Steering control device, power steering device, steering control method, and program

Abstract

In the present invention, a target steering torque setting unit sets a target steering torque on the basis of the steering state of a steering mechanism, a current driving unit controls a driving current of a motor for rotating a steering shaft of the steering mechanism to generate a steering assist torque, and a torque feedback computation unit computes the steering assist torque such that the steering torque that acts on the steering shaft follows the target steering torque. The target steering torque setting unit computes a base torque, which is a basic component of the steering torque, computes a hysteresis-feel torque that includes a hysteresis component with respect to the target steering torque, corrects the hysteresis component on the basis of a steering torque that includes at least part of the hysteresis component and the base torque, and sets the target steering torque to include the base torque and the corrected hysteresis component.

Description

Steering control device, power steering device, steering control method, and program

[0001] The present disclosure relates to a steering control device, a power steering device, a steering control method, and a program.

[0002] The steering control device described in Patent Document 1 controls steering characteristics so that the steering torque follows a target steering torque. The target steering torque includes a viscosity adjustment torque as a torque component. The viscosity adjustment torque is used to adjust the viscosity feeling of the steering system mechanism given to the driver when steering. The viscosity adjustment torque is obtained by multiplying the time rate of change of the road load by a viscosity adjustment gain. The viscosity adjustment gain is variable depending on the driver power. The driver power is calculated from the steering torque and the steering angular velocity.

[0003] Japanese Patent Application Laid-Open No. 2016-203855

[0004] The steering control device described in Patent Document 1 has a complex structure when the viscosity adjustment gain is used to vary the viscous feel felt when operating the steering wheel. This is because a new state index value, called driver power, is calculated. Furthermore, because the viscosity adjustment gain is varied based on the steering torque detected from the movement of the steering wheel, a delay occurs with respect to the steering torque that is the control target. Because the viscous feel torque increases when the steering speed is fast, the impact of the delay on the steering feel tends to be significant when the steering speed fluctuates suddenly.

[0005] An object of the present disclosure is to provide a steering control device, a power steering device, a steering control method, and a program that solve the above-mentioned problems.

[0006] A first aspect is a steering control device comprising: a target steering torque setting unit that sets a target steering torque based on the steering state of a steering mechanism; a current driving unit that generates a steering assist torque by controlling the driving current of a motor that rotates a steering shaft of the steering mechanism; and a torque feedback calculation unit that calculates the steering assist torque so that the steering torque acting on the steering shaft follows the target steering torque, wherein the target steering torque setting unit comprises: a base torque calculation unit that calculates a base torque that is a basic component of the steering torque; a hysteresis feeling torque calculation unit that calculates a hysteresis feeling torque that includes a hysteresis component with respect to the target steering torque; and a hysteresis correction unit that corrects the hysteresis component based on the base torque and a steering torque that includes at least a part of the hysteresis component, and sets the target steering torque including the base torque and the hysteresis component after correction.

[0007] A second aspect is a steering control method in a steering control device, which executes a target steering torque setting step of setting a target steering torque based on the steering state of a steering mechanism, a current driving step of generating a steering assist torque by controlling a drive current of a motor that rotates a steering shaft of the steering mechanism, and a torque feedback calculation step of calculating the steering assist torque so that the steering torque acting on the steering shaft follows the target steering torque, and the target steering torque setting step has a base torque calculation step of calculating a base torque that is a basic component of the steering torque, a hysteresis feeling torque calculation step of calculating a hysteresis feeling torque including a hysteresis component with respect to the target steering torque, a hysteresis correction step of correcting the hysteresis component based on the base torque and a steering torque including at least a part of the hysteresis component, and a target steering torque setting step of setting the target steering torque including the base torque and the hysteresis component after correction.

[0008] A third aspect is a program for causing a computer to function as a steering control device, the steering control device comprising: a target steering torque setting unit that sets a target steering torque based on the steering state of a steering mechanism; a current driving unit that controls the driving current of a motor that rotates the steering shaft of the steering mechanism to generate a steering assist torque; and a torque feedback calculation unit that calculates the steering assist torque so that the steering torque acting on the steering shaft follows the target steering torque, wherein the target steering torque setting unit comprises: a base torque calculation unit that calculates a base torque that is a basic component of the steering torque; a hysteresis feeling torque calculation unit that calculates a hysteresis feeling torque that includes a hysteresis component for the target steering torque; and a hysteresis correction unit that corrects the hysteresis component based on the base torque and a steering torque that includes at least a part of the hysteresis component, and the steering control device functions as a steering control device that sets the target steering torque including the base torque and the hysteresis component after correction.

[0009] According to the present disclosure, it is possible to improve the operational feel associated with the operation of the steering mechanism and suppress an increase in the amount of calculation associated with the control of the steering torque.

[0010] FIG. 1 is a schematic block diagram showing an example configuration of an electric power steering device according to a first embodiment of the present disclosure. FIG. 1 is a schematic block diagram showing an example configuration of a control unit according to the first embodiment of the present disclosure. FIG. 2 is a flowchart showing an example of steering control processing according to the first embodiment of the present disclosure. FIG. 3 is a block diagram showing an example configuration of a target steering torque setting unit according to the first embodiment of the present disclosure. FIG. 4 is a block diagram showing a first example configuration of a base torque calculation unit according to the first embodiment of the present disclosure. FIG. 5 is a block diagram showing a second example configuration of a base torque calculation unit according to the first embodiment of the present disclosure. FIG. 6 is a diagram showing a first example configuration of a base map according to the first embodiment of the present disclosure. FIG. 7 is a diagram showing a second example configuration of a base map according to the first embodiment of the present disclosure. FIG. 8 is a diagram showing an example of a friction feel gain according to the first embodiment of the present disclosure. FIG. 9 is a schematic block diagram showing a first example configuration of a viscous feel torque calculation unit according to the first embodiment of the present disclosure. FIG. 10 is a schematic block diagram showing a second example configuration of a viscous feel torque calculation unit according to the first embodiment of the present disclosure. FIG. 11 is a diagram showing an example of a viscous feel gain map according to the first embodiment of the present disclosure. FIG. 12 is a diagram showing an example of a viscous feel torque map according to the first embodiment of the present disclosure. Fig. 10 is a diagram showing a relationship between a steering angle and a target steering torque during steering. Fig. 11 is a flowchart showing an example of a configuration of a target steering torque setting unit according to a second embodiment of the present disclosure. Fig. 12 is a flowchart showing an example of a configuration of a target steering torque setting unit according to a third embodiment of the present disclosure. Fig. 13 is a flowchart showing an example of a configuration of a target steering torque setting unit according to a fourth embodiment of the present disclosure. Fig. 14 is a flowchart showing an example of a configuration of a hysteresis correction unit according to the fourth embodiment of the present disclosure. Fig. 15 is a flowchart showing an example of a configuration of a target steering torque setting unit according to a fifth embodiment of the present disclosure.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Elements that are common to or correspond to each other in the various drawings are given the same reference numerals, and unless otherwise specified, the description thereof will be incorporated herein by reference. <Embodiment 1> First, embodiment 1 of the present disclosure will be described. FIG. 1 is a schematic block diagram showing an example configuration of an electric power steering device PS according to this embodiment. The electric power steering device PS includes a steering wheel 1, a steering shaft 2, steered wheels 3, a steering angle sensor 4, a torque sensor 5, a motor 6, a reduction gear mechanism 7, a vehicle speed sensor 8, a current sensor 9, a motor rotation angle sensor 10, a control unit 11, and an axle 13.

[0012] The steering wheel 1 is a member operated by a vehicle driver to apply a steering angle to the steered wheels 3 of the vehicle. The steering wheel 1 corresponds to a so-called steering wheel. The steering wheel 1 has a substantially annular shape. In response to operation of the steering wheel 1, the steering wheel 1 rotates around a steering shaft 2 connected to its center. One end of the steering shaft 2 is connected to the center of the steering wheel 1, and the other end is connected to an axle 13. The longitudinal direction of the steering shaft 2 is perpendicular to the main surface of the steering wheel 1 and forms a rotation axis. The steering shaft 2 rotates around the rotation axis in response to rotation of the steering wheel 1.

