Control device, motor device, electric power steering device, control method, and program

Abstract

The present invention provides an electric power steering system that can suppress the decrease in steering feel perceived by the driver. [Solution] The control device comprises an assist control unit that generates input torque based on torsion bar torque, a model-following control unit that generates a first correction torque to correct the input torque based on a nominal model based on the configuration of the controlled object, and a correction unit that takes torsion bar torque as input and outputs a second correction torque to correct the input torque. The model-following control unit is configured such that the transfer function of the controlled object is constrained to the transfer function of the nominal model. The controlled object receives an input torque in which the first correction torque and the second correction torque have been subtracted. The gain of the transfer function of the correction unit in the first frequency band below a predetermined frequency is greater than the gain of the transfer function of the correction unit in the second frequency band above the predetermined frequency.

Description

[Technical Field]

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

[0002] An electric power steering system installed in a vehicle is known (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-183046 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In the electric power steering system described above, for example, model-following control can be used to suppress disturbances transmitted to the driver who is steering the vehicle. However, in this case, even the transmission of torque that is preferable for the driver to receive in order to obtain a suitable steering feel, such as torque transmitted from the road surface on which the vehicle is traveling, is suppressed, resulting in a problem in which the steering feel perceived by the driver is reduced.

[0005] In view of the above circumstances, one of the objectives of the present invention is to provide a control device, a motor device, an electric power steering device, a control method, and a program that can suppress a decrease in the steering feel perceived by the driver. [Means for solving the problem]

[0006] One aspect of the control device of the present invention is a control device for controlling a portion of an electric power steering system mounted on a vehicle, which has an input shaft to which a steering wheel operated by an helmsman is connected, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, the portion including the motor being controlled, the control device comprising: an assist control unit that generates an input torque input to the control device based on the torsion bar torque generated in the torsion bar; a model following control unit that generates a first correction torque to correct the input torque based on a nominal model based on the configuration of the control device; and a correction unit that takes the torsion bar torque as input and outputs a second correction torque to correct the input torque. The model following control unit is configured such that the transfer function of the control device is constrained to the transfer function of the nominal model in a frequency band where the complementary sensitivity gain, which is the gain in the gain characteristics of the complementary sensitivity function for the modeling error between the control device and the nominal model, is approximately 1. The control device receives the input torque in a state in which the first correction torque and the second correction torque have been subtracted. The gain of the transfer function of the correction unit in the first frequency band below a predetermined frequency is greater than the gain of the transfer function of the correction unit in the second frequency band higher than the predetermined frequency.

[0007] One embodiment of the motor device of the present invention comprises the control device described above and the motor.

[0008] One embodiment of the electric power steering device of the present invention comprises the above-described motor device and a steering mechanism having the input shaft, the output shaft, and the torsion bar.

[0009] One aspect of the control method of the present invention is a control method for controlling a portion of an electric power steering system mounted on a vehicle, which has an input shaft to which a steering wheel operated by a driver is connected, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, the portion including the motor being controlled, the method comprising: generating an input torque input to the control target based on the torsion bar torque generated in the torsion bar; performing model-following control to generate a first correction torque for correcting the input torque based on a nominal model based on the configuration of the control target; and correcting the modeling error between the control target and the nominal model by the model-following control. This includes constraining the transfer function of the controlled object to the transfer function of the nominal model in a frequency band where the complementary sensitivity gain, which is the gain in the gain characteristics of the complementary sensitivity function, is approximately 1; outputting a second correction torque that corrects the input torque, taking the torsion bar torque as input; inputting the input torque to the controlled object in a state in which the first correction torque and the second correction torque have been subtracted; and making the gain of the transfer function from the torsion bar torque to the second correction torque in a first frequency band below a predetermined frequency greater than the gain of the transfer function from the torsion bar torque to the second correction torque in a second frequency band higher than the predetermined frequency.

[0010] One aspect of the program of the present invention involves causing a computer to execute the above-described control method. [Effects of the Invention]

[0011] According to one aspect of the present invention, in an electric power steering system, it is possible to suppress a decrease in the steering feel perceived by the driver. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram showing an electric power steering system according to one embodiment. [Figure 2] Figure 2 is a block diagram showing the configuration of a control device according to one embodiment. [Figure 3] Figure 3 is a functional block diagram showing the functions of the processor in a control device according to one embodiment. [Figure 4] Figure 4 is a graph illustrating the gain characteristics of the complementary sensitivity function in one embodiment, and the gain characteristics 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] Figure 5 is a graph showing an example of the relationship between steering angle and self-aligning torque. [Figure 6] Figure 6 is a graph showing an example of the gain characteristics of the transfer function of the correction unit in one embodiment. [Figure 7] Figure 7 is a simplified block diagram showing a control device in one embodiment. [Figure 8] Figure 8 is a graph showing an example of the gain characteristics of the transfer function from steering torque to the controlled object in one embodiment. [Modes for carrying out the invention]

[0013] The electric power steering system 1000 of this embodiment, shown in Figure 1, is mounted on a vehicle. As shown in Figure 1, the electric power steering system 1000 comprises a steering mechanism 530 and a control device 100. The steering mechanism 530 has a steering mechanism section 520 and an auxiliary mechanism section 540. The electric power steering system 1000 controls the auxiliary mechanism section 540 by the control device 100, thereby generating a steering torque T in the steering mechanism section 520 when the driver operating the vehicle steers the steering wheel 521. h It generates an auxiliary torque to assist the driver. This auxiliary torque reduces the burden on the driver when operating the steering wheel 521. The driver of the vehicle is the helmsman who steers the vehicle's steering wheel 521.

[0014] The steering mechanism 520 includes a steering wheel 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 tires 529A, 529B. In other words, the steering mechanism 530 includes a steering wheel 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 tires 529A, 529B.

[0015] The steering shaft 522 is a shaft that extends from the steering wheel 521, which is operated by the driver. One end of the input shaft 524a is connected to the end of the steering shaft 522 opposite to the side 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.

[0016] 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 the range in which the torsion bar 546, described later, can twist.

[0017] The auxiliary mechanism unit 540 includes a steering torque sensor 541, a steering angle sensor 542, a motor 543, a speed reduction mechanism 544, an inverter 545, and a torsion bar 546. That is, the steering mechanism 530 includes a steering torque sensor 541, a steering angle sensor 542, a motor 543, a speed reduction mechanism 544, an inverter 545, and a torsion bar 546. The torsion bar 546 connects the input shaft 524a and the output shaft 524b. The torsion bar 546 is arranged 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 be twisted around the rotation axis R.

[0018] The steering torque sensor 541 detects the steering torque T in the steering mechanism unit 520 by detecting the amount of twist around the rotation axis R of the torsion bar 546. h to detect. The steering torque T h is the torsion bar torque generated in the torsion bar 546 and is the torsional moment around the rotation axis R. The steering angle sensor 542 can detect the rotation angle θ a around the rotation axis R of the input shaft 524a. The rotation angle θ a of the input shaft 524a is equal to the steering angle θ h of the steering wheel 521. That is, the steering angle sensor 542 can detect the steering angle θ a of the input shaft 524a, and thereby detect the steering angle θ h of the steering wheel 521. Based on the steering torque sensor 541 and the steering angle sensor 542, it is possible to detect the rotation angle θ b of the output shaft 524b. The rotation angle θ b of the output shaft 524b is the steering angle θ s .

[0019] The inverter 545 converts DC power, which is a pseudo-sine wave of U-phase, V-phase, and W-phase, into three-phase AC power according to the motor drive signal input from the control device 100 and supplies it to the motor 543. The motor 543 is connected to the output shaft 524b via the reduction mechanism 544. The motor 543 is supplied with three-phase AC power from the inverter 545. The motor 543 is, for example, an Interior Permanent Magnet Synchronous Motor (IPMSM), a Surface Mounted Permanent Magnet Synchronous Motor (SPMSM), or a Switched Reluctance Motor (SRM). The motor 543, supplied with three-phase AC power from the inverter 545, provides steering torque T h It generates an auxiliary torque corresponding to the current. The motor 543 transmits the generated auxiliary torque to the output shaft 524b via the reduction mechanism 544.

