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

Abstract

A target steering torque setting section sets a target steering torque based on a steering state of a steering mechanism, a current drive section controls a drive current of an electric motor that rotates a steering shaft of the steering mechanism to generate a steering assist torque, and a torque feedback operation section operates the steering assist torque so that a steering torque acting on the steering shaft follows the target steering torque. The target steering torque setting section operates a base torque that is a basic component of the steering torque, operates a hysteresis feeling torque that includes a hysteresis component for the target steering torque, corrects the hysteresis component based on a steering torque that includes 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.

Description

Technical Field

[0001] This disclosure relates to a steering control device, a power steering device, a steering control method, and a procedure. Background Technology

[0002] The steering control device described in Patent Document 1 controls steering characteristics by having the steering torque follow a target steering torque. The target steering torque, as a torque component, includes a viscous adjustment torque. This viscous adjustment torque is used to adjust the viscous feel of the steering system mechanism supplied to the driver during steering. The viscous adjustment torque is obtained by multiplying the time-varying rate of change of road load by a viscous adjustment gain. The viscous adjustment gain is variable depending on the driver's power. The driver's power is calculated based on the steering torque and steering angular velocity. Existing technical documents Patent documents

[0003] Patent Document 1: Japanese Patent Application Publication No. 2016-203855 Summary of the Invention

[0004] In the steering control device described in Patent Document 1, the structure becomes complex when the viscous sensation felt when operating the steering wheel is variable by adjusting the viscous gain. This is because a new state index value of driver power needs to be calculated. Furthermore, since the viscous adjustment gain is set to be variable based on the steering torque detected from the steering wheel movement, a delay occurs relative to the steering torque set as the control target. Because the viscous torque increases at higher steering speeds, the impact of the delay on the handling feel easily becomes significant when the steering speed changes abruptly.

[0005] One object of this disclosure is to provide a steering control device, power steering device, steering control method and procedure that solve the above-mentioned technical problems. Technical solutions to solve technical problems

[0006] The first aspect is 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 such 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 as a basic component of the steering torque; a hysteresis torque calculation unit that calculates a hysteresis torque including a hysteresis component for the target steering torque; and a hysteresis correction unit that corrects the hysteresis component based on a steering torque including at least a portion of the base torque and the hysteresis component. The target steering torque setting unit sets the target steering torque by including the base torque and the corrected hysteresis component.

[0007] The second aspect is a steering control method for a steering control device, comprising the following steps: a target steering torque setting step, which sets a target steering torque based on the steering state of the steering mechanism; a current driving step, which controls the drive current of a motor that rotates the steering shaft of the steering mechanism to generate a steering assist torque; and a torque feedback calculation step, which calculates the steering assist torque such that the steering torque acting on the steering shaft follows the target steering torque, wherein the target steering torque setting step includes: a base torque calculation step, which calculates a base torque as a basic component of the steering torque; a hysteresis torque calculation step, which calculates a hysteresis torque including a hysteresis component for the target steering torque; a hysteresis correction step, which corrects the hysteresis component based on a steering torque including at least a portion of the base torque and the hysteresis component; and a target steering torque setting step, which sets the target steering torque by including the base torque and the corrected hysteresis component.

[0008] The third aspect is a program for enabling 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 drive unit that controls the drive 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 such that the steering torque acting on the steering shaft follows the target steering torque, the target steering torque setting unit comprising: a base torque calculation unit that calculates a base torque as a basic component of the steering torque; a hysteresis torque calculation unit that calculates a hysteresis torque including a hysteresis component for the target steering torque; and a hysteresis correction unit that corrects the hysteresis component based on a steering torque including at least a portion of the base torque and the hysteresis component, the target steering torque setting unit setting the target steering torque by including the base torque and the corrected hysteresis component. Invention Effects

[0009] According to this disclosure, it is possible to improve the feel of operation of the steering mechanism and suppress the increase in computational load involved in controlling the steering torque. Attached Figure Description

[0010] Figure 1 This is a simplified block diagram illustrating a structural example of the electric power steering device according to Embodiment 1 of this disclosure. Figure 2 This is a simplified block diagram illustrating a structural example of the control unit according to Embodiment 1 of this disclosure. Figure 3 This is a flowchart illustrating an example of the steering control process involved in Embodiment 1 of this disclosure. Figure 4 This is a block diagram illustrating a structural example of the target steering torque setting unit according to Embodiment 1 of this disclosure. Figure 5 This is a block diagram illustrating a first structural example of the basic torque calculation unit according to Embodiment 1 of this disclosure. Figure 6 This is a block diagram illustrating a second structural example of the basic torque calculation unit according to Embodiment 1 of this disclosure. Figure 7 This is a diagram illustrating a first example of the basic mapping involved in Embodiment 1 of this disclosure. Figure 8 This is a diagram illustrating a second example of the basic mapping involved in Embodiment 1 of this disclosure. Figure 9This is a diagram illustrating an example of the frictional gain according to Embodiment 1 of this disclosure. Figure 10 This is a simplified block diagram illustrating a first structural example of the viscous torque calculation unit according to Embodiment 1 of this disclosure. Figure 11 This is a simplified block diagram illustrating a second structural example of the viscous torque calculation unit according to Embodiment 1 of this disclosure. Figure 12 This is a diagram illustrating an example of the viscous gain mapping involved in Embodiment 1 of this disclosure. Figure 13 This is a diagram illustrating an example of the viscous torque mapping involved in Embodiment 1 of this disclosure. Figure 14 This is a simplified block diagram illustrating a structural example of the hysteresis correction unit according to Embodiment 1 of this disclosure. Figure 15 This is a diagram illustrating an example of the viscosity correction gain mapping involved in Embodiment 1 of this disclosure. Figure 16 This is a diagram illustrating a structural example of the torque feedback calculation unit according to Embodiment 1 of this disclosure. Figure 17 It is a graph showing the relationship between the steering angle and the target steering torque during steering. Figure 18 This is a flowchart illustrating a structural example of the target steering torque setting unit according to Embodiment 2 of this disclosure. Figure 19 This is a flowchart illustrating a structural example of the target steering torque setting unit according to Embodiment 3 of this disclosure. Figure 20 This is a flowchart illustrating a structural example of the target steering torque setting unit according to Embodiment 4 of this disclosure. Figure 21 This is a flowchart illustrating a structural example of the hysteresis correction unit according to Embodiment 4 of this disclosure. Figure 22 This is a flowchart illustrating a structural example of the target steering torque setting unit according to Embodiment 5 of this disclosure. Detailed Implementation

[0011] The embodiments of this disclosure will now be described with reference to the accompanying drawings. Common or corresponding elements in the various figures are labeled with the same reference numerals, and unless otherwise specified, their descriptions will follow. <Implementation Method 1> First, the first embodiment of this disclosure will be described. Figure 1 This is a simplified block diagram illustrating a structural example of the electric power steering device PS according to this embodiment. The electric power steering system PS includes a steering wheel 1, a steering shaft 2, a steering wheel 3, a steering angle sensor 4, a torque sensor 5, a motor 6, a reduction 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 component operated by the driver of a vehicle to apply a steering angle to the steering wheels 3. The steering wheel 1 is equivalent to a steering wheel in general. The steering wheel 1 has a roughly ring-shaped design. Depending on the operation, the steering wheel 1 rotates about the 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 the axle 13. The long side of the steering shaft 2 is orthogonal to the main surface of the steering wheel 1, forming a rotation axis. The steering shaft 2 rotates around the rotation axis according to the rotation of the steering wheel 1.

