Steering device

Abstract

A steering device (1) includes a rotational speed detection portion (3) that detects a rotational speed of a steering wheel (2), a torque detection portion (5) that detects torque acting on a rotary shaft (4) of the steering wheel (2), a motor (6), a controller (7) that controls the motor (6), wherein the controller (7) includes a steering gain calculation portion (72) that obtains a steering gain based on the rotational speed detected by the rotational speed detection portion (3), a torque command filter (73) that filters a torque command and reduces a gain in a high-frequency band when the steering gain has decreased, and a motor control portion (74) that generates a control command for controlling the motor (6) based on the torque command filtered by the torque command filter (73) and the torque detected by the torque detection portion (5), and reduces the gain in a high-frequency band when the steering gain has decreased.

Description

STEERING DEVICE

[0001] The present invention relates to a steering device.

[0002] For example, as disclosed in JP 2020-199968 A, a conventional steering device includes an input shaft connected to a steering wheel of a vehicle, an output shaft connected to a pinion meshed with a rack shaft that drives a wheel of the vehicle, a torsion bar that connects the input shaft and the output shaft, a torque sensor that detects torsion of the torsion bar and detects torque generated when a driver operates the steering wheel, a motor that rotationally drives a worm meshed with a worm wheel provided on an outer circumference of the output shaft, and a controller that obtains an amount of current to be supplied to the motor from the torque detected by the torque sensor through map calculation and supplies a current of the obtained amount of current to the motor.

[0003] In the steering device configured as described above, the motor is caused to output assist torque according to the torque when the driver operates the steering wheel. Thus, the steering can be assisted without impairing the driver's steering feeling.

[0004] Patent 2020-199968

[0005] As described above, in the conventional steering device, the torque sensor detects the torque to grasp the operation amount of the steering wheel of the driver, and the motor is caused to output assist torque corresponding to the detected torque.

[0006] To output the assist torque with good followability and responsiveness with respect to the detected torque, it is preferable to use a compensator having a relatively high gain in the controller, but a high-frequency noise component superimposed on the detected torque is amplified by the controller.

[0007] When the high-frequency noise component is amplified, the motor applies high-frequency assist torque to the steering wheel even though the steering wheel is not rotated when the driver holds the steering wheel without changing the steering angle, and the steering wheel slightly vibrates at a high frequency, causing the driver to feel uneasy and uncomfortable. Thus, the conventional steering device has room for improvement in steering feeling.

[0008] An object of the present invention is to provide a steering device capable of improving a steering feeling of a steering wheel.

[0009] To achieve the above-described object, a steering device in a solution to the problem of the present invention includes a rotational speed detection portion that detects a rotational speed of a steering wheel of a vehicle, a torque detection portion that detects torque acting on a rotary shaft of the steering wheel, a motor capable of applying additional torque to the steering wheel, a controller that controls the motor by inputting a torque command, the torque detected by the torque detection portion, and a steering gain, wherein the controller includes a steering gain calculation portion that obtains the steering gain based on the rotational speed detected by the rotational speed detection portion, a torque command filter that filters the torque command and reduces a gain in a high-frequency band when the steering gain has decreased, and a motor control portion that generates a control command for controlling the motor based on the torque command filtered by the torque command filter and the torque detected by the torque detection portion, and reduces the gain in a high-frequency band to remove a high-frequency component of the control command when the steering gain has decreased.

[0010] In the steering device configured as described above, when the driver is operating and rotating the steering wheel, the value of the steering gain increases to increase the gain in the high-frequency band in the torque command filter and the motor control portion to also increase the high-frequency component of the control command generated through the input of the torque command and the torque. Thus, the motor can apply additional torque to the steering wheel with good followability and responsiveness according to the operation of the steering wheel. On the other hand, according to the steering device, when the driver holds the steering angle of the steering wheel without changing the steering angle, the high-frequency component of the control command generated through the input of the torque command and the torque is removed. Thus, the control command of the motor control portion is stabilized, and the output of the motor does not slightly vibrate at a high frequency. Therefore, the driver does not feel uneasy or uncomfortable.

