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

Abstract

This steering control device comprises: a target steering torque setting unit that sets a target steering torque; a calculation unit that calculates a steering assist torque necessary for enabling the steering torque to follow the target steering torque; and a current drive unit that controls the current flowing in the motor and generates the steering assist torque. The target steering torque setting unit comprises: a base torque calculation unit that derives a base torque that is a basic component of the steering torque; and a friction torque calculation unit that calculates a friction torque on the basis of a basic function for calculating a rise in friction and a friction amplitude that is the amplitude of the friction. The target steering torque is calculated on the basis of the base torque and the friction torque. The friction torque calculation unit changes the friction amplitude on the basis of a vehicle speed variable signal based on the vehicle speed and a steering angle variable signal based on the steering angle.

Description

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

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

[0002] The electric power steering device of Patent Document 1 is configured to obtain a uniform steering feeling regardless of the vehicle by setting the characteristic of the steering force with respect to the steering angle (hereinafter referred to as the "steering force angle characteristic") to a desired steering force characteristic (target steering force angle characteristic). In setting the target steering torque, a friction component corresponding to the friction torque felt by the driver through the steering wheel is included, and this friction component is configured to vary a parameter Kf, which is the amplitude of friction, based on the amount of response delay of the vehicle behavior based on the vehicle speed.

[0003] The vehicle steering device of Patent Document 2, like Patent Document 1, has a hysteresis correction unit that calculates a viscous torque signal similar to the above-mentioned friction component in control to follow the target steering torque, and it is possible to make the hysteresis width corresponding to the amplitude of friction variable depending on the vehicle speed and steering angle.

[0004] JP 2003-285754 A JP 2021-123288 A

[0005] In Patent Document 1, the friction amplitude, which is the magnitude of the friction torque felt by the driver through the steering wheel, is varied depending on the vehicle speed. However, there is no mention of variation depending on the steering angle, so the magnitude of the friction torque felt by the driver's hand is the same when starting to turn the steering wheel from a neutral position and when turning back. As a result, it is not possible to optimally set the steering feel when starting to turn the steering wheel from a neutral position, when turning back, or when holding the steering wheel.

[0006] Although Patent Document 2 states that the hysteresis width, which corresponds to the amplitude of friction, may be varied depending on the vehicle speed and steering angle, it does not disclose any specific configuration, action, or effect. As a result, it is unclear how the friction amplitude relative to the vehicle speed and steering angle should be configured to optimize the steering feel and facilitate its adjustment.

[0007] The present invention has been made in view of the above-mentioned problems, and has an object to provide a steering control device and an electric power steering device that can optimize the steering feeling according to the angle of the steering wheel while easily achieving this adjustment.

[0008] A first aspect of the present disclosure is a steering control device comprising: a target steering torque setting unit that sets a target steering torque for a steering mechanism; a calculation unit that calculates a steering assist torque required to make the steering torque follow the target steering torque based on a deviation between the target steering torque and the steering torque acting on a steering shaft of the steering mechanism; and a current drive unit that controls a current flowing to a motor to generate the steering assist torque for the steering mechanism, wherein the target steering torque setting unit comprises a base torque calculation unit that determines a base torque which is a basic component of the steering torque, and a friction torque calculation unit that calculates friction torque based on a basic function that calculates a rise in friction and a friction amplitude which is the amplitude of friction, and calculates the target steering torque based on the base torque and the friction torque, and the friction torque calculation unit varies the friction amplitude based on a vehicle speed variable signal based on a vehicle speed and a steering angle variable signal based on a steering angle.

[0009] A second aspect of the present disclosure is a steering control method in a steering control device, comprising: a target steering torque setting step of setting a target steering torque for a steering mechanism; a torque feedback calculation step of calculating a steering assist torque required to make the steering torque follow the target steering torque based on a deviation between the target steering torque and the steering torque acting on a steering shaft of the steering mechanism; and a current driving step of controlling a current flowing through a motor to generate the steering assist torque for the steering mechanism, wherein the target steering torque setting step comprises a base torque calculation step of determining a base torque which is a basic component of the steering torque, and a friction torque calculation step of calculating a friction torque based on a basic function which calculates a rise in friction and a friction amplitude which is the amplitude of friction, and the target steering torque is calculated based on the base torque and the friction torque, and the friction torque calculation step varies the friction amplitude based on a vehicle speed variable signal which is based on a vehicle speed and a steering angle variable signal which is based on a steering angle.

[0010] A third aspect of the present disclosure is a program for causing a computer to function as a steering control device, the program comprising: a target steering torque setting unit that sets a target steering torque for a steering mechanism; a torque feedback calculation unit that calculates a steering assist torque required to make the steering torque follow the target steering torque based on a deviation between the target steering torque and the steering torque acting on a steering shaft of the steering mechanism; and a current drive unit that controls a current flowing to a motor to generate the steering assist torque for the steering mechanism, wherein the target steering torque setting unit comprises a base torque calculation unit that determines a base torque which is a basic component of the steering torque, and a friction torque calculation unit that calculates friction torque based on a basic function that calculates a rise of friction and a friction amplitude which is the amplitude of friction, and calculates the target steering torque based on the base torque and the friction torque, and the friction torque calculation unit varies the friction amplitude based on a vehicle speed variable signal based on a vehicle speed and a steering angle variable signal based on a steering angle.

[0011] According to the present disclosure, the friction amplitude is varied based on a vehicle speed variable signal based on the vehicle speed and a steering angle variable signal based on the steering angle. Therefore, the magnitude of the friction torque felt by the driver's hand can be set differently when starting to turn the steering wheel from near the neutral position and when turning back. This allows the steering feel (steering sensation) to be optimally set for starting to turn the steering wheel from near the neutral position, when turning back, and when maintaining steering. In addition, for example, the vehicle speed variable signal based on the vehicle speed can adjust the magnitude of the basic friction torque, and the steering angle variable signal can adjust the application of friction torque according to the steering angle separately, so that an unprecedentedly comfortable steering feel can be obtained through simple adjustments.