[0013] Steering wheels 3 are respectively disposed at both ends of axle 13. The steering wheels 3 change direction according to the rotation of steering shaft 2, thereby steering. In addition, in this application, the mechanism that causes the steering wheels 3 to turn is sometimes referred to as a "steering gear" or "steering mechanism". The steering mechanism includes steering wheel 1, steering shaft 2 and axle 13. Steering angle sensor 4 is located at the center of steering wheel 1. Steering angle sensor 4 detects the steering angle of steering wheel 1.

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

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

[0016] Next, an example of the structure of the control unit 11 according to this embodiment will be described. The control unit 11 functions as a steering control device. Figure 2 This is a simplified block diagram illustrating a structural example 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 drive unit 12.

[0017] The rotation angle of the motor 6 is input from the motor rotation angle sensor 10 to the differentiator 24a. The differentiator 24a differentiates the rotation angle of the motor 6 and calculates the rotational angular velocity of the motor 6 (hereinafter, sometimes referred to as "motor rotational angular velocity"). The differentiator 24a outputs the calculated motor rotational angular velocity to the target steering torque setting unit 22. Furthermore, the differentiator 24a can also be integrated with the motor rotation angle sensor 10 to form the motor rotation angular velocity detection unit 24. Alternatively, the differentiator 24a can be integrally formed with the motor rotation angle sensor 10. In this case, the differentiator 24a can be omitted from the control unit 11.

[0018] The target steering torque setting unit 22 sets the 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 from the vehicle speed sensor 8, and the motor rotational angular velocity as the steering angular velocity from the motor rotational angular velocity detection unit 24. Figure 2 In the example, the steering angle sensor 4 is installed 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 is equivalent to an example of a physical quantity representing the steering state of the steering gear. The target steering torque setting unit 22 sets the target steering torque based on the steering angle, vehicle speed, and 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 of the structure of the target steering torque setting unit 22 will be described later.

[0019] The torque feedback calculation unit 23 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 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 calculated steering assist torque to the current drive unit 12. The current drive unit 12 controls the current of the drive motor 6 so that the steering mechanism generates steering assist torque input from the torque feedback calculation unit 23.

[0020] Furthermore, in the control unit 11, part or all of the differentiator 24a, the target steering torque setting unit 22, and the torque feedback calculation unit 23 can be implemented using a microcomputer equipped with a processor and memory. The microcomputer can also be configured as an electronic control unit (ECU). The processor can also be configured as a central processing unit (CPU). The memory can include both volatile and non-volatile memory. The current drive unit 12 can, for example, be configured as an analog circuit with multiple switching elements. Field-effect transistors (FETs) can be used as switching elements, for example.

[0021] Next, an example of the steering control process involved in this embodiment will be described. Figure 3 This is a flowchart illustrating an example of the steering control processing involved in this embodiment. Figure 3 The process shown repeats itself according to a preset control cycle. (Step S02) The control unit 11 acquires the steering angle, which is an example of a physical quantity representing the steering state, detected in the steering state detection unit 21; the vehicle speed, detected in the vehicle speed sensor 8; the steering torque, detected in the torque sensor 5; and the motor rotation angle, detected in the motor rotation angle sensor. The differentiator 24a of the control unit 11 differentiates the acquired motor rotation angle and calculates 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 unit 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 unit 22 and the steering torque detected in the torque sensor 5. (Step S08) The current drive unit 12 of the control unit 11 controls the current supplied to the motor 6 so that the steering mechanism generates the steering assist torque calculated in the torque feedback calculation unit 23. Then, the process ends. Figure 3 The processing.

[0023] Next, a structural example of the target steering torque setting unit 22 according to this embodiment will be described. Figure 4 This is a block diagram illustrating a structural example of the target steering torque setting unit 22 according to this embodiment. The target steering torque setting unit 22 includes a basic torque calculation unit 25, a hysteresis torque calculation unit 26, a hysteresis correction unit 29, and adders 30a and 30c. The basic torque calculation unit 25 calculates the basic torque using the steering angle and vehicle speed. The basic torque is equivalent to the fundamental component of the steering torque. The basic torque has the characteristic that it increases with the larger the steering angle. The basic torque does not exhibit hysteresis relative to the steering angle.

[0024] The hysteresis torque calculation unit 26 calculates the hysteresis torque using the steering angle and vehicle speed input to itself. The hysteresis torque is equivalent to the hysteresis component of the target steering torque. The hysteresis component includes the viscous torque as the first hysteresis component and the frictional torque as the second hysteresis component. The hysteresis torque calculation unit 26 includes a friction torque calculation unit 27, a viscous torque calculation unit 28, and an adder 30b.

[0025] The friction torque calculation unit 27 calculates the friction torque using the steering angle and vehicle speed. The friction torque has a polarity corresponding to the steering direction. The steering direction refers to the left-right direction relative to the vehicle chassis orientation. That is, the steering direction is represented by the polarity of the steering angular velocity. The steering angular velocity is obtained by differentiating the steering direction input to itself over time. The viscous torque calculation unit 28 performs time differentiation on the steering direction to calculate the steering angular velocity, and uses the calculated steering angular velocity and vehicle speed to calculate the viscous torque. The viscous torque increases with the increase of the steering angular velocity. Adder 30b adds the frictional torque input from frictional torque calculation unit 27 and the viscous torque input from viscous torque calculation unit 28. Adder 30b outputs the sum obtained by addition as the pre-correction hysteresis torque to adder 30a.

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

[0027] The hysteresis correction unit 29 includes a hysteresis adjustment unit 29m and an adder 30d. The hysteresis adjustment unit 29m uses the viscous torque (before correction) input from the viscous torque calculation unit 28 and the target steering torque before correction input from the adder 30a to calculate the viscous torque after correction. Adder 30d adds the corrected viscous torque input from hysteresis correction unit 29 and the friction torque input from friction torque calculation unit 27. Adder 30d calculates the sum obtained by addition as the corrected hysteresis torque.

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

[0029] Next, an example of the structure of the basic torque calculation unit 25 involved in this embodiment will be described. Figure 5 This is a block diagram illustrating a first structural example of the basic torque calculation unit 25 according to this embodiment. Figure 5 In the example, the basic torque calculation unit 25 includes a basic mapping processing unit 25a, a sign determination unit 25b, and a multiplier 25c. In the basic mapping processing unit 25a, at least the information representing the correspondence between the steering angle and the basic torque is set as a basic mapping. The steering angle is represented by its absolute value. The basic torque is set to a non-negative real value greater than or equal to 0. The correspondence between the steering angle and the basic torque may be constant regardless of vehicle speed, or it may vary depending on vehicle speed.

