 and a phase compensator 212.

[0039] The base assist calculation unit 211 calculates the steering torque T h and vehicle speed. The base assist calculation unit 211 calculates the steering torque T h and the vehicle speed. For example, the base assist calculation unit 211 calculates the base assist torque based on the steering torque T h The base assist calculation unit 211 has a look-up table (LUT) that defines the relationship between the vehicle speed and the base assist torque. The base assist calculation unit 211 refers to the look-up table to calculate the steering torque T h The base assist torque calculation unit 211 can determine a corresponding base assist torque based on the steering torque T h The base assist gain can be determined based on a gradient defined by the ratio of the amount of change in the base assist torque to the amount of fluctuation in the torque.

[0040] The phase compensator 212 in this embodiment adjusts the assist gain within a range of possible steering frequencies when the driver operates the steering wheel 521, and compensates for the stiffness of the torsion bar 546. The possible range of steering frequencies is, for example, 5 Hz or less. When the steering frequency is 5 Hz or less, the phase compensator 212 adjusts the steering torque T h , i.e., the torsion bar torque, may be subjected to, for example, first-order phase compensation. The first-order phase compensation is expressed by, for example, the transfer function of Equation (1).

[0041]

number

[0042] In equation (1), s is the Laplace transformer, f1 is the frequency [Hz] of the zero point of the transfer function, and f2 is the frequency [Hz] of the pole of the transfer function. A graph with gain or loop gain on the vertical axis and the logarithm of frequency on the horizontal axis is called a gain diagram. In a gain diagram, the zero point represents the intersection of the gain curve with the horizontal axis representing 0 dB, and the pole represents the maximum point of the gain curve. For example, phase lead compensation can be applied by making the pole frequency higher than the zero point frequency. The greater the distance between the pole frequency and the zero point frequency, the greater the amount of phase lead.

[0043] The phase compensator 212 calculates the input torque T based on the base assist torque and base assist gain output from the base assist calculation unit 211. r For example, the phase compensator 212 is a stabilization compensator and can apply stability phase compensation to the base assist torque. The phase compensator 212 can have a second-order or higher transfer function whose frequency characteristics are variable depending on the base assist gain. A second-order or higher transfer function is expressed using a response parameter and a damping parameter. A second-order or higher transfer function can be expressed by, for example, equation (2). By making the order of the transfer function second-order, damping can be applied to the characteristics of the transfer function. Changing the damping makes it possible to adjust the phase characteristics.

[0044]

number

[0045] In equation (2), s is the Laplace transformer, ω1 is the frequency of the zero point of the transfer function, ω2 is the frequency of the pole point of the transfer function, ζ1 is the damping ratio of the zero point, and ζ2 is the damping ratio of the pole. The pole frequency ω2 is lower than the zero frequency ω1.

[0046] The assist control section 230 controls the input torque T r Correction torque T f is generated based on the output of the controlled object 560 and the nominal model. f is the input torque T r The nominal model is an internal model used as a model that constrains the controlled object 560 when controlling the controlled object 560. The nominal model will be described in detail later. In this embodiment, the assist control unit 230 is a model following controller configured to perform model following control. The specific configuration of the assist control unit 230 will be described in detail later.

[0047] The subtractor SU1 calculates the input torque T r Therefore, the correction torque T output from the assist control unit 230 f The output from the subtractor SU1 is input to an adder AD1 and the assist control unit 230. The adder AD1 adds the output from the subtractor SU1 to the output from the state feedback unit 280, and outputs the result to an adder AD2. The adder AD2 adds the disturbance torque T d The value obtained by adding the above is output to the control object 560.

[0048] Disturbance torque T d is the difference between the ideal output torque of the motor 543 and the actual output torque of the motor 543. d includes the disturbance torque applied from outside to the controlled object 560. d includes, for example, excess torque generated by friction and rattle due to mechanical elements such as motor 543 and reduction mechanism 544, torque ripple generated in motor 543, self-aligning torque, and disturbance torque that may occur when traveling on an unpaved, bumpy road or a gravel road. Self-aligning torque refers to torque that acts in the direction in which steering wheel 521 returns due to the elasticity of the tire that twists when steering wheel 521 is turned.

[0049] In this embodiment, the assist control section 230 calculates the angular velocity ω θ Correction torque T based on f generates an input torque T r Feedback to the angular velocity ω θ is a value equivalent to the angular velocity of the motor 543 theoretically calculated from the rotation angle θa of the input shaft 524a. For example, immediately after the steering wheel 521 is started to be rotated by the driver, the input shaft 524a rotates as the steering wheel 521 rotates, but the motor 543 has not yet started to drive and the output shaft 524b may not be rotating. In this case, the actual angular velocity ω of the motor 543 is zero, but theoretically, if the input shaft 524a rotates, the motor 543 will also rotate and the output shaft 524b will also rotate. Angular velocity ω θ is a value equivalent to the angular velocity of the motor 543 when the motor 543 is theoretically rotated. θ may differ from the actual angular velocity ω of the motor 543. θ The rotation angle θa used to calculate the rotation angle θb of the output shaft 524b may be a value detected by the steering angle sensor 542, or may be a value calculated from the rotation angle θb of the output shaft 524b.

[0050] The assist control unit 230 includes an inverse nominal model 231, a low-pass filter 232, a high-pass filter 233, an assist adjustment unit 270, a subtractor SU2, and an adder AD3. The high-pass filter 233 has a first cutoff frequency Cf1. The first cutoff frequency Cf1 is, for example, not less than 2 Hz and not more than 10 Hz, and preferably not less than 5 Hz and not more than 7 Hz.

[0051] The low-pass filter 232 has a second cut-off frequency Cf2 that is higher than the first cut-off frequency Cf1. The second cut-off frequency Cf2 is, for example, not less than 3 Hz and not more than 50 Hz. However, the upper limit of the second cut-off frequency Cf2 can be set in the range of not less than 140 Hz and not more than 200 Hz. The order of the low-pass filter 232 is third or higher. The low-pass filter 232 may be composed of, for example, multiple low-pass filters. The low-pass filter 232 and the high-pass filter 233 are coupled in series.

[0052] When the transfer function of the low-pass filter 232 is Q(s) and the transfer function of the high-pass filter 233 is HPF(s), the assist control section 230 calculates whether the transfer function P(s) of the controlled object 560 is equal to the transfer function P of a predetermined nominal model in a frequency band where the gain in the gain characteristic of Q(s)·HPF(s) is 1. n (s). Q(s)·HPF(s) is the complementary sensitivity function T(s) of the inner loop configured by assist control unit 230. As shown in FIG. 4, Q(s)·HPF(s), i.e., the complementary sensitivity function T(s), has a gain of 0 dB, i.e., a gain in the transfer function of 1, in a frequency band where frequency f is equal to or greater than first cutoff frequency Cf1 and equal to or less than second cutoff frequency Cf2. FIG. 4 shows the absolute value of complementary sensitivity function T(s). Note that in this specification, "the transfer function of the controlled object is constrained by the transfer function of the nominal model" means that the controlled object is controlled so that the transfer function of the controlled object appears to be the transfer function of the nominal model when, for example, the input / output relationship is viewed.

[0053] The inverse nominal model 231 is an inverse model of a predetermined nominal model (plant model) used to constrain the controlled object 560. In this embodiment, the transfer function P n (s) is expressed by the following equation (3): The transfer function P n -1 (s) is expressed by the following equation (4).