[0012] 5B is a block diagram showing an example of an internal configuration of a friction torque calculation unit according to the first embodiment of the present disclosure. FIG. 6 is a block diagram showing an example of a steering angle / vehicle speed map used in the friction torque calculation unit shown in FIG. 7. FIG. 7 is a diagram showing an example of a vehicle speed map used in the friction torque calculation unit shown in FIG. 7. FIG. 8 is a diagram showing an example of a time constant map used in the friction torque calculation unit shown in FIG. 7. FIG. 8 is a block diagram showing an example of a configuration of a viscous torque calculation unit according to the first embodiment of the present disclosure. FIG. 9 is a block diagram showing another example of a configuration of a viscous torque calculation unit according to the first embodiment of the present disclosure. FIG. 9B is a diagram showing an example of a damper gain map used in the viscous torque calculation unit shown in FIG. 9A. FIG. 9C is a diagram showing an example of a damper torque map used in the viscous torque calculation unit shown in FIG. 9B. FIG. 9D is a block diagram showing an example of the internal configuration of a torque feedback calculation unit according to embodiment 1 of the present disclosure. FIG. 9E is a diagram showing the relationship between the steering angle and the steering torque when the steering wheel is steered according to embodiment 1 of the present disclosure. FIG. 9F is a diagram showing the characteristics of a basic function calculation unit according to embodiment 1 of the present disclosure. FIG. 9G is a diagram showing the effect of the basic function calculation unit varying the time constant according to the friction amplitude according to embodiment 1 of the present disclosure. FIG. 9H is a block diagram showing an example of the internal configuration of a friction torque calculation unit according to embodiment 2 of the present disclosure. FIG. 9I is a block diagram showing an example of the internal configuration of a friction torque calculation unit according to embodiment 3 of the present disclosure.

[0013] Hereinafter, a steering control device, an electric power steering device, a steering control method, and a program according to embodiments of the present disclosure will be described in detail with reference to the drawings. In each embodiment, the same or corresponding parts are designated by the same reference numerals, and a description of overlapping parts will be omitted.

[0014] 1 is a block diagram showing the configuration of the main parts of an electric power steering device PS according to embodiment 1 of the present disclosure. As shown in Fig. 1, the electric power steering device PS according to this embodiment includes a steering wheel 1, a steering shaft 2, steered wheels 3, a steering angle sensor 4, a torque sensor 5 (steering torque detection unit), a motor 6, a speed reduction mechanism 7, a vehicle speed sensor 8, a current sensor 9, a motor rotation angle sensor 10, a control unit 11 (steering control device), and an axle 13.

[0015] The steering wheel 1 is a so-called handle that is operated by the driver of the vehicle to apply a steering angle to the steered wheels 3 of the vehicle. 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 the rotation of the steering wheel 1.

[0016] The steerable wheels 3 are provided on both ends of the axle 13. The steerable wheels 3 are steered by changing their direction in response to the rotation of the steering shaft 2. The mechanism for steering the steerable wheels 3, including the steering wheel 1, the steering shaft 2, and the axle 13, is sometimes called the "steering" or "steering mechanism."

[0017] The steering angle sensor 4 is disposed at the center of the steering wheel 1 and detects the steering angle of the steering wheel 1. The torque sensor 5 is disposed on the steering shaft 2 and detects the steering torque acting on the steering shaft 2. The motor 6 is connected to the steering shaft 2 via a reduction gear mechanism 7. The motor 6 consumes electricity to rotate. The torque generated by the rotation provides steering assist torque to the steering shaft 2 via the reduction gear mechanism 7. The vehicle speed sensor 8 detects the vehicle speed. The current sensor 9 detects the current flowing through the motor 6. The motor rotation angle sensor 10 detects the rotation angle of the motor 6.

[0018] The control unit 11 generates a steering assist torque for the steering mechanism by controlling the drive of the motor 6 based on all or some of the detection results of the steering angle sensor 4, torque sensor 5, vehicle speed sensor 8, current sensor 9, and motor rotation angle sensor 10. Specifically, the control unit 11 calculates the steering assist torque to be applied to the steering shaft 2 based on the above detection results, and controls the current of the motor 6 required to generate the steering assist torque.

[0019] Next, the control unit 11 according to the first embodiment of the present disclosure will be described. The control unit 11 functions as a steering control device. FIG. 2 is a block diagram showing the main configuration of the control unit 11 according to the first embodiment. As shown in FIG. 2, the control unit 11 includes a differentiator 24a, a target steering torque setting unit 22, a torque feedback calculation unit 23 (calculation unit), and a current driving unit 12. 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, sometimes referred to as the "motor rotation angular velocity"). The differentiator 24a outputs the motor rotation angular velocity (steering 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 integrated with the motor rotation angle sensor 10. In that case, the differentiator 24 a may be omitted from the control unit 11 .

[0020] The target steering torque setting unit 22 sets a target steering torque for the steering mechanism. Here, the steering angle of the steering wheel 1 detected by a steering state detection unit 21 including the steering angle sensor 4, the vehicle speed of the vehicle detected by the vehicle speed sensor 8, and the motor rotational angular velocity detected by the motor rotational angular velocity detection unit 24 are input to the target steering torque setting unit 22 as steering angular velocities. 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. In other words, the steering angle of the steering wheel 1 corresponds to an example of a physical quantity that indicates the steering state of the steering. The target steering torque setting unit 22 sets a target steering torque for the steering mechanism using these detection results. Note that the target steering torque setting unit 22 will be described in detail later. Hereinafter, the motor rotational angular velocity and the steering angular velocity may be considered to be the same.