[0030] exist Figure 7 The basic mapping example illustrates the correspondence between the absolute value of the steering angle and the basic torque for low, medium, and high vehicle speeds. In the basic mapping processing unit 25a, speed ranges are preset for low, medium, and high vehicle speeds. As the speed range corresponding to medium vehicle speed, a speed range that includes speeds higher than low vehicle speed is set. As the speed range corresponding to high vehicle speed, a speed range that includes speeds higher than medium vehicle speed is set. exist Figure 7 In the example, as the steering angle increases, the base torque also increases. However, as the steering angle increases, the rate of increase of the base torque relative to the increase in steering angle tends to decrease. Furthermore, the base torque tends to increase at higher vehicle speeds. Basic mapping processing unit 25a is determined Figure 7 The illustrated base mapping corresponds to the vehicle speed input to itself. The base mapping processing unit 25a, referring to the determined base mapping, determines the non-negative base torque corresponding to the absolute value of the steering angle input to itself. The base mapping processing unit 25a outputs the determined base torque to the multiplier 25c.

[0031] return Figure 5 The sign determination unit 25b determines the polarity, i.e., whether the sign is positive (+) or negative (-), based on whether the input turning angle is 0 or above. The sign determination unit 25b outputs a specified integer value (+1 or -1) with 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 mapping processing unit 25a by the integer value input from the sign determination unit 25b.

[0032] Figure 6 This is a block diagram illustrating a second structural example of the basic torque calculation unit 25 according to this embodiment. Figure 6 In this example, the basic torque calculation unit 25 includes a basic mapping processing unit 25a. The sign determination unit 25b and the multiplier 25c are omitted. In this structural example, the correspondence between the steering angle and the basic torque can be constant regardless of the vehicle speed, but it can also be variable depending on the vehicle speed. Figure 8 This example illustrates the underlying mappings involved in this structure. Figure 8 The illustrated base mapping shows the correspondence between steering angle and base torque for each vehicle speed. Figure 8 In the illustrated base mapping, the larger the steering angle, the more monotonically the base torque increases. The further the steering angle deviates from 0, the lower the rate of increase of the base torque relative to the increase in steering angle tends to be. Figure 7 Unlike the previous example, for steering angles that are negative (below 0), a base torque that is also set to be negative is also provided. Figure 8 The basic mapping shown in the example also illustrates the correspondence between steering angle and basic torque for low, medium, and high vehicle speeds. Basic mapping processing unit 25a is determined Figure 8 The illustrated base mapping corresponds to the vehicle speed input to itself. The base mapping processing unit 25a, referring to the determined base mapping, determines the base torque corresponding to the steering angle input to itself. The base mapping processing unit 25a outputs the determined base torque to the multiplier 25c.

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

[0034] [Mathematical Expression 1]

[0035] Furthermore, the friction gain Tf can be a constant value independent of vehicle speed, or it can be variable based on vehicle speed. In the case where it is variable based on vehicle speed, a correspondence between vehicle speed and friction gain Tf is preset in the friction torque calculation unit 27. The friction torque calculation unit 27 can determine the friction gain corresponding to the vehicle speed input to it by referring to the preset correspondence. Based on the determined friction gain and steering angular velocity, the friction torque calculation unit 27 can calculate the friction torque according to equation (1).

[0036] Next, an example illustrating the relationship between vehicle speed and friction gain will be provided. Figure 9 This example illustrates the relationship between vehicle speed and friction gain mapping. The friction gain Tf reaches its maximum value when the vehicle speed is zero. a When the vehicle speed reaches a certain critical value v b When it becomes the positive minimum value Tf b That is, the frictional gain Tf increases with vehicle speed from zero to a critical value v. b It decreases as the vehicle speed increases, and increases as the vehicle speed exceeds a critical value. However, the frictional gain Tf decreases relative to the speed exceeding the critical value v. b The rate of increase in vehicle speed is greater than the frictional gain Tf relative to a value less than the critical value v. b The rate of decrease in vehicle speed should be gradual.

[0037] Furthermore, the friction torque calculation unit 27 can also perform low-pass filtering on the friction torque calculated using equation (1). The cutoff frequency of the low-pass filter can be preset to a value that extracts frequency components within the frequency band of the steering angle that changes over time. Typically, the driver's limit steering frequency is approximately 5 Hz, and the resonant frequency of the steering shaft 2 is approximately 13 to 18 Hz. In this case, the cutoff frequency only needs to be a value higher than 5 Hz and lower than 10 Hz.

[0038] Next, a structural 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 steering angular velocity and vehicle speed. Figure 10This is a simplified block diagram illustrating a first structural example of the viscous torque calculation unit 28 according to this embodiment. The viscous torque calculation unit 28 according to this structural example includes a viscous gain mapping processing unit 28a and a multiplier 28b. In the viscous gain mapping processing unit 28a, at least information representing the correspondence between the absolute value of the steering angular velocity and the viscous gain is provided as a viscous gain mapping. The magnitude of the steering angular velocity is represented by its absolute value. As the viscous gain, a non-negative real value greater than or equal to 0 is set. The correspondence between the steering angular velocity and the viscous gain may be constant regardless of vehicle speed, but it may also be variable depending on vehicle speed.

[0039] exist Figure 12 The viscous gain mapping illustrated in the example shows the correspondence between the absolute value of the steering angular velocity and the viscous gain for low, medium, and high vehicle speeds, respectively. In the viscous gain mapping processing unit 28a, a range of vehicle speeds is preset for each of the low, medium, and high vehicle speeds. As the range corresponding to the medium vehicle speed, a range is set that includes vehicle speeds higher than the low vehicle speed. As the range corresponding to the high vehicle speed, a range is set that includes vehicle speeds higher than the medium vehicle speed. As the magnitude of the steering angular velocity increases, the viscous gain also increases. However, as the steering angular velocity increases, the rate of increase of the viscous gain relative to the increase of the steering angular velocity decreases, tending to approach a constant value approximately. Furthermore, the higher the vehicle speed, the greater the tendency for the viscous gain to increase.

[0040] return Figure 10 Viscous gain mapping processing unit 28a determines Figure 12 The illustrated viscous gain mapping corresponds to the vehicle speed input to itself. The viscous gain mapping processing unit 28a determines the viscous gain corresponding to the absolute value of the steering angular velocity by referring to the determined viscous gain mapping. The viscous gain mapping processing unit 28a outputs the viscous gain to the multiplier 28b. Multiplier 28b multiplies the viscous gain input from viscous gain mapping processing unit 28a with the steering angular velocity derived from steering angle, and calculates the product as viscous torque.

[0041] Figure 11This is a simplified block diagram illustrating a second structural example of the viscous torque calculation unit 28 according to this embodiment. The viscous torque calculation unit 28 according to this structural example includes a viscous torque mapping processing unit 28c, a sign determination unit 28d, and a multiplier 28e. In the viscous torque mapping processing unit 28c, at least information representing the correspondence between the absolute value of the steering angular velocity and the viscous torque is provided as a viscous torque mapping. The viscous torque is set to a non-negative real value greater than or equal to 0. The correspondence between the steering angular velocity and the viscous torque may be constant regardless of vehicle speed, but it may also vary depending on the vehicle speed.