[0054]

number

[0055]

number

[0056] In equations (3) and (4), s is the Laplace transformer, and J STGn is a parameter that represents the moment of inertia of the nominal model, and B STGn is a parameter representing the viscous friction coefficient of the nominal model, and ω 1n is the transfer function P n is the frequency of the zero point of (s), and ω 2n is the transfer function P n is the frequency of the pole of (s), and ζ 1n is the transfer function P n is the damping ratio at the zero point of (s), and ζ 2n is the transfer function P n (s) is the damping ratio at the pole.

[0057] In this embodiment, the nominal model is a model having frequency characteristics between those of a one-inertia system and a two-inertia system. The transfer function P n The equation (3) expressing (s) is an equation expressing a two-inertia system with a damping term added. In the above equation (3), the damping term is 2ζ 1n ω 1n s and 2ζ 2n ω 2n s. The equation obtained by removing these damping terms from equation (3) becomes an equation representing a two-inertia system. In this embodiment, the transfer function P n The degree of (s) is 3.

[0058] In this embodiment, the nominal model is a model that takes into consideration the mechanical characteristics when the helmsman steers the steering wheel 521. As described above, the controlled object 560 approaches a one-inertia system the more tightly the helmsman grips the steering wheel 521, and approaches a two-inertia system the more loosely the helmsman grips the steering wheel 521. Therefore, the transfer function P(s) of the controlled object 560 changes between the one-inertia system and the two-inertia system depending on how force is applied to the steering wheel 521 from the helmsman's arms. In this embodiment, by setting the nominal model to a model having frequency characteristics between the one-inertia system and the two-inertia system, the transfer function P(s) of the nominal model can be set to any state between the one-inertia system and the two-inertia system, regardless of whether the state of the controlled object 560 is in the one-inertia system or the two-inertia system. n This prevents the modeling error Δ(s) between (s) and the transfer function P(s) of the controlled object 560 from becoming too large. Therefore, the controlled object 560 can be suitably controlled using the nominal model regardless of how the helmsman steers the steering wheel 521. As described above, in this embodiment, the nominal model is a model that takes into account the mechanical characteristics that are imparted to the controlled object 560 depending on how the helmsman grips the steering wheel 521. The control device 100 can perform suitable control of the controlled object 560 by having such a nominal model as an internal model.

[0059] In this specification, the phrase "the nominal model is a model that takes into account the mechanical characteristics when the helmsman steers the steering wheel" means, for example, that the nominal model is a model that can compensate for at least a part of the influence that is exerted on the controlled object by the mechanical characteristics when the helmsman steers the steering wheel. The nominal model may also be, for example, a model that directly incorporates the mechanical characteristics of the helmsman's arm movement.

[0060] 3, the output of the controlled object 560 is input to the inverse nominal model 231. Specifically, the inverse nominal model 231 receives the angular velocity ω calculated from the rotation angle θa of the input shaft 524a. θ The inverse nominal model 231 is obtained by using the above equation (4) and the input angular velocity ω θ and based on the torque T pThat is, the assist control section 230 outputs the torque T p Calculate the torque T p is equal to the value of the torque input to the nominal model when the output value of the nominal model is the same as the output value of the controlled object 560.

[0061] The subtractor SU2 subtracts the output of the subtractor SU1 from the output of the inverse nominal model 231 to obtain the differential torque T a That is, the subtractor SU2 generates the correction torque T f After being fed back, the state compensation value V s The input torque T before being fed back r , torque T p Subtract the differential torque T a Generates a differential torque T a For example, the disturbance torque T d The differential torque T output from the subtractor SU2 is a is filtered by a low-pass filter 232 and a high-pass filter 233, which are connected in series, in this order, and is input to an adder AD3. a In other words, the differential torque T filtered by the low-pass filter 232 and the high-pass filter 233 is in a state in which frequency components lower than the first cut-off frequency Cf1 and frequency components higher than the second cut-off frequency Cf2 are removed. a is the frequency component T above the first cutoff frequency Cf1 and below the second cutoff frequency Cf2. aM is.

[0062] The assist adjuster 270 generates a compensation value for friction and disturbances to adjust the differential torque T a In this embodiment, the assist adjustment unit 270 adjusts the differential torque T a Among the frequency components T aMThe assist adjustment section 270 is connected in parallel to the high-pass filter 233. The assist adjustment section 270 has a friction compensation value calculation section 250, a disturbance compensation value calculation section 260, and a subtractor SU3.

[0063] The subtractor SU3 subtracts the output value from the high-pass filter 233 from the output value from the low-pass filter 232. Here, the output value from the low-pass filter 232 is the differential torque T a The output value from the high-pass filter 233 is a value obtained by removing frequency components higher than the second cutoff frequency Cf2 from the differential torque T a The value output from the subtractor SU3 is the differential torque T a The frequency component T aL The output of the subtractor SU3 is input to a friction compensation value calculation unit 250 and a disturbance compensation value calculation unit 260. The frequency component T aL includes friction force, self-aligning torque, disturbance torque caused by backlash of the controlled object 560, and torque ripple occurring in the controlled object 560.

[0064] The friction compensation value calculation unit 250 calculates a friction compensation value V that compensates for at least a part of the friction force generated in the controlled object 560. f The differential torque T a As described above, the value from the subtractor SU3 input to the friction compensation value calculation unit 250 is calculated based on the differential torque T a The frequency component T aL Therefore, in this embodiment, the friction compensation value calculation unit 250 calculates the differential torque T a The friction compensation value V is calculated based on the frequency component lower than the first cutoff frequency Cf1. f Calculate.

[0065] The friction compensation value calculation unit 250 has a limiter 252 and a gain adjuster 253. The limiter 252 limits the output value from the subtractor SU3. If the input value exceeds an upper or lower threshold, the limiter 252 clips the input value to the upper or lower threshold. The gain adjuster 253 multiplies the output value from the limiter 252 by a gain K1. The friction compensation value calculation unit 250 calculates the differential torque T a The friction compensation value V is calculated by applying a limit to the frequency components lower than the first cutoff frequency Cf1 using the limiter 252 and a gain K1. f The threshold value of the limiter 252 and the value of the gain K1 are determined in advance based on the frictional force actually generated in the controlled object 560, for example.

[0066] Correction torque T used for model following control in the assist control unit 230 f To apply friction compensation to the friction compensation calculation unit 250, attention must be paid to the stability conditions of the model-following control. This condition, based on the small gain theorem described below, requires that the gain in the gain characteristic of the transfer function of the friction compensation value calculation unit 250, which is constrained to a characteristic that takes stability into consideration, does not exceed 1. This is derived from the design conditions of the low-pass filter 232. In this embodiment, the value of the gain K1 in the gain adjuster 253 is set to a maximum of 1, and a subtractor SU3 is provided before the limiter 252 to apply subtraction processing so that the gain in the gain characteristic becomes 1 under this condition. In other words, the friction compensation value calculation unit 250 behaves as a low-pass filter having a transfer function of 1-HPF(s).