[0020] The control device 100 controls the portion of the steering mechanism 530 mounted on the vehicle that includes at least the motor 543, as the controlled object 560. In this embodiment, the controlled object 560 includes a steering mechanism 520, a torsion bar 546, a motor 543, and a reduction mechanism 544. Since the controlled object 560 includes an input shaft 524a and an output shaft 524b that can rotate relative to each other via the torsion bar 546, the motion of the controlled object 560 cannot be described by the equations of motion of a simple one-inertial frame alone. The controlled object 560 changes between one-inertial frames and two-inertial frames depending on how hard the driver grips the steering wheel 521. The harder the driver grips the steering wheel 521, the closer the controlled object 560 is to one-inertial frames. The looser the driver grips the steering wheel 521, the closer the controlled object 560 is to two-inertial frames. Thus, the controlled object 560 is composed of two inertial frames.

[0021] The control device 100 is electrically connected to the inverter 545. Based on detection signals detected by the steering torque sensor 541, the steering angle sensor 542, and the vehicle speed sensor 300 mounted on the vehicle, the control device 100 generates a motor drive signal and outputs it to the inverter 545. The control device 100 controls the controlled object 560 by controlling the rotation of the motor 543 via the inverter 545. More specifically, the control device 100 controls the switching operation of multiple switching elements in the inverter 545. Specifically, the control device 100 generates a control signal to control the switching operation of each switching element and outputs it to the inverter 545. Each switching element is, for example, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). In the following description, the control signal that controls the switching operation of each switching element will be called a "gate control signal".

[0022] The control device 100 controls the steering torque T h A torque command value is generated based on these factors, and the torque and rotational speed of the motor 543 are controlled, for example, by 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 mutually orthogonal current component. The control device 100 is not limited to vector control and can perform other closed-loop control methods. The rotational speed of the motor 543 is expressed, for example, as the number of revolutions per minute [rpm (revolutions per minute)] or the number of revolutions per second [rps (revolutions per second)].

[0023] Furthermore, the control device 100 receives the steering torque T directly from the steering torque sensor 541. h The value may be input, or the control device 100 may input the steering torque T from the output value of the steering torque sensor 541. h The value of may be calculated. The control device 100 directly receives the steering angle θ of the steering wheel 521 from the steering angle sensor 542. hThe value may be input, or the control device 100 may input the steering angle θ from the output value of the steering angle sensor 542. h You may also calculate the value of .

[0024] In this embodiment, the electric power steering system 1000 includes a motor unit 100a. The motor unit 100a includes a control device 100, a motor 543, and an inverter 545. The motor unit 100a can be manufactured and sold independently of the other parts of the electric power steering system 1000. Furthermore, the control device 100 can be manufactured and sold independently of the other parts of the motor unit 100a as a control device for controlling the electric power steering system 1000.

[0025] Figure 2 shows a typical 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 interface 114, a drive circuit 115, a ROM 116, and a processor 200. The control device 100 can be implemented as a printed circuit board (PCB) on which these electronic components are mounted.

[0026] The vehicle speed sensor 300, steering torque sensor 541, and steering angle sensor 542 mounted on the vehicle are connected to the processor 200 so that signals can be input to the processor 200. The vehicle speed is input to the processor 200 from the vehicle speed sensor 300. The steering torque T is input to the processor 200 from the steering torque sensor 541. h The following is input: The processor 200 receives the steering angle θ from the steering angle sensor 542. h The following is entered.

[0027] The processor 200 is a semiconductor integrated circuit, also known as a central processing unit (CPU) or microprocessor. The processor 200 sequentially executes a computer program stored in the ROM 116, which contains instructions for controlling the motor drive, to achieve the desired processing. In addition to the processor 200, or in place of the processor 200, the control device 100 may have an FPGA (Field Programmable Gate Array) equipped with a CPU, a GPU (Graphics Processing Unit), an ASIC (Application Specific Integrated Circuit), an ASSP (Application Specific Standard Product), or a combination of two or more circuits selected from these circuits. The processor 200 sets a current command value according to the actual current value and the rotation angle of the motor 543 rotor, generates a PWM (Pulse Width Modulation) signal, and outputs the PWM signal to the drive circuit 115.

[0028] The power supply circuit 111 is connected to an external power supply (not shown). The power supply circuit 111 generates the DC voltage required for each part of the control device 100. The DC voltage generated by the power supply circuit 111 is, for example, 3V or 5V.

[0029] The angle sensor 112 detects the rotation angle of the motor 543's rotor and outputs it to the processor 200. The angle sensor 112 may be a resolver, a Hall element such as a Hall IC, or an MR sensor having a magnetoresistive element. The processor 200 can calculate the angular velocity ω [rad / s] of the motor 543 based on the electrical angle of the motor 543 obtained from the angle sensor 112. The control device 100 may also be equipped with a speed sensor capable of detecting the rotational angular velocity of the motor 543 and an acceleration sensor capable of detecting the rotational angular acceleration of the motor 543 instead of the angle sensor 112.

[0030] The input circuit 113 receives the motor current value detected by a current sensor (not shown). 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 the input level of the processor 200 as needed, 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.

[0031] Communication I / F114 is an input / output interface for transmitting and receiving data in accordance with, for example, an in-vehicle control area network (CAN: Controller Area Network).

[0032] The drive circuit 115 is typically a gate driver or pre-driver. The drive circuit 115 generates gate control signals according to the PWM signal and applies gate control signals to the gates of the 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 as a gate driver may not be necessary. In that case, the gate driver function of the drive circuit 115 can be implemented in the processor 200.

[0033] ROM116 is electrically connected to processor 200. ROM116 is, for example, writable memory, rewritable memory, or read-only memory. Examples of writable memory include PROM (Programmable Read Only Memory). Examples of rewritable memory include flash memory and EEPROM (Electrically Erasable Programmable Read Only Memory). ROM116 stores a control program containing instructions for processor 200 to control motor drive. For example, the control program stored in ROM116 is temporarily loaded into RAM (not shown) during boot-up.

[0034] Figure 3 shows an example of the functional blocks of the processor 200 in this embodiment. The processor 200, which is a computer, sequentially executes the processing or tasks necessary for controlling the motor 543 using each functional block. Each functional block of the processor 200 shown in Figure 3 may be implemented in the processor 200 as software such as firmware, as hardware, or as both software and hardware. Typically, the processing of each functional block in the processor 200 is described in a computer program in software module units and stored in the ROM 116. However, when using an FPGA or the like, all or part of these functional blocks may be implemented as hardware accelerators. Furthermore, the control method for the controlled object 560 in this embodiment is executed by the processor 200, which is a computer, executing a program stored in the control device 100. In other words, the program of this embodiment stored in the control device 100 causes the processor 200, which is a computer, to execute the control method for the controlled object 560 in this embodiment.

[0035] The processor 200 has a controller 200a. The controller 200a has an assist control unit 210, a model following control unit 230, a state feedback unit 280, a correction unit 290, and subtractors SU1 and SU4. In other words, the control device 100 is equipped with an assist control unit 210, a model following control unit 230, a state feedback unit 280, a correction unit 290, and subtractors SU1 and SU4. To put it another way, the processor 200 of the control device 100 has functions implemented that correspond to the assist control unit 210, the model following control unit 230, the state feedback unit 280, the correction unit 290, and subtractors SU1 and SU4, respectively.

[0036] The assist control unit 210 receives the steering torque T detected by the steering torque sensor 541. h The input torque T is input to the controlled object 560. The assist control unit 210 receives the input torque T from the controlled object 560. r steering torque T hIn other words, it is generated based on the torsion bar torque generated in the torsion bar 546. To put it another way, the control method of the controlled object 560 is the input torque T input to the controlled object 560. r steering torque T h This includes generating based on the input torque T. r This is the target torque of motor 543 and is the torque command value. The assist control unit 210 receives the input torque T r The assist control unit 210 controls the reaction force transmitted to the helmsman from the steering wheel 521 by generating a steering torque T when the steering frequency or steering speed is within a predetermined range. 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 steering wheel 521's operation by the steering wheel operator. The steering speed is the speed of the steering angle that changes based on the steering wheel 521's operation by the steering wheel operator. The assist control unit 210 illustrated in Figure 3 includes a base assist calculation unit 211 and a phase compensator 212.

[0037] The base assist calculation unit 211 calculates the steering torque T h The system also acquires the vehicle speed. The base assist calculation unit 211 calculates the steering torque T h And it generates base assist torque based on vehicle speed. For example, the base assist calculation unit 211 calculates the steering torque T h It has a lookup table (LUT) that defines the relationship between vehicle speed and base assist torque. The base assist calculation unit 211 refers to the lookup table and calculates the steering torque T h Based on the vehicle speed, the corresponding base assist torque can be determined. The base assist calculation unit 211 calculates the steering torque T h The base assist gain can be determined based on the slope defined by the ratio of the change in base assist torque to the change in the amount of fluctuation.