[0042] exist Figure 13 The illustrated viscous torque mapping shows the correspondence between the absolute value of the steering angular velocity and the viscous torque at low, medium, and high vehicle speeds, respectively. The rate of increase of the viscous torque relative to the steering angular velocity decreases relatively gradually with increasing steering angular velocity. The greater the steering angular velocity, the greater the viscous torque. Furthermore, the higher the vehicle speed, the greater the tendency for the viscous torque to increase.

[0043] return Figure 12 Viscous torque mapping processing unit 28c determines Figure 13 The illustrated viscous torque mapping corresponds to the viscous torque input to the vehicle speed. The viscous torque mapping processing unit 28c, referring to the determined viscous torque mapping, determines the viscous torque corresponding to the absolute value of the steering angular velocity. The viscous torque mapping processing unit 28c outputs the viscous gain to the multiplier 28e. The sign determination unit 28d determines whether the sign of the steering angular velocity is positive (+) or negative (-) based on whether the steering angular velocity input to itself is 0 or higher. The sign determination unit 28d outputs a predetermined integer value (+1 or -1) with the determined sign to the multiplier 28e. The multiplier 28e multiplies the viscous torque input from the viscous torque mapping processing unit 28c by the integer value input from the sign determination unit 28d, and uses the product obtained by multiplication as the viscous gain.

[0044] Next, an example of the structure of the hysteresis correction unit 29 according to this embodiment will be described. Figure 14 This is a simplified block diagram illustrating a structural example 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 mapping processing unit 29b, and a multiplier 29c. The absolute value calculation unit 29a calculates the absolute value of the target steering torque before correction, which is input from the adder 30a. The absolute value calculation unit 29a outputs the absolute value of the target steering torque before correction obtained through calculation to the viscous correction gain mapping processing unit 29b.

[0045] In the viscous correction gain mapping processing unit 29b, at least the information representing the correspondence between the absolute value of the target steering torque before correction and the viscous correction gain is set as a viscous correction gain mapping. The viscous correction gain is set to a non-negative real value greater than or equal to 0. The correspondence between the target steering torque before correction and the viscous correction gain may be constant regardless of vehicle speed, but it may also be variable depending on vehicle speed. exist Figure 15 The illustrated viscous correction gain mapping shows the correspondence between the absolute value of the target steering torque before correction and the viscous correction gain for low, medium, and high vehicle speeds, respectively. In the viscous correction gain mapping processing unit 29b, a range of vehicle speeds is preset for each of the low, medium, and high vehicle speeds. As the range corresponding to the medium vehicle speed, a range is set that includes vehicle speeds higher than the low vehicle speed. As the range corresponding to the high vehicle speed, a range is set that includes vehicle speeds higher than the medium vehicle speed. As the target steering torque before correction increases, the viscous correction gain decreases. The higher the vehicle speed, the greater the target steering torque before correction, and the greater the decrease in viscous correction gain tends to be. When the target steering torque before correction is zero, the viscous correction gain remains approximately constant regardless of vehicle speed.

[0046] return Figure 14 Viscosity correction gain mapping processing unit 29b determines Figure 15 The illustrated viscous correction gain mapping corresponds to the vehicle speed input to itself. The viscous correction gain mapping processing unit 29b, referring to the determined viscous correction gain mapping, determines the viscous correction gain corresponding to the absolute value of the target steering torque before correction. The viscous correction gain mapping processing unit 29b outputs the determined viscous correction gain to the multiplier 29c. Multiplier 28b multiplies the viscous correction gain input from viscous correction gain mapping processing unit 29b and the viscous torque before correction input from viscous torque calculation unit 28, and calculates the product obtained by multiplication as the viscous torque after correction.

[0047] Next, an example of the structure of the torque feedback calculation unit 23 according to this embodiment will be described. Figure 16 This is a simplified block diagram illustrating a structural example of the torque feedback calculation unit 23 according to this embodiment. The torque feedback calculation unit 23 is configured to include 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 the 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] Subtractor 31 subtracts the steering torque input from torque sensor 5 from the target steering torque input from target steering torque setting unit 22, and outputs the deviation obtained by subtraction to first steering auxiliary torque calculation unit 32 and third steering auxiliary 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 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 as the first steering assist torque to the adder 35.

[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 multiplication as the second steering assist torque to the adder 35. 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 multiplication as the third steering assist torque to the adder 35. 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 addition as the steering assist torque to the current drive unit 12.

[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, based on the driver's operation, the steering torque is controlled to follow the target steering torque. This assists the driver in steering. The steering assist torque includes a motor control component. This motor control component corresponds to a 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, suppose the driver removes their hands from the steering wheel 1 and stops operating the vehicle. In this case, the steering torque does not immediately become zero, but is adjusted between zero and the target steering torque. By following the target steering torque, smooth steering is achieved. Furthermore, by including the motor speed control component in the steering assist torque, control stabilization is achieved even when the motor 6 and torque sensor 5 are separated. Moreover, since there is no derivative with the target steering torque, excessive noise generation is avoided.

[0051] The steering assist torque includes a proportional control component. This proportional control component is equivalent to the third steering assist torque. The proportional component responds faster than the integral control component. By improving the following response, overshoot can be reduced. For example, when the driver holds the steering wheel to steer, the steering torque stably follows the target steering torque, achieving smoother steering. In the above description, an example is given with a torque feedback calculation unit 23, aiming to improve stability and following performance, but it is not limited to this. For example, parts 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, which sets a target steering torque according to the steering condition and controls the steering torque to follow the target steering torque. When the driver sets the steering feel (steering sensation) of the vehicle, the target steering angle characteristics are adapted so that the target steering torque set by the control unit 11 has the desired characteristics. In this example of operation, the following situation is assumed: at the vehicle speed set as the adaptation target, the steering wheel 1 is operated so that the time change of the steering angle becomes a sine wave with a predetermined frequency (e.g., 0.2Hz), and the steering is performed so that the amplitude of the lateral acceleration generated by the turning of the vehicle is below a predetermined reference acceleration (e.g., 0.2G).

[0053] Figure 17 This is a graph illustrating the relationship between the steering angle and the target steering torque during steering. Figure 17 In the diagram, the horizontal and vertical axes represent steering angle and torque, respectively. "Base torque" refers to the base torque. Base torque does not exhibit hysteresis; that is, it is independent of whether the steering angle increases and is uniquely determined relative to the steering angle. "No correction technology" indicates that... Figure 4 The target steering torque setting unit 22 shown in the example does not have a hysteresis correction unit 29, and other conditions are set to be the same as in this embodiment to adapt to the target steering angle characteristics to obtain the target steering torque as a comparative example.

[0054] "Before Correction" refers to the target steering torque obtained by adding the base torque and the hysteresis torque in this embodiment. "After Correction" refers to the target steering torque obtained by adding the base torque and the corrected hysteresis torque in this embodiment. In "After Correction", adjustments are made for full steering and steering return to center to optimize steering feel. In the "corrected" state, the lag is significantly different from the "uncorrected" state when the steering wheel is fully turned and then straightened. Full steering corresponds to a steering angle far from zero, while straightening corresponds to a steering angle close to zero. Figure 17 In the example, by correcting the hysteresis component, the hysteresis component is suppressed in the respective situations of turning full and returning to center.