[0067] The friction compensation value V output from the friction compensation value calculation unit 250 f is the differential torque T a Frequency component T aL Generally, since a moderate amount of friction is required for the controlled object 560, the friction compensation value calculation unit 250 sets a value smaller than the friction force actually generated in the controlled object 560 as the friction compensation value V fThis makes it possible to achieve highly accurate friction compensation while leaving an appropriate friction force on the controlled object 560. The friction compensation value V f The targets of friction compensation by this include, for example, the friction of the motor 543, the friction of the reduction mechanism 544, and the difference in friction between the left and right sides of the reduction mechanism 544.

[0068] Here, the differential torque T a Frequency component T aL In addition to the friction force component, the frequency component T also includes the self-aligning torque generated in the controlled object 560, the disturbance torque caused by the backlash generated in the controlled object 560, and the torque ripple generated in the controlled object 560. aL The friction compensation value V obtained by processing the f The compensation value also includes a compensation value for compensating for at least a part of the self-aligning torque occurring in the controlled object 560, the disturbance torque caused by backlash occurring in the controlled object 560, and the torque ripple occurring in the controlled object 560.

[0069] A vehicle equipped with the electric power steering device 1000 can travel in accordance with a driving mode that includes an automatic driving mode and a manual driving mode. In this case, the gain K1 of the gain adjuster 253 may be switched depending on the driving mode. The greater the gain K1 of the gain adjuster 253, the greater the degree of friction reduction. It is preferable that the gain K1 in the automatic driving mode be greater than the gain K1 set in the manual driving mode. This makes it possible to apply optimal friction compensation to the automatic driving mode, which requires greater friction reduction.

[0070] The disturbance compensation value calculation unit 260 calculates a disturbance compensation value V that compensates for at least a part of the self-aligning torque generated in the controlled object 560. d In this embodiment, the disturbance compensation value V dincludes a compensation value for compensating for at least a part of the friction force occurring in the controlled object 560, the disturbance torque due to backlash occurring in the controlled object 560, and the torque ripple occurring in the controlled object 560. The disturbance compensation value calculation unit 260 calculates the torque T p and input torque T r The differential torque T a Based on the disturbance compensation value V d That is, the disturbance compensation value calculation unit 260 calculates the torque T p and input torque T r The differential torque T a Based on the disturbance compensation value V d As described above, the value from the subtractor SU3 input to the disturbance compensation value calculation unit 260 is calculated as the differential torque T a , which is a frequency component lower than the first cutoff frequency Cf1. a The disturbance compensation value V is calculated based on the frequency component lower than the first cutoff frequency Cf1. d Calculate.

[0071] The disturbance compensation value calculation unit 260 has a limiter 262 and a gain adjuster 263. The limiter 262 limits the output value from the subtractor SU3. If the input value exceeds the upper or lower threshold, the limiter 262 clips the input value to the upper or lower threshold. The threshold of the limiter 262 is different from the threshold of the limiter 252, for example. The gain adjuster 263 multiplies the output value from the limiter 262 by a gain K2. When the transfer function P(s) of the controlled object 560 is equal to the transfer function P of the nominal model, n The maximum value of gain K2 of gain adjuster 263 is determined under the condition that is constrained by (s). The value of gain K2 is different from the value of gain K1, for example. The value of gain K2 is, for example, equal to or greater than 0.3 and equal to or less than 0.8. Gain K2 of gain adjuster 263 may be switched depending on the driving mode of the vehicle.

[0072] Disturbance compensation value V dis the differential torque T a Frequency component T aL The disturbance compensation value calculation unit 260 may set a value equivalent to, for example, about half of the self-aligning torque actually generated in the controlled object 560 as the disturbance compensation value V d The self-aligning torque actually generated in the controlled object 560 is experimentally determined in advance for each frequency, for example. The threshold value and the value of the gain K2 of the limiter 262 of the disturbance compensation value calculation unit 260 are set to a value approximately half the magnitude of the self-aligning torque determined in advance, and the disturbance compensation value V d The disturbance compensation value V calculated by the disturbance compensation value calculation unit 260 is adjusted to the calculated value. d is the friction compensation value V calculated by the friction compensation value calculation unit 250. f is a different value.

[0073] Here, the differential torque T a Frequency component T aL In addition to the self-aligning torque, the frequency component T aL The disturbance compensation value V obtained by processing the d The compensation value also includes a compensation value for compensating for at least a part of the frictional force occurring in the controlled object 560, the disturbance torque caused by backlash occurring in the controlled object 560, and the torque ripple occurring in the controlled object 560.

[0074] The adder AD3 adds the output value from the assist adjustment unit 270 to the output value from the high-pass filter 233. That is, the adder AD3 adds the frequency component T aM Friction compensation value V f and disturbance compensation value V d The adder AD3 outputs the frequency component T aM and friction compensation value V f and disturbance compensation value V d The corrected torque T is calculated by adding fThe corrected torque T output from the adder AD3 f is the input of the controlled object 560, i.e., the input torque T r In this manner, in this embodiment, the assist control section 230 uses the high-pass filter 233 to remove frequency components lower than the first cutoff frequency Cf1 and feeds back the differential torque T a , i.e., frequency component T aM Whereas, the friction compensation value V f and disturbance compensation value V d Adding these together gives the correction torque T f Generate.

[0075] The state feedback unit 280 calculates the apparent transfer function of the controlled object 560 based on the output of the controlled object 560 as a transfer function P n To get closer to (s), the state compensation value V s The input torque T r The apparent transfer function of the controlled object 560 is, for example, the transfer function of a portion located inside the feedback loop created by the assist control unit 230 when the portion is considered as one portion. Specifically, in this embodiment, the apparent transfer function of the controlled object 560 is the transfer function of the entire portion from the subtractor SU1 to the output of the controlled object 560, and is the transfer function of the combined portion of the state feedback unit 280 and the controlled object 560. In this embodiment, the state feedback unit 280 calculates the correction torque T f and before being input to the controlled object 560. r For the state compensation value V s Provide feedback.

[0076] State compensation value V s includes a compensation value that compensates for at least a part of the inertial force occurring in the controlled object 560, the viscous force occurring in the controlled object 560, and the frictional force occurring in the controlled object 560. More specifically, the state compensation value V sincludes a compensation value that compensates for at least a part of the inertial force generated in the motor 543, the viscous force generated in the motor 543, and the frictional force generated in the motor 543. In this embodiment, the state compensation value V s is a compensation value that includes the inertial force generated in the motor 543, the viscous force generated in the motor 543, and the frictional force generated in the motor 543.

[0077] The state feedback unit 280 has an inertia compensator 281, a viscosity compensator 282, and a friction compensator 283. The inertia compensator 281 calculates a compensation value for compensating for at least a part of the inertial force generated in the motor 543 based on the angular velocity ω of the motor 543. The viscosity compensator 282 calculates a compensation value for compensating for at least a part of the viscous force generated in the motor 543 based on the angular velocity ω of the motor 543. The friction compensator 283 calculates a compensation value for compensating for at least a part of the friction force generated in the motor 543 based on the angular velocity ω of the motor 543. In this embodiment, the state compensation value V s is composed of a compensation value calculated by the inertia compensator 281, a compensation value calculated by the viscosity compensator 282, and a compensation value calculated by the friction compensator 283. The compensation value calculated by the inertia compensator 281, the compensation value calculated by the viscosity compensator 282, and the compensation value calculated by the friction compensator 283 are output to an adder AD1, and a correction torque T f The input torque T after correction by r is added to.