[0011] Fig. 1 is a diagram illustrating a steering device according to an embodiment.Fig. 2 is a configuration diagram of a controller in the steering device according to the embodiment.Fig. 3 is a diagram illustrating a configuration of a steering gain calculation portion.Fig. 4 is a diagram illustrating a map of a relationship between a rotational speed and a steering gain.Fig. 5 is a Bode plot illustrating frequency characteristics in a compensator in a motor control portion.Fig. 6 is a flowchart illustrating an example of a processing procedure of the steering device according to the embodiment.Fig. 7 is a diagram illustrating another example of the steering device.

[0012] Hereinafter, the present invention will be described based on an embodiment illustrated in the drawings. As illustrated in Fig. 1, a steering device 1 according to an embodiment is mounted on a vehicle (not illustrated) and includes a rotational speed detection portion 3 that detects a rotational speed of a steering wheel 2 of the vehicle, a torque detection portion 5 that detects torque acting on a rotary shaft 4 of the steering wheel 2, a motor 6 capable of applying additional torque to the steering wheel 2, and a controller 7 that controls the motor 6. In the present embodiment, the steering device 1 is an electric power steering device that transmits a rotation operation of the steering wheel 2 to a steering mechanism S connected to wheels W of the vehicle via the rotary shaft 4. When the driver of the vehicle operates the steering wheel 2, the steering device causes the motor 6 to apply assist torque for assisting the operation.

[0013] Hereinafter, each portion of the steering device 1 will be described in detail. First, the steering wheel 2 is rotatable with respect to the vehicle via the rotary shaft 4 and is installed in a vehicle interior (not illustrated) of the vehicle.

[0014] The steering mechanism S includes a rack shaft 8 installed so as to be able to reciprocate in a lateral direction of the vehicle with respect to the vehicle, and a tie rod 9 that connects each of both ends of the rack shaft 8 and a knuckle arm (not illustrated) that rotatably holds a corresponding one of the wheels W disposed on the right and left in front of the vehicle.

[0015] The rotary shaft 4 includes a pinion gear 11 that has one end connected to the rotation center of the steering wheel 2 and meshes with the rack 8a of the rack shaft 8 on the outer circumference of the other end. When the steering wheel 2 is steered by the driver of the vehicle, the rotary shaft 4 rotates about the axis, transmits the steering torque of the driver to the rack shaft 8 via the pinion gear 11, and drives the rack shaft 8 in a lateral direction of the vehicle. The rack shaft 8 is driven in the lateral direction of the vehicle that is also in the direction opposite to the rotation direction of the steering wheel 2, and gives a steering angle to the wheels W so as to cause the vehicle to travel in the steering direction of the steering wheel 2 according to the steering amount of the steering wheel 2 of the driver.

[0016] Although not illustrated, a universal joint is interposed in a middle portion of the rotary shaft 4, which prevent the rotary shaft 4 from occupying a space such as an engine room. A worm wheel 12 is provided on the outer circumference on the steering mechanism S side, which is the other end side of the rotary shaft 4. A worm 13 connected to a rotor (not illustrated) of the motor 6 meshes with the worm wheel 12. Thus, when the motor 6 is energized to drive the worm 13, the power of the motor 6 can be transmitted to the rotary shaft 4 via the worm wheel 12, and the motor 6 can apply assist torque for assisting the driver's operation of the steering wheel 2 to the steering wheel 2 as additional torque. In the present embodiment, the motor 6 includes an armature having coils of three phases (not illustrated) and a rotor (not illustrated), and includes an angle sensor 6a that detects a mechanical angle of the rotor because the mechanical angle of the rotor is required for driving.