[0013] The steerable wheels 3 are provided on both ends of the axle 13. The steerable wheels 3 are steered by changing their direction in accordance with the rotation of the steering shaft 2. In this application, the mechanism for steering the steerable wheels 3 may be referred to as the "steering" or "steering mechanism." The steering mechanism includes the steering wheel 1, the steering shaft 2, and the axle 13. The steering angle sensor 4 is disposed in the center of the steering wheel 1. The steering angle sensor 4 detects the steering angle of the steering wheel 1.

[0014] The torque sensor 5 is disposed on the steering shaft 2. The torque sensor 5 detects the steering torque acting on the steering shaft 2. The motor 6 is connected to the steering shaft 2 via a reduction mechanism 7. The motor 6 consumes electric power to rotate. The torque generated by the rotation is transmitted to the steering shaft 2 via the reduction mechanism 7 as steering assist torque.

[0015] The vehicle speed sensor 8 detects the vehicle speed. The current sensor 9 detects the current driving the motor 6. The motor rotation angle sensor 10 detects the rotation angle of the motor 6. The control unit 11 drives the motor 6 based on the detected amounts detected by all or some of the steering angle sensor 4, torque sensor 5, vehicle speed sensor 8, current sensor 9, and motor rotation angle sensor 10, to generate a steering assist torque for steering. Here, the control unit 11 calculates the steering assist torque to be applied to the steering shaft 2 based on the detected amounts, and controls the current driving the motor 6 to generate the calculated steering assist torque.

[0016] Next, an example of the configuration of the control unit 11 according to this embodiment will be described. The control unit 11 functions as a steering control device. Fig. 2 is a schematic block diagram showing an example of the configuration of the control unit 11 according to this embodiment. The control unit 11 includes a target steering torque setting unit 22, a torque feedback calculation unit 23, a differentiator 24a, and a current driver 12.

[0017] The differentiator 24a receives the rotation angle of the motor 6 from the motor rotation angle sensor 10. The differentiator 24a differentiates the rotation angle of the motor 6 to calculate the rotation angular velocity of the motor 6 (hereinafter, may be referred to as the "motor rotation angular velocity"). The differentiator 24a outputs the motor rotation angular velocity obtained by the calculation to the target steering torque setting unit 22. The differentiator 24a may constitute the motor rotation angular velocity detection unit 24 together with the motor rotation angle sensor 10. The differentiator 24a may be configured integrally with the motor rotation angle sensor 10. In that case, the differentiator 24a may be omitted from the control unit 11.

[0018] The target steering torque setting unit 22 sets a target steering torque for the steering mechanism. Here, the target steering torque setting unit 22 receives the steering angle of the steering wheel 1 from the steering angle sensor 4, the vehicle speed of the vehicle from the vehicle speed sensor 8, and the motor rotational angular velocity as a steering angular velocity from the motor rotational angular velocity detection unit 24. In the example of FIG. 2 , the steering angle sensor 4 is provided in the steering state detection unit 21. The steering state detection unit 21 detects the steering state of the steering mechanism. That is, the steering angle of the steering wheel 1 corresponds to an example of a physical quantity indicating the steering state of the steering. The target steering torque setting unit 22 sets the target steering torque based on the steering angle, the vehicle speed, and the steering angular velocity. The target steering torque setting unit 22 outputs the set target steering torque to the torque feedback calculation unit 23. An example configuration of the target steering torque setting unit 22 will be described later.

[0019] The torque feedback calculation unit 23 calculates a steering assist torque required to make the steering torque follow the target steering torque, based on the deviation between the target steering torque input from the target steering torque setting unit 22 and the steering torque input from the torque sensor 5. The torque feedback calculation unit 23 outputs the steering assist torque obtained by the calculation to the current drive unit 12. The current drive unit 12 controls the current that drives the motor 6 in order to make the steering mechanism generate the steering assist torque input from the torque feedback calculation unit 23.

[0020] In the control unit 11, the differentiator 24a, the target steering torque setting unit 22, and the torque feedback calculation unit 23 may be partly or entirely implemented using a microcomputer including a processor and a memory. The microcomputer may be configured as an electronic control unit (ECU). The processor may include a central processing unit (CPU). The memory may include both volatile memory and non-volatile memory. The current driver 12 may include, for example, an analog circuit including a plurality of switching elements. For example, field effect transistors (FETs) may be used as the switching elements.

[0021] Next, an example of steering control processing according to this embodiment will be described. FIG. 3 is a flowchart showing an example of steering control processing according to this embodiment. The processing shown in FIG. 3 is repeatedly started at preset control cycles. (Step S02) The control unit 11 acquires the steering angle, the vehicle speed detected by the vehicle speed sensor 8, the steering torque detected by the torque sensor 5, and the motor rotation angle detected by the motor rotation angle sensor as examples of physical quantities indicating the steering state detected by the steering state detection unit 21. The differentiator 24a of the control unit 11 differentiates the acquired motor rotation angle to calculate the motor rotation angular velocity as the steering angular velocity. (Step S04) The target steering torque setting unit 22 of the control unit 11 sets the target steering torque using the acquired steering angle, vehicle speed, and steering angular velocity.

[0022] (Step S06) The torque feedback calculation section 23 of the control unit 11 calculates the steering assist torque required to make the steering torque follow the target steering torque, based on the deviation between the target steering torque set in the target steering torque setting section 22 and the steering torque detected by the torque sensor 5. (Step S08) The current drive section 12 of the control unit 11 controls the current supplied to the motor 6 to make the steering mechanism generate the steering assist torque calculated in the torque feedback calculation section 23. Thereafter, the processing in FIG. 3 ends.

[0023] Next, an example of the configuration of the target steering torque setting unit 22 according to this embodiment will be described. FIG. 4 is a block diagram showing an example of the configuration of the target steering torque setting unit 22 according to this embodiment. The target steering torque setting unit 22 includes a base torque calculation unit 25, a hysteresis sense torque calculation unit 26, a hysteresis correction unit 29, and adders 30a and 30c. The base torque calculation unit 25 calculates the base torque using the steering angle and the vehicle speed. The base torque corresponds to the basic component of the steering torque. The base torque has a characteristic that increases as the steering angle increases. No hysteresis occurs in the base torque with respect to the steering angle.

[0024] Hysteresis feel torque calculation unit 26 calculates a hysteresis feel torque using the steering angle and vehicle speed input thereto. The hysteresis feel torque corresponds to a hysteresis component with respect to the target steering torque. The hysteresis component includes a viscous feel torque as a first hysteresis component and a friction feel torque as a second hysteresis component. Hysteresis feel torque calculation unit 26 includes a friction feel torque calculation unit 27, a viscous feel torque calculation unit 28, and an adder 30b.

[0025] Frictional feel torque calculation unit 27 calculates a frictional feel torque using the steering angle and vehicle speed. The frictional feel torque has a polarity corresponding to the steering direction. The steering direction indicates the left / right direction relative to the orientation of the chassis. That is, the steering direction is expressed by the polarity of the steering angular velocity. The steering angular velocity is obtained by time differentiating the steering direction input to this unit. Viscous feel torque calculation unit 28 calculates the steering angular velocity by time differentiating the steering direction, and calculates the viscous feel torque using the calculated steering angular velocity and vehicle speed. The viscous feel torque increases as the steering angular velocity increases. Adder 30b adds the frictional feel torque input from frictional feel torque calculation unit 27 and the viscous feel torque input from viscous feel torque calculation unit 28. Adder 30b outputs the sum obtained by the addition to adder 30a as the pre-correction hysteresis feel torque.

[0026] The adder 30a adds the base torque input from the base torque calculation unit 25 and the pre-correction hysteresis sense torque input from the adder 30b. The adder 30a outputs the sum obtained by the addition to the hysteresis correction unit 29 as the pre-correction target steering torque.

[0027] Hysteresis correction unit 29 includes hysteresis adjustment unit 29m and adder 30d. Hysteresis adjustment unit 29m calculates a corrected viscous feel torque using the viscous feel torque (pre-correction viscous feel torque) input from viscous feel torque calculation unit 28 and the pre-correction target steering torque input from adder 30a. Adder 30d adds the corrected viscous feel torque input from hysteresis correction unit 29 and the frictional feel torque input from frictional feel torque calculation unit 27. Adder 30d calculates the sum obtained by the addition as a corrected hysteresis feel torque.