[0038] In this embodiment, the phase compensator 212 adjusts the base assist gain within the range of steering frequencies that the helmsman can take when operating the steering wheel 521, and compensates for the rigidity of the torsion bar 546. The range of steering frequencies that can take 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 In other words, a first-order phase compensation may be applied to the torsion bar torque. The first-order phase compensation is represented, for example, by the transfer function of equation (1).

[0039]

number

[0040] In equation (1), s is a Laplace transformer, f1 is the zero frequency [Hz] of the transfer function, and f2 is the pole frequency [Hz] 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 and 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 setting the pole frequency higher than the zero frequency. The larger the distance between the pole frequency and the zero frequency, the greater the phase lead.

[0041] The phase compensator 212 uses the base assist torque and base assist gain output from the base assist calculation unit 211 to determine the input torque T r This generates a stable phase compensator. For example, the phase compensator 212 is a stabilization compensator, and stabilization phase compensation can be applied to the base assist torque. The phase compensator 212 may have a transfer function of order 2 or higher whose frequency characteristics are variable according to the base assist gain. A transfer function of order 2 or higher is expressed using a responsiveness parameter and a damping ratio parameter. A transfer function of order 2 or higher can be expressed by equation (2), for example. By making the order of the transfer function 2, damping can be applied to the characteristics of the transfer function. By changing the damping, it is possible to adjust the phase characteristics.

[0042]

number

[0043] In equation (2), s is a Laplace transformer, ω1 is the zero frequency of the transfer function, ω2 is the pole frequency of the transfer function, ζ1 is the zero attenuation ratio, and ζ2 is the pole attenuation ratio. The pole frequency ω2 is lower than the zero frequency ω1.

[0044] The model following control unit 230 controls the input torque T r The first corrective torque T corrects for the above. f1 This is generated based on a nominal model based on the configuration of the controlled object 560. In this embodiment, the first corrected torque T f1 The input torque T r This is the feedback torque that is fed back to the control target 560. The nominal model is an internal model used as a constraint model for the control target 560 when controlling the control target 560. The nominal model will be described in detail later. The model following control unit 230 is a controller configured to perform model following control. The control method for the control target 560 is the input torque T r The first corrective torque T corrects for the above. f1 This includes performing model-following control, which generates a model based on a nominal model derived from the configuration of the controlled object 560. The specific configuration of the model-following control unit 230 will be described in detail later.

[0045] The subtractor SU1 receives an input torque T r From there, the first corrected torque T output from the model following control unit 230 f1Subtract the disturbance torque T from the output of adder AD1. The output from subtractor SU1 is input to subtractor SU4 and model following control unit 230. Subtractor SU4 outputs to adder AD1 the value obtained by subtracting the output from correction unit 290 from the output of subtractor SU1. Adder AD1 outputs to adder AD2 the value obtained by adding the output from state feedback unit 280 to the output from subtractor SU4. Adder AD2 outputs to adder AD1 the disturbance torque T d The value obtained by adding this value is output to the controlled device 560.

[0046] Disturbance Torque T d This is the difference between the output torque of the ideal motor 543 and the actual output torque of the motor 543. Disturbance torque T d This includes disturbance torques applied externally to the controlled object 560. Disturbance torque T d This includes, for example, excess torque caused by friction and play resulting from mechanical elements such as the motor 543 and reduction mechanism 544, torque ripple in the motor 543, and self-aligning torque T. SAT , external disturbance torque that may occur when driving on unpaved, bumpy or gravel roads, and steering torque T h This includes the torque T shown in Figure 3. da is the disturbance torque T d Of which, steering torque T h This is the torque excluding the disturbance torque T. d Torque T da and steering torque T h Torque T is the sum of these two values. da Self-aligning torque T SAT Includes.

[0047] In this embodiment, the model following control unit 230 controls the steering angle θ s Based on the first corrected torque T f1 Generates input torque T rThe model following control unit 230 includes an inverse nominal model 231, a first filter 232a, a second filter 232b, an assist adjustment unit 270, a subtractor SU2, and an adder AD3. In this embodiment, the first filter 232a is a high-pass filter. The first filter 232a has a first cutoff frequency Cf1. The first cutoff frequency Cf1 is, for example, 2Hz or more and 10Hz or less. In this embodiment, the first cutoff frequency Cf1 is higher than 5Hz and lower than 10Hz.

[0048] In this embodiment, the second filter 232b is a low-pass filter. The second filter 232b has a second cutoff frequency Cf2 that is higher than the first cutoff frequency Cf1. The second cutoff frequency Cf2 is, for example, 3 Hz or more and 50 Hz or less. However, the upper limit of the second cutoff frequency Cf2 may be set to a range of approximately 140 Hz or more and 200 Hz or less. The order of the second filter 232b is third order or higher. The second filter 232b may be composed of, for example, multiple low-pass filters. The first filter 232a and the second filter 232b are connected in series.

[0049] The model-following control unit 230 ensures that in the frequency band where the complementary sensitivity gain GT, which is the gain in the gain characteristic of the complementary sensitivity function T(s) for the modeling error between the controlled object 560 and the nominal model, is approximately 1, the transfer function P(s) of the controlled object 560 is equal to the transfer function P of the nominal model. n It is configured to be constrained to (s). In other words, the control method of this embodiment uses model following control to determine the transfer function P(s) of the controlled object 560 in a frequency band where the complementary sensitivity gain GT is approximately 1, compared to the transfer function P of the nominal model. nThis includes being constrained to (s). "The complementary sensitivity gain GT is approximately 1" includes not only the case where the complementary sensitivity gain GT is 1, but also, for example, the case where the complementary sensitivity gain GT is 0.8 or more and 1.2 or less. This numerical range is, for example, the range in which the gain of the effective disturbance suppression characteristic can be adjusted to 1, taking into account the positive and negative efficiency of the worm gear when the reduction mechanism 544 connected to the motor 543 has a worm gear. Since the efficiency of the worm gear is about 0.8, it is necessary to adjust the gain by ±0.2 relative to the target value of 1.

[0050] The complementary sensitivity function T(s) is the complementary sensitivity function of the inner loop composed of the model following control unit 230. Figure 4 shows the complementary sensitivity gain GT in the complementary sensitivity function T(s). The complementary sensitivity gain GT is the gain of the complementary sensitivity function T(s) as a transfer function, and is the absolute value of the complementary sensitivity function T(s). In the graph of Figure 4, the horizontal axis represents frequency f [Hz], and the vertical axis represents the complementary sensitivity gain GT. As shown in Figure 4, the complementary sensitivity function T(s) has a gain of approximately 0 dB, i.e., the complementary sensitivity gain GT in the transfer function is approximately 1, in at least a portion of the frequency band where the frequency f is above the first cutoff frequency Cf1 and below the second cutoff frequency Cf2. In the example in Figure 4, the complementary sensitivity gain GT is 1 in the frequency band where the frequency f1a is higher than the first cutoff frequency Cf1 and below the second cutoff frequency Cf2 and below the second cutoff frequency Cf2. Frequency f1a is lower than frequency f2a. In the frequency band between frequency f1a and frequency f2a, the complementary sensitivity gain GT may be, for example, a value of 0.95 or more and less than 1. The complementary sensitivity gain GT at the first cutoff frequency Cf1 is smaller than the complementary sensitivity gain GT at frequency f1a. The complementary sensitivity gain GT at the second cutoff frequency Cf2 is smaller than the complementary sensitivity gain GT at frequency f2a. In this embodiment, the frequency band in which the complementary sensitivity gain GT is approximately 1 is the frequency band between frequency f1b and frequency f2b. Frequency f1b is higher than the first cutoff frequency Cf1 and lower than frequency f1a. Frequency f2b is lower than the second cutoff frequency Cf2 and higher than frequency f2a. In the frequency band between frequency f1b and frequency f2b, the complementary sensitivity gain GT is, for example, 0.8 or more and less and less than 1. In this specification, "the transfer function of the controlled object is constrained to the transfer function of the nominal model" means, for example, that the controlled object is controlled in such a way that, when looking at the input-output relationship, its transfer function appears to be the transfer function of the nominal model.

[0051] The transfer function P(s) of the controlled object 560 is a plant characteristic on which model-following control is performed. The transfer function P(s) of the controlled object 560 is expressed, for example, by the following equation (3).

[0052]

number

[0053] The inverse nominal model 231 is the inverse model of a given nominal model used to constrain the controlled object 560. The transfer function P of the nominal model. n(s) is represented by, for example, the following formula (4). The transfer function P of the inverse nominal model 231 n -1 (s) is represented by, for example, the following formula (5).