[0017] In the steering device 1 according to the present embodiment, rotational speed detection portion 3 includes the angle sensor 6a attached to the motor 6 and used to detect the position of the rotor for controlling the motor 6, and a speed calculation portion 71 that obtains the rotational speed of the steering wheel 2 from the mechanical angle of the rotor in the motor 6 detected by the angle sensor 6a. In the present embodiment, the speed calculation portion 71 is integrated in the controller 7, but an arithmetic processing device that obtains the rotational speed from the mechanical angle of the rotor may be provided separately from the controller 7.

[0018] The torque detection portion 5 is a torque sensor that detects a torsional angle of a torsion bar (not illustrated) provided partway in the rotary shaft 4 and detects the torque acting on the steering wheel 2 from the torsional angle. The torque detection portion 5 only needs to be able to detect the steering torque acting on the rotary shaft 4. Thus, it may be a torque sensor other than the torque sensor described above.

[0019] As illustrated in Fig. 2, the controller 7 includes the above-described speed calculation portion 71, a steering gain calculation portion 72 that obtains a steering gain based on the rotational speed obtained through calculation by the speed calculation portion 71 in the rotational speed detection portion 3, a torque command filter 73 that filters a torque command, and a motor control portion 74 that controls the motor 6 based on the torque command filter 73, the torque detected by the torque detection portion 5, and the steering gain.

[0020] The steering device 1 causes the additional torque according to the torque command to act on the steering wheel 2 through the input of the torque command. When the torque command indicates the assist torque, the steering device 1 causes the additional torque to act on the steering wheel 2 so as to assist the steering of the steering wheel 2 by the driver of the vehicle. In addition, as illustrated in Fig. 7, in the case of a steer-by-wire steering device in which the rotary shaft 4 of the steering wheel 2 is not connected to the steering mechanism S, the motor 6 is installed so as to be able to apply torque to the steering wheel 2 via the rotary shaft 4, the motor 6 detects the steering amount of the steering wheel 2, and the steering mechanism S is driven by a motor 20 separately provided with the steering mechanism S, the torque command may be a command to output, to the motor 6, reaction torque to be applied to the steering wheel 2 according to self-alignment torque applied to the wheel in the vehicle. In the steering device 1 illustrated in Fig. 7, the motor 6 may transmit additional torque to the steering wheel 2 via a speed reducer.

[0021] The speed calculation portion 71 obtains the rotational speed of the steering wheel 2 from the angular speed of the rotor obtained by differentiating the mechanical angle of the rotor detected by the angle sensor 6a attached to the motor 6 and the reduction ratio between the worm wheel 12 and the worm 13. The rotational speed of the steering wheel 2 obtained by the speed calculation portion 71 is input to the steering gain calculation portion 72.

[0022] As illustrated in Fig. 3, the steering gain calculation portion 72 includes a low-pass filter 72a1 that removes a high-frequency component of the rotational speed obtained by the speed calculation portion 71, an absolute value calculation portion 72a2 that obtains an absolute value of the rotational speed filtered by the low-pass filter 72a1, a map calculation portion 72a3 that obtains a steering gain from the absolute value of the rotational speed, and a gradual increase / decrease processing portion 72a4 that performs gradual increase / decrease processing on the steering gain obtained by the map calculation portion 72a3.

[0023] As illustrated in Fig. 4, the map calculation portion 72a3 uses a map that defines the relationship between the rotational speed of the steering wheel 2 and the steering gain to obtain the steering gain from the rotational speed. In the map illustrated in Fig. 4, when the rotational speed is equal to or less than a predetermined speed threshold with respect to the rotational speed, the steering gain takes a predetermined minimum value Glow, when the rotational speed exceeds an upper limit value set to a value larger than a preset lower limit value, the steering gain takes 1 in which the steering gain becomes maximum, and when the rotational speed exceeds the lower limit value and is equal to or less than the upper limit value, the steering gain changes from the minimum value Glow to 1 in proportion to the rotational speed. The map is set such that the steering gain to be input to the motor control portion 74 is appropriate in controlling the motor 6. The value of the minimum value Glow can be freely set according to the design of the motor control portion 74, and the maximum value can also be set to a value larger than 1. The gradual increase / decrease processing portion 72a4 clamps the change rate of the steering gain and performs processing of alleviating a sudden change in value of the steering gain.