[0021] 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 set by the target steering torque setting unit 22 and the steering torque detected by the torque sensor 5. The current drive unit 12 controls the current flowing through the motor 6 to cause the steering mechanism to generate the steering assist torque calculated by the torque feedback calculation unit 23. Note that part or all of the components of the control unit 11 (the differentiator 24a, the target steering torque setting unit 22, and the torque feedback calculation unit 23) excluding the current drive unit 12 may be realized 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 a volatile memory and a non-volatile memory. The current drive unit 12 may include, for example, an analog circuit including multiple switching elements. As the switching element, for example, a field effect transistor (FET) may be applied.

[0022] Next, an example of steering control processing according to this embodiment will be described. Fig. 3 is a flowchart showing an outline of the operation of the control unit 11 as a steering control device according to embodiment 1. The processing of the flowchart shown in Fig. 3 is repeatedly performed at a predetermined control cycle. When the processing starts, the control unit 11 first acquires the steering angle detected by the steering state detection unit 21, 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 10 of the motor rotation angular velocity detection unit 24. Then, the differentiator 24a of the motor rotation angular velocity detection unit 24 of the control unit 11 differentiates the acquired motor rotation angle to obtain the motor rotation angular velocity (step S1).

[0023] Next, the target steering torque setting unit 22 of the control unit 11 sets a target steering torque using the acquired steering angle and vehicle speed, and the motor rotational angular velocity obtained as the steering angular velocity (step S2).

[0024] Next, 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 by the target steering torque setting unit 22 and the steering torque detected by the torque sensor 5 (step S3).

[0025] Next, the current driver 12 of the control unit 11 controls the current flowing through the motor 6 in order to generate the steering assist torque calculated by the torque feedback calculator 23 in the steering mechanism (step S4).

[0026] Next, a configuration example 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 internal configuration of the target steering torque setting unit 22 according to the first embodiment of the present disclosure. As shown in Fig. 4, the target steering torque setting unit 22 includes a base torque calculation unit (first torque calculation unit) 27, a friction torque calculation unit 28, and a viscous torque calculation unit 29.

[0027] The base torque calculation unit 27 calculates the base torque using the steering angle and the vehicle speed. The base torque corresponds to the fundamental component of the steering torque.

[0028] A friction torque calculation unit 28 calculates friction torque using the steering angle, steering angular velocity, and vehicle speed. A viscous torque calculation unit 29 calculates viscous torque using the steering angular velocity and vehicle speed. An adder 30b calculates the sum of the friction torque and viscous torque. An adder 30a calculates the sum of the base torque and the output of the adder 30b to calculate the target steering torque.

[0029] The base torque calculation unit 27 calculates the base torque based on a base map that indicates a characteristic in which the magnitude of the base torque gradually increases as the magnitude of the steering angle increases.

[0030] Fig. 5A is a block diagram showing an example configuration of the base torque calculation unit 27 according to the first embodiment of the present disclosure. The base torque calculation unit 27 shown in Fig. 5A includes a base map 27a, a sign determination unit 27b, and a multiplier 27c. The base map 27a is a map in which a base torque corresponding to a steering angle is defined. Fig. 6A is a diagram showing an example of the base map 27a used in the base torque calculation unit 27 shown in Fig. 5A. The base map 27a shown in Fig. 6A has a characteristic in which the magnitude of the base torque in the positive direction shown on the vertical axis gradually increases as the magnitude (absolute value) of the steering angle shown on the horizontal axis increases.

[0031] Furthermore, a different base map 27a is prepared for each vehicle speed. In the example shown in FIG. 6A , a different base map 27a is prepared for each of "low vehicle speed," "medium vehicle speed," and "high vehicle speed." When such base maps 27a are prepared, the base torque calculation unit 27 changes the base map 27a according to the vehicle speed. However, it is not necessarily required that a different base map 27a be prepared for each vehicle speed. The sign determination unit 27b determines whether the sign of the steering angle is positive (+1) or negative (-1). The multiplier 27c multiplies the magnitude of the base torque calculated using the base map 27a by the sign determined by the sign determination unit 27b.

[0032] In the base torque calculation unit 27, one base map 27a is specified in accordance with the input vehicle speed. The magnitude of the base torque (first torque) is calculated using the steering angle input to the base torque calculation unit 27 and the specified base map 27a. The sign of the input steering angle is determined by a sign determination unit 27b. The magnitude of the base torque (first torque) calculated using the base map 27a is then multiplied by a multiplier 27c by the sign of the steering angle determined by the sign determination unit 27b, thereby calculating the base torque (first torque).

[0033] Fig. 5B is a block diagram showing another example configuration of the base torque calculation unit 27 provided in the base torque calculation unit 27 according to the first embodiment of the present disclosure. The base torque calculation unit 27 shown in Fig. 5B includes only a base map 27a. The base map 27a shown in Fig. 5B is a map in which a base torque corresponding to a steering angle is defined, similar to the base map 27a shown in Fig. 5A. Fig. 6B is a diagram showing an example of a base map used in the base calculation unit shown in Fig. 5B.

[0034] As shown in FIG. 6B , the base map 27a has a characteristic in which the magnitude of the base torque in the positive direction, shown on the vertical axis, gradually increases as the magnitude of the steering angle in the positive direction, shown on the horizontal axis, increases, and the magnitude of the base torque in the negative direction, shown on the vertical axis, gradually increases as the magnitude of the steering angle in the negative direction, shown on the horizontal axis, increases. The base map 27a shown in FIG. 6B also has a different base map 27a prepared for each vehicle speed. In the example shown in FIG. 6B , similar to the example shown in FIG. 6A , different base maps 27a are prepared for each of the "low vehicle speed," "medium vehicle speed," and "high vehicle speed." When such base maps 27a are prepared, the base torque calculation unit 27 changes the base map 27a according to the vehicle speed. However, it is not necessary to prepare a different base map 27a for each vehicle speed.