[0055] In "uncorrected steering technology," parameters are adjusted during return to center to provide the driver with optimal steering feel. However, the driver's steering feel is not optimized during return to center. This is confirmed by the following situation: Figure 17 In quadrants 2 and 4, the steering torque after correction was not significantly different from that without correction. However, in quadrants 1 and 3, the steering torque without correction was greater than that after correction. One possible reason for this is that, in the "uncorrected technology," the increase or decrease in the hysteresis component from the base torque during hysteresis correction based on the hysteresis correction unit 29 is the same when the steering wheel is fully turned and returning to center.

[0056] On the other hand, in this embodiment, with hysteresis correction as a prerequisite, the frictional torque and viscous torque, which constitute the hysteresis torque, are adjusted. By correcting at least a portion of the hysteresis torque based on the base torque and the hysteresis torque before correction, the increase or decrease of the hysteresis component from the base torque during full steering and return steering, as shown in "After Correction," can be made different. Therefore, optimal steering feel can be obtained in either full steering or return steering.

[0057] The hysteresis correction unit 29 has a structure that corrects a portion of the hysteresis torque based on the normally calculated base torque and the hysteresis torque. Therefore, since the newly added computational load is suppressed, the software scale or computational processing load involved in the computation is suppressed. Furthermore, in the above description, the friction gain mapping in the friction torque calculation unit 27 of the hysteresis torque calculation unit 26, the viscous gain mapping or viscous torque mapping in the viscous torque calculation unit 28, and the viscous correction gain mapping in the hysteresis correction unit 29 are all set to be variable relative to the vehicle speed. This allows for the setting of an appropriate control gain to account for the road reaction force characteristics that vary with vehicle speed. Moreover, by setting a target steering torque corresponding to the vehicle speed, steering feel can be improved. Furthermore, not all mappings need to be variable relative to vehicle speed. It is also possible to make at least one mapping, or the gain obtained through a mapping, variable relative to vehicle speed, while other mappings or gains are set to constant regardless of vehicle speed.

[0058] In the above description, an example is given of a steering angle sensor 4 installed in the steering state detection unit 21, where the steering angle detected by the steering angle sensor 4 is used as a physical quantity representing the steering state in the basic torque calculation unit 25. However, instead of the steering angle detected by the steering angle sensor 4, a steering angle calculated based on the motor rotation angle detected by the motor rotation angle sensor can also be used. For example, the rotation angle around 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 can also be used as the steering angle. Furthermore, sometimes the motor rotation angle is also defined as a relative angle with respect to the steering shaft 2. In this case, the absolute angle of the steering shaft 2 can be obtained by correcting the motor rotation angle, which has deviated to a relative angle of zero in straight-line motion, based on the angular velocity of the turning motion detected by a yaw angle sensor or the like (not shown) provided in the vehicle.

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

[0060] <Implementation Method 2> Next, the electric power steering device PS according to Embodiment 2 of this disclosure will be described. In the following description, the differences from Embodiment 1 will be the main focus. Unless otherwise specified, the commonalities with Embodiment 1 will follow the description in Embodiment 1. The control unit 11 in this embodiment omits the adder 30b in the target steering torque setting unit 22. Furthermore, the structure of the hysteresis correction unit 29 in this embodiment differs from the structure of the hysteresis correction unit 29 in Embodiment 1.

[0061] Next, a structural example of the target steering torque setting unit 22 according to this embodiment will be described. Figure 18 This is a simplified block diagram illustrating a structural example of the target steering torque setting unit 22 according to this embodiment. The viscous torque calculation unit 28 of this embodiment outputs the viscous torque to the adder 30a. Adder 30a adds the base torque input from the base torque calculation unit 25 and the viscous torque input from the viscous torque calculation unit 28. Adder 30a outputs the sum obtained by addition as the added torque to the hysteresis correction unit 29. That is, the adder 30a according to this embodiment differs from the adder 30a according to Embodiment 1 in that it adds the viscous torque to the base torque instead of the hysteresis torque before correction. The hysteresis torque before correction includes both the viscous torque and the frictional torque.

[0062] Hysteresis correction unit 29 corrects the viscous torque input from viscous torque calculation unit 28 based on the added torque input from adder 30a, and outputs the corrected viscous torque to adder 30d. That is, the hysteresis correction unit 29 according to this embodiment differs from the hysteresis correction unit 29 according to embodiment 1 in that it corrects the viscous torque based on the added torque instead of the target steering torque before correction.

[0063] In the hysteresis correction unit 29 of this embodiment, the absolute value calculation unit 29a (see reference) Figure 14 The absolute value of the added torque input from adder 30a is output to the viscous correction gain mapping processing unit 29b (see reference). Figure 14 In the viscous correction gain mapping processing unit 29b, the absolute value of the target steering torque before correction is replaced, and information representing the correspondence between the absolute value of the added torque and the viscous correction gain is set as the viscous correction gain mapping.

[0064] In viscosity-corrected gain mapping, Figure 15 The absolute value of the added torque can be set on the horizontal axis. The viscous correction gain mapping involved in this embodiment shows a trend of decreasing viscous correction gain as the absolute value of the added torque increases. In addition, when the added torque is zero, the viscous correction gain is approximately constant regardless of vehicle speed. However, in the viscous correction gain mapping involved in this embodiment, the value of the viscous correction gain corresponding to the added torque is pre-adjusted to a value different from the value of the viscous correction gain corresponding to the target steering torque before correction in the viscous correction gain mapping involved in Embodiment 1. The hysteresis correction unit 29 refers to the viscous correction gain mapping, determines the viscous correction gain corresponding to the absolute value of the added torque, and outputs the determined viscous correction gain to the multiplier 29c.

[0065] Since the added torque is obtained by adding viscous torque to the base torque, it exhibits hysteresis characteristics. That is, the added torque is also the same as the target steering torque before correction, in that its absolute value at full steering input is greater than its absolute value at return to center. In the hysteresis correction unit 29 of this embodiment, a viscous torque corrected based on the viscous correction gain corresponding to the added torque is obtained. As a result, the corrected viscous torque at full steering input can be greater than the corrected viscous torque at return to center. Therefore, similar to Embodiment 1, the steering feel is improved. Furthermore, in this embodiment, the calculation process is simplified because the adder 30b involved in Embodiment 1 can be omitted.

[0066] <Implementation Method 3> Next, the electric power steering device PS according to Embodiment 3 of this disclosure will be described. In the following description, the differences from Embodiments 1 and 2 will be the main focus. Unless otherwise specified, the commonalities with Embodiment 1 will follow the description in Embodiment 1. In the control unit 11 of this embodiment, the adder 30b is also omitted from the target steering torque setting unit 22. The structure of the hysteresis correction unit 29 of this embodiment is different from the structure of the hysteresis correction unit 29 of embodiments 1 and 2.