[0024] Thus, the value of the steering gain becomes smaller than 1 when the absolute value of the rotational speed of the steering wheel 2 becomes equal to or less than the upper limit value, and becomes the minimum value Glow when the absolute value of the rotational speed of the steering wheel 2 becomes equal to or less than the lower limit value.

[0025] The torque command filter 73 that pre-compensates for the torque command is a filter that changes the frequency characteristics according to the value of the steering gain. When the steering gain decreases, the gain in the high-frequency band is reduced, and the filtered torque command is output with a reduced high-frequency component. The torque command filter 73 increases the gain in the high-frequency band when the value of the steering gain increases, and the filtered torque command is output with an increased high-frequency component. The torque command filter 73 has a characteristic that when the value of the steering gain has become the minimum value Glow, the gain in the band of at least 100 Hz or more in its own frequency characteristic becomes 0 dB or less, and removes the high-frequency component of the torque command. In this manner, the torque command filter 73 changes the magnitude of the torque command according to the rotational speed of the steering wheel 2.

[0026] Since the steering gain calculation portion 72 holds the steering gain at the minimum value Glow when the rotational speed is equal to or less than the lower limit value, the characteristic of the torque command filter 73 does not change, and the gain in the high-frequency band is set to 0 dB or less. Thus, the torque command filter 73 outputs the torque command from which the high-frequency component has been removed. The minimum value Glow of the steering gain is set to a value of 0 or more and 0.5 or less.

[0027] As illustrated in Fig. 2, the motor control portion 74 includes a compensator 74a that generates a control command instructing a target current to be supplied to the motor 6 based on the torque command filtered by the torque command filter 73 and the torque detected by the torque detection portion 5, and a driver 74b that supplies a current to the motor 6 by inputting the control command generated by the compensator 74a.

[0028] Although not illustrated in detail, the compensator 74a is a stabilization compensator obtained by integrating functions such as an observer that estimates a state quantity which is an output of the system of the steering device 1 by inputting a torque command and torque, an observer that estimates a disturbance to be input to the system through the input of the torque command and the torque, and a phase compensator that compensates for a phase of a control command to be obtained and a compensator that improves control robustness in addition to a function of obtaining a target torque to be output to the motor 6 from the torque command by feeding back the state quantity estimated by each observer and the disturbance and obtaining a deviation between the target torque and the actual torque to perform PID compensation to generate a control command indicating the target current. The compensator 74a changes the characteristics according to the steering gain obtained by the steering gain calculation portion 72.

[0029] Specifically, for example, the frequency characteristic of the compensator 74a changes according to the value of the steering gain as illustrated in Fig. 5, and the compensator 74a decreases the gain in the high-frequency band when the steering gain decreases, and outputs the control command generated through the input of the torque command and the torque from which the high-frequency component has been removed. The compensator 74a increases the gain in the high-frequency band when the value of the steering gain increases, and increases and outputs the control command generated through the input of the torque command and the torque with an increased high-frequency component. When the value of the steering gain has become the minimum value Glow, the compensator 74a changes the gain in the band of at least 100 Hz or more in its own frequency characteristic to 0 dB or less, and generates a control command including almost no high-frequency vibration component. In this manner, the compensator 74a changes the frequency characteristic according to the rotational speed of the steering wheel 2 to change the control command to be generated.

[0030] The compensator 74a may be a compensator that generates a control command by performing PID compensation or PI compensation on the deviation between the torque command and the torque without including an observer, and the design of the compensator can be changed in any manner as long as it can control the motor 6 as the steering device 1. Even in this case, the frequency characteristic of the compensator 74a changes according to the steering gain, and is designed such that the gain in the high-frequency band decreases as the value of the steering gain decreases.