[0054]

Number

[0055]

Number

[0056] In formulas (4) and (5), s is the Laplace transform variable, and J n is a parameter representing the moment of inertia of the nominal model, and B n is a parameter representing the viscous friction coefficient of the nominal model. Note that the transfer function P n (s) of the nominal model and the transfer function P n -1 (s) of the inverse nominal model 231 are not limited to the examples shown in formulas (4) and (5), and are not particularly limited.

[0057] As shown in FIG. 3, the output of the control object 560 is input to the inverse nominal model 231. In this embodiment, the steering angle θ s is input to the inverse nominal model 231. That is, in this embodiment, the steering angle θ s is input to the model following control unit 230 as the output of the control object 560. The inverse nominal model 231 outputs torque T s based on the above formula (5) and the input steering angle θ p . That is, the model following control unit 230 calculates the torque T p using the nominal model based on the output of the control object 560. 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 control object 560.

[0058] The subtractor SU2 subtracts the output from the subtractor SU1 from the output of the inverse nominal model 231 to obtain the differential torque T. a It generates the first corrected torque T. The output from subtractor SU1 is the first corrected torque T. f1 This is after the subtraction of the second corrected torque T described later. f2 Input torque T before subtraction r Therefore, the model following control unit 230 has a first corrected torque T f1 After subtraction, and the second corrected torque T f2 Input torque T before subtraction r The input is given. In this embodiment, the subtractor SU2 is the first corrected torque T f1 After the feedback is received, the state compensation value V, which will be described later, s This is before the feedback is given, and the second corrected torque T described later. f2 Input torque T before subtraction r Torque T p Subtracting the difference torque T a Generates the differential torque T. a For example, disturbance torque T d The second corrected torque T, which will be described later, f2 This is an estimated value after subtracting the difference torque T output from the subtractor SU2. a The signal is input to the second filter 232b, where it undergoes low-pass filtering, and then input to the first filter 232a, where it undergoes high-pass filtering. The differential torque T after filtering by the first filter 232a and the second filter 232b is then input to the first filter 232a and the second filter 232b. a This is input to adder AD3. The differential torque T filtered in the first filter 232a and the second filter 232b a This is a state in which frequency components lower than the first cutoff frequency Cf1 and frequency components higher than the second cutoff frequency Cf2 have been removed. In other words, the differential torque T filtered by the first filter 232a and the second filter 232b is... a This refers to frequency components T, which are above the first cutoff frequency Cf1 and below the second cutoff frequency Cf2. aM That is the case.

[0059] The assist adjustment unit 270 generates compensation values ​​for friction and disturbances, and adjusts the differential torque T a Adjusts the differential torque T. In this embodiment, the assist adjustment unit 270 adjusts the differential torque T. a Among them, frequency component T aM The assist adjustment unit 270 is connected in parallel to the first filter 232a. The assist adjustment unit 270 includes a friction compensation value calculation unit 250, a disturbance compensation value calculation unit 260, and a subtractor SU3.

[0060] The subtractor SU3 subtracts the output value from the first filter 232a from the output value from the second filter 232b. Here, the output value from the second filter 232b is the differential torque T. a This is the value after removing frequency components higher than the second cutoff frequency Cf2. The output value from the first filter 232a is the differential torque T a This is the value from which frequency components higher than the second cutoff frequency Cf2 and frequency components lower than the first cutoff frequency Cf1 have been removed. Therefore, the value output from the subtractor SU3 is the differential torque T a Among these, the frequency component T is lower than the first cutoff frequency Cf1. aL The output of the subtractor SU3 is input to the friction compensation value calculation unit 250 and the disturbance compensation value calculation unit 260. Frequency component T aL This includes frictional force and self-aligning torque T SAT This includes disturbance torque caused by play in the controlled object 560, and torque ripple occurring in the controlled object 560.

[0061] The friction compensation value calculation unit 250 calculates a friction compensation value V that compensates for at least a portion of the friction force generated in the controlled object 560. f The difference torque T a The calculation is based on the following: As described above, the value from the subtractor SU3 input to the friction compensation value calculation unit 250 is the differential torque T a Among these, the frequency component T is lower than the first cutoff frequency Cf1. aL Therefore, in this embodiment, the friction compensation value calculation unit 250 calculates the differential torque T aBased on the component with a frequency lower than the first cutoff frequency Cf1, the friction compensation value V f Calculate.

[0062] The friction compensation value calculation unit 250 includes 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 applies a gain K1 to the output value from the limiter 252. The friction compensation value calculation unit 250 calculates the differential torque T a For the components with frequencies lower than the first cutoff frequency Cf1, the limiter 252 and the gain K1 are applied to obtain a friction compensation value V. f The threshold value of the limiter 252 and the gain K1 value are predetermined, for example, based on the frictional force actually generated on the controlled object 560.

[0063] Friction compensation value V output from friction compensation value calculation unit 250 f is the differential torque T a The frequency component T aL This value compensates for at least a portion of the frictional force component included in the control object 560. Generally, a moderate amount of friction is required for the control object 560, so the friction compensation value calculation unit 250 sets the friction compensation value V to a value smaller than the frictional force actually generated in the control object 560. f This is calculated as follows. This makes it possible to achieve highly accurate friction compensation while leaving an appropriate amount of frictional force on the controlled object 560. Friction compensation value V f The friction compensation provided by this system includes, 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.

[0064] A vehicle equipped with an electric power steering system 1000 can be driven according to driving modes that include an automatic driving mode and a manual driving mode. In this case, the gain K1 of the gain adjuster 253 may be switched according to the driving mode. The larger the gain K1 of the gain adjuster 253, the greater the degree of friction reduction. It is preferable that the gain K1 in automatic driving mode is larger than the gain K1 set in manual driving mode. This makes it possible to apply optimal friction compensation to the automatic driving mode, where friction reduction is more important.

[0065] The disturbance compensation value calculation unit 260 calculates the self-aligning torque T generated in the controlled object 560. SAT Disturbance compensation value V compensates for at least a portion of it. d The disturbance compensation value V is calculated in this embodiment. d This includes a compensation value that compensates for at least a portion of the frictional force generated in the controlled object 560, the disturbance torque caused by the play in the controlled object 560, and the torque ripple generated in the controlled object 560. The disturbance compensation value calculation unit 260 calculates the torque T output from the inverse nominal model 231. p and input torque T r The difference is the differential torque T. a Based on this, the disturbance compensation value V d The disturbance compensation value calculation unit 260 calculates the torque T based on the output of the controlled object 560 using a nominal model. p and input torque T r The difference is the differential torque T. a Based on this, the disturbance compensation value V d The differential torque T is calculated. As described above, the value from the subtractor SU3 input to the disturbance compensation value calculation unit 260 is the differential torque T. a Among these, the frequency component is lower than the first cutoff frequency Cf1. Therefore, in this embodiment, the disturbance compensation value calculation unit 260 calculates the differential torque T a The disturbance compensation value V is based on the component with a frequency lower than the first cutoff frequency Cf1. d Calculate.

[0066] The disturbance compensation value calculation unit 260 includes a limiter 262 and a gain adjuster 263. The limiter 262 limits the output value from the subtractor SU3. If the input value exceeds an 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, for example, the threshold of the limiter 252. The gain adjuster 263 applies a gain K2 to the output value from the limiter 262. The transfer function P(s) of the controlled object 560 is the transfer function P of the nominal model. n The maximum value of the gain K2 of the gain adjuster 263 is determined under the constraint of (s). The value of gain K2 is different from, for example, the value of gain K1. The value of gain K2 is, for example, between 0.1 and 0.8. The gain K2 of the gain adjuster 263 may be switched according to the vehicle's driving mode.

[0067] Disturbance compensation value V d is the differential torque T a The frequency component T aL This value compensates for at least a portion of the self-aligning torque component included in the control. The disturbance compensation value calculation unit 260 calculates, for example, the self-aligning torque T that actually occurs in the control target 560. SAT The disturbance compensation value V is approximately half of the value of the disturbance compensation value. d The self-aligning torque T that actually occurs in the controlled object 560 is calculated as follows. SAT For example, the threshold value and gain K2 of the limiter 262 of the disturbance compensation value calculation unit 260 are determined in advance by the self-aligning torque T SAT The disturbance compensation value V is set to a value between 0.1 and 0.8 times the magnitude of the disturbance. d The value is adjusted to the value at which the disturbance compensation value V is calculated in the disturbance compensation value calculation unit 260. d This is the friction compensation value V calculated in the friction compensation value calculation unit 250. f This is a different value.