[0028] The adder 30c adds the base torque input from the base torque calculation unit 25 and the corrected hysteresis sense torque input from the adder 30d to calculate the corrected target steering torque. The corrected target steering torque obtained by the addition is input to the torque feedback calculation unit 23.

[0029] Next, a configuration example of the base torque calculation unit 25 according to this embodiment will be described. FIG. 5 is a block diagram showing a first configuration example of the base torque calculation unit 25 according to this embodiment. In the example of FIG. 5, the base torque calculation unit 25 includes a base map processing unit 25a, a sign determination unit 25b, and a multiplier 25c. Information indicating at least the correspondence relationship between the magnitude of the steering angle and the base torque is set as a base map in the base map processing unit 25a. The magnitude of the steering angle is represented by the absolute value of the steering angle. A non-negative real value equal to or greater than 0 is set as the base torque. The correspondence relationship between the steering angle and the base torque may be constant regardless of the vehicle speed, or may be variable depending on the vehicle speed.

[0030] The base map illustrated in FIG. 7 shows the correspondence relationship between the absolute value of the steering angle and the base torque for each of low, medium, and high vehicle speeds. The base map processing unit 25a presets a vehicle speed range for each of low, medium, and high vehicle speeds. A range including vehicle speeds higher than low vehicle speeds is set as the range corresponding to medium vehicle speed. A range including vehicle speeds higher than medium vehicle speeds is set as the range corresponding to high vehicle speed. In the example illustrated in FIG. 7, the base torque increases as the steering angle increases. However, the larger the steering angle, the lower the rate of increase in base torque relative to an increase in steering angle tends to be. Furthermore, the higher the vehicle speed, the higher the base torque tends to be. The base map processing unit 25a identifies a base map corresponding to the vehicle speed input to the unit from among the base maps illustrated in FIG. 7. The base map processing unit 25a references the identified base map to identify a non-negative base torque corresponding to the absolute value of the steering angle input to the unit. The base map processing unit 25a outputs the identified base torque to the multiplier 25c.

[0031] 5, the sign determination unit 25b determines the polarity, i.e., whether the sign is positive (+) or negative (-), depending on whether the steering angle input thereto is equal to or greater than 0. The sign determination unit 25b outputs a predetermined integer value (+1 or -1) having the determined sign to the multiplier 25c. The multiplier 25c calculates the base torque by multiplying the non-negative base torque input from the base map processing unit 25a by the integer value input from the sign determination unit 25b.

[0032] FIG. 6 is a block diagram showing a second configuration example of the base torque calculation unit 25 according to this embodiment. In the example of FIG. 6, the base torque calculation unit 25 includes a base map processing unit 25a. The sign determination unit 25b and the multiplier 25c are omitted. In this configuration example, the correspondence relationship between the steering angle and the base torque may be constant regardless of the vehicle speed, or may be variable depending on the vehicle speed. FIG. 8 shows an example of a base map according to this configuration example. The base map shown in FIG. 8 shows the correspondence relationship between the steering angle and the base torque for each vehicle speed. In the base map shown in FIG. 8, the base torque increases monotonically as the steering angle increases. The rate of increase of the base torque relative to an increase in the steering angle tends to decrease as the steering angle becomes farther from 0. Unlike the example of FIG. 7, a negative base torque is set even for a steering angle that is a negative value less than or equal to 0. The base map shown in FIG. 8 also shows the correspondence relationship between the steering angle and the base torque for low, medium, and high vehicle speeds. The base map processing unit 25a identifies a base map corresponding to the vehicle speed input to the unit itself from among the base maps exemplified in Fig. 8. The base map processing unit 25a refers to the identified base map to identify a base torque corresponding to the steering angle input to the unit itself. The base map processing unit 25a outputs the identified base torque to the multiplier 25c.

[0033] Next, an example of the configuration of the frictional torque calculation unit 27 according to this embodiment will be described. The frictional torque calculation unit 27 calculates the frictional torque based on the steering angular velocity and the vehicle speed. The frictional torque calculation unit 27 can calculate the steering angle by time-differentiating the steering velocity input to the unit itself. The frictional torque is calculated, for example, based on the steering angular velocity dθ and the frictional torque gain Tf according to equation (1). The polarity of the frictional torque is the same as the polarity of the steering angular velocity dθ. However, when the steering angular velocity dθ is zero, the frictional torque is zero. The magnitude of the frictional torque tends to increase as the magnitude of the steering angular velocity dθ increases. In the example of equation (1), the frictional torque asymptotically approaches Tf as the steering angular velocity dθ approaches positive infinity. The frictional torque asymptotically approaches −Tf as the steering angular velocity dθ approaches negative infinity.

[0034]

[0035] The frictional feel gain Tf may be a constant value independent of the vehicle speed, or may be variable depending on the vehicle speed. If the frictional feel gain Tf is variable depending on the vehicle speed, a correspondence relationship between the vehicle speed and the frictional feel gain Tf is set in advance in the frictional feel torque calculation unit 27. The frictional feel torque calculation unit 27 can identify the frictional feel gain corresponding to the vehicle speed input to the frictional feel torque calculation unit 27 by referring to the set correspondence relationship. The frictional feel torque calculation unit 27 can calculate the frictional feel torque according to equation (1) based on the identified frictional feel gain and the steering angular velocity.

[0036] Next, an example of the relationship between the vehicle speed and the frictional feel gain will be described. Fig. 9 shows an example of a frictional feel gain map showing the relationship between the vehicle speed and the frictional feel gain. The frictional feel gain Tf is at its maximum value Tf when the vehicle speed is zero. ａ When the vehicle speed reaches a critical value v ｂ When this occurs, the minimum positive value Tf ｂ That is, the frictional feeling gain Tf is calculated as the vehicle speed increases from zero to the critical value v ｂ However, as the vehicle speed exceeds the critical value, the value decreases. ｂ The rate of increase in the frictional feel gain Tf with respect to an increase in vehicle speed exceeding the critical value v ｂ The decrease rate of the frictional feel gain Tf with respect to an increase in vehicle speed is slower than the decrease rate of the frictional feel gain Tf with respect to an increase in vehicle speed of less than 1 / 200.​

[0037] The frictional torque calculation unit 27 may perform low-pass filtering on the frictional torque calculated using equation (1). A value that can extract frequency components in the frequency band of the steering angle that changes over time is set in advance as the cutoff frequency of the low-pass filter. Typically, the driver's limit steering frequency is about 5 Hz, and the resonance frequency of the steering shaft 2 is about 13 to 18 Hz. In this case, the cutoff frequency may be a value higher than 5 Hz and equal to or lower than 10 Hz.

[0038] Next, a configuration example of the viscous torque calculation unit 28 according to this embodiment will be described. The viscous torque calculation unit 28 calculates the viscous torque using the steering angular velocity and the vehicle speed. FIG. 10 is a schematic block diagram showing a first configuration example of the viscous torque calculation unit 28 according to this embodiment. The viscous torque calculation unit 28 according to this configuration example includes a viscous gain map processing unit 28a and a multiplier 28b. Information indicating a correspondence relationship between at least the absolute value of the steering angular velocity and the viscous gain is set as a viscous gain map in the viscous gain map processing unit 28a. The magnitude of the steering angular velocity is represented by the absolute value of the steering angular velocity. A non-negative real value equal to or greater than 0 is set as the viscous gain. The correspondence relationship between the steering angular velocity and the viscous gain may be constant regardless of the vehicle speed, or may be variable depending on the vehicle speed.

[0039] The viscosity feeling gain map illustrated in FIG. 12 shows the correspondence relationship between the absolute value of the steering angular velocity and the viscosity feeling gain for each of low, medium, and high vehicle speeds. Vehicle speed ranges are preset in the viscosity feeling gain map processing unit 28a for each of low, medium, and high vehicle speeds. A value range that includes vehicle speeds higher than low vehicle speeds is set as the value range corresponding to medium vehicle speeds. A value range that includes vehicle speeds higher than medium vehicle speeds is set as the value range corresponding to high vehicle speeds. The viscosity feeling gain increases as the magnitude of the steering angular velocity increases. However, as the steering angular velocity increases, the rate of increase in the viscosity feeling gain relative to an increase in the steering angular velocity decreases, and tends to asymptotically approach a constant value. Furthermore, the viscosity feeling gain tends to increase as the vehicle speed increases.