[0035] In the base torque calculation unit 27, one base map 27a is specified depending on the input vehicle speed. The base torque (first torque) is calculated using the steering angle input to the base torque calculation unit 27 and the specified base map 27a.

[0036] The friction torque calculation unit 28 calculates the second torque, which is the friction torque, based on the steering angle, the steering angular velocity, and the vehicle speed.

[0037] FIG. 7 is a block diagram showing an example of the internal configuration of the friction torque calculation unit 28 according to the first embodiment of the present disclosure, and includes a vehicle speed map 28a, a steering angle / vehicle speed map 28b, an adder 28c, a time constant map 28d, a sign determination unit 28e, a basic function calculation unit 28f, a multiplier 28g, and a steering angle limit 28h.

[0038] The vehicle speed map 28a is a map in which a vehicle speed variable signal corresponding to the magnitude of the vehicle speed is set. The steering angle / vehicle speed map 28b is a map in which a steering angle / vehicle speed variable signal corresponding to the magnitude of the vehicle speed and steering angle is set. The vehicle speed variable signal obtained from the vehicle speed map 28a and the steering angle / vehicle speed variable signal obtained from the steering angle / vehicle speed map 28b are added together by an adder 28c to calculate the friction amplitude.

[0039] The time constant map 28d is a map in which a time constant correlation signal F corresponding to the magnitude of the friction amplitude is set. The time constant correlation signal F obtained from the time constant map 28d is input to a basic function calculation unit 28f.

[0040] A basic function calculation unit 28f calculates the rise of the friction torque based on the steering angular velocity and the time constant correlation signal F, and outputs the basic friction torque X. A sign determination unit 28e determines whether the sign of the steering angular velocity is positive (+1), zero (0), or negative (-1).

[0041] The multiplier 28g multiplies the basic friction torque X output from the basic function calculation unit 28f by the friction amplitude calculated by the adder 28c and the sign determined by the sign determination unit 28e.

[0042] The steering angle limiter 28h calculates a normalized steering angle by multiplying the steering angle by a coefficient based on the vehicle speed to limit the upper steering angle limit. Note that the adder 28c can be configured as a multiplier because equivalent conversion is possible through addition and multiplication. Furthermore, since the vehicle speed map 28a already exists, equivalent conversion is possible, so the steering angle / vehicle speed map 28b may be a steering angle map in which a steering angle variable signal based only on the steering angle is set.

[0043] 8B is a diagram showing an example of the vehicle speed map 28a. The vehicle speed map shown in FIG. 8B has a transition point, and has a characteristic that as the magnitude of the vehicle speed shown on the horizontal axis increases up to a certain vehicle speed, the magnitude of the vehicle speed variable signal shown on the vertical axis gradually increases in the positive direction, and as the vehicle speed increases beyond the certain vehicle speed, the magnitude of the vehicle speed variable signal gradually decreases in the positive direction. However, the vehicle speed map 28a does not necessarily have to have a transition point.

[0044] FIG. 8A is a diagram showing an example of a steering angle / vehicle speed map 28b. The steering angle / vehicle speed map shown in FIG. 8A has a characteristic in which the magnitude of the steering angle / vehicle speed variable signal shown on the vertical axis gradually decreases as the normalized steering angle shown on the horizontal axis increases. Furthermore, different steering angle / vehicle speed maps 28b are prepared for different vehicle speeds. In the example shown in FIG. 8A, different steering angle / vehicle speed maps 28b are prepared for "low vehicle speed," "medium vehicle speed," and "high vehicle speed." When such steering angle / vehicle speed maps 28b are prepared, the friction torque calculation unit (second torque calculation unit) 28 changes the steering angle / vehicle speed map 28b according to the vehicle speed. However, it is not necessary to prepare different steering angle / vehicle speed maps 28b for different vehicle speeds. As described above, the steering angle / vehicle speed map 28b shown in FIG. 8A may be the steering angle map shown in FIG. 8D in which a steering angle variable signal based only on the steering angle is set, with the characteristic that the magnitude of the steering angle variable signal shown on the vertical axis gradually decreases as the normalized steering angle shown on the horizontal axis increases.

[0045] 8C is a diagram showing an example of a time constant map (time constant correlation signal map) 28 d. The time constant map 28 d shown in FIG. 8C has a characteristic that the magnitude of the time constant correlation signal F shown on the vertical axis gradually decreases as the friction amplitude shown on the horizontal axis increases.

[0046] If the steering angular velocity is dθ and the friction amplitude is Kf, the friction torque (second torque) is expressed by Equation (1). The basic friction torque X is calculated using the basic function shown on the right side of the second line of Equation (1). As can be seen from Equation (1) below, as the steering angular velocity dθ increases, the friction torque gradually reaches a constant magnitude based on the time constant correlation signal F and reaches a saturated state. The basic function corresponds to a value obtained by calculating an exponential function based on the absolute value abs(dθ) of the steering angular velocity dθ and the time constant correlation signal F and subtracting the resultant value from 1. In other words, the basic function calculates the rise of the friction torque based on the steering angular velocity dθ of the steering mechanism. The basic function also varies the rise of the friction torque based on the friction amplitude Kf.

[0047]

[0048] In addition, the friction torque calculation unit 28 may perform low-pass filtering on the calculated friction torque (second torque) using a low-pass filter. Here, the cutoff frequency of the low-pass filter is set to a value that can extract frequency components that are set to include the steering frequency of the driver. Generally, the driver's limit steering frequency is about 5 [Hz], and the resonance frequency of the steering shaft 2 is around 10 [Hz]. Therefore, the cutoff frequency is set to a value greater than 0 and equal to or less than 10 [Hz].