[0067] Next, a structural example of the target steering torque setting unit 22 according to this embodiment will be described. Figure 19 This is a simplified block diagram illustrating a structural example of the target steering torque setting unit 22 according to this embodiment. The friction torque calculation unit 27 in this embodiment outputs the friction torque to the adder 30a. Adder 30a adds the base torque input from base torque calculation unit 25 and the friction torque input from friction torque calculation unit 27. Adder 30a outputs the sum obtained by addition as the added torque to hysteresis correction unit 29. That is, in this embodiment, the friction torque is added to the base torque instead of the hysteresis torque or viscous torque before correction, which is different from embodiments 1 and 2.

[0068] Hysteresis correction unit 29 corrects the viscous torque input from viscous torque calculation unit 28 based on the added torque input from adder 30a, and outputs the corrected viscous torque to adder 30d. That is, the hysteresis correction unit 29 according to this embodiment differs from the hysteresis correction unit 29 according to embodiments 1 and 2 in that it corrects the viscous torque based on the added torque including the basic torque and the frictional torque as components.

[0069] In the hysteresis correction unit 29 of this embodiment, the absolute value calculation unit 29a (see reference) Figure 14 The absolute value of the added torque input from adder 30a is output to the viscous correction gain mapping processing unit 29b (see reference). Figure 14 In the viscous correction gain mapping processing unit 29b, information representing the correspondence between the absolute value of the added torque and the viscous correction gain is set as the viscous correction gain mapping. In the correction gain mapping according to this embodiment, similarly to Embodiment 2, in... Figure 15 The absolute value of the added torque can be set on the horizontal axis. The viscous correction gain mapping involved in this embodiment shows a trend that the viscous correction gain decreases as the absolute value of the added torque increases. In addition, when the added torque is zero, the viscous correction gain is approximately constant regardless of vehicle speed. However, in the viscous correction gain mapping involved in this embodiment, the value of the viscous correction gain corresponding to the added torque is pre-adjusted to a value that is different from the value of the viscous correction gain corresponding to the target steering torque before correction in the viscous correction gain mapping involved in Embodiment 1, and the value of the viscous correction gain corresponding to the added gain in the viscous correction gain mapping involved in Embodiment 2. The viscous correction gain mapping processing unit 29b refers to the viscous correction gain mapping, determines the viscous correction gain corresponding to the absolute value of the added torque, and outputs the determined viscous correction gain to the multiplier 29c.

[0070] The added torque in this embodiment is obtained by adding a viscous torque to the base torque, and therefore has hysteresis characteristics. That is, the added torque in this embodiment is also the same as the target steering torque before correction in Embodiment 1 and the added torque in Embodiment 2, in that its absolute value at full steering is greater than its absolute value at return to center. In the hysteresis correction unit 29 in this embodiment, a viscous torque corrected based on the viscous correction gain corresponding to the added torque is obtained. As a result, the corrected viscous torque at full steering is greater than the corrected viscous torque at return to center. Therefore, similar to Embodiments 1 and 2, the steering feel is improved. Furthermore, in this embodiment, the calculation process is simplified because the adder 30b in Embodiment 1 can be omitted.

[0071] In Embodiments 1 to 3, the case where the hysteresis correction unit 29 corrects the viscous torque is taken as an example. In these examples, the adder 30d calculates the sum of the corrected viscous torque and the frictional torque as the corrected hysteresis torque, and the adder 30c calculates the sum of the base torque and the corrected hysteresis torque as the corrected target steering torque. However, it is not limited to these examples; the hysteresis correction unit 29 may also correct the frictional torque instead of the viscous torque, and calculate the sum of the base torque and the corrected frictional torque as the corrected target steering torque. This is because the frictional torque is also a component of the hysteresis torque.

[0072] Summarizing the examples above, the control unit 11 involved in this application functions as a steering control device, which includes a target steering torque setting unit 22, a current drive unit 12, and a torque feedback calculation unit 23 that calculates the 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 gear. Here, the target steering torque setting unit 22 includes a basic torque calculation unit 25, a hysteresis torque calculation unit 26, and a hysteresis correction unit 29. The basic torque calculation unit 25 calculates the basic component of the steering torque, i.e., the basic torque. The hysteresis torque calculation unit 26 calculates the hysteresis torque, which includes the hysteresis component for the target steering torque. The hysteresis correction unit 29 corrects the hysteresis component based on the steering torque, which includes at least a portion of the basic torque and the hysteresis component. The target steering torque is set by including the basic torque and the corrected hysteresis component.

[0073] Furthermore, if the viscous torque is defined as the first hysteresis component and the frictional torque as the second hysteresis component, then the hysteresis torque includes either or both of the first and second hysteresis components. The hysteresis correction unit 29 corrects the first and second hysteresis components based on the steering torque, which includes the base torque and either or both of the first and second hysteresis components.

[0074] As mentioned above, the magnitude of the steering torque, which includes either or both of the base torque and hysteresis components, may differ between the fully turned and straightened states. By correcting the first or second hysteresis component based on this steering torque, steering characteristics that differ in the feeling or magnitude of hysteresis between the fully turned and straightened states can be achieved. For example, it is possible to make the corrected target steering torque at full turn greater than the corrected target steering torque at straightened state. Therefore, the steering feel for the vehicle driver is improved.

[0075] <Implementation Method 4> Next, the electric power steering device PS according to Embodiment 4 of this disclosure will be described. In the following description, the differences from Embodiment 1 will be the main focus. Unless otherwise specified, the commonalities with Embodiment 1 will follow the description in Embodiment 1. In the control unit 11 of this embodiment, the adder 30b is also omitted from the target steering torque setting unit 22. The structures of the hysteresis torque calculation unit 26 and the hysteresis correction unit 29 of this embodiment are different from those of the hysteresis torque calculation unit 26 and the hysteresis correction unit 29 of embodiments 1 to 3.

[0076] Next, a structural example of the target steering torque setting unit 22 according to this embodiment will be described. Figure 20 This is a simplified block diagram illustrating a structural example of the target steering torque setting unit 22 according to this embodiment. The hysteresis torque calculation unit 26 of this embodiment outputs either the viscous torque or the frictional torque as the hysteresis torque to the adder 30a and the hysteresis correction unit 29. In this respect, it differs from embodiments 1 to 3, which output the sum of the viscous torque and the frictional torque as the hysteresis torque. In the hysteresis torque calculation unit 26 according to this embodiment, the structure involving the hysteresis component that is not output as hysteresis torque to the adder 30a and the hysteresis correction unit 29 may also be omitted. For example, if the viscous torque is output as hysteresis torque and the friction torque is not output, the friction torque calculation unit 27 may also be omitted.

[0077] Adder 30a adds the basic torque input from the basic torque calculation unit 25 and the hysteresis torque input from the hysteresis torque calculation unit 26. Adder 30a outputs the sum obtained by addition as the hysteresis torque before correction to hysteresis correction unit 29. Hysteresis correction unit 29 corrects the hysteresis torque input from hysteresis torque calculation unit 26 based on the target steering torque before correction input from adder 30a. This differs from the hysteresis correction unit 29 in Embodiment 1, which corrects the viscous torque based on the target steering torque before correction, including the base torque, viscous torque, and frictional torque. Hysteresis correction unit 29 outputs the corrected hysteresis torque obtained through correction to adder 30c.