[0068] Here, the differential torque T a The frequency component T aLThis includes the frictional force generated in the first controlled object 560 and the self-aligning torque T generated in the controlled object 560. SAT This includes disturbance torque caused by play in the controlled object 560, and torque ripple occurring in the controlled object 560. Therefore, the frequency component T aL The friction compensation value V obtained by processing with limiter 252 and gain adjuster 253 f This includes disturbances other than friction, namely the self-aligning torque T generated in the controlled object 560. SAT This also includes compensation values ​​that compensate for at least a portion of the disturbance torque caused by play in the controlled object 560, and the torque ripple that occurs in the controlled object 560. Furthermore, the frequency component T aL The disturbance compensation value V obtained by processing with limiter 262 and gain adjuster 263 is obtained. d Self-aligning torque T SAT This also includes compensation values ​​that compensate for other disturbances, namely frictional forces occurring in the controlled object 560, disturbance torques resulting from play in the controlled object 560, and at least a portion of the torque ripple occurring in the controlled object 560.

[0069] The first corrected torque T used for model following control in the model following control unit 230 f1In order to apply friction compensation and disturbance compensation performed in the assist adjustment unit 270, it is necessary to pay attention to the stability conditions of the model following control. This condition, according to the small gain theorem described later, is that the gain in the gain characteristics of the transfer function of the assist adjustment unit 270, constrained to characteristics that consider stability, does not exceed 1. This is derived from the design conditions of the second filter 232b. In this embodiment, the values ​​of gains K1 and K2 in the gain adjusters 253 and 263 are set to a maximum of 1, and subtraction processing is applied by providing a subtractor SU3 before the limiters 252 and 262 so that the gain in the gain characteristics under these conditions becomes 1. In other words, the assist adjustment unit 270 behaves as a low-pass filter having a transfer function of 1-Q1(s). Q1(s) is the transfer function of the first filter 232a, which is a high-pass filter. The assist adjustment unit 270 applies a low-pass filter process with a transfer function of 1-Q1(s) to the torque output from the second filter 232b, and the friction compensation value calculation unit 250 and the disturbance compensation value calculation unit 260 adjust and output the processed value, respectively.

[0070] The adder AD3 adds the output value from the assist adjustment unit 270 to the output value from the first filter 232a. In other words, the adder AD3 adds the frequency component T aM Friction compensation value V f and disturbance compensation value V d Add and . Adder AD3 outputs the frequency component T aM and friction compensation value V f and disturbance compensation value V d The first corrected torque T is calculated by adding these together. f1 The following is output. The first corrected torque T is output from adder AD3. f1 This is the input to the controlled object 560, i.e., the input torque T. r This is fed back to the model following control unit 230. In this embodiment, the model following control unit 230 receives the differential torque T from which frequency components lower than the first cutoff frequency Cf1 have been removed by the first filter 232a, which is a high-pass filter. a , that is, frequency component T aM For this, the friction compensation value V fand disturbance compensation value V d Adding these together gives the first corrected torque T f1 Generates.

[0071] The state feedback unit 280 determines the apparent transfer function of the controlled object 560 based on the output of the controlled object 560, and the transfer function P of the nominal model. n (s) should be approached, state compensation value V s Input torque T r Feedback is provided to the control target 560. The apparent transfer function of the control target 560 is, for example, the transfer function of a single part when the part located inside the feedback loop created by the model following control unit 230 is considered as a single part. Specifically, in this embodiment, the apparent transfer function of the control target 560 is the transfer function of the entire part from the subtractor SU1 to the output of the control target 560, and is the transfer function of the combined part of the state feedback unit 280 and the control target 560. In this embodiment, the state feedback unit 280 is the first corrected torque T f1 and second corrected torque T f2 The input torque T after correction and before being input to the controlled object 560. r For this, the state compensation value V s The state feedback unit 280 provides feedback to the value output from the subtractor SU4, using a state compensation value V. s Provide feedback.

[0072] State compensation value V s This includes a compensation value that compensates for at least a portion of the inertial force, viscous force, and frictional force acting on the controlled object 560. More specifically, the state compensation value V s This includes a compensation value that compensates for at least a portion of the inertial force, viscous force, and frictional force generated in the motor 543. In this embodiment, the state compensation value V s This is a compensation value that includes the inertial force, viscous force, and frictional force acting on the motor 543, respectively.

[0073] The state feedback unit 280 includes an inertia compensator 281, a viscosity compensator 282, and a friction compensator 283. The inertia compensator 281 controls the steering angle θ s Based on this, a compensation value is calculated to compensate for at least a portion of the inertial force generated in the motor 543. The viscous compensator 282 controls the steering angle θ s Based on this, a compensation value is calculated to compensate for at least a portion of the viscous force generated in the motor 543. The friction compensator 283 controls the steering angle θ. s Based on this, a compensation value is calculated that compensates for at least a portion of the frictional force generated in the motor 543. In this embodiment, the state compensation value V s This consists 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 the adder AD1 to form the first corrected torque T f1 Input torque T after correction r It will be added to.

[0074] The correction unit 290 controls the input torque T r The second corrective torque T corrects for the above. f2 Torsion bar torque, i.e., steering torque T h It is generated based on the steering torque T. The correction unit 290 is used to generate the steering torque T. h The following is input. The correction unit 290 performs the second correction torque T f2 The result is output to the subtractor SU4. In this embodiment, the correction unit 290 controls the steering torque T h A low-pass filter is applied to the second corrected torque T f2The correction unit 290 generates the following. The gain characteristics of the transfer function F(s) of the correction unit 290 are represented, for example, as shown in the graph in Figure 6. In the graph in Figure 6, the horizontal axis represents the frequency f [Hz], and the vertical axis represents the gain of the transfer function F(s) of the correction unit 290. In the low-pass filter processing performed by the correction unit 290, the cutoff frequency is the third cutoff frequency Cf3. In this embodiment, the third cutoff frequency Cf3 corresponds to a "predetermined frequency". The third cutoff frequency Cf3 is, for example, 5 Hz or more and 15 Hz or less. The value of the third cutoff frequency Cf3 is not particularly limited.

[0075] As shown in Figure 6, the frequency band below the third cutoff frequency Cf3 is the first frequency band FB1. The frequency band above the third cutoff frequency Cf3 is the second frequency band FB2. The gain of the transfer function F(s) of the correction unit 290 in the first frequency band FB1 is greater than the gain of the transfer function F(s) of the correction unit 290 in the second frequency band FB2. The gain of the transfer function F(s) in the first frequency band FB1 is approximately 1. "The gain of the transfer function F(s) is approximately 1" includes not only the case where the gain of the transfer function F(s) is 1, but also the case where the gain of the transfer function F(s) is greater than or equal to the value of the gain of the transfer function F(s) at the third cutoff frequency Cf3. The gain of the transfer function F(s) at the third cutoff frequency Cf3 is less than 1. The gain of the transfer function F(s) at the third cutoff frequency Cf3 is, for example, 1 / √2. The gain of the transfer function F(s) is 1 in the frequency band below the third cutoff frequency Cf3, specifically below frequency fa. In the frequency band above frequency fa, the gain of the transfer function F(s) decreases as the frequency f increases.

[0076] In at least a portion of the second frequency band FB2, the gain of the transfer function F(s) of the correction unit 290 increases as the frequency f decreases. In this embodiment, throughout the entire second frequency band FB2, the gain of the transfer function F(s) of the correction unit 290 increases as the frequency f decreases. In other words, throughout the entire second frequency band FB2, the gain of the transfer function F(s) of the correction unit 290 decreases as the frequency f increases.

[0077] Second Correction Torque T f2 is steering torque T h The second corrected torque T is generated by multiplying it by the gain of the transfer function F(s) of the correction unit 290. f2 Of these, the component in the first frequency band FB1 has a gain of approximately 1 in the transfer function F(s), therefore the steering torque T h The component of the first frequency band FB1 has approximately the same value. Second corrected torque T f2 Of these, the component in the second frequency band FB2 has a smaller gain in the transfer function F(s) than the component in the first frequency band FB1, resulting in steering torque T h The second correction torque T is lower than the component in the second frequency band FB2. f2 Of these, the component in the second frequency band FB2 shows that as the frequency f increases, the steering torque T increases. h Of these, the component in the second frequency band FB2 becomes smaller.