[0049] The viscous torque calculation unit 29 calculates the viscous torque, which is the damper torque, based on the steering angular velocity and the vehicle speed.

[0050] Fig. 9A is a block diagram showing an example of the configuration of the viscous torque calculation unit 29 according to the first embodiment of the present disclosure. The viscous torque calculation unit 29 shown in Fig. 9A includes a damper gain map 29a and a multiplier 29b. The damper gain map 29a is a map in which a damper gain corresponding to the steering angular velocity (motor rotation angular velocity) is defined. Fig. 10A is a diagram showing an example of the damper gain map used in the viscous torque calculation unit 29 shown in Fig. 9A.

[0051] 10A has a characteristic that, once the magnitude (absolute value) of the motor rotational angular velocity shown on the horizontal axis exceeds a certain value, the magnitude of the damper gain shown on the vertical axis gradually increases as the magnitude (absolute value) of the motor rotational angular velocity increases. Note that the magnitude of the damper gain is zero until the magnitude (absolute value) of the steering angular velocity reaches a certain value.

[0052] Furthermore, a different damper gain map 29a is prepared for each vehicle speed. In the example shown in Fig. 10A, a different damper gain map 29a is prepared for each of "low vehicle speed," "medium vehicle speed," and "high vehicle speed." When such damper gain maps 29a are prepared, the viscous torque calculation unit 29 changes the damper gain map 29a according to the vehicle speed. However, it is not necessary to prepare a different damper gain map 29a for each vehicle speed. The multiplier 29b multiplies the steering angular velocity by the damper gain calculated using the damper gain map 29a.

[0053] In the viscous torque calculation unit 29, one damper gain map 29a is specified in accordance with the input vehicle speed. A damper gain is calculated using the specified damper gain map 29a and the motor rotational angular velocity input to the viscous torque calculation unit 29. Then, the damper gain calculated using the damper gain map 29a is multiplied by the motor rotational angular velocity in a multiplier 29b to calculate the damper torque (viscous torque).

[0054] Fig. 9B is a block diagram showing another example configuration of the viscous torque calculation unit 29 according to the first embodiment of the present disclosure. The viscous torque calculation unit 29 shown in Fig. 9B includes a damper torque map 29c, a sign determination unit 29d, and a multiplier 29b. The damper torque map 29c is a map in which the damper torque corresponding to the steering angular velocity (motor rotation angular velocity) is defined. Fig. 10B is a diagram showing an example of the damper torque map used in the viscous torque calculation unit 29 shown in Fig. 9B.

[0055] The damper torque map 29c shown in Fig. 10B has the same characteristics as the damper gain map 29a shown in Fig. 10A. That is, the damper torque map 29c shown in Fig. 10B has a characteristic that, once the magnitude (absolute value) of the motor rotational angular velocity shown on the horizontal axis exceeds a certain value, the magnitude of the damper torque shown on the vertical axis gradually increases as the magnitude (absolute value) of the motor rotational angular velocity increases. Note that the magnitude of the damper torque is zero until the magnitude (absolute value) of the steering angular velocity reaches a certain value.

[0056] Furthermore, different damper torque maps 29c are prepared for each vehicle speed. In the example shown in FIG. 10B , different damper torque maps 29c are prepared for each of "low vehicle speed," "medium vehicle speed," and "high vehicle speed." When such damper torque maps 29c are prepared, the viscous torque calculation unit 29 changes the damper torque map 29c according to the vehicle speed. However, it is not necessary to prepare different damper torque maps 29c for each vehicle speed. The sign determination unit 29d determines whether the sign of the steering angular velocity is positive (+1) or negative (-1). The multiplier 29b multiplies the magnitude of the damper torque calculated using the damper torque map 29c by the sign determined by the sign determination unit 29d.

[0057] In the viscous torque calculation unit 29, one damper torque map 29c is specified in accordance with the input vehicle speed. The magnitude of the damper torque (viscous torque) is determined using the motor rotational angular velocity input to the viscous torque calculation unit 29 and the specified damper torque map 29c. The sign of the input motor rotational angular velocity is determined by a sign determination unit 29d. The magnitude of the damper torque (viscous torque) determined using the damper torque map 29c is then multiplied by the sign of the steering angular velocity determined by the sign determination unit 29d in a multiplier 29b, thereby determining the damper torque (viscous torque).

[0058] 4, the target steering torque setting unit 22 includes adders 30a and 30b, and adds together the base torque (first torque) calculated by the base torque calculation unit 27, the friction torque (second torque) calculated by the friction torque calculation unit 28, and the damper torque (viscous torque) calculated by the viscous torque calculation unit 29. Specifically, the friction torque (second torque) and the damper torque (viscous torque) are added together by the adder 30b, and the torque output from the adder 30b and the base torque (first torque) are added together by the adder 30a, and the torque obtained is output as the target steering torque.

[0059] 11 is a block diagram showing an example of the internal configuration of the torque feedback calculation unit 23 according to the first embodiment of the present disclosure. As shown in Fig. 11, 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 (viscous steering assist torque calculation unit) 34, and an adder 35. 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 set by the target steering torque setting unit 22 and the steering torque detected by the torque sensor 5.

[0060] The subtractor 31 determines the deviation between the target steering torque set by the target steering torque setting unit 22 and the steering torque detected by the torque sensor 5. The first steering assist torque calculation unit 32 includes an integrator 32a and a multiplier 32b, and calculates the first steering assist torque by integrating the deviation determined by the subtractor 31 with the integrator 32a and multiplying the integrated deviation by an integral control gain KTI with the multiplier 32b.

[0061] The second steering assist torque calculation unit 33 includes a multiplier 33a, and calculates a second steering assist torque by multiplying the steering angular velocity (motor rotation angular velocity) by a speed control gain KTV using the multiplier 33a. The third steering assist torque calculation unit 34 includes a multiplier 34a, and calculates a third steering assist torque (viscous steering assist torque) by multiplying the deviation obtained by the subtractor 31 by a proportional control gain KTP using the multiplier 34a.