[0078] Next, an example of the structure of the hysteresis correction unit 29 according to this embodiment will be described. Figure 21 This is a simplified block diagram illustrating a structural example 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 mapping processing unit 29d, and a multiplier 29c. The absolute value calculation unit 29a calculates the absolute value of the target steering torque before correction, which is input from the adder 30a. The absolute value calculation unit 29a outputs the absolute value of the target steering torque before correction obtained through calculation to the hysteresis correction gain mapping processing unit 29d.

[0079] In the hysteresis correction gain mapping processing unit 29d, at least information representing the correspondence between the absolute value of the target steering torque before correction and the hysteresis correction gain is set as a hysteresis correction gain mapping. The hysteresis correction gain is set to a non-negative real value greater than or equal to 0. The correspondence between the target steering torque before correction and the hysteresis correction gain can be constant regardless of vehicle speed, or it can vary depending on vehicle speed. The hysteresis correction gain can be set to decrease as the target steering torque before correction increases; the higher the vehicle speed, the greater the decrease in the target steering torque before correction. When the target steering torque before correction is zero, the hysteresis correction gain is approximately constant regardless of vehicle speed. However, in the hysteresis correction gain mapping according to this embodiment, the value of the hysteresis correction gain corresponding to the target steering torque before correction is pre-adjusted to a value different from the value of the viscous correction gain corresponding to the target steering torque before correction in the viscous correction gain mapping according to Embodiment 1.

[0080] Hysteresis correction gain mapping processing unit 29d determines a hysteresis correction gain mapping corresponding to the vehicle speed input to itself from a preset hysteresis correction gain mapping. Referring to the determined hysteresis correction gain mapping, hysteresis correction gain mapping processing unit 29d determines a hysteresis correction gain corresponding to the absolute value of the target steering torque before correction. Hysteresis correction gain mapping processing unit 29d outputs the determined hysteresis correction gain to multiplier 29c. Multiplier 29c multiplies the hysteresis correction gain input from hysteresis correction gain mapping processing unit 29d and the pre-correction hysteresis torque input from adder 30a, and uses the product obtained by multiplication as the post-correction hysteresis torque.

[0081] As described above, the hysteresis correction unit 29 of this embodiment corrects the hysteresis component based on the steering torque, which includes the base torque and the hysteresis component before correction. In other words, the target steering torque before correction is obtained by adding the hysteresis torque to the base torque. The viscous torque or frictional torque is used as the hysteresis gain, and its magnitude differs between the fully turned steering wheel and the straightening steering wheel. Therefore, the absolute value of the target steering torque before correction in the fully turned steering wheel situation is smaller than the absolute value of the target steering torque before correction in the straightening steering wheel situation. Furthermore, the hysteresis correction unit 29 calculates the corrected hysteresis torque by multiplying the target steering torque before correction by the hysteresis correction gain obtained based on the target steering torque before correction. Therefore, the magnitude of the hysteresis torque in the fully turned steering wheel situation is also corrected to be smaller than the magnitude of the hysteresis torque in the straightening steering wheel situation. Therefore, it is possible to make the corrected target steering torque in the fully turned steering wheel situation greater than the corrected target steering torque in the straightening steering wheel situation, thereby improving the steering feel.

[0082] <Implementation Method 5> Next, the electric power steering device PS according to Embodiment 5 of this disclosure will be described. In the following description, the differences from Embodiments 1 and 4 will be the main focus. Unless otherwise specified, the commonalities with Embodiments 1 and 4 will follow the descriptions in Embodiments 1 and 4. In the control unit 11 of this embodiment, the input-output relationship differs from that of the control unit 11 of other embodiments in that the adder 30a is omitted.

[0083] More specifically, the basic torque calculation unit 25 outputs the basic torque to the adder 30c. The hysteresis torque calculation unit 26 outputs the hysteresis torque to the hysteresis correction unit 29. The hysteresis torque calculation unit 26 involved in this embodiment can output either the viscous torque or the frictional torque as the hysteresis torque, similar to Embodiment 4. Alternatively, it can output the sum of the viscous torque and the frictional torque as the hysteresis torque, similar to Embodiments 1 to 3.

[0084] Hysteresis correction unit 29 corrects the hysteresis torque input from hysteresis torque calculation unit 26 based on the corrected target steering torque fed back from adder 30c. In this respect, it differs from the hysteresis correction unit 29 in embodiment 4, which uses the uncorrected target steering torque. Adder 30c calculates the sum of the basic torque input from the basic torque calculation unit 25 and the corrected hysteresis torque input from the hysteresis correction unit 29 as the corrected target steering torque. Adder 30c feeds back the corrected target steering torque obtained by addition to the hysteresis correction unit 29.

[0085] The hysteresis correction unit 29 in this embodiment has the same structure as the hysteresis correction unit 29 in embodiment 4 (see reference). Figure 21 However, in the absolute value calculation unit 29a of the hysteresis correction unit 29 according to this embodiment, the corrected target steering torque is input to replace the original target steering torque. In the hysteresis correction gain mapping processing unit 29d, the absolute value of the original target steering torque is replaced, and information representing the correspondence between the absolute value of the corrected target steering torque and the hysteresis correction gain is set as hysteresis correction gain mapping.

[0086] The relationship between the corrected target steering torque and the hysteresis correction gain can be constant regardless of vehicle speed, or it can be variable depending on vehicle speed. The hysteresis correction gain can be set to decrease as the corrected target steering torque increases; the higher the vehicle speed, the greater the decrease in the corrected target steering torque. When the corrected target steering torque is zero, the hysteresis correction gain is approximately constant regardless of vehicle speed. However, in the hysteresis correction gain mapping involved in this embodiment, the value of the hysteresis correction gain corresponding to the corrected target steering torque is pre-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 mapping involved in Embodiment 3.

[0087] Hysteresis correction gain mapping processing unit 29d determines a hysteresis correction gain mapping corresponding to the vehicle speed input to itself from a preset hysteresis correction gain mapping. Referring to the determined hysteresis correction gain mapping, hysteresis correction gain mapping processing unit 29d determines the hysteresis correction gain corresponding to the absolute value of the corrected target steering torque. Hysteresis correction gain mapping processing unit 29d outputs the determined hysteresis correction gain to multiplier 29c. Multiplier 29c multiplies the hysteresis correction gain input from hysteresis correction gain mapping processing unit 29d and the pre-correction hysteresis torque input from adder 30a, and uses the product obtained by multiplication as the post-correction hysteresis torque.