[0031] The driver 74b includes a drive circuit that PWM-drives the motor 6 based on the control command generated by the compensator 74a, and also includes a current sensor (not illustrated) that detects a current flowing through the motor 6. The driver supplies an amount of current according to a target current instructed by the control command to the motor 6 through current feedback. The driver 74b grasps the mechanical angle of the motor 6 from the angle sensor 6a of the motor 6, and energizes the coils of the three phases (not illustrated) at an energization timing suitable for the mechanical angle of the motor 6 to drive the motor 6.

[0032] As illustrated in Fig. 6, in the steering device 1 configured as described above, while the vehicle is traveling, the rotational speed detection portion 3 detects the rotational speed, and the torque detection portion 5 detects the torque acting on the rotary shaft 4 of the steering wheel 2 (step S1).

[0033] Subsequently, the controller 7 obtains a steering gain from the obtained rotational speed (step S2). Further, the controller 7 changes the frequency characteristic of the torque command filter 73 and the frequency characteristic in the compensator 74a in the motor control portion 74 according to the obtained steering gain (step S3).

[0034] The controller 7 filters the torque command with the torque command filter 73 (step S4), generates a control command based on the filtered torque command and the torque detected by the torque detection portion 5 (step S5), and controls the motor 6 (step S6).

[0035] The controller 7 repeatedly executes the processing procedure, processes the rotational speed detected by the rotational speed detection portion 3 and the torque detected by the torque detection portion 5, obtains a control command, and controls the motor 6.

[0036] In this manner, in the steering device 1, when the rotational speed is equal to or less than the lower limit value, the rotational speed of the steering wheel 2 is low, and it is recognized that the driver holds the steering wheel 2 so as not to rotate the steering wheel 2, the value of the steering gain becomes the minimum value Glow, the gain in the high-frequency band in the frequency characteristics of the torque command filter 73 and the compensator 74a in the motor control portion 74 is reduced, and the high-frequency component of the control command generated through the input of the torque command and the torque is removed and output.

[0037] Thus, in a state where the driver holds the steering wheel 2 so as to maintain the steering angle of the steering wheel 2, the high-frequency component is removed from the control command to be given to the motor 6. Thus, even though the torque detected by the torque detection portion 5 includes disturbance such as noise, the motor 6 in the steering device 1 does not generate constant torque, and the torque does not slightly vibrate at a high frequency. Therefore, the driver does not feel uneasy or uncomfortable.

[0038] Although not illustrated, the hardware resources of the controller 7 in the steering device 1 may be specifically configured to include, for example, except for the drive circuit in the driver 74b, an interface for fetching signals output from the angle sensor 6a and the torque detection portion 5, a storage device such as a read only memory (ROM) in which a program used for processing necessary for fetching the rotational speed and the torque and controlling the motor 6 is stored, an arithmetic device such as a central processing unit (CPU) that executes processing based on the program, and a storage device such as a random access memory (RAM) that provides a storage area for the CPU. Each portion in the controller 7 can be realized through execution of the program of the CPU. In addition, the controller 7 may be realized by an analog electronic circuit instead of being realized through execution of the program of the CPU.

[0039] The steering device 1 according to the present embodiment includes the rotational speed detection portion 3 that detects a rotational speed of the steering wheel 2 of a vehicle, the torque detection portion 5 that detects torque acting on the rotary shaft 4 of the steering wheel 2, the motor 6 capable of applying additional torque to the steering wheel 2, the controller 7 that controls the motor 6 by inputting a torque command, the torque detected by the torque detection portion 5, and a steering gain, wherein the controller 7 includes the steering gain calculation portion 72 that obtains the steering gain based on the rotational speed detected by the rotational speed detection portion 3, the torque command filter 73 that filters the torque command and reduces a gain in a high-frequency band when the steering gain has decreased, and the motor control portion 74 that generates a control command for controlling the motor 6 based on the torque command filtered by the torque command filter 73 and the torque detected by the torque detection portion 5, and reduces the gain in a high-frequency band to remove a high-frequency component of the control command when the steering gain has decreased.