[0062] The adder 35 adds together the first steering assist torque calculated by the first steering assist torque calculation unit 32, the second steering assist torque calculated by the second steering assist torque calculation unit 33, and the third steering assist torque calculated by the third steering assist torque calculation unit 34. Then, the adder 35 outputs the torque obtained by the addition as the steering assist torque.

[0063] Here, because the steering assist torque includes an integral control component (first steering assist torque), the driver's steering torque follows the target steering torque. This allows the driver to steer with an appropriate torque. Furthermore, when the driver releases his / her hands from the steering wheel 1, the steering torque can be adjusted to a value between the target steering torque and zero by using a motor speed control component (second steering assist torque) obtained by multiplying the steering angular velocity (motor rotational angular velocity) by the speed control gain KTV. This allows the steering torque to follow the target steering torque, thereby achieving smooth steering. Furthermore, by using the motor speed control component (second steering assist torque), control stability can be ensured even when the motor 6 and the torque sensor 5 are located far apart. Furthermore, because differentiation of the target steering torque is not required, noise can be suppressed, and smooth and stable steering can be achieved.

[0064] The steering assist torque proportional control component (viscous steering assist torque or third steering assist torque) has a faster response than the steering assist torque integral control component (first steering assist torque), and therefore, the tracking response can be made faster and overshoot can be reduced. As a result, when the driver is gripping the steering wheel 1 to steer, the steering torque stably tracks the target steering torque, and smoother steering can be achieved. Note that in this embodiment, an example has been described in which the torque feedback calculation unit 23 that performs torque feedback is provided as a configuration for achieving stability and tracking. However, the present invention is not limited to a configuration that performs torque feedback as long as it is possible to feed back the deviation between the target steering torque and the steering torque.

[0065] Next, the effects of providing the control unit (steering control device) 11 described above will be described. In the steering control device 11, which 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 has the desired characteristic. A specific adaptation method is assumed to be a steering method in which the steering wheel 1 is operated with a sine wave of about 0.2 [Hz] at the desired vehicle speed, and the lateral acceleration is 0.2 [G] or less.

[0066] The technology disclosed in the aforementioned Patent Document 1 varies the friction amplitude, which is the magnitude of the friction torque felt by the driver through the steering wheel, depending on the vehicle speed, but does not mention variation depending on the steering angle. As a result, the magnitude of the friction torque felt by the driver's hand is the same when starting to turn the steering wheel from a neutral position and when changing direction. As a result, it is not possible to optimally set the steering feel when starting to turn, changing direction, or when holding the steering wheel.

[0067] Furthermore, Patent Document 2 states that the hysteresis width, which corresponds to the amplitude of friction, may be varied depending on the vehicle speed and steering angle, but does not disclose any specific configuration, action, or effect. As a result, it is unclear how the friction amplitude relative to the vehicle speed and steering angle should be configured to optimize the steering feel and facilitate its adjustment.

[0068] 12 is a diagram showing the relationship between the steering angle and the steering torque when the steering wheel is steered in the first embodiment of the present disclosure. The post-correction characteristic Ch1 is a waveform obtained in this embodiment. The pre-correction trajectory (characteristic) Ch2 is a waveform obtained when the configuration for varying the friction amplitude based on the vehicle speed variable signal based on the vehicle speed and the steering angle variable signal based on the steering angle is disabled.

[0069] 12 , in this embodiment, the provision of a friction torque calculation unit (second torque calculation unit) 28 makes it possible to provide a characteristic in which the steering torque is large when turning the steering wheel from near the neutral position, and the hysteresis of the steering torque does not change when the steering wheel is turned back. As a result, excessive steering near the neutral position of the steering wheel can be suppressed without changing the characteristic when the steering wheel is turned back. Here, "near the neutral position of the steering wheel" refers to a range from the neutral position of the steering wheel with a margin, such as a steering angle of ±1° from the neutral position of the steering wheel. Therefore, the vicinity of the neutral position of the steering wheel includes the neutral position of the steering wheel.

[0070] Furthermore, in this embodiment, the vehicle speed map 28a and steering angle / vehicle speed map 28b of the friction torque calculation unit (second torque calculation unit) 28 are variable with respect to vehicle speed. This allows the friction torque to be flexibly set according to vehicle speed, thereby realizing a wide variety of steering feelings. Note that it is not necessary to make all gains variable with respect to vehicle speed; at least one gain or map may be variable with respect to vehicle speed.

[0071] According to the configuration of the present disclosure, the friction amplitude is varied based on a vehicle speed variable signal based on the vehicle speed and a steering angle variable signal based on the steering angle, so that the magnitude of the friction torque felt by the driver's hand can be set differently when starting to turn the steering wheel from near the neutral position and when changing direction. Therefore, the steering feel can be optimally set for starting to turn the steering wheel from near the neutral position, when changing direction, and when maintaining steering. In addition, for example, the basic magnitude of the friction torque can be adjusted using the vehicle speed variable signal based on the vehicle speed, and the application of friction torque according to the steering angle can be adjusted separately using the steering angle variable signal, so that an unprecedented comfortable feeling can be obtained through easy adjustment.

[0072] 13 is a diagram showing the characteristics of the basic function calculation unit 28f in the first embodiment of the present disclosure. Referring to Fig. 13, the basic function calculation unit 28f sets the basic friction torque, which is the output of the basic function, to zero when the steering angular velocity is zero, and as the steering angular velocity increases, the basic friction torque gradually becomes a constant magnitude based on the time constant correlation signal F and reaches a saturated state.