[0040] Returning to Fig. 10, the viscosity feeling gain map processing unit 28a identifies a viscosity feeling gain map corresponding to the vehicle speed input to the unit itself, from among the viscosity feeling gain maps exemplified in Fig. 12. The viscosity feeling gain map processing unit 28a identifies a viscosity feeling gain corresponding to the absolute value of the steering angular velocity by referring to the identified viscosity feeling gain map. The viscosity feeling gain map processing unit 28a outputs the viscosity feeling gain to the multiplier 28b. The multiplier 28b multiplies the viscosity feeling gain input from the viscosity feeling gain map processing unit 28a by the steering angular velocity derived from the steering angle, and calculates the product obtained by the multiplication as a viscosity feeling torque.

[0041] 11 is a schematic block diagram showing a second configuration example of the viscous torque calculation unit 28 according to this embodiment. The viscous torque calculation unit 28 according to this configuration example includes a viscous torque map processing unit 28c, a sign determination unit 28d, and a multiplier 28e. Information indicating the correspondence between at least the absolute value of the steering angular velocity and the viscous torque is set as a viscous torque map in the viscous torque map processing unit 28c. A non-negative real value greater than or equal to 0 is set as the viscous torque. The correspondence between the steering angular velocity and the viscous torque may be constant regardless of the vehicle speed, or may be variable depending on the vehicle speed.

[0042] The viscous feel torque map illustrated in FIG. 13 shows the correspondence relationship between the absolute value of the steering angular velocity and the viscous feel torque for each of low, medium, and high vehicle speeds. The rate of increase of the viscous feel torque relative to an increase in the steering angular velocity tends to decrease relatively gradually as the steering angular velocity increases. The magnitude of the viscous feel torque increases as the steering angular velocity increases. Furthermore, the viscous feel torque tends to increase as the vehicle speed increases.

[0043] Returning to FIG. 12 , the viscous torque map processing unit 28c identifies a viscous torque map corresponding to the vehicle speed input to the viscous torque map processing unit 28c from among the viscous torque maps illustrated in FIG. 13 . The viscous torque map processing unit 28c identifies a viscous torque corresponding to the absolute value of the steering angular velocity by referring to the identified viscous torque map. The viscous torque map processing unit 28c outputs a viscous torque gain to the multiplier 28e. The sign determination unit 28d determines whether the sign of the steering angular velocity input to the viscous torque map processing unit 28c is positive (+) or negative (−) depending on whether the steering angular velocity input to the viscous torque map processing unit 28c is equal to or greater than 0. The sign determination unit 28d outputs a predetermined integer value (+1 or −1) having the determined sign to the multiplier 28e. The multiplier 28e multiplies the viscous torque input from the viscous torque map processing unit 28c by the integer value input from the sign determination unit 28d, and calculates the product obtained by the multiplication as the viscous torque gain.

[0044] Next, an example of the configuration of the hysteresis correction unit 29 according to this embodiment will be described. Fig. 14 is a schematic block diagram showing an example of the configuration of the hysteresis correction unit 29 according to this embodiment. The hysteresis correction unit 29 includes an absolute value calculation unit 29a, a viscosity correction gain map processing unit 29b, and a multiplier 29c. The absolute value calculation unit 29a calculates the absolute value of the pre-correction target steering torque input from the adder 30a. The absolute value calculation unit 29a outputs the absolute value of the pre-correction target steering torque obtained by the calculation to the viscosity correction gain map processing unit 29b.

[0045] The viscosity correction gain map processing unit 29b is set with information indicating at least the correspondence relationship between the absolute value of the pre-correction target steering torque and the viscosity correction gain as a viscosity correction gain map. A non-negative real value greater than or equal to 0 is set as the viscosity correction gain. The correspondence relationship between the pre-correction target steering torque and the viscosity correction gain may be constant regardless of the vehicle speed, or may be variable depending on the vehicle speed. The viscosity correction gain map illustrated in FIG. 15 indicates the correspondence relationship between the absolute value of the pre-correction target steering torque and the viscosity correction gain for each of low, medium, and high vehicle speeds. The viscosity correction gain map processing unit 29b is set with vehicle speed ranges in advance for each of low, medium, and high vehicle speeds. A value range corresponding to medium vehicle speed is set to include vehicle speeds higher than low vehicle speed. A value range corresponding to high vehicle speed is set to include vehicle speeds higher than medium vehicle speed. The viscosity correction gain decreases as the pre-correction target steering torque increases. The viscosity correction gain tends to decrease more as the vehicle speed increases and the pre-correction target steering torque increases. When the pre-correction target steering torque is zero, the viscosity correction gain is substantially constant regardless of the vehicle speed.

[0046] Returning to Fig. 14, the viscosity correction gain map processing unit 29b identifies a viscosity correction gain map corresponding to the vehicle speed input to the processing unit itself, from among the viscosity correction gain maps exemplified in Fig. 15. The viscosity correction gain map processing unit 29b references the identified viscosity correction gain map to identify a viscosity correction gain corresponding to the absolute value of the pre-correction target steering torque. The viscosity correction gain map processing unit 29b outputs the identified viscosity correction gain to the multiplier 29c. The multiplier 28b multiplies the viscosity correction gain input from the viscosity correction gain map processing unit 29b by the pre-correction viscosity feeling torque input from the viscosity feeling torque calculation unit 28, and calculates the product obtained by the multiplication as the post-correction viscosity feeling torque.

[0047] Next, an example of the configuration of the torque feedback calculation unit 23 according to this embodiment will be described. Fig. 16 is a schematic block diagram showing an example of the configuration of the torque feedback calculation unit 23 according to this embodiment. The torque feedback calculation unit 23 includes a subtractor 31, a first steering assist torque calculation unit 32, a second steering assist torque calculation unit 33, a third steering assist torque calculation unit 34, and an adder 35. The torque feedback calculation unit 23 calculates a steering assist torque for making the steering torque follow the target steering torque, based on the deviation between the target steering torque set in the target steering torque setting unit 22 and the steering torque detected by the torque sensor 5.

[0048] The subtractor 31 subtracts the steering torque input from the torque sensor 5 from the target steering torque input from the target steering torque setting unit 22, and outputs the deviation obtained by the subtraction to the first steering assist torque calculation unit 32 and the third steering assist torque calculation unit 34. The first steering assist torque calculation unit 32 includes an integrator 32a and a multiplier 32b. The integrator 32a integrates the deviation input from the subtractor 31, and outputs the integral value obtained by the integration to the multiplier 32b. The multiplier 32b multiplies the integral value input from the integrator 32a by a preset integral control gain KTI, and outputs the product obtained by the multiplication to the adder 35 as the first steering assist torque.

[0049] The second steering assist torque calculation unit 33 includes a multiplier 33a. The multiplier 33a multiplies the steering angular velocity input from the motor rotational angular velocity detection unit 24 by a preset speed control gain KTV and outputs the product obtained by the multiplication to the adder 35 as a second steering assist torque. The third steering assist torque calculation unit 34 includes a multiplier 34a. The multiplier 34a multiplies the deviation input from the subtractor 31 by a preset proportional control gain KTP and outputs the product obtained by the multiplication to the adder 35 as a third steering assist torque. The adder 35 adds the first steering assist torque input from the first steering assist torque calculation unit 32, the second steering assist torque input from the second steering assist torque calculation unit 33, and the third steering assist torque input from the third steering assist torque calculation unit 34 and outputs the sum obtained by the addition to the current drive unit 12 as a steering assist torque.

[0050] The steering assist torque obtained by the torque feedback calculation unit 23 includes an integral control component. The integral control component corresponds to the first steering assist torque. Therefore, the steering torque is controlled to follow the target steering torque in response to the driver's operation. This assists the driver's steering. The steering assist torque includes a motor control component. The motor control component corresponds to the second steering assist torque. The second steering assist torque is obtained by multiplying the steering angular velocity, i.e., the motor rotational speed, by the speed control gain KTV. For example, assume that the driver releases his or her hands from the steering wheel 1 and stops operating the steering wheel. In this case, the steering torque does not immediately become zero but is adjusted between zero and the target steering torque. The steering torque following the target steering torque achieves smooth steering. Furthermore, by including the motor speed control component in the steering assist torque, stable control is achieved even when the motor 6 and the torque sensor 5 are located far apart. Furthermore, since no differentiation of the target steering torque is involved, excessive noise is avoided.