[0078] As shown in Figure 3, the second corrected torque T f2 In the subtractor SU4, the first corrected torque T f1 Input torque T after subtraction r It is subtracted from the second corrected torque T. f2 Input torque T after subtraction r In adder AD1, the state compensation value V s The values ​​are added, and the disturbance torque T is in the adder AD2. d The first corrected torque T is input to the controlled object 560 after it has been added. f1 The input torque T after correction and before being input to the controlled object 560. r From the second corrected torque T f2 This is subtracted. The controlled object 560 has the first corrected torque T f1 and the second corrected torque T f2 Input torque T after subtraction r The following is entered.

[0079] Next, the control by the model-following control unit 230 will be described in more detail. The model-following control unit 230 controls the controlled object 560 using the inverse model of the nominal model it has as an internal model, i.e., the inverse nominal model 231. In this embodiment, the feedback loop created by the model-following control unit 230 makes it possible to compensate for torque ripple and other factors that depend on the angular velocity ω of the motor 543.

[0080] The model-following control unit 230 is structurally similar to a conventional disturbance estimator (disturbance observer), but its intended function and effect are different. Conventional disturbance estimators estimate disturbance torque by using an inverse plant model, which is an internal model, that closely resembles the controlled object 560, and reduce the effect of disturbances by pre-adding or subtracting the disturbance torque.

[0081] In this embodiment, the control by the model-following control unit 230 is performed by a feedback loop so that the transfer function P(s) of the controlled object 560 is the transfer function P of the nominal model which has an internal model. n The effect of being constrained by (s) is utilized. For example, if the nominal model is defined so that there is no torque ripple, the transfer function P(s) of the controlled object 560 is constrained to the characteristic of having no torque ripple by model following control, and as a result, torque ripple can be reduced by applying torque ripple compensation. Alternatively, 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. Alternatively, 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 model following control unit 230, in addition to torque ripple compensation for the motor 543, for example, lost torque compensation or motor inertia compensation is performed. In the above-mentioned equations (4) and (5), J n and B n By appropriately setting this, the desired frequency characteristics can be imparted to the transfer function P(s) of the controlled object 560.

[0082] Transfer function P(s) of the controlled object 560 and the transfer function P of the nominal model n When the modeling error with (s) is Δ(s), the transfer function P(s) of the controlled object 560 can be expressed, for example, by the following equation (6).

[0083]

number

[0084] The gain characteristics of the transfer function P(s) of the controlled object 560 have peaks at two frequency values, for example. The modeling error Δ(s) appears, for example, near the higher frequency peak of the two peaks in the gain characteristics of the controlled object 560. Therefore, as shown in Figure 4, the reciprocal of the modeling error Δ(s), 1 / Δ(s), has a bottom in the relatively high-frequency region. In Figure 4, the modeling error Δ(s) is shown as an absolute value. As the modeling error Δ(s) increases, 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 using the nominal model by the model-following control unit 230 becomes unstable. Therefore, in the region where the modeling error Δ(s) is relatively small, the gain of the complementary sensitivity function T(s) is set to approximately 1, and the controlled object 560 is constrained to the nominal model, thereby enabling stable and suitable control of the controlled object 560. Transfer function P of the nominal model n (s) J n and B n By adjusting the modeling error Δ(s), the frequency characteristics of the modeling error Δ(s) are adjusted. By adjusting the first cutoff frequency Cf1 and the second cutoff frequency Cf2, the frequency band in which the gain of the complementary sensitivity function T(s) is approximately 1 is adjusted. This allows the gain of the complementary sensitivity function T(s) to be approximately 1 in the frequency band in which the modeling error Δ(s) is small.

[0085] In Figure 4, 1 / Δ(s) is relatively high in the frequency band below the second cutoff frequency Cf2, and decreases sharply in the frequency band above the second cutoff frequency Cf2. Model-following control, which constrains the controlled object 560 to the nominal model, can be performed stably, for example, in the range where 1 / Δ(s) is greater than 1, i.e., greater than 0 dB. Therefore, as shown in Figure 4, by adjusting 1 / Δ(s) to be greater than 1 in the frequency band where the gain of the complementary sensitivity function T(s) is approximately 1, the controlled object 560 can be stably and suitably controlled by constraining it to the nominal model when the gain of the complementary sensitivity function T(s) is approximately 1.

[0086] For example, in order to broaden the frequency band over which the controlled object 560 can be stably and suitably controlled while constrained to the nominal model, the second cutoff frequency Cf2 should be increased within the range where 1 / Δ(s) is not less than 1, that is, within the frequency band lower than the frequency at which the curve representing 1 / Δ(s) in Figure 4 intersects with the horizontal axis. However, if the second cutoff frequency Cf2 is increased too much, the gain of the complementary sensitivity function T(s) may remain relatively high in the frequency band above the second cutoff frequency Cf2, even though 1 / Δ(s) has decreased, which may lead to unstable control. In contrast, in this embodiment, since the order of the second filter 232b, which is a low-pass filter, is set to the third order or higher, the gain of the complementary sensitivity function T(s) can be sharply reduced in the region where the frequency is higher than the second cutoff frequency Cf2. This allows the gain of the complementary sensitivity function T(s) to be quickly reduced in frequency bands higher than the second cutoff frequency Cf2, even when the second cutoff frequency Cf2 is set relatively high, thereby suppressing instability in the control of the controlled device 560.

[0087] The robust stability of the model-following control unit 230 is guaranteed when the small gain theorem shown in equation (7) below holds between the complementary sensitivity function T(s) and the modeling error Δ(s).

[0088]

number

[0089] As described above, in order to perform model following control using a nominal model in the model following control unit 230, the complementary sensitivity gain GT of the complementary sensitivity function T(s) only needs to be approximately 1. However, considering robust stability, it is necessary to satisfy equation (7) above. As can be understood from this, it is not possible to reconcile making the complementary sensitivity gain GT approximately 1 in all frequency bands with satisfying equation (7), and thus the suppression of disturbances by the model following control unit 230 and robust stability are incompatible.

[0090] As shown in Figure 4, even in the low-frequency region FA1, where the frequency f is lower than the first cutoff frequency Cf1, the complementary sensitivity gain GT of the complementary sensitivity function T(s) becomes less than 1. In the region where the complementary sensitivity gain GT of the complementary sensitivity function T(s) becomes less than 1, the assist control unit 210 controls the input torque T r The controlled object 560 is controlled by performing this control. In the high-frequency region FA2, where the frequency is higher than the second cutoff frequency Cf2, the complementary sensitivity gain GT of the complementary sensitivity function T(s) is greatly reduced, and the first corrected torque T from the model following control unit 230 is reduced. f1 This results in a state where there is almost no feedback to the input of the controlled object 560. On the other hand, in the low-frequency region FA1, the complementary sensitivity gain GT of the complementary sensitivity function T(s) is set to a certain magnitude, and the first corrected torque T f1 This is fed back to the input of the controlled device 560. In the low-frequency region FA1, the compensation value generated in the assist adjustment unit 270 described above is fed back to the input of the controlled device 560 according to the complementary sensitivity gain GT of the complementary sensitivity function T(s).

[0091] When the disturbance torque is accurately estimated by the model following control performed in the model following control unit 230, the control device 100 can be represented simply as shown in the block diagram in Figure 7. QA(s) shown in Figure 7 is the transfer function of the filter unit 233 shown in Figure 3. The filter unit 233 is part of the model following control unit 230. In this embodiment, the filter unit 233 is composed of a first filter 232a, a second filter 232b, an assist adjustment unit 270, and an adder AD3. In the simplified block diagram shown in Figure 7, the steering torque T input to the controlled object 560 as a disturbance is shown. h The input torque T is multiplied by the transfer function (1-F(s))(1-QA(s)). r It is added to. In the simplified block diagram shown in Figure 7, the disturbance torque T d Torque T, which is part of the Torque T da The input torque T is multiplied by the transfer function shown by (1-QA(s)). r It will be added to.

[0092] The transfer function denoted by (1-F(s))(1-QA(s)) has the gain characteristics shown in the graph in Figure 8, for example. In the graph in Figure 8, the horizontal axis represents the frequency f [Hz], and the vertical axis represents the gain of the transfer function denoted by (1-F(s))(1-QA(s)). In the following explanation, the transfer function denoted by (1-F(s))(1-QA(s)) will be referred to as the transfer function FQ(s). As shown in Figure 8, the gain of the transfer function FQ(s) in the first frequency band FB1 below the third cutoff frequency Cf3 is smaller than the gain of the transfer function FQ(s) in the second frequency band FB2 which is higher than the third cutoff frequency Cf3.