[0073] The provision of the basic function calculation unit 28f makes it possible to continuously calculate the rise of friction based on the steering angular velocity, thereby realizing a natural feeling that simulates dynamic friction. Furthermore, when the steering wheel is held steady, the basic friction torque becomes zero, and by the friction torque becoming zero, the steering torque when the steering wheel is held steady can be reduced.

[0074] FIG. 14 is a diagram illustrating the effect of the basic function calculation unit 28f varying the time constant in accordance with the friction amplitude in the first embodiment of the present disclosure. The time constant refers to the reciprocal of the time constant correlation signal F. Referring to FIG. 14, if the time constant is not varied when the friction amplitude is large, the rise gradient of the friction torque will be the same as when the friction amplitude is small, resulting in a steep rise gradient and instability. By varying the time constant, the rise gradient of the friction torque becomes gentler, ensuring stability even when the friction amplitude is large. Although the basic function calculation unit 28f varies the rise gradient based on the time constant signal value, this is not necessarily required. In this case, stability will be reduced, but the effect of varying the friction amplitude based on the steering angular velocity (motor rotation angular velocity) can be obtained.

[0075] In addition, the friction torque calculation unit 28 includes a vehicle speed map 28a corresponding to the vehicle speed and a steering angle / vehicle speed map 28b corresponding to the vehicle speed and steering angle. This makes it possible to set the basic friction using the vehicle speed map and the friction at the start of steering and at the end of steering using the steering angle / vehicle speed map separately for each vehicle speed. This makes it possible to easily set the magnitude of friction appropriate for the vehicle speed and steering angle, resulting in a comfortable feeling.

[0076] Next, the effect of the steering angle limit 28h will be described. By normalizing the steering angle, the steering angle / vehicle speed map can be handled as a unified index with the normalized steering angle as the horizontal axis, which has the effect of facilitating map adaptation.

[0077] Furthermore, in this embodiment, the steering state detection unit 21 is provided with a steering angle sensor 4, and the steering angle detected by the steering angle sensor 4 is used. However, instead of the detection result of the steering angle sensor 4, the result of converting the motor rotation angle detected by the motor rotation angle sensor 10 into a steering angle may be used. For example, the result of converting the motor rotation angle detected by the motor rotation angle sensor 10 into the angle of the steering shaft 2 using the reduction ratio of the reduction mechanism 7 may be used. Furthermore, when the motor rotation angle is a relative angle with respect to the angle of the steering shaft 2, a yaw rate sensor or the like (not shown) provided in the vehicle may be used to determine that the vehicle is traveling straight ahead, and the motor rotation angle offset so that the relative angle becomes zero may be used as the absolute angle of the steering shaft 2.

[0078] 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.

[0079] The basic configuration of the control unit (steering control device) 11 according to this embodiment is the same as that of the control unit 11 according to embodiment 1. However, the configuration of the friction torque calculation unit (second torque calculation unit) 28 provided in the target steering torque setting unit 22 of the control unit 11 is different. The friction torque calculation unit 282 will be described below.

[0080] FIG. 15 is a block diagram showing the configuration of a friction torque calculator (second torque calculator) 282 according to the second embodiment of the present disclosure. As shown in FIG. 15, friction torque calculator 282 according to the present embodiment differs from friction torque calculator 28 shown in FIG. 7 in that the input to basic function calculator 28f of friction torque calculator 28 is replaced by steering angle instead of steering angular velocity. The other configurations are the same. In this case, basic function calculator 28f calculates the rise of the friction torque based on the steering angle and the time constant correlation signal F, and outputs basic friction torque X. This calculation method is the same as that of the first embodiment.

[0081] In this embodiment, too, the friction amplitude is varied based on a vehicle speed variable signal based on the vehicle speed and a steering angle variable signal based on the steering angle, so the magnitude of the friction torque felt by the driver's hand can be set differently when starting to turn the steering wheel from near the neutral position and when turning back. This allows the steering feel to be optimally set for starting to turn the steering wheel from near the neutral position, turning back, and maintaining the steering wheel. In addition, for example, the vehicle speed variable signal based on the vehicle speed can adjust the magnitude of the basic friction torque, and the steering angle variable signal can adjust the application of friction torque according to the steering angle separately, so that an unprecedentedly comfortable steering feel can be obtained through simple adjustments. Furthermore, the effect of varying the time constant of the basic function can be obtained by the friction amplitude.

[0082] 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 embodiment. Unless otherwise specified, the description of the first embodiment will be used for points in common with the first embodiment.

[0083] The basic configuration of the control unit (steering control device) 11 according to this embodiment is the same as that of the control unit 11 according to embodiment 1. However, the configuration of the friction torque calculation unit (second torque calculation unit) 28 provided in the target steering torque setting unit 22 of the control unit 11 is different. The friction torque calculation unit 283 will be described below.

[0084] FIG. 16 is a block diagram showing the configuration of a friction torque calculator (second torque calculator) 283 according to a third embodiment of the present disclosure. As shown in FIG. 16, the friction torque calculator 283 according to this embodiment differs from the friction torque calculator 28 shown in FIG. 7 in that the time constant map 28d of the friction torque calculator 28 shown in FIG. 16 is configured to vary depending on the steering angle. In this case, the time constant map 28d is a map in which time constant signal values ​​corresponding to the steering angle are defined. The time constant map 28d has a characteristic in which the magnitude in the positive direction gradually increases as the steering angle increases. This is a conversion that operates equivalently to the time constant map 28d of the first embodiment, and therefore, the same effect as that of the first embodiment can be obtained.

[0085] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments and can be freely modified without departing from the spirit of the present disclosure. For example, the electric power steering device PS described in the above embodiments may be a column-type electric power steering device PS or a rack-and-pinion type electric power steering device PS. Furthermore, in terms of performing feedback control based on a target steering torque, the present disclosure may also be applied to a steer-by-wire reaction force device that includes at least a torque sensor. Furthermore, the figures used in the description of the above embodiments show examples and are not limited thereto.