[0078] Next, the control by the assist control unit 230 will be described in more detail. The assist control unit 230 controls the controlled object 560 using an inverse model of the nominal model it has as an internal model, i.e., an inverse nominal model 231. In this embodiment, the feedback loop created by the assist control unit 230 makes it possible to compensate for torque ripple that depends on the angular velocity ω of the motor 543. The angular velocity ω signal used for control can be corrected for each type of motor 543, and the accuracy of the angular velocity ω signal can be improved compared to current signals, etc. As a result, highly accurate torque ripple compensation can be applied to torque control.

[0079] The assist control unit 230 is similar in configuration to a conventional disturbance estimator (disturbance observer), but has different intended actions and effects. A conventional disturbance estimator estimates disturbance torque by using an inverse plant model, which is an internal model, as a model close to the control target 560, and reduces the influence of the disturbance by adjusting the disturbance torque in advance.

[0080] The control by the assist control section 230 according to this embodiment is performed by a feedback loop in which the transfer function P(s) of the controlled object 560 is converted into the transfer function P(s) of the nominal model included as an internal model. n The effect of being constrained to (s) is utilized. For example, if a nominal model is defined so that there is no torque ripple, the transfer function P(s) of the controlled object 560 is constrained to a torque ripple-free characteristic by model following control. As a result, torque ripple can be reduced by applying torque ripple compensation. Also, by making the nominal model a low inertia model and constraining the controlled object 560 with the nominal model, the controlled object 560 can be treated as a low inertia model. Also, by making the nominal model a low viscosity model and constraining the controlled object 560 with the nominal model, the controlled object 560 can be treated as a low viscosity model. By executing model following control by the assist control unit 230, in addition to compensation for torque ripple of the motor 543, for example, loss torque compensation or motor inertia compensation is performed. In the above equations (3) and (4), J STGn and B STGn By appropriately setting, it is possible to impart a desired frequency characteristic to the transfer function P(s) of the controlled object 560.

[0081] Transfer function P(s) of the controlled object 560 and transfer function P of the nominal model n When the modeling error between (s) and (s) is Δ(s), the transfer function P(s) of the controlled object 560 is expressed by the following equation (5).

[0082]

number

[0083] The gain characteristic of the transfer function P(s) of the controlled object 560 has peaks at, for example, two frequency values. The modeling error Δ(s) appears, for example, near the higher frequency of the two peaks in the gain characteristic of the controlled object 560. Therefore, as shown in FIG. 4, the reciprocal 1 / Δ(s) of the modeling error Δ(s) has a bottom in a relatively high frequency region. In FIG. 4, the modeling error Δ(s) is shown as an absolute value. When the modeling error Δ(s) becomes large, the difference between the transfer function P(s) of the controlled object 560 and the transfer function P of the nominal model n The deviation from (s) becomes large, and the control of the controlled object 560 by the assist control unit 230 using the nominal model becomes unstable. Therefore, in a region where the modeling error Δ(s) is relatively small, the control object 560 can be constrained to the nominal model by setting the gain of the complementary sensitivity function T(s), i.e., Q(s)·HPF(s) to 1, thereby enabling stable and suitable control of the controlled object 560. The frequency characteristic of the modeling error Δ(s) is expressed as the transfer function P n J in (s) STGn and B STGn The frequency band where the gain of Q(s)·HPF(s) is 1 can be adjusted by adjusting the first cutoff frequency Cf1 and the second cutoff frequency Cf2. This allows the gain of Q(s)·HPF(s) to be adjusted to 1 in the frequency band where the modeling error Δ(s) is small.

[0084] 4, 1 / Δ(s) is relatively high in the frequency band equal to or lower than the second cutoff frequency Cf2 and drops sharply in the frequency band higher than the second cutoff frequency Cf2. Model-following control that constrains the controlled object 560 to the nominal model can be performed stably, for example, in a range where 1 / Δ(s) is greater than 1, i.e., a range where 1 / Δ(s) is greater than 0 dB. Therefore, as shown in FIG. 4, by adjusting 1 / Δ(s) to be greater than 1 in the frequency band where the gain of Q(s)·HPF(s) is 1, when the gain of Q(s)·HPF(s) is 1, the controlled object 560 can be constrained to the nominal model and controlled stably and appropriately.

[0085] For example, to broaden the frequency band in which stable and suitable control can be achieved by constraining the controlled object 560 to the nominal model, the second cutoff frequency Cf2 may be increased within a range in which 1 / Δ(s) is not less than 1, i.e., within a frequency band lower than the frequency at which the curve representing 1 / Δ(s) intersects with the horizontal axis in FIG. 4. However, if the second cutoff frequency Cf2 is increased too much, the gain of Q(s)·HPF(s) may remain relatively high in a frequency band higher than the second cutoff frequency Cf2, resulting in unstable control. In contrast, in this embodiment, the order of the low-pass filter 232 is set to third or higher, allowing the gain of Q(s)·HPF(s) to be sharply reduced in a frequency range higher than the second cutoff frequency Cf2. As a result, even if the second cutoff frequency Cf2 is set relatively high, the gain of Q(s)·HPF(s) can be immediately reduced in the frequency band higher than the second cutoff frequency Cf2, thereby preventing the control of the controlled object 560 from becoming unstable.

[0086] The robust stability of the assist control section 230 is guaranteed when the small gain theorem shown in the following equation (6) holds between the complementary sensitivity function T(s) and the modeling error Δ(s).

[0087]

number

[0088] As described above, in order to perform model following control using a nominal model in the assist control unit 230, it is sufficient if T(s) = 1, but in consideration of robust stability, it is necessary to satisfy the above formula (6). As can be seen from this, it is not possible to achieve both T(s) = 1 and formula (6) in all frequency bands, and suppression of disturbances and the like by the assist control unit 230 and robust stability are not compatible.

[0089] As shown in Fig. 4, even in a region where the frequency is lower than the first cutoff frequency Cf1, the gain of Q(s)·HPF(s), i.e., the gain of the complementary sensitivity function T(s), is smaller than 1. In a region where the gain of Q(s)·HPF(s) is smaller than 1, the reaction force control unit 210 calculates the input torque T r As described above, in the region where the frequency is higher than the second cutoff frequency Cf2, the gain of Q(s)·HPF(s) is significantly reduced to control the correction torque T f is hardly fed back to the input of the controlled object 560. On the other hand, in the region where the frequency is lower than the first cutoff frequency Cf1, the gain of Q(s)·HPF(s) is set to a certain magnitude, and the correction torque T f is fed back to the input of the controlled object 560. In a region where the frequency is lower than the first cutoff frequency Cf1, the compensation value generated in the above-described assist adjustment unit 270 is fed back to the input of the controlled object 560 in accordance with the gain of Q(s)·HPF(s).

[0090] The control device 100 performs torque control in the reaction force control unit 210 for torque signals with low frequencies lower than the first cutoff frequency Cf1, and performs control such that the angular velocity ω≈0 for disturbances with high frequencies higher than the second cutoff frequency Cf2, thereby realizing stabilization of steering so that the steering wheel 521 does not move. To achieve this objective, the control device 100 uses the reaction force control unit 210 to reduce the high-frequency gain of the torque control, and uses the assist control unit 230 to constrain the transfer function P(s) of the control target 560 to a characteristic that reduces the high-frequency gain. The reason for performing the latter process is to prevent the control target 560 from reacting to a disturbance when the disturbance is input to the control target 560.