[0093] In the second frequency band FB2, the gain of the transfer function FQ(s) is approximately 1. "The gain of the transfer function FQ(s) is approximately 1" includes not only the case where the gain of the transfer function FQ(s) is 1, but also the case where the gain of the transfer function FQ(s) is greater than or equal to the gain of the transfer function FQ(s) at the third cutoff frequency Cf3. The gain of the transfer function FQ(s) at the third cutoff frequency Cf3 is less than 1. For example, the gain of the transfer function FQ(s) at the third cutoff frequency Cf3 is 1 / √2. The gain of the transfer function FQ(s) is 1 in frequency bands above the third cutoff frequency Cf3 (frequency fb and above). Strictly speaking, in frequency bands above frequency fb, the gain of the transfer function FQ(s) decreases as the frequency f decreases, but it can be practically considered to be 1. In frequency bands below frequency fb, the gain of the transfer function FQ(s) decreases as the frequency f decreases.

[0094] In at least a portion of the first frequency band FB1, the gain of the transfer function FQ(s) increases as the frequency f increases. In this embodiment, throughout the entire first frequency band FB1, the gain of the transfer function FQ(s) increases as the frequency f increases. In other words, throughout the entire first frequency band FB1, the gain of the transfer function FQ(s) decreases as the frequency f decreases.

[0095] In the block diagram of Figure 7, since disturbances are accurately estimated by model following control, the steering torque T in the frequency band where the gain of the transfer function FQ(s) is 1 is h The frequency components are compensated 100%. For example, in a frequency band where the gain of the transfer function FQ(s) is 0.5, the steering torque T in that frequency band is compensated. h Half of the frequency components are compensated.

[0096] Here, steering torque T h When this is 100% compensated by model following control, the steering torque T h Torque ripple that occurs is compensated, while steering torque T from the road surface on which the vehicle is traveling is compensated.h This also compensates for the torque transmitted to the driver. As a result, there was a problem in that the driver had difficulty feeling the road surface conditions from the steering wheel 521. Consequently, there was a problem in that the steering feel perceived by the driver was reduced.

[0097] To address the above problem, according to this embodiment, the control device 100 controls the steering torque T h The input is the input torque T r The second corrective torque T corrects for the above. f2 It includes a correction unit 290 that outputs the first corrected torque T. The controlled object 560 has a first corrected torque T. f1 and the second corrected torque T f2 Input torque T after subtraction r The input is as follows: The gain of the transfer function F(s) of the correction unit 290 in the first frequency band FB1, which is below the predetermined third cutoff frequency Cf3, is greater than the gain of the transfer function F(s) of the correction unit 290 in the second frequency band FB2, which is higher than the third cutoff frequency Cf3. In other words, the control method for controlling the controlled object 560 is the steering torque T h With input T, r The second corrective torque T corrects for the above. f2 The output is to provide the first corrected torque T to the controlled object 560. f1 and the second corrected torque T f2 Input torque T after subtraction r Inputting the steering torque T in the first frequency band FB1 h From the second corrected torque T f2 This includes making the gain of the transfer function F(s) up to a certain point greater than the gain of the transfer function F(s) in the second frequency band FB2. Therefore, in the first frequency band FB1 which is lower than the second frequency band FB2, the generated second corrected torque T f2 The value of the frequency component of the steering torque T h It is easy to make the value of the frequency component the same as, or close to, the value of the steering torque T. The frequency of the torque received from the road surface, which is preferable to be transmitted to the helmsman via the steering wheel 521, is the steering torque T. hIt is lower than the frequency of torque ripple that occurs. Therefore, in the first frequency band FB1, which is lower than the second frequency band FB2, the second corrected torque T f2 The frequency components of the steering torque T h Set the frequency component to the same or close value as the second corrected torque T. f2 Input torque T r By subtracting from this, the steering torque T that is preferable to be transmitted to the helmsman is determined. h The frequency components of the input torque T r It can be subtracted from this. This allows the steering torque T that is preferable to be transmitted to the helmsman from the disturbance input to the controlled object 560. h At least a portion of the frequency components can be reduced, and the steering torque T that is transmitted to the helmsman is preferable. h The frequency components of the signal can be suppressed from being compensated by model following control. Therefore, the steering torque T that is preferable to be transmitted to the helmsman is also preferable. h The frequency components can be easily transmitted to the helmsman via the steering wheel 521. Therefore, the steering torque T received from the steering wheel 521 can be easily transmitted. h This allows the driver to feel the condition of the road surface and suppresses a decrease in the steering feel perceived by the driver. On the other hand, in the second frequency band FB2, which is higher than the first frequency band FB1, the gain of the transfer function F(s) of the correction unit 290 is smaller than that of the first frequency band FB1, so the generated second corrected torque T f2 The value of the frequency component of the steering torque T h This makes the frequency components smaller than those of the steering torque T. h Among these, the torque ripple component with a relatively high frequency is the second corrected torque T f2 Input torque T r Even after subtracting from it, it can remain as a disturbance applied to the controlled object 560. Therefore, steering torque T h Among these, components such as torque ripple with relatively high frequencies can be compensated for by model following control, suppressing their transmission to the helmsman. Therefore, unwanted vibrations are suppressed from being transmitted to the helmsman, and the reduction in the steering feel perceived by the helmsman is further suppressed.

[0098] Note that steering torque T h The frequency f of the torque ripple that occurs is, for example, higher than 15 Hz. Steering torque T from the road surface on which the vehicle is traveling. h The preferred frequency f of torque transmitted to the helmsman, such as torque transmitted to the helmsman, is, for example, approximately 5 Hz or more and 15 Hz or less.

[0099] According to this embodiment, in at least a portion of the second frequency band FB2, the gain of the transfer function F(s) of the correction unit 290 increases as the frequency f decreases. In other words, the control method of the controlled object 560 is such that in at least a portion of the second frequency band FB2, the steering torque T h From the second corrected torque T f2 This includes increasing the gain of the transfer function F(s) up to a certain frequency as the frequency f decreases. Therefore, in at least a portion of the second frequency band FB2, the second corrected torque T increases as the frequency f decreases. f2 This allows for a larger second correction torque T in the relatively lower frequency band of the second frequency band FB2. f2 It is easier to increase the steering torque T in the second frequency band FB2. h A certain frequency component in a lower frequency band of the frequency components can be transmitted to the helmsman with a certain magnitude. Therefore, steering torque T can be transmitted throughout the entire second frequency band FB2. h Compared to a case where the entire frequency component is not transmitted to the helmsman, this method can suppress the feeling of unnaturalness in the steering feel perceived by the helmsman, and can further suppress the decrease in the steering feel perceived by the helmsman.

[0100] According to this embodiment, the first corrected torque T f1 The input torque T after correction and before being input to the controlled object 560. r From the second corrected torque T f2 This is subtracted. The model following control unit 230 receives the output of the controlled object 560 and the first corrected torque T f1 After subtraction, and the second corrected torque T f2Input torque T before subtraction r The following is input. In other words, the control method for the controlled object 560 is the first corrected torque T f1 The input torque T after correction and before being input to the controlled object 560. r From the second corrected torque T f2 Subtracting the output of the controlled object 560 and the first corrected torque T f1 After subtraction, and the second corrected torque T f2 Input torque T before subtraction r Based on this, the model following control is performed, and so on. Thus the input torque T r From the second corrected torque T f2 By subtracting this, the second corrected torque T f2 Steering torque T h This can be made uncompensated by model following control. Therefore, the second corrected torque T f2 This allows for optimal transmission of steering feel to the helmsman, further suppressing any decrease in the steering feel perceived by the helmsman.

[0101] According to this embodiment, the correction unit 290 controls the steering torque T h A low-pass filter is applied to the second corrected torque T f2 This generates the steering torque T. In other words, the control method for the controlled object 560 is the steering torque T. h A low-pass filter is applied to the second corrected torque T f2 This includes generating a second corrected torque T in which the frequency components of the first frequency band FB1 are large and the frequency components of the second frequency band FB2 are small. f2 steering torque T h It can be easily generated based on this.

[0102] In this embodiment, the steering torque T is compensated by model following control. h The frequency characteristics are such that, by adjusting the transfer function F(s), the frequency characteristics become similar to the waveform of the transfer function FQ(s) shown in Figure 8. This suppresses a decrease in the steering feel of the driver while maintaining steering torque T hTorque ripple can be suitably compensated for by model following control.