[0088] As described above, the hysteresis correction unit 29 in this embodiment corrects the hysteresis component based on the steering torque, which includes the base torque and the corrected hysteresis component. In other words, the corrected target steering torque is obtained by adding the corrected hysteresis torque to the base torque. Viscous torque or frictional torque is used as the hysteresis gain, and its magnitude differs between the fully turned steering position and the straightening position. The hysteresis gain is corrected based on the corrected target steering torque. Therefore, the absolute value of the corrected target steering torque in the fully turned steering position is less than the absolute value of the corrected target steering torque in the straightening position. Therefore, the magnitude of the hysteresis torque in the fully turned steering position is also corrected to be less than the magnitude of the hysteresis torque in the straightening position. Therefore, the corrected target steering torque in the fully turned steering position can be made greater than the corrected target steering torque in the straightening position, thus improving the steering feel. Furthermore, in this embodiment, since the corrected target steering torque is used for hysteresis correction, the adder 30b involved in Embodiment 4 is omitted. Therefore, in this embodiment, the computation process is simpler than in Embodiment 4.

[0089] The embodiments of this disclosure have been described above, but this disclosure is not limited to the embodiments described above. The drawings used in the above description are exemplary and are not limited thereto. The above embodiments can be freely modified without departing from the spirit of this disclosure. For example, the steering assist method of the aforementioned electric power steering device PS can be any of the following: column assist, rack and pinion assist, etc. Furthermore, the feedback control based on the target steering torque disclosed herein can also be applied to steer-by-wire reaction force devices that at least have a torque sensor.

[0090] Furthermore, the basic torque calculation unit 25 can also use road load instead of steering angle to calculate the basic torque. Since the basic road load for the steering mechanism depends on the steering angle, the basic torque is inferred based on the road load. The viscous torque calculation unit 28 can also calculate the viscous torque by substituting the steering angular velocity with the time derivative of the road load. Based on the dependence of the basic road load on the steering angle, the viscous torque is inferred based on the time derivative of the road load. The correspondence between input and output values ​​shown in the above mappings (i.e., basic mapping, frictional gain mapping, viscous torque mapping, viscous correction gain mapping, etc.) can be constructed as a data table representing the output values ​​relative to the input values, or it can be defined as a function used to calculate the output values ​​based on the input values.

[0091] Furthermore, the aforementioned control unit 11 may be constructed using dedicated hardware or may include a computer system. The computer system can execute the processing involved in each or both of the structures included in the control unit 11, such as the target steering torque setting unit 22 and the torque feedback calculation unit 23, by reading and executing a program stored in a computer-readable storage medium. "Reading and executing a program recorded on a recording medium" includes installing the program into the computer system. The "computer system" includes not only the processor and main memory, but also software such as an operating system (OS) and hardware such as peripheral devices. The "computer system" is not limited to a single computer device, but may include multiple computer devices connected via networks including communication lines such as the Internet, WAN (Wide Area Network), LAN (Local Area Network), and dedicated lines. "Computer-readable recording medium" refers to storage devices such as floppy disks, magneto-optical disks, ROM (Read Only Memory), CD-ROMs, and hard disks built into the computer system. Thus, the recording medium storing the program can also be a non-temporary recording medium such as a CD-ROM.

[0092] Additionally, the recording medium also includes internally or externally located recording media that can be accessed from the distribution server for distributing the program. Furthermore, the program can be divided into multiple parts at the distribution server providing the source. The divided programs can be downloaded at different times, merged in the control unit 11, and restored to a single program. The distribution servers distributing the divided programs can also be different. Furthermore, the "computer-readable recording medium" can include a medium that retains the program for a certain period of time, such as volatile memory (e.g., RAM) within a computer system acting as a server or client when sending the program over a network. Additionally, the program described above can be a program used to implement some of the aforementioned functions. The program described above can also be a program capable of implementing some or all of the aforementioned functions through combination with programs already recorded in the computer system, i.e., a so-called differential file (differential program). Industrial practicality

[0093] According to the steering control device, power steering device, steering control method, and program disclosed herein, the tactile feedback of the steering mechanism can be improved, and the increase in computational load related to steering torque control can be suppressed. Label Explanation

[0094] 1. Steering wheel 2. Steering shaft 5 Torque Sensor 6 Electric motors 11 Control Unit 12 Current Drive Unit 21 Steering Condition Detection Unit 22 Target Steering Torque Setting Unit 23 Torque Feedback Calculation Unit 24. Motor Rotational Angular Velocity Detection Unit 25. Basic Torque Calculation Unit 26 Hysteresis Torque Calculation Unit 27 Friction Torque Calculation Unit 28 Viscous Torque Calculation Unit 29 Hysteresis Correction Department 30a Adder 30b Adder 30c adder 30d adder PS Electric power steering.

Claims

1. A steering control device, characterized in that, include: The target steering torque setting unit sets the target steering torque based on the steering state of the steering mechanism; A current drive unit controls the drive current of the electric motor that rotates the steering shaft of the steering mechanism to generate steering assist torque; and A torque feedback calculation unit calculates the steering assist torque so that the steering torque acting on the steering shaft follows the target steering torque. The target steering torque setting unit includes: A basic torque calculation unit calculates the basic torque, which is the basic component of the steering torque; A hysteresis torque calculation unit calculates the hysteresis torque, which includes a hysteresis component for the target steering torque; and The hysteresis correction unit corrects the hysteresis component based on the steering torque, which includes at least a portion of the base torque and the hysteresis component. The target steering torque setting unit sets the target steering torque by including the base torque and the corrected hysteresis component.

2. The steering control device as described in claim 1, characterized in that, The hysteresis component includes a first hysteresis component and a second hysteresis component. The hysteresis correction unit corrects the first hysteresis component based on the steering torque, which includes the base torque and one or both of the first hysteresis component and the second hysteresis component.

3. The steering control device as described in claim 1, characterized in that, The hysteresis correction unit corrects the hysteresis component based on the steering torque, which includes the base torque and the hysteresis component before correction.

4. The steering control device as described in claim 1, characterized in that, The hysteresis correction unit corrects the hysteresis component based on the steering torque, which includes the base torque and the corrected hysteresis component.

5. The steering control device as described in claim 2, characterized in that, The hysteresis torque calculation unit calculates the viscous torque that increases with the increase of the steering angular velocity of the steering mechanism, and uses it as the first hysteresis component. The frictional torque having polarity corresponding to the steering direction of the steering mechanism is calculated as the second hysteresis component.

6. A power steering device, characterized in that, include: The steering control device as described in any one of claims 1 to 5; The electric motor; as well as The driving force of the electric motor is transmitted to the reduction mechanism of the steering shaft.

7. A steering control method, which is a steering control method for a steering control device, characterized in that, Perform the following steps: The target steering torque setting step sets the target steering torque based on the steering state of the steering mechanism; A current-driven step controls the drive current of the electric motor that rotates the steering shaft of the steering mechanism to generate steering assist torque. as well as The torque feedback calculation step calculates the steering assist torque so that the steering torque acting on the steering shaft follows the target steering torque. The target steering torque setting step includes: The basic torque calculation step calculates the basic torque, which is the basic component of the steering torque; The hysteresis torque calculation step calculates the hysteresis torque, which includes a hysteresis component for the target steering torque. A hysteresis correction step, which corrects the hysteresis component based on a steering torque that includes at least a portion of the base torque and the hysteresis component; and The target steering torque setting step includes the base torque and the corrected hysteresis component to set the target steering torque.

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

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