[0091] The effective range of model following control by assist control unit 230 is a region equal to or greater than the first cutoff frequency Cf1 and equal to or less than the second cutoff frequency Cf2. In other words, the lower limit frequency of the effective range of model following control depends on the first cutoff frequency Cf1. Therefore, the lower limit frequency of the effective range of model following control is determined by adjusting the first cutoff frequency Cf1 of high-pass filter 233 so as not to impede the control of reaction force control unit 210 in the low-frequency region.

[0092] According to this embodiment, the input torque T r Correction torque T f The assist control unit 230 generates the transfer function P(s) of the controlled object 560 based on the output of the controlled object 560 and the nominal model. The assist control unit 230 calculates the transfer function P(s) of the controlled object 560 in a frequency band where the gain in the gain characteristic of the complementary sensitivity function T(s) for the modeling error Δ(s) between the controlled object 560 and the nominal model is 1. n Specifically, in a region where the modeling error Δ(s) between the nominal model and the controlled object 560 is small, the gain in the gain characteristic of Q(s)·HPF(s) is set to 1, and the difference in output between the controlled object 560 and the nominal model is calculated as the correction torque T f as the input torque T rBy feeding back to the n (s). Therefore, for example, by using a model in which no torque ripple occurs as the nominal model, it is possible to remove or reduce torque ripple from the output of controlled object 560 in the frequency band where the gain in the gain characteristics of Q(s)·HPF(s) is 1. Furthermore, by using a low-inertia and low-viscosity model as the nominal model, it is possible to constrain controlled object 560 to a low-inertia and low-viscosity model, making it easier to control controlled object 560.

[0093] For example, a conventional disturbance estimator has an internal model that is close to the controlled object 560, and compensates for disturbances that occur in the controlled object 560. However, it is difficult to have an internal model that is completely identical to the controlled object 560, and a modeling error Δ(s) inevitably occurs. Therefore, in conventional disturbance estimators, the gain in the gain characteristic of Q(s)·HPF(s) is set to a value smaller than 1 in all frequency bands in order to suppress control instability. Furthermore, because conventional disturbance estimators only approximate the internal model to the actual model of the controlled object 560, they can estimate disturbances applied externally to the controlled object 560, but cannot remove torque ripples and the like that occur in the controlled object 560 itself.

[0094] In contrast to this, in this embodiment, the nominal model that control device 100 has as an internal model is set as an ideal model for control object 560, rather than a model that attempts to reproduce a model of the actual control object 560, and the gain of Q(s)·HPF(s) is set to 1 in a region where the modeling error Δ(s) is small. In this way, by appropriately setting the nominal model, it is possible to remove not only external disturbances applied to the actual control object 560 from the outside, but also torque ripples and the like that occur internally in control object 560. Therefore, according to this embodiment, control device 100 can appropriately control control object 560, and the steering feel felt by the steering operator can be improved.

[0095] Furthermore, for example, the steering mechanism 530 has a structure in which the input shaft 524a and the output shaft 524b are connected via the torsion bar 546, and is not a simple one-inertia system. Therefore, if the object controlled by the control device 100 is a one-inertia system including, for example, only the motor 543, it may be difficult to sufficiently compensate for torque ripple and disturbances. In contrast, as in the present embodiment, it is conceivable to consider the part including both sides of the torsion bar 546 as the controlled object 560, but this does not mean that the controlled object 560 can be considered a simple two-inertia system. As described above, the controlled object 560 changes between a one-inertia system and a two-inertia system depending on the steering manner of the steering wheel 521 by the helmsman. Therefore, even if the controlled object 560 is simply modeled as a two-inertia system, it may be difficult to sufficiently compensate for torque ripple and disturbances.

[0096] In contrast, according to this embodiment, the nominal model is a model that takes into account the mechanical characteristics when the helmsman steers the steering wheel 521. Therefore, the nominal model can be suitably matched to the characteristics of the controlled object 560 that change depending on how the helmsman steers the steering wheel 521. As a result, by constraining the controlled object 560 to the nominal model through the above-described model following control, it is possible to more suitably compensate for torque ripple, disturbances, and the like. Therefore, the steering feel felt by the helmsman can be further improved.

[0097] Furthermore, according to this embodiment, the transfer function P n The order of (s) is 3 or more. Here, the inventors have clarified that the order of the transfer function of the steering mechanism 530 is, for example, 6. Therefore, the transfer function P n By setting (s) to a high-order transfer function closer to the order of the transfer function of the steering mechanism 530, the control device 100 can more suitably control the steering mechanism 530. Therefore, the steering feel felt by the steerer can be further improved.

[0098] In this embodiment, the controlled object is considered within the range of a third-order transfer function, and the transfer function P n The order of (s) is also set to 3. However, for example, if the controlled object is considered in the range of a transfer function of 4th order or more, and the transfer function P n The order of (s) may be set to 4 or more. The order of the transfer function of the range to be considered as the controlled object and the transfer function P of the nominal model n The closer the order of (s) is to the sixth order, which is the order of the transfer function of the steering mechanism 530, the more suitable the control can be. For example, if the steering torque sensor 541 is a resolver or the like, the transfer function of the steering torque sensor 541 may be second order. Therefore, for example, if the control object is a control object obtained by adding the steering torque sensor 541 to the control object 560 of this embodiment, and the transfer function P n If the order of (s) is set to 5th order, more suitable control can be achieved.

[0099] Furthermore, according to this embodiment, the nominal model is a model having frequency characteristics between the one-inertia system and the two-inertia system. As described above, the characteristics of the controlled object 560 change between the one-inertia system and the two-inertia system depending on how the helmsman steers the steering wheel 521. Therefore, by using the nominal model as a model having frequency characteristics between the one-inertia system and the two-inertia system, the controlled object 560 can be more suitably controlled using the nominal model. Therefore, the steering feel felt by the helmsman can be further improved.

[0100] Furthermore, according to this embodiment, the transfer function P n The equation for (s) is an equation that adds a damping term to the equation for a two-inertia system. Therefore, the transfer function P n (s) can be conveniently and easily modeled to have frequency characteristics between those of a one-inertia system and a two-inertia system.

[0101] Furthermore, according to this embodiment, the transfer function P n (s) is expressed by the above equation (3). Therefore, the transfer function P n(s) can be more suitably and easily modeled as a model having frequency characteristics between those of a one-inertia system and a two-inertia system.

[0102] As described above, by considering the controlled object 560 as a system broader than a single-inertia system and setting a nominal model to match the controlled object 560, the nominal model can be used to compensate for disturbances, including torque ripples, over a wider frequency band than conventional systems through feedback control. This makes it possible to broaden the frequency band in which disturbances can be suppressed. Specifically, for example, torque ripples occurring in the controlled object 560 include torque ripples caused by the worm gear used in the reduction mechanism 544. The torque ripples caused by the worm gears may be disturbances of, for example, about 50 Hz. Conventional configurations such as disturbance estimators were unable to suppress torque ripples in the first place, and the frequency band in which they could be suppressed as disturbances was lower than 50 Hz, making it impossible to suppress the torque ripples caused by the worm gears. In contrast, according to the configuration and method of the present embodiment, by appropriately setting the nominal model, the assist control unit 230 can compensate for the relatively high-frequency torque ripples caused by the worm gears, thereby suppressing the relatively high-frequency torque ripples.