[0040] In the steering device 1 configured as described above, when the driver is operating and rotating the steering wheel 2, the value of the steering gain increases to increase the gain in the high-frequency band in the torque command filter 73 and the motor control portion 74 to also increase the high-frequency component of the control command generated through the input of the torque command and the torque. Thus, the motor 6 can output additional torque to the steering wheel 2 with good followability and responsiveness according to the operation of the steering wheel 2. On the other hand, when the rotational speed of the steering wheel 2 is low, and the driver holds the steering angle of the steering wheel 2 without changing the steering angle, the value of the steering gain increases to decrease the gain in the high-frequency band in the torque command filter 73 and the motor control portion 74, and the high-frequency component of the control command generated through the input of the torque command and the torque can be removed. In this manner, according to the steering device 1, when the driver holds the steering angle of the steering wheel 2 without changing the steering angle, the high-frequency component of the control command generated through the input of the torque command and the torque is removed. Thus, the control command of the motor control portion 74 is stabilized, and the output of the motor 6 does not slightly vibrate at a high frequency. Therefore, the driver does not feel uneasy or uncomfortable.

[0041] According to the steering device 1 of the present embodiment, the steering feeling of the steering wheel can be improved. In addition, according to the steering device 1, the frequency characteristics of the torque command filter 73 and the compensator 74a of the motor control portion 74 are changed according to the steering gain. Thus, it is not necessary to separately provide a filter that processes the torque command or the torque, and the torque command and the torque signal are not delayed. Thus, the characteristics of the entire system including the motor control portion 74 do not fluctuate, and the controllability of the motor 6 is not adversely affected.

[0042] The steering gain calculation portion 72 in the steering device 1 according to the present embodiment minimizes the steering gain when the rotational speed is less than or equal to a predetermined lower limit value, and the torque command filter 73 and the motor control portion 74 set the gain in the band of at least 100 Hz in the frequency characteristics to 0 dB or less when the steering gain is minimized. According to the steering device 1 configured as described above, when the steering gain has become equal to or less than the lower limit value, the torque command filter 73 and the motor control portion 74 set the gain in the band of at least 100 Hz in their frequency characteristics to 0 dB or less. Thus, an unnecessary high-frequency component is not included in the control command generated when the driver holds the steering angle of the steering wheel 2. Therefore, the motor 6 is not caused to output constant torque to cause the steering wheel 2 to vibrate at a high frequency, and the driver does not feel uneasy or uncomfortable.

[0043] Although the preferred embodiment of the present invention has been described above in detail, modifications, variations, and changes can be made thereto without departing from the claims.

[0044] 1 steering device 2 steering wheel 3 rotation speed detection portion 4 rotary shaft 5 torque detection portion 6 motor 7 controller 72 steering gain calculation portion 73 torque command filter 74 motor control portion

Claims

1. A steering device comprising: a rotational speed detection portion that detects a rotational speed of a steering wheel of a vehicle; a torque detection portion that detects torque acting on a rotary shaft of the steering wheel; a motor capable of applying additional torque to the steering wheel; and a controller that controls the motor by inputting a torque command, the torque detected by the torque detection portion, and a steering gain, wherein the controller includes: a steering gain calculation portion that obtains the steering gain based on the rotational speed detected by the rotational speed detection portion; a torque command filter that filters the torque command and reduces a gain in a high-frequency band when the steering gain has decreased; and a motor control portion that generates a control command for controlling the motor based on the torque command filtered by the torque command filter and the torque detected by the torque detection portion, and reduces the gain in a high-frequency band to remove a high-frequency component of the control command when the steering gain has decreased.

2. The steering device according to claim 1, wherein the steering gain calculation portion minimizes the steering gain when the rotational speed has become equal to or less than a predetermined lower limit value, and the torque command filter and the motor control portion set a gain in a band of at least 100 Hz in frequency characteristics to 0 dB or less when the steering gain is minimized.

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