[0051] The steering assist torque includes a steering assist torque proportional control component. The steering assist torque proportional control component corresponds to the third steering assist torque. The steering assist torque proportional component has a faster response than the integral control component. By improving the tracking response, overshoot can be reduced. For example, when a driver grips the steering wheel to steer, the steering torque stably tracks the target steering torque, achieving smoother steering. In the above description, the torque feedback calculation unit 23 is provided to improve stability and tracking, but this is not limiting. For example, some of the first steering assist torque calculation unit 32, the second steering assist torque calculation unit 33, and the third steering assist torque calculation unit 34 may be omitted. Furthermore, the feedback of the deviation between the target steering torque and the steering torque to the steering torque is not necessarily limited to torque feedback.

[0052] Next, an example of the operation of the control unit 11 according to this embodiment will be described. The control unit 11 functions as a steering control device that sets a target steering torque according to the steering situation and controls the steering torque to follow the target steering torque. When the driver sets the steering feeling of the vehicle, the target steering force angle characteristic is adapted so that the target steering torque set by the control unit 11 has the desired characteristic. In this example of operation, it is assumed that the steering wheel 1 is operated so that the time change of the steering angle at the target vehicle speed becomes a sine wave having a predetermined frequency (e.g., 0.2 Hz), and the steering is performed so that the amplitude of the lateral acceleration caused by turning the vehicle is equal to or less than a predetermined reference acceleration (e.g., 0.2 G).

[0053] FIG. 17 is a diagram illustrating the relationship between the steering angle and the target steering torque during steering. In FIG. 17, the horizontal axis and vertical axis represent the steering angle and torque, respectively. "Base torque" represents the base torque. The base torque does not have a hysteresis characteristic. That is, the base torque is uniquely determined for the steering angle regardless of whether the steering angle increases or not. "No correction technique" represents a comparative example of the target steering torque obtained by adapting the target steering force angle characteristic while not including the hysteresis correction unit 29 in the target steering torque setting unit 22 illustrated in FIG. 4 and keeping the other conditions the same as in this embodiment.

[0054] "Before correction" indicates the pre-correction target steering torque obtained by adding the base torque and the hysteresis feel torque according to this embodiment. "After correction" indicates the corrected target steering torque obtained by adding the base torque and the corrected hysteresis feel torque according to this embodiment. "After correction" is adjusted to optimize the steering feel for both steering in and steering back. "After correction" has a significantly different hysteresis width from "before correction" in each of the steering in and steering back phases. "Steady steering" corresponds to a phase in which the steering angle moves away from zero, and steering back corresponds to a phase in which the steering angle approaches zero. In the example of FIG. 17 , the hysteresis component is suppressed in each of the steering in and steering back phases by correcting the hysteresis component.

[0055] With "no correction technique," parameters are adjusted to provide the driver with an optimal steering feel when steering back. However, the steering feel for the driver is not optimized when steering back. This is supported by the fact that, while there is no significant difference between the steering torque "after correction" and the steering torque "without correction technique" in the second and fourth quadrants of FIG. 17 , the steering torque "without correction technique" is greater than the steering torque "after correction" in the first and third quadrants. One reason for this is presumably that, with "no correction technique," the hysteresis correction by the hysteresis correction unit 29 causes the increase / decrease in the hysteresis component from the base torque to be the same during steering and during returning.

[0056] On the other hand, in this embodiment, the frictional torque and viscous torque, which are components of the hysteresis torque, are adjusted on the assumption that hysteresis correction is performed. By correcting at least some of the components of the hysteresis torque based on the base torque and the hysteresis torque before correction, it is possible to change the amount of increase or decrease in the hysteresis component from the base torque between turning the steering wheel and returning the steering wheel, as shown in "after correction." This allows for an optimal steering feel in both turning the steering wheel and returning the steering wheel.

[0057] The hysteresis correction unit 29 is configured to correct some components of the hysteresis feel torque based on the base torque and hysteresis feel torque that are normally calculated. This reduces the amount of newly added calculations, thereby reducing the software size and processing load involved in the calculations. In the above description, the friction feel gain map in the friction feel torque calculation unit 27 of the hysteresis feel torque calculation unit 26, the viscosity feel gain map or viscosity feel torque map in the viscosity feel torque calculation unit 28, and the viscosity correction gain map in the hysteresis correction unit 29 are all variable with respect to vehicle speed. This allows appropriate control gains to be set for road reaction force characteristics that vary with vehicle speed. Furthermore, setting a target steering torque according to vehicle speed can improve steering feel. Note that each individual map does not necessarily have to be variable with respect to vehicle speed. At least one map or a gain obtained by the map may be variable with respect to vehicle speed, while the other maps or gains may be constant and independent of vehicle speed.

[0058] In the above description, the steering state detection unit 21 is provided with the steering angle sensor 4, and the steering angle detected by the steering angle sensor 4 is used in the base torque calculation unit 25 as an example of a physical quantity indicating the steering state. However, instead of the steering angle detected by the steering angle sensor 4, a steering angle converted from the motor rotation angle detected by the motor rotation angle sensor may be used. For example, the rotation angle about the steering shaft 2 obtained by converting the motor rotation angle detected by the motor rotation angle sensor 10 using the reduction ratio of the reduction mechanism 7 may be used as the steering angle. Furthermore, the motor rotation angle may be defined as a relative angle with respect to the angle of the steering shaft 2. In this case, the motor rotation angle may be offset so that the relative angle in linear motion becomes zero based on the angular velocity of turning motion detected by a yaw rate sensor or the like (not shown) provided in the vehicle, and corrected as the absolute angle of the steering shaft 2.

[0059] In the above description, the target steering torque setting unit 22 uses the steering angular velocity obtained by differentiating the motor rotation angle, but the present invention is not limited to this. The target steering torque setting unit 22 may convert the angular velocity obtained by differentiating the steering angle detected by the steering angle sensor 4 using the reduction ratio of the reduction mechanism 7, and use the converted value as the steering angular velocity.

[0060] <Second Embodiment> Next, an electric power steering device PS according to a second embodiment of the present disclosure will be described. The following description will mainly focus on differences from the first embodiment. Unless otherwise specified, the description of the first embodiment will be used for points in common with the first embodiment. In the control unit 11 according to this embodiment, the adder 30b is omitted from the target steering torque setting section 22. Also, the configuration of the hysteresis correction section 29 according to this embodiment differs from the configuration of the hysteresis correction section 29 according to the first embodiment.

[0061] Next, an example of the configuration of the target steering torque setting unit 22 according to this embodiment will be described. FIG. 18 is a schematic block diagram showing an example of the configuration of the target steering torque setting unit 22 according to this embodiment. The viscous feel torque calculation unit 28 according to this embodiment outputs the viscous feel torque to the adder 30a. The adder 30a adds the viscous feel torque input from the viscous feel torque calculation unit 28 to the base torque input from the base torque calculation unit 25. The adder 30a outputs the sum obtained by the addition to the hysteresis correction unit 29 as the post-addition torque. That is, the adder 30a according to this embodiment differs from the adder 30a according to the first embodiment in that the viscous feel torque is added to the base torque instead of the pre-correction hysteresis feel torque. The pre-correction hysteresis feel torque includes both the viscous feel torque and the friction feel torque.

[0062] Hysteresis correction unit 29 corrects the viscous feel torque input from viscous feel torque calculation unit 28 based on the added torque input from adder 30a, and outputs the corrected viscous feel torque to adder 30d. That is, hysteresis correction unit 29 according to this embodiment differs from hysteresis correction unit 29 according to the first embodiment in that it corrects the viscous feel torque based on the added torque instead of the pre-correction target steering torque.