[0103] Furthermore, according to this embodiment, the control device 100 calculates the apparent transfer function of the controlled object 560 based on the output of the controlled object 560 as the transfer function P n To get closer to (s), the state compensation value V s The input torque T rTherefore, the control object 560 to be controlled by feedback from the assist control unit 230 can be made to appear to be close to the nominal model that is included as an internal model. As a result, when model following control is performed by the assist control unit 230, the control object 560 can be regarded as a model that is close to the nominal model, and the modeling error Δ(s) between the control object 560 and the nominal model can be reduced. Therefore, when the gain in the gain characteristic of Q(s)·HPF(s) is set to 1, the transfer function P(s) of the control object 560 can be made to appear to be close to the transfer function P of the nominal model n This widens the frequency band in which the steering force can be constrained to (s), thereby enabling the assist control section 230 to perform model following control over a wider frequency band, thereby improving the steering feel felt by the steerer.

[0104] Furthermore, according to this embodiment, the state feedback unit 280 calculates the correction torque T f and before being input to the controlled object 560. r For the state compensation value V s Therefore, the feedback from the state feedback unit 280 can be included in the feedback loop of the assist control unit 230. This allows the state feedback unit 280 and the control object 560 to be regarded as a single control object from the perspective of the assist control unit 230. Therefore, by regarding the transfer function of the single control object as the apparent transfer function P(s) of the control object 560, the control by the assist control unit 230 using the nominal model can be more suitably performed.

[0105] Furthermore, according to this embodiment, the state compensation value V s includes a compensation value that compensates for at least a part of the inertial force occurring in the controlled object 560, the viscous force occurring in the controlled object 560, and the frictional force occurring in the controlled object 560. Therefore, the apparent transfer function of the controlled object 560 is calculated by the transfer function P nIn this embodiment, the inertia compensator 281, the viscosity compensator 282, and the friction compensator 283 calculate a state compensation value V s By feeding back the apparent transfer function of the controlled object 560, the transfer function P n The gains of the inertia compensator 281, the viscosity compensator 282, and the friction compensator 283 are appropriately set to values ​​that bring the controlled object 560 closer to the nominal model.

[0106] Furthermore, according to this embodiment, the state compensation value V s includes a compensation value that compensates for at least a part of the inertial force generated in the motor 543, the viscous force generated in the motor 543, and the frictional force generated in the motor 543. Therefore, the inertial force generated in the motor 543 can be compensated so as to approach the nominal model. As a result, the apparent transfer function of the controlled object 560 can be calculated by the transfer function P n (s) can be more suitably approached.

[0107] According to this embodiment, the assist control section 230 calculates the torque T p and correction torque T f After being corrected by the state compensation value V s The input torque T before being fed back r Based on the difference between f That is, the subtractor SU2 of the assist control unit 230 generates the state compensation value V s The input torque T before being added r Therefore, it is easier for the assist control unit 230 to regard the state feedback unit 280 and the controlled object 560 as a single controlled object. This makes it possible to more appropriately bring the apparent transfer function P(S) of the controlled object 560 as seen from the assist control unit 230 closer to the nominal model.

[0108] Also, for example, in a two-inertia system, it is difficult to estimate the motion of the entire two-inertia system from the motion of the inertia system on the output side. In other words, even in this embodiment, it is difficult to estimate the motion of the nominal model between the one-inertia system and the two-inertia system only from the information on the rotation angle θb of the output shaft 524b, and the torque T p In contrast to this, according to this embodiment, the assist control section 230 calculates the correction torque T based on the rotation angle θa of the input shaft 524a. f Therefore, by using the rotation angle θa of the input shaft 524a on the input side, the motion of the nominal model between the one-inertia system and the two-inertia system can be suitably estimated. As a result, the torque T output from the inverse nominal model 231 is p can be calculated appropriately, and the correction torque T f can be suitably produced.

[0109] Furthermore, the self-aligning torque is transmitted to the steerer as a response when the steerer steers the steering wheel 521. Therefore, for example, in the low-frequency region including the self-aligning torque, it is conceivable to significantly reduce the gain of the assist control unit 230 so that the self-aligning torque is not compensated for. In this case, compensation by the assist control unit 230 is not performed, and the reaction force control unit 210 applies compensation to control the controlled object 560. However, in this case, the amount of compensation in the reaction force control unit 210 becomes large, and the gain of the reaction force control unit 210 may become too large. As a result, there is a risk that the control by the control device 100 may become unstable.

[0110] In contrast to this, according to this embodiment, the assist control section 230 calculates a disturbance compensation value V d The external disturbance compensation value calculation unit 260 calculates the correction torque T f is the disturbance compensation value V dTherefore, even in the low-frequency region including the self-aligning torque, the assist control unit 230 can perform compensation at least by the amount required to compensate for the self-aligning torque. This reduces the amount of compensation required in the reaction force control unit 210, allowing the gain in the reaction force control unit 210 to be reduced. This prevents the control by the control device 100 from becoming unstable. This further improves the steering feel felt by the steerer. Furthermore, by compensating for at least a portion of the self-aligning torque by the assist control unit 230, the reaction force applied to the steerer when the steerer steers the steering wheel 521 can be reduced. This further improves the steering feel felt by the steerer. In particular, in this embodiment, by compensating for only a portion of the self-aligning torque by the assist control unit 230, the steerer can be given an appropriate sense of resistance when steering the steering wheel 521, making it easier for the steerer to steer the steering wheel 521.

[0111] Furthermore, according to this embodiment, the disturbance compensation value V d includes a compensation value that compensates for at least a part of the friction force occurring in the controlled object 560, the disturbance torque caused by the backlash occurring in the controlled object 560, and the torque ripple occurring in the controlled object 560. Therefore, the disturbance compensation value V calculated by the disturbance compensation value calculation unit 260 of the assist control unit 230 is d This makes it possible to compensate not only for the self-aligning torque but also for at least a portion of the frictional force, the disturbance torque caused by backlash, and the torque ripple. This makes it possible to compensate for at least a portion of the frictional force, the disturbance torque caused by backlash, and the torque ripple even in the low-frequency range below the first cutoff frequency Cf1 where model following control cannot be performed. Therefore, the steering feel felt by the steerer can be further improved in the low-frequency range below the first cutoff frequency Cf1.

[0112] According to this embodiment, the disturbance compensation value calculation unit 260 calculates the torque T p and input torque T r The differential torque Ta Based on the disturbance compensation value V d Therefore, the differential torque T a The self-aligning torque and other values ​​can be estimated appropriately from the d can be suitably calculated.

[0113] According to this embodiment, the disturbance compensation value calculation unit 260 calculates the differential torque T a The frequency component lower than the first cutoff frequency Cf1, i.e., the frequency component T aL Based on the disturbance compensation value V d The self-aligning torque is calculated by the relatively low frequency component T aL Since it is included in the frequency component T aL Based on the disturbance compensation value V d By calculating the frequency component T aL also includes the frictional force occurring in the controlled object 560, the disturbance torque caused by the backlash occurring in the controlled object 560, and the torque ripple occurring in the controlled object 560. aL is processed by a limiter 262 and a gain adjuster 263 to obtain a disturbance compensation value V d By calculating the above, the disturbance compensation value V can be calculated, which can compensate for not only the self-aligning torque but also the frictional force generated in the controlled object 560, the disturbance torque caused by the backlash generated in the controlled object 560, and the torque ripple generated in the controlled object 560. d can be calculated.