[0103] At least some of the functions of each component of the control device 100 described above may be implemented by hardware including circuit sections such as LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), and GPU (Graphics Processing Unit), or by the cooperation of software and hardware. The storage unit that stores the program causing the processor 200 of the control device 100, which is a computer, to execute the control method described above, is implemented by a storage medium such as RAM (Random Access Memory), ROM (Read Only Memory), HDD (hard disk drive), and flash memory. The storage unit is not particularly limited as long as it can store the program causing the computer to execute the control method described above, and may be a microcomputer or a disk medium such as a CD-ROM. The storage unit may be provided separately from the control device 100. In this case, the control device 100 may communicate with the storage unit by wired communication or wireless communication and execute the program stored in the storage unit.

[0104] The present invention is not limited to the embodiments described above, and other configurations and methods may be adopted within the scope of the technical idea of ​​the present invention. The gain of the transfer function of the correction unit may have any frequency characteristics as long as it is greater in the first frequency band than in the second frequency band. The gain of the transfer function of the correction unit may increase as the frequency decreases in only a part of the second frequency band. In this case, the gain of the transfer function of the correction unit in the other part of the second frequency band may be constant, for example, or decrease as the frequency decreases. The correction unit may generate the second correction torque in any way as long as it outputs a second correction torque in response to the input of torsion bar torque (steering torque).

[0105] Furthermore, this technology can be configured as follows: [1] A control device for controlling the portion of an electric power steering system mounted on a vehicle, which includes an input shaft to which a steering wheel operated by the driver is connected, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, the control device comprising: an assist control unit that generates an input torque input to the control device based on the torsion bar torque generated in the torsion bar; a model following control unit that generates a first correction torque to correct the input torque based on a nominal model based on the configuration of the control device; and a second correction torque that takes the torsion bar torque as input and corrects the input torque. A control device comprising: a correction unit that outputs torque, wherein the model-following control unit is configured such that the transfer function of the controlled object is constrained to the transfer function of the nominal model in a frequency band where the complementary sensitivity gain, which is the gain in the gain characteristic of the complementary sensitivity function for the modeling error between the controlled object and the nominal model, is approximately 1, the controlled object receives the input torque obtained by subtracting the first correction torque and the second correction torque, and the gain of the transfer function of the correction unit in a first frequency band below a predetermined frequency is greater than the gain of the transfer function of the correction unit in a second frequency band higher than the predetermined frequency. [2] The control device according to [1], wherein in at least a portion of the second frequency band, the gain of the transfer function of the correction unit increases as the frequency decreases. [3] The control device according to [1] or [2], wherein the second correction torque is subtracted from the input torque after it has been corrected by the first correction torque and before it is input to the controlled object, and the output of the controlled object and the input torque after the first correction torque has been subtracted and before the second correction torque has been subtracted are input to the model following control unit. [4] The control device according to any one of [1] to [3], wherein the correction unit generates the second correction torque by applying a low-pass filter to the torsion bar torque. A motor device comprising a control device described in any one of items [1] to [4], and the motor. An electric power steering system comprising the motor device described in [6] [5] and a steering mechanism having the input shaft, the output shaft, and the torsion bar. [7] A control method for controlling the portion of an electric power steering system mounted on a vehicle, which includes an input shaft to which a steering wheel operated by a driver is connected, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, wherein the control method involves generating an input torque input to the control object based on the torsion bar torque generated in the torsion bar, and performing model-following control to generate a first correction torque for correcting the input torque based on a nominal model based on the configuration of the control object, and by the model-following control, the gain of a complementary sensitivity function for the modeling error between the control object and the nominal model. A control method comprising: constraining the transfer function of the controlled object to the transfer function of the nominal model in a frequency band where the complementary sensitivity gain, which is the gain in the characteristics, is approximately 1; outputting a second correction torque that corrects the input torque, taking the torsion bar torque as input; inputting the input torque to the controlled object in a state in which the first correction torque and the second correction torque have been subtracted; and making the gain of the transfer function from the torsion bar torque to the second correction torque in a first frequency band below a predetermined frequency greater than the gain of the transfer function from the torsion bar torque to the second correction torque in a second frequency band higher than the predetermined frequency. [8] The control method according to [7], which includes increasing the gain of the transfer function from the torsion bar torque to the second correction torque as the frequency decreases in at least a portion of the second frequency band. [9] The control method according to [7] or [8], comprising subtracting the second correction torque from the input torque after it has been corrected by the first correction torque and before it has been input to the controlled object, and performing the model following control based on the output of the controlled object and the input torque after the first correction torque has been subtracted and before the second correction torque has been subtracted.

[10] The control method according to any one of [7] to [9], comprising applying a low-pass filter to the torsion bar torque to generate the second corrected torque.

[11] A program that causes a computer to execute one of the control methods described in any one of items [7] through

[10] .

[0106] The configurations and methods described herein can be combined as appropriate, within the bounds of non-inconsistency. [Explanation of Symbols]

[0107] 100...Control device, 100a...Motor device, 210...Assist control unit, 230...Model following control unit, 290...Correction 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, Cf3...Third cutoff frequency (predetermined frequency), FB1...First frequency band, FB2...Second frequency band, GT...Complementary sensitivity gain, T(s)...Complementary sensitivity function, T f1 ...First correction torque, T f2 ...Second correction torque, T r ...input torque

Claims

1. A control device for controlling the portion of an electric power steering system mounted on a vehicle, which includes an input shaft to which a steering wheel operated by the driver is connected, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, wherein the control device controls the portion including the motor, An assist control unit that generates an input torque to the controlled object based on the torsion bar torque generated in the torsion bar, A model-following control unit that generates a first correction torque for correcting the input torque based on a nominal model based on the configuration of the controlled object, A correction unit that takes the torsion bar torque as input and outputs a second correction torque that corrects the input torque, Equipped with, The model-following control unit is configured such that the transfer function of the controlled object is constrained to the transfer function of the nominal model in a frequency band where the complementary sensitivity gain, which is the gain in the gain characteristic of the complementary sensitivity function for the modeling error between the controlled object and the nominal model, is approximately 1. The control target receives the input torque in which the first corrected torque and the second corrected torque have been subtracted. A control device wherein the gain of the transfer function of the correction unit in a first frequency band below a predetermined frequency is greater than the gain of the transfer function of the correction unit in a second frequency band higher than the predetermined frequency.

2. The control device according to claim 1, wherein in at least a portion of the second frequency band, the gain of the transfer function of the correction unit increases as the frequency decreases.

3. The second correction torque is subtracted from the input torque after it has been corrected by the first correction torque and before it is input to the controlled object. The control device according to claim 1, wherein the model following control unit receives the output of the controlled object and the input torque after the first correction torque has been subtracted and before the second correction torque has been subtracted.

4. The control device according to claim 1, wherein the correction unit generates the second corrected torque by applying a low-pass filter to the torsion bar torque.

5. A control device according to any one of claims 1 to 4, The motor and, A motor device equipped with the following features.

6. The motor device according to claim 5, A steering mechanism having the input shaft, the output shaft, and the torsion bar, An electric power steering system equipped with this system.

7. A control method for controlling the portion of an electric power steering system mounted on a vehicle, which includes an input shaft to which a steering wheel operated by the driver is connected, an output shaft connected to the input shaft via a torsion bar, and a motor connected to the output shaft, wherein the control method controls the portion including the motor, The input torque input to the controlled object is generated based on the torsion bar torque generated in the torsion bar, This involves performing model-following control to generate a first correction torque for correcting the input torque based on a nominal model based on the configuration of the controlled object, The model-following control constrains the transfer function of the controlled object to the transfer function of the nominal model in a frequency band where the complementary sensitivity gain, which is 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 system takes the torsion bar torque as input and outputs a second correction torque that corrects the input torque. The input torque is input to the control target in a state in which the first corrected torque and the second corrected torque have been subtracted. The gain of the transfer function from the torsion bar torque to the second correction torque in a first frequency band below a predetermined frequency is made greater than the gain of the transfer function from the torsion bar torque to the second correction torque in a second frequency band higher than the predetermined frequency. A control method including

8. The control method according to claim 7, comprising increasing the gain of the transfer function from the torsion bar torque to the second correction torque as the frequency decreases in at least a portion of the second frequency band.

9. Subtracting the second correction torque from the input torque after it has been corrected by the first correction torque and before it is input to the controlled object, The model following control is performed based on the output of the controlled object and the input torque after the first correction torque has been subtracted and before the second correction torque has been subtracted. The control method according to claim 7, including the method described in claim 7.

10. The control method according to claim 7, further comprising applying a low-pass filter to the torsion bar torque to generate the second corrected torque.

11. A program that causes a computer to execute the control method described in any one of claims 7 to 10.

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