[0063] In the hysteresis correction unit 29 according to this embodiment, the absolute value calculation unit 29a (see FIG. 14) outputs the absolute value of the post-addition torque input from the adder 30a to the viscosity correction gain map processing unit 29b (see FIG. 14). In place of the absolute value of the pre-correction target steering torque, information indicating the correspondence between the absolute value of the post-addition torque and the viscosity correction gain is set in the viscosity correction gain map processing unit 29b as a viscosity correction gain map.

[0064] In the viscosity correction gain map, the absolute value of the post-addition torque may be set on the horizontal axis of FIG. 15. The viscosity correction gain map according to this embodiment shows a tendency for the viscosity correction gain to decrease as the absolute value of the post-addition torque increases. Furthermore, when the post-addition torque is zero, the viscosity correction gain is set to a substantially constant value regardless of the vehicle speed. However, in the viscosity correction gain map according to this embodiment, the value of the viscosity correction gain corresponding to the post-addition torque is adjusted to a value different from the value of the viscosity correction gain corresponding to the pre-correction target steering torque in the viscosity correction gain map according to the first embodiment. The hysteresis correction unit 29 refers to the viscosity correction gain map to identify the viscosity correction gain corresponding to the absolute value of the post-addition torque, and outputs the identified viscosity correction gain to the multiplier 29c.

[0065] The post-addition torque has a hysteresis characteristic because it is obtained by adding the viscous feel torque to the base torque. That is, the post-addition torque is similar to the pre-correction target steering torque in that its absolute value during steering is greater than its absolute value during steering back. The hysteresis correction unit 29 according to this embodiment obtains a viscous feel torque corrected based on the viscosity correction gain corresponding to the post-addition torque. As a result, the corrected viscous feel torque during steering can be made greater than the corrected viscous feel torque during steering back. Therefore, the steering feel is improved as in the first embodiment. Furthermore, in this embodiment, the adder 30b according to the first embodiment can be omitted, simplifying the calculation process.

[0066] <Third Embodiment> Next, an electric power steering device PS according to a third embodiment of the present disclosure will be described. The following description will mainly focus on differences from the first and second embodiments. Unless otherwise specified, the description of the first embodiment will be used for points in common with the first embodiment. In the control unit 11 according to this embodiment, the adder 30b is also omitted from the target steering torque setting section 22. The configuration of the hysteresis correction section 29 according to this embodiment differs from the configuration of the hysteresis correction section 29 according to the first and second embodiments.

[0067] Next, an example of the configuration of the target steering torque setting unit 22 according to this embodiment will be described. Fig. 19 is a schematic block diagram showing an example of the configuration of the target steering torque setting unit 22 according to this embodiment. The frictional torque calculation unit 27 according to this embodiment outputs the frictional torque to the adder 30a. The adder 30a adds the frictional torque input from the frictional torque calculation unit 27 to the base torque input from the base torque calculation unit 25. The adder 30a outputs the sum obtained by the addition to the hysteresis correction unit 29 as the post-addition torque. That is, this embodiment differs from the first and second embodiments in that the frictional torque is added to the base torque instead of the pre-correction hysteresis torque or viscous torque.

[0068] Hysteresis correction unit 29 corrects the viscous feeling torque input from viscous feeling torque calculation unit 28 based on the added torque input from adder 30a, and outputs the corrected viscous feeling torque to adder 30d. That is, hysteresis correction unit 29 according to this embodiment differs from hysteresis correction unit 29 according to the first and second embodiments in that it corrects the viscous feeling torque based on the added torque that includes the base torque and the frictional feeling torque as components.

[0069] In the hysteresis correction unit 29 according to this embodiment, the absolute value calculation unit 29a (see FIG. 14) outputs the absolute value of the post-addition torque input from the adder 30a to the viscosity correction gain map processing unit 29b (see FIG. 14). Information indicating the correspondence between the absolute value of the post-addition torque and the viscosity correction gain is set as a viscosity correction gain map in the viscosity correction gain map processing unit 29b. In the correction gain map according to this embodiment, as in the second embodiment, the absolute value of the post-addition torque is set on the horizontal axis of FIG. 15. The viscosity correction gain map according to this embodiment shows a tendency for the viscosity correction gain to decrease as the absolute value of the post-addition torque increases. Furthermore, when the post-addition torque is zero, the viscosity correction gain is set to an approximately constant value regardless of the vehicle speed. However, in the viscosity correction gain map according to the present embodiment, the value of the viscosity correction gain corresponding to the post-addition torque is adjusted to a value different from the value of the viscosity correction gain corresponding to the pre-correction target steering torque in the viscosity correction gain map according to Embodiment 1 and the value of the viscosity correction gain corresponding to the post-addition gain in the viscosity correction gain map according to Embodiment 2. The viscosity correction gain map processing unit 29b refers to the viscosity correction gain map to identify the viscosity correction gain corresponding to the absolute value of the post-addition torque, and outputs the identified viscosity correction gain to the multiplier 29c.

[0070] The post-addition torque according to this embodiment has a hysteresis characteristic because it is obtained by adding the viscous feel torque to the base torque. That is, the post-addition torque according to this embodiment is similar to the pre-correction target steering torque according to the first embodiment and the post-addition torque according to the second embodiment in that its absolute value during steering is greater than its absolute value during steering return. The hysteresis correction unit 29 according to this embodiment obtains a viscous feel torque corrected based on the viscosity correction gain corresponding to the post-addition torque. As a result, the corrected viscous feel torque during steering can be made greater than the corrected viscous feel torque during steering return. This improves the steering feel, as in the first and second embodiments. Furthermore, this embodiment also simplifies the calculation process by eliminating the adder 30b according to the first embodiment.

[0071] In the first to third embodiments, the hysteresis correction unit 29 corrects the viscous feel torque. In these examples, the adder 30d calculates the sum of the corrected viscous feel torque and the frictional feel torque as the corrected hysteresis feel torque, and the adder 30c calculates the sum of the base torque and the corrected hysteresis feel torque as the corrected target steering torque. The present invention is not limited to these examples. The hysteresis correction unit 29 may correct the frictional feel torque instead of the viscous feel torque, and calculate the sum of the base torque and the corrected frictional feel torque as the corrected target steering torque. This is because the frictional feel torque is also a component of the hysteresis feel torque.

[0072] To summarize the above examples, the control unit 11 according to the present application functions as a steering control device including a target steering torque setting unit 22, a current driving unit 12, and a torque feedback calculation unit 23 that calculates a steering assist torque so that the steering torque acting on the steering shaft 2 follows the target steering torque. The target steering torque setting unit 22 sets the target steering torque based on the steering state of the steering wheel. Here, the target steering torque setting unit 22 includes a base torque calculation unit 25, a hysteresis feel torque calculation unit 26, and a hysteresis correction unit 29. The base torque calculation unit 25 calculates a base torque that is a basic component of the steering torque. The hysteresis feel torque calculation unit 26 calculates a hysteresis feel torque that includes a hysteresis component with respect to the target steering torque. The hysteresis correction unit 29 corrects the hysteresis component based on the base torque and the steering torque that includes at least a part of the hysteresis component. The target steering torque is set including the base torque and the corrected hysteresis component.

[0073] If the viscous torque is defined as a first hysteresis component and the frictional torque is defined as a second hysteresis component, the hysteresis torque includes either the first hysteresis component or the second hysteresis component, or both. The hysteresis correction unit 29 corrects the first hysteresis component and the second hysteresis component based on the base torque and the steering torque including either the first hysteresis component or the second hysteresis component, or both.

[0074] As described above, the magnitude of the steering torque including either or both of the base torque and the hysteresis component may differ between the steering phase and the returning phase. By correcting the first hysteresis component or the second hysteresis component based on this steering torque, steering characteristics with different hysteresis feel and hysteresis width between the steering phase and the returning phase are realized. For example, the magnitude of the corrected target steering torque during the steering phase can be made larger than the magnitude of the corrected target steering torque during the returning phase. This improves the steering feel experienced by the driver of the vehicle.

[0075] <Fourth Embodiment> Next, an electric power steering device PS according to a fourth embodiment of the present disclosure will be described. The following description will mainly focus on differences from the first embodiment. Unless otherwise specified, the description of the first embodiment will be used for points in common with the first embodiment. In the control unit 11 according to this embodiment, the adder 30b is also omitted from the target steering torque setting unit 22. The configurations of the hysteresis sense torque calculation unit 26 and the hysteresis correction unit 29 according to this embodiment are different from the configurations of the hysteresis sense torque calculation unit 26 and the hysteresis correction unit 29 according to the first to third embodiments, respectively.