[0086] 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.

[0087] 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.

[0088] <Fourth Embodiment> A fourth embodiment of the present disclosure is a steering control method for a steering control device, including: a target steering torque setting step of setting a target steering torque for a steering mechanism; a torque feedback calculation step of calculating a steering assist torque required to make the steering torque follow the target steering torque based on a deviation between the target steering torque and the steering torque acting on a steering shaft of the steering mechanism; and a current driving step of controlling a current flowing through a motor to generate the steering assist torque for the steering mechanism, wherein the target steering torque setting step includes a base torque calculation step of determining a base torque that is a basic component of the steering torque, and a friction torque calculation step of calculating a friction torque based on a basic function that calculates a rise in friction and a friction amplitude that is the amplitude of friction, and the target steering torque is calculated based on the base torque and the friction torque, and the friction torque calculation step varies the friction amplitude based on a vehicle speed variable signal based on a vehicle speed and a steering angle variable signal based on a steering angle. This embodiment is a steering control method corresponding to the steering control device 11 of the first embodiment, and therefore can achieve effects similar to those of the first embodiment.

[0089] Fifth Embodiment A fifth embodiment of the present disclosure is a program for causing a computer to function as a steering control device, the program including: a target steering torque setting unit that sets a target steering torque for a steering mechanism; a torque feedback calculation unit that calculates a steering assist torque required to make the steering torque follow the target steering torque based on a deviation between the target steering torque and the steering torque acting on a steering shaft of the steering mechanism; and a current drive unit that controls a current flowing through a motor to generate the steering assist torque for the steering mechanism, the target steering torque setting unit including a base torque calculation unit that calculates a base torque that is a basic component of the steering torque, and a friction torque calculation unit that calculates a friction torque based on a basic function that calculates a friction rise time and a friction amplitude that is the amplitude of friction, and calculates the target steering torque based on the base torque and the friction torque, and the friction torque calculation unit varies the friction amplitude based on a vehicle speed variable signal based on a vehicle speed and a steering angle variable signal based on a steering angle. This embodiment is a program corresponding to the steering control device 11 of the first embodiment, and therefore can achieve the same effects as those of the first embodiment.

[0090] 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, 27...Base torque calculation section, 28...Friction torque calculation section, 29...Viscosity torque calculation section, 29a...Damper gain map, 29c...Damper torque map, PS...Electric power steering device

Claims

1. A target steering torque setting unit that sets a target steering torque for a steering mechanism, a torque feedback calculation unit that calculates a steering assist torque necessary to cause the steering torque to follow the target steering torque based on a deviation between the target steering torque and the steering torque acting on a steering shaft of the steering mechanism, and a current drive unit that controls a current flowing through a motor to generate the steering assist torque for the steering mechanism. The target steering torque setting unit includes a base torque calculation unit that obtains a base torque that is a basic component of the steering torque, and a friction torque calculation unit that calculates a friction torque based on a basic function for calculating a rise of friction and a friction amplitude that is an amplitude of the friction. The target steering torque is calculated based on the base torque and the friction torque. The friction torque calculation unit is a steering control device that variably changes the friction amplitude based on a vehicle speed variable signal based on a vehicle speed and a steering angle variable signal based on a steering angle.

2. The steering control device according to claim 1, wherein the basic function calculates a rise of the friction torque based on an angular velocity of steering of the steering mechanism.

3. The steering control device according to claim 1, wherein the basic function variably changes a rise of the friction torque based on the friction amplitude.

4. The steering control device according to claim 1, wherein the friction torque calculation unit calculates the friction amplitude based on the vehicle speed variable signal based on a vehicle speed map corresponding to the vehicle speed and the steering angle variable signal based on a steering angle map corresponding to the steering angle.

5. An electric power steering apparatus including the steering control device according to any one of claims 1 to 4, a motor that outputs the steering assist torque for assisting steering of the steering mechanism, and a speed reduction mechanism that transmits a driving force of the motor to the steering shaft.

6. A steering control method in a steering control device, comprising: a target steering torque setting step of setting a target steering torque for a steering mechanism; a torque feedback calculation step of calculating a steering assist torque necessary to cause the steering torque to follow the target steering torque based on a deviation between the target steering torque and the steering torque acting on a steering shaft of the steering mechanism; and a current drive step of controlling a current flowing through a motor to generate the steering assist torque for the steering mechanism. The target steering torque setting step includes a base torque calculation step of obtaining a base torque that is a basic component of the steering torque, and a friction torque calculation step of calculating a friction torque based on a basic function for calculating a rise of friction and a friction amplitude that is an amplitude of the friction, and calculates the target steering torque based on the base torque and the friction torque. The friction torque calculation step is a steering control method for variably setting the friction amplitude based on a vehicle speed variable signal based on a vehicle speed and a steering angle variable signal based on a steering angle.

7. A program for causing a computer to function as a steering control device, the program comprising: a target steering torque setting unit that sets a target steering torque for a steering mechanism; a torque feedback calculation unit that calculates a steering assist torque necessary to cause a steering torque to follow the target steering torque based on a deviation between the target steering torque and the steering torque acting on a steering shaft of the steering mechanism; and a current drive unit that controls a current flowing through a motor to generate the steering assist torque for the steering mechanism. The target steering torque setting unit includes a base torque calculation unit that obtains a base torque that is a basic component of the steering torque, and a friction torque calculation unit that calculates a friction torque based on a basic function for calculating a rise of friction and a friction amplitude that is an amplitude of the friction, and calculates the target steering torque based on the base torque and the friction torque. The friction torque calculation unit variably sets the friction amplitude based on a vehicle speed variable signal based on a vehicle speed and a steering angle variable signal based on a steering angle.

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