[0114] Furthermore, according to this embodiment, the assist control section 230 calculates a friction compensation value V f The differential torque T a The assist control section 230 includes a friction compensation value calculation section 250 that calculates the friction compensation value based on the first cutoff frequency Cf1. The high-pass filter 233 filters out the frequency component T aL The differential torque T with a , i.e., frequency component T aM Whereas, the friction compensation value V f and disturbance compensation value Vd Adding these together gives the correction torque T f Therefore, the assist control unit 230 can more appropriately compensate for the frictional force generated in the controlled object 560.

[0115] According to this embodiment, the friction compensation value calculation unit 250 calculates the differential torque T a The frequency component lower than the first cutoff frequency Cf1, i.e., the frequency component T aL Based on the friction compensation value V f Therefore, the frictional force can be suitably compensated even in a low frequency range lower than the first cutoff frequency Cf1 where model following control cannot be performed. This allows the gain of the reaction force control unit 210 to be further reduced in a low frequency range lower than the first cutoff frequency Cf1, and makes it possible to further prevent the control of the controlled object 560 from becoming unstable.

[0116] Furthermore, in conventional friction compensation control, when the angular velocity ω of the motor 543 is near zero, the change in the friction compensation value relative to the angular velocity ω of the motor 543 must be made gradual in order to prevent chattering. As a result, there are cases where high-precision friction compensation control cannot be performed. According to the inventor's investigation, in order to solve this problem, it is desirable to sequentially estimate and compensate for friction. According to friction compensation by the friction compensation value calculation unit 250 of this embodiment, friction is sequentially estimated and the friction compensation value V f This allows us to calculate the above, thereby solving the problem.

[0117] Furthermore, an auxiliary device has been developed that recognizes lane marks, such as white or yellow lines, when traveling on a highway, and assists the vehicle in autonomous driving by following the lane. It is known that in a vehicle equipped with such an auxiliary device and an electric power steering device, a difference in friction between the left and right sides of the reduction gear 544 can affect the control of the auxiliary device, which drives the vehicle straight along the center of the lane. The friction compensation performed by the friction compensation value calculation unit 250 of this embodiment can solve the above problem by sequentially estimating friction even when there is a difference in friction between the left and right sides of the reduction gear 544. The angular velocity ω of the motor 543, which is the output of the controlled object 560, includes information regarding the difference in friction between the left and right sides of the reduction gear 544.

[0118] The inventors have confirmed the effects obtained by applying the model following control by the control device 100 of the above-described embodiment by performing measurements on an actual vehicle. In the measurements on the actual vehicle, torque ripple, viscosity feeling, friction, and inertia feeling were compared between a case where the model following control was not applied and a case where the model following control was applied.

[0119] Figures 5, 7, 9, and 11 show the measurement results of the steering angle [deg] and torsion torque [Nm] when model following control is not applied. Figures 6, 8, 10, and 12 show the measurement results of the steering angle [deg] and torsion torque [Nm] when model following control is applied. In each graph of Figures 5 to 12, the horizontal axis is the steering angle [deg] and the vertical axis is the torsion torque [Nm]. The torsion torque is the torsion bar torque, and the steering torque T h is.

[0120] Figures 5 and 6 show waveforms when the steering wheel 521 is steered at 90 [deg / s]. Looking at the enlarged views of Figures 5 and 6, it can be seen that the torque ripple is reduced in the waveform of Figure 6, where model following control is applied, compared to the waveform of Figure 5, where model following control is not applied. This confirms that applying model following control can reduce torque ripple when steering the steering wheel 521.

[0121] 7 and 8 show waveforms obtained when steering wheel 521 is steered at a steering frequency of 2 Hz. From Fig. 7 and Fig. 8, it can be seen that the amount of fluctuation D1em of torsion torque in waveform EM1 in Fig. 8, in which model following control is applied, is smaller than the amount of fluctuation D1ce of torsion torque in waveform CE1 in Fig. 7, in which model following control is not applied. This confirms that the application of model following control can reduce the feeling of viscousness when steering steering wheel 521.

[0122] 9 and 10 show waveforms obtained when the steering wheel 521 is steered at ±10 degrees with a steering frequency of 0.5 Hz. It can be seen from FIGS. 9 and 10 that the width D2em indicated by the arrow in the waveform EM2 in FIG. 10, in which model following control is applied, is smaller than the width D2ce indicated by the arrow in the waveform CE2 in FIG. 9, in which model following control is not applied. The widths D2ce and D2em each correspond to the magnitude of friction. It can therefore be seen that applying model following control can reduce friction when steering the steering wheel 521.

[0123] 11 and 12 show waveforms obtained when steering the steering wheel 521 at a steering frequency of 2 Hz. In FIG. 11, the dashed ellipse Ece indicates the portion of the waveform obtained when the steering wheel 521 is turned. In FIG. 12, the dashed ellipse Eem indicates the portion of the waveform obtained when the steering wheel 521 is turned. From FIGS. 11 and 12, it was confirmed that the resistance due to inertia when turning the steering wheel 521 in the waveform EM3 in FIG. 12, in which model following control is applied, is smaller than the resistance due to inertia when turning the steering wheel 521 in the waveform CE3 in FIG. 11, in which model following control is not applied. This confirms that the sense of inertia when steering the steering wheel 521 can be reduced by applying model following control.

[0124] The present invention is not limited to the above-described embodiment, and other configurations and methods may be adopted within the scope of the technical concept of the present invention. In the above-described embodiment, the assist control unit is configured so that the transfer function of the controlled object is constrained to the transfer function of the nominal model in a frequency band where the gain in the gain characteristic of the complementary sensitivity function with respect to the modeling error between the controlled object and the nominal model is 1. However, this is not limiting. The assist control unit may be configured so that the transfer function of the controlled object is constrained to the transfer function of the nominal model in a frequency band where the gain in the gain characteristic of the complementary sensitivity function with respect to the modeling error between the controlled object and the nominal model is approximately 1. "The gain is approximately 1" includes not only a gain of 1 but also, for example, a gain of 0.8 or more and 1.2 or less. For example, when a reduction mechanism connected to a motor has a worm gear, this numerical range is a range in which the gain of the disturbance suppression characteristic can be substantially adjusted to 1, taking into account the forward efficiency and reverse efficiency of the worm gear. Since the efficiency of a worm gear is approximately 0.8, the gain needs to be adjusted within ±0.2 of the target value of 1.

[0125] In the above embodiment, the complementary sensitivity function is a function expressed as Q(s)·HPF(s) where Q(s) is the transfer function of the low-pass filter and HPF(s) is the transfer function of the high-pass filter, but is not limited to this. For example, when the transfer function of the controlled object and the transfer function of the nominal model are equal, the complementary sensitivity function may be expressed as Q(s).

[0126] The nominal model may have any transfer function. For example, if the controlled object is a one-inertia system including a motor, the transfer function P n (s) may be expressed as the following equation (7).

[0127]

number

[0128] In equation (7), s is the Laplace transformer, and J mn is a parameter that represents the moment of inertia of the nominal model, and B mn is a parameter representing the viscous friction coefficient of the nominal model.