[0076] Next, an example of the configuration of the target steering torque setting unit 22 according to this embodiment will be described. FIG. 20 is a schematic block diagram showing an example of the configuration of the target steering torque setting unit 22 according to this embodiment. The hysteresis feel torque calculation unit 26 according to this embodiment outputs either the viscous feel torque or the frictional feel torque as the hysteresis feel torque to the adder 30a and the hysteresis correction unit 29. In this respect, it differs from the first to third embodiments in that the sum obtained by adding the viscous feel torque and the frictional feel torque is output as the hysteresis feel torque. In the hysteresis feel torque calculation unit 26 according to this embodiment, the configuration related to the hysteresis component that is not output as the hysteresis feel torque to the adder 30a and the hysteresis correction unit 29 may be omitted. For example, if the viscous feel torque is output as the hysteresis feel torque and the frictional feel torque is not output, the frictional feel torque calculation unit 27 may be omitted.

[0077] Adder 30a adds the hysteresis feel torque input from hysteresis feel torque calculation unit 26 to the base torque input from base torque calculation unit 25. Adder 30a outputs the sum obtained by the addition to hysteresis correction unit 29 as pre-correction hysteresis feel torque. Hysteresis correction unit 29 corrects the hysteresis feel torque input from hysteresis feel torque calculation unit 26 based on the pre-correction target steering torque input from adder 30a. This point differs from the hysteresis correction unit 29 according to the first embodiment in that it corrects the viscous feel torque based on the pre-correction target steering torque including all of the base torque, viscous feel torque, and friction feel torque. Hysteresis correction unit 29 outputs the corrected hysteresis feel torque to adder 30c.

[0078] Next, an example of the configuration of the hysteresis correction unit 29 according to this embodiment will be described. Fig. 21 is a schematic block diagram showing an example of the configuration of the hysteresis correction unit 29 according to this embodiment. The hysteresis correction unit 29 includes an absolute value calculation unit 29a, a hysteresis correction gain map processing unit 29d, and a multiplier 29c. The absolute value calculation unit 29a calculates the absolute value of the pre-correction target steering torque input from the adder 30a. The absolute value calculation unit 29a outputs the absolute value of the pre-correction target steering torque obtained by the calculation to the hysteresis correction gain map processing unit 29d.

[0079] The hysteresis correction gain map processing unit 29d is configured with information indicating at least the correspondence relationship between the absolute value of the pre-correction target steering torque and the hysteresis correction gain as a hysteresis correction gain map. A non-negative real value greater than or equal to 0 is configured as the hysteresis correction gain. The correspondence relationship between the pre-correction target steering torque and the hysteresis correction gain may be constant regardless of vehicle speed, or may be variable depending on vehicle speed. The hysteresis correction gain may be configured to decrease as the pre-correction target steering torque increases, and the decrease in the pre-correction target steering torque increases as the vehicle speed increases. When the pre-correction target steering torque is zero, the hysteresis correction gain is set to be approximately constant regardless of vehicle speed. However, in the hysteresis correction gain map according to this embodiment, the value of the hysteresis correction gain corresponding to the pre-correction target steering torque is adjusted to a value different from the value of the viscosity correction gain corresponding to the pre-correction target steering torque in the viscosity correction gain map according to the first embodiment.

[0080] The hysteresis correction gain map processing unit 29d identifies a hysteresis correction gain map corresponding to the vehicle speed input to the unit itself, from among preset hysteresis correction gain maps. The hysteresis correction gain map processing unit 29d identifies a hysteresis correction gain corresponding to the absolute value of the pre-correction target steering torque by referring to the identified hysteresis correction gain map. The hysteresis correction gain map processing unit 29d outputs the identified hysteresis correction gain to the multiplier 29c. The multiplier 29c multiplies the hysteresis correction gain input from the hysteresis correction gain map processing unit 29d by the pre-correction hysteresis sense torque input from the adder 30a, and calculates the product obtained by the multiplication as the post-correction hysteresis sense torque.

[0081] As described above, the hysteresis correction unit 29 according to this embodiment corrects the hysteresis component based on the base torque and the steering torque including the pre-correction hysteresis component. In other words, the pre-correction target steering torque is obtained by adding the hysteresis feel torque to the base torque. The viscous feel torque or friction feel torque is used as a hysteresis feel gain, and its magnitude differs between the steering phase and the steering return phase. Therefore, the absolute value of the pre-correction target steering torque during the steering phase is smaller than the absolute value of the pre-correction target steering torque during the steering return phase. The hysteresis correction unit 29 then multiplies the pre-correction target steering torque by the hysteresis correction gain obtained based on the pre-correction target steering torque to calculate the corrected hysteresis feel torque. Therefore, the magnitude of the hysteresis feel torque during the steering phase is also corrected to be smaller than the magnitude of the hysteresis feel torque during the steering return phase. Therefore, the corrected target steering torque when turning the steering wheel can be made larger than the corrected target steering torque when turning the steering wheel back, thereby improving the steering feel.

[0082] <Fifth Embodiment> Next, an electric power steering device PS according to a fifth embodiment of the present disclosure will be described. The following description will mainly focus on differences from the first and fourth embodiments. Unless otherwise specified, the description of the first and fourth embodiments will be used for points common to the first and fourth embodiments. The control unit 11 according to this embodiment differs in input / output relationship from the control unit 11 according to the other embodiments in that the adder 30a is omitted.

[0083] More specifically, the base torque calculation unit 25 outputs the base torque to the adder 30c. The hysteresis feeling torque calculation unit 26 outputs the hysteresis feeling torque to the hysteresis correction unit 29. The hysteresis feeling torque calculation unit 26 according to this embodiment may output either the viscous feeling torque or the frictional feeling torque as the hysteresis feeling torque, as in the fourth embodiment, or may output the sum obtained by adding the viscous feeling torque and the frictional feeling torque as the hysteresis feeling torque, as in the first to third embodiments.

[0084] Hysteresis correction unit 29 corrects the hysteresis sense torque input from hysteresis sense torque calculation unit 26 based on the corrected target steering torque fed back from adder 30c. In this respect, it differs from hysteresis correction unit 29 according to the fourth embodiment in that it uses the pre-correction target steering torque. Adder 30c calculates the sum obtained by adding the base torque input from base torque calculation unit 25 and the corrected hysteresis sense torque input from hysteresis correction unit 29 as the corrected target steering torque. Adder 30c feeds back the corrected target steering torque obtained by the addition to hysteresis correction unit 29.

[0085] The hysteresis correction unit 29 according to this embodiment has the same configuration as the hysteresis correction unit 29 according to the fourth embodiment (see FIG. 21). However, the post-correction target steering torque is input to an absolute value calculation unit 29a of the hysteresis correction unit 29 according to this embodiment, instead of the pre-correction target steering torque. Information indicating the correspondence between the absolute value of the post-correction target steering torque and the hysteresis correction gain is set as a hysteresis correction gain map in a hysteresis correction gain map processing unit 29d, instead of the absolute value of the pre-correction target steering torque.

[0086] The correspondence relationship between the corrected target steering torque and the hysteresis correction gain may be constant regardless of the vehicle speed, or may be variable depending on the vehicle speed. The hysteresis correction gain may be set so that it decreases as the corrected target steering torque increases, and the higher the vehicle speed, the greater the degree of decrease in the corrected target steering torque. When the corrected target steering torque is zero, the hysteresis correction gain is set to be approximately constant regardless of the vehicle speed. However, in the hysteresis correction gain map according to this embodiment, the value of the hysteresis correction gain corresponding to the corrected target steering torque is adjusted to a value different from the value of the hysteresis correction gain corresponding to the corrected target steering torque in the hysteresis correction gain map according to the third embodiment.

[0087] The hysteresis correction gain map processing unit 29d identifies a hysteresis correction gain map corresponding to the vehicle speed input to the unit itself, from among preset hysteresis correction gain maps. The hysteresis correction gain map processing unit 29d identifies a hysteresis correction gain corresponding to the absolute value of the corrected target steering torque by referring to the identified hysteresis correction gain map. The hysteresis correction gain map processing unit 29d outputs the identified hysteresis correction gain to the multiplier 29c. The multiplier 29c multiplies the hysteresis correction gain input from the hysteresis correction gain map processing unit 29d by the pre-correction hysteresis sense torque input from the adder 30a, and calculates the product obtained by the multiplication as the corrected hysteresis sense torque.

[0088] As described above, the hysteresis correction unit 29 according to this embodiment corrects the hysteresis component based on the base torque and the steering torque including the corrected hysteresis component. In other words, the corrected target steering torque is obtained by adding the corrected hysteresis feel torque to the base torque. The viscous feel torque or friction feel torque is used as a hysteresis feel gain, and its magnitude differs between the steering phase and the steering return phase. The hysteresis feel gain is corrected based on the corrected target steering torque. Therefore, the absolute value of the corrected target steering torque during the steering phase is smaller than the absolute value of the corrected target steering torque during the steering return phase. Therefore, the magnitude of the hysteresis feel torque during the steering phase is also corrected to be smaller than the magnitude of the hysteresis feel torque during the steering return phase. Therefore, the corrected target steering torque during the steering phase can be made larger than the corrected target steering torque during the steering return phase, improving the steering feel. Furthermore, in this embodiment, the corrected target steering torque is used for hysteresis correction, so the adder 30b according to the fourth embodiment is omitted. Therefore, in this embodiment, the calculation process is simpler than in the fourth embodiment.

[0089] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments. The drawings used in the above description are merely examples and are not intended to limit the scope of the present disclosure. The above embodiments may be freely modified without departing from the spirit of the present disclosure. For example, the steering assist system of the electric power steering device PS may be a column assist system, a rack-and-pinion system, or the like. Furthermore, the feedback control based on the target steering torque according to the present disclosure can also be applied to a steer-by-wire reaction force system that includes at least a torque sensor.

[0090] Furthermore, the base torque calculation unit 25 may calculate the base torque using a road load instead of the steering angle. Since the basic road load on the steering mechanism depends on the steering angle, the base torque is estimated based on the road load. The viscous feel torque calculation unit 28 may calculate the viscous feel torque based on the time derivative of the road load instead of the steering angular velocity. Due to the dependency of the basic road load on the steering angle, the viscous feel torque is estimated based on the time derivative of the road load. The correspondence relationship between input values ​​and output values ​​shown in the above maps (i.e., the base map, frictional feel gain map, viscous feel torque map, viscosity correction gain map, etc.) may be configured as a data table showing the output value for the input value, or may be defined as a function for calculating the output value from the input value.

[0091] Furthermore, the control unit 11 may be configured with dedicated hardware or may include a computer system. The computer system may load a program stored in a computer-readable storage medium and execute the loaded program to execute the processes associated with each component of the control unit 11, such as the target steering torque setting unit 22 and the torque feedback calculation unit 23, or both. "Loading and executing a program stored in a storage medium" includes installing the program in a computer system. The term "computer system" includes a processor, a main memory, software such as an operating system (OS), and hardware such as peripheral devices. The term "computer system" is not limited to a single computer device, but may also include multiple computer devices connected via a network, including communication lines such as the Internet, a wide area network (WAN), a local area network (LAN), or a dedicated line. The term "computer-readable storage medium" refers to portable media such as a flexible disk, a magneto-optical disk, a read-only memory (ROM), or a CD-ROM, or a storage device such as a hard disk built into a computer system. In this way, the storage medium storing the program may be a non-transitory storage medium such as a CD-ROM.

[0092] The recording medium also includes internal or external recording media accessible from a distribution server for distributing the program. The program may be divided into multiple parts by the distribution server. The divided programs may be downloaded at different times and then combined in the control unit 11 to restore a single program. Each divided program may be distributed by a different distribution server. Furthermore, the term "computer-readable recording medium" may also include a memory that stores a program for a certain period of time, such as volatile memory (e.g., random access memory (RAM)) within a computer system that serves as a server or client when a program is transmitted over a network. The program may also be a program for realizing part of the above functions. The program may also be a so-called differential file (differential program) that can realize part or all of the above functions in combination with a program already stored in the computer system.

[0093] The steering control device, power steering device, steering control method, and program disclosed herein can improve the operational feel of the steering mechanism and suppress an increase in the amount of calculation required to control the steering torque.

[0094] 1...Steering wheel, 2...Steering shaft, 5...Torque sensor, 6...Motor, 11...Control unit, 12...Current drive section, 21...Steering state detection section, 22...Target steering torque setting section, 23...Torque feedback calculation section, 24...Motor rotation angular velocity detection section, 25...Base torque calculation section, 26...Hysteresis feeling torque calculation section, 27...Friction feeling torque calculation section, 28...Viscous feeling torque calculation section, 29...Hysteresis correction section, 30a...Adder, 30b...Adder, 30c...Adder, 30d...Adder, PS...Electric power steering device

Claims

1. A steering control device comprising: a target steering torque setting unit that sets a target steering torque based on a steering state of a steering mechanism; a current drive unit that controls a drive current of a motor that rotates a steering shaft of the steering mechanism to generate a steering assist torque; and a torque feedback calculation unit that calculates the steering assist torque so that a steering torque acting on the steering shaft follows the target steering torque, wherein the target steering torque setting unit includes: a base torque calculation unit that calculates a base torque that is a basic component of the steering torque; a hysteresis torque calculation unit that calculates a hysteresis torque including a hysteresis component with respect to the target steering torque; and a hysteresis correction unit that corrects the hysteresis component based on the steering torque including at least a part of the base torque and the hysteresis component, and sets the target steering torque including the base torque and the corrected hysteresis component.

2. The steering control device according to claim 1, wherein the hysteresis component includes a first hysteresis component and a second hysteresis component, and the hysteresis correction unit corrects the first hysteresis component based on the steering torque including the base torque, the first hysteresis component, and one or both of the second hysteresis components.

3. The steering control device according to claim 1, wherein the hysteresis correction unit corrects the hysteresis component based on the steering torque including the base torque and the hysteresis component before correction.

4. The steering control device according to claim 1, wherein the hysteresis correction unit corrects the hysteresis component based on the steering torque including the base torque and the hysteresis component after correction.

5. The steering control device according to claim 2, wherein the hysteresis torque calculation unit calculates, as the first hysteresis component, a viscous torque that increases as the steering angular velocity of the steering mechanism increases, and calculates, as the second hysteresis component, a frictional torque having a polarity corresponding to the steering direction of the steering mechanism.

6. A power steering device comprising: the steering control device according to any one of claims 1 to 5; the motor; and a speed reduction mechanism that transmits a driving force of the motor to the steering shaft.

7. A steering control method in a steering control device, comprising: a target steering torque setting step of setting a target steering torque based on the steering state of a steering mechanism; a current drive step of controlling a drive current of a motor that rotates a steering shaft of the steering mechanism to generate a steering assist torque; and a torque feedback calculation step of calculating the steering assist torque so that a steering torque acting on the steering shaft follows the target steering torque. The target steering torque setting step includes: a base torque calculation step of calculating a base torque that is a basic component of the steering torque; a hysteresis torque calculation step of calculating a hysteresis torque including a hysteresis component with respect to the target steering torque; a hysteresis correction step of correcting the hysteresis component based on the steering torque including at least a part of the base torque and the hysteresis component; and a target steering torque setting step of setting the target steering torque including the base torque and the corrected hysteresis component.

8. A program for causing a computer to function as a steering control device, the computer comprising: a target steering torque setting unit that sets a target steering torque based on the steering state of a steering mechanism; a current drive unit that controls a drive current of a motor that rotates a steering shaft of the steering mechanism to generate a steering assist torque; and a torque feedback calculation unit that calculates the steering assist torque so that a steering torque acting on the steering shaft follows the target steering torque. The target steering torque setting unit includes: a base torque calculation unit that calculates a base torque that is a basic component of the steering torque; a hysteresis torque calculation unit that calculates a hysteresis torque including a hysteresis component with respect to the target steering torque; and a hysteresis correction unit that corrects the hysteresis component based on the steering torque including at least a part of the base torque and the hysteresis component.

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