[0129] The correction torque generated by the assist control unit may be any torque that corrects the input torque. The assist control unit may correct the input torque with the correction torque in control other than feedback control, such as feedforward control.

[0130] The control target of the control device and control method of the present disclosure may be any part of the steering mechanism as long as it includes at least a motor. The control target may be a one-inertia system control target or a two-or-more-inertia system control target. [Explanation of symbols]

[0131] 100...control device, 210...reaction force control unit, 230...assist control unit, 232...low-pass filter, 233...high-pass filter, 250...friction compensation value calculation unit, 260...disturbance compensation value calculation unit, 280...state feedback unit, 521...steering wheel, 524a...input shaft, 524b...output shaft, 530...steering mechanism, 543...motor, 546...torsion bar, 560...controlled object, 1000...electric power steering device, Cf1...first cutoff frequency, Cf2...second cutoff frequency, P(s)...transfer function of controlled object, P n (s)...transfer function of the nominal model, T(s)...complementary sensitivity function, T a … differential torque, T f …corrected torque, T h …Steering torque (torsion bar torque), T p …torque, T r …input torque, V d …disturbance compensation value, V f …Friction compensation value, V s ...state compensation value, θa...rotation angle

Claims

1. A control device that controls, as a control target, a portion of a steering mechanism that includes an input shaft to which a steering wheel operated by a driver is connected, an output shaft that is connected to the input shaft via a torsion bar, and a motor that is connected to the output shaft, the control device comprising: a reaction force control unit that generates an input torque input to the controlled object based on a torsion bar torque generated in the torsion bar and controls a reaction force transmitted from the steering wheel to the steering operator; an assist control unit that generates a correction torque for correcting the input torque based on the output of the controlled object and a nominal model; a state feedback unit that feeds back a state compensation value to the input torque based on an output of the controlled object; Equipped with the assist control section is configured such that a transfer function of the controlled object is constrained to a transfer function of the nominal model in a frequency band in which a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the controlled object and the nominal model is approximately 1; The control device wherein the state feedback unit feeds back the state compensation value based on an output of the controlled object so as to bring an apparent transfer function of the controlled object closer to a transfer function of the nominal model.

2. The control device according to claim 1 , wherein the state feedback unit feeds back the state compensation value to the input torque after it has been corrected by the correction torque and before it is input to the controlled object.

3. 3. The control device according to claim 1, wherein the state compensation value includes a compensation value that compensates for at least a part of an inertial force occurring in the controlled object, a viscous force occurring in the controlled object, and a frictional force occurring in the controlled object.

4. A control device that controls, as a control target, a portion of a steering mechanism that includes an input shaft to which a steering wheel operated by a driver is connected, an output shaft that is connected to the input shaft via a torsion bar, and a motor that is connected to the output shaft, the control device comprising: a reaction force control unit that generates an input torque input to the controlled object based on a torsion bar torque generated in the torsion bar and controls a reaction force transmitted from the steering wheel to the steering operator; an assist control unit that generates a correction torque for correcting the input torque based on the output of the controlled object and a nominal model; a state feedback unit that feeds back, to the input torque, a state compensation value that compensates for at least a part of an inertial force generated in the controlled object, a viscous force generated in the controlled object, and a frictional force generated in the controlled object; Equipped with the assist control section is configured such that a transfer function of the controlled object is constrained to a transfer function of the nominal model in a frequency band in which a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the controlled object and the nominal model is approximately 1; The control device wherein the state feedback unit feeds back the state compensation value to the input torque after it has been corrected by the correction torque and before it is input to the controlled object.

5. The assist control unit a high pass filter having a first cutoff frequency; a low-pass filter having a second cutoff frequency higher than the first cutoff frequency; and 5. The control device according to claim 1, wherein the complementary sensitivity function is expressed as Q(s)·HPF(s), where Q(s) is a transfer function of the low-pass filter and HPF(s) is a transfer function of the high-pass filter.

6. The control device according to claim 5 , wherein the order of the low-pass filter is third or greater.

7. The control device according to claim 1 , wherein the state compensation value includes a compensation value that compensates for at least a part of an inertial force generated in the motor, a viscous force generated in the motor, and a frictional force generated in the motor.

8. 8. The control device according to claim 1, wherein the assist control unit generates the correction torque based on a difference between a torque calculated using the nominal model based on an output of the controlled object and the input torque after being corrected by the correction torque and before the state compensation value is fed back.

9. The control device according to claim 1 , wherein the assist control section generates the correction torque based on a rotation angle of the input shaft.

10. the assist control unit includes a disturbance compensation value calculation unit that calculates a disturbance compensation value that compensates for at least a part of the self-aligning torque generated in the controlled object, The control device according to claim 1 , wherein the correction torque includes the disturbance compensation value.

11. 11. The control device according to claim 10, wherein the disturbance compensation value includes a compensation value that compensates for at least a part of a frictional force occurring in the controlled object, a disturbance torque due to backlash occurring in the controlled object, and a torque ripple occurring in the controlled object.

12. The assist control unit a friction compensation value calculation unit that calculates a friction compensation value that compensates for at least a part of a friction force generated in the controlled object based on a differential torque that is a difference between a torque calculated using the nominal model based on an output of the controlled object and the input torque; and and generating the correction torque by adding the friction compensation value and the disturbance compensation value to the differential torque from which frequency components lower than a first cutoff frequency have been removed by a high-pass filter having the first cutoff frequency.

13. the friction compensation value calculation unit calculates the friction compensation value based on a frequency component of the differential torque that is lower than the first cutoff frequency, The control device according to claim 12, wherein the disturbance compensation value calculation unit calculates the disturbance compensation value based on a component of the differential torque that has a frequency lower than the first cutoff frequency.

14. A control device according to any one of claims 1 to 13; the steering mechanism; An electric power steering device comprising:

15. A control method for controlling a steering mechanism including an input shaft connected to a steering wheel operated by a driver, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, the method comprising the steps of: generating an input torque input to the controlled object based on a torsion bar torque generated in the torsion bar, and controlling a reaction force transmitted from the steering wheel to the helmsman; generating a correction torque for correcting the input torque based on the output of the controlled object and a nominal model; feeding back a state compensation value based on an output of the controlled object to the input torque; Including, generating the correction torque includes constraining a transfer function of the controlled object to a transfer function of the nominal model in a frequency band where a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the controlled object and the nominal model is approximately 1; a control method in which feeding back the state compensation value to the input torque includes feeding back the state compensation value based on an output of the controlled object so as to cause an apparent transfer function of the controlled object to approach a transfer function of the nominal model.

16. A control method for controlling a steering mechanism including an input shaft connected to a steering wheel operated by a driver, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, the method comprising the steps of: generating an input torque input to the controlled object based on a torsion bar torque generated in the torsion bar, and controlling a reaction force transmitted from the steering wheel to the helmsman; generating a correction torque for correcting the input torque based on the output of the controlled object and a nominal model; feeding back, to the input torque, a state compensation value that compensates for at least a part of an inertial force generated in the controlled object, a viscous force generated in the controlled object, and a frictional force generated in the controlled object; Including, generating the correction torque includes constraining a transfer function of the controlled object to a transfer function of the nominal model in a frequency band where a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the controlled object and the nominal model is approximately 1; a control method in which feeding back the state compensation value to the input torque includes feeding back the state compensation value to the input torque after it has been corrected by the correction torque and before it is input to the controlled object.

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