Steering device

Abstract

A steering device (1) includes: a reaction motor (3) that is configured to apply a reaction torque to a steering wheel (2) that is not mechanically connected to a steering system (S); and a controller (7) that controls the reaction motor (3), in which the controller (7) includes a base torque calculation unit (72) that calculates a base torque (τb) based on a traveling speed (v) of a vehicle and a steering angle (θ) of the steering wheel (2), a return torque calculation unit (73) that calculates a return torque (τr) based on the traveling speed (v), the steering angle (θ), and a steering torque (τ) acting on the steering wheel (2), and a reaction motor control unit (77) that controls the reaction motor (3) based on the base torque (τb) and the return torque (τr).

Description

STEERING DEVICE

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

[0002] In recent years, from the viewpoint of improving the degree of freedom of a structure on a front side of a vehicle, reducing the weight of the vehicle, and being advantageous for adoption of automated driving, a steering device has been developed that implements a steer-by-wire system that enables steering of steerable wheels without mechanically connecting a steering system including the steerable wheels and a steering rack that drives the steerable wheels to a steering wheel in a vehicle compartment.

[0003] In the steering device adopting such a steer-by-wire system, the steering wheel and the steering rack are not mechanically connected as described above. Therefore, a reaction force with respect to an operation of the steering wheel is not input to the steering wheel as it is, an appropriate steering feel cannot be provided to a driver of the vehicle, as a result of which the steering wheel cannot be returned to a neutral position.

[0004] Therefore, for example, as disclosed in JP 2019-119253 A, the steering device adopting the steer-by-wire system includes a reaction motor that applies a reaction torque to provide the reaction force to the steering wheel in the vehicle compartment in response to an operation by the driver.

[0005] JP 2019-119253 A

[0006] The steering device according to the related art includes a controller that controls the reaction motor. The controller includes a steering angle sensor that detects a steering angle of the steering wheel and a vehicle speed sensor that detects a traveling speed of the vehicle. The controller calculates a target reaction torque based on the steering angle of the steering wheel obtained by the steering angle sensor and the traveling speed obtained by the vehicle speed sensor, and controls the reaction motor according to the target reaction torque.

[0007] More specifically, in the steering device according to the related art, the target reaction torque is calculated by adding a spring component that takes a larger value as the steering angle increases and a friction component that takes a constant value in a state in which the steering angle is equal to or larger than a certain angle.

[0008] As described above, in the steering device according to the related art, the target reaction torque is calculated by the total value of the spring component and the friction component. However, the reaction torque depending on the steering angle is output regardless of a steering condition by the driver, and thus, an appropriate self-alignment torque cannot be applied to the steering wheel as the reaction torque, and a steering feel equivalent to that of a system in which the steering wheel and the steering system are mechanically connected to each other cannot be obtained.

[0009] An object of the present invention is to provide a steering device capable of improving a steering feel of a steering wheel.

[0010] In order to achieve the above object, a steering device in the solution to the problem of the present invention includes: a reaction motor that is configured to apply a reaction torque to a steering wheel that is not mechanically connected to a steering system including steerable wheels and a steering rack connected to the steerable wheels in a vehicle; and a controller that controls the reaction motor, in which the controller includes a base torque calculation unit that calculates a base torque for returning the steering wheel to a neutral position, a return torque calculation unit that calculates a return torque for returning the steering wheel to the neutral position according to a steering condition, and a reaction motor control unit that controls the reaction motor based on the base torque and the return torque, the base torque calculation unit calculates the base torque based on a traveling speed of the vehicle and a steering angle of the steering wheel, and the return torque calculation unit calculates, based on the traveling speed, the steering angle, and a steering torque acting on the steering wheel, the return torque that takes a small value when the steering torque is large.

[0011] In the steering device configured as described above, since the return torque tends to decrease in a situation in which a driver is steering the steering wheel, the reaction torque tends to decrease. However, since the base torque does not decrease, it is possible to prevent a resistance from becoming excessive while applying an appropriate resistance for the steering of the steering wheel by the driver, and in a situation in which the driver is not steering the steering wheel or the steering torque is small, the return torque tends to increase, and thus, the reaction torque tends to increase. Accordingly, a torque for returning the steering wheel to the neutral position increases, and the steering wheel can be returned to the neutral position even when the steering angle is small.

[0012] Fig. 1 is a diagram illustrating a steering device according to an embodiment.Fig. 2 is a configuration diagram of a controller in the steering device according to the embodiment.Fig. 3 is a diagram illustrating a configuration of a base torque calculation unit.Fig. 4 is a diagram illustrating a configuration of a return torque calculation unit.Fig. 5 is a diagram illustrating a configuration of a friction torque calculation unit.Fig. 6 is a diagram illustrating a configuration of a damping torque calculation unit.Fig. 7 is a diagram illustrating a configuration of a reaction torque calculation unit.Fig. 8 is a diagram illustrating a configuration of a reaction motor control unit.Fig. 9 is a flowchart illustrating an example of a processing procedure of the steering device according to the embodiment.

[0013] Hereinafter, the present invention will be described based on an embodiment illustrated in the drawings. As illustrated in Fig. 1, a steering device 1 according to an embodiment is mounted on a vehicle (not illustrated), and includes a reaction motor 3 that can apply a reaction torque to a steering wheel 2 in the vehicle, a speed detection unit 4 that detects a traveling speed v of the vehicle, a steering angle detection unit 5 that detects a steering angle θ of the steering wheel 2, a torque detection unit 6 that detects a steering torque τ acting on the steering wheel 2, and a controller 7 that controls the reaction motor 3. Further, the vehicle includes a steering system S including a steering rack 8 connected to steerable wheels W of the vehicle, a steering motor 9 that drives the steering rack 8 in a left-right direction in Fig. 1 to turn the steerable wheels W, and a steering controller 10 that controls the steering motor 9.

[0014] The steering wheel 2 in the steering device 1 and the steering rack 8 in the steering system S are not mechanically connected to each other. An operation of the steering wheel 2 is transmitted from the controller 7 to the steering controller 10, and the steering controller 10 controls the steering motor 9 according to an operation amount of the steering wheel 2, so that the operation of the steering wheel 2 is transmitted to the steerable wheels W to steer the steerable wheels W.

[0015] Therefore, the steering device 1 according to the present embodiment forms, together with the steering system S, a steer-by-wire system in which the steering wheel 2 and the steering system S are not mechanically connected to each other. The controller 7 in the steering device 1 may be integrated with the steering controller 10 and included in the steering controller 10.

[0016] Specifically, as illustrated in Fig. 1, the steering system S includes the steering rack 8 installed so as to be able to reciprocate in a lateral direction of the vehicle with respect to the vehicle and having both ends connected to the left and right steerable wheels W of the vehicle via tie rods 13, the steering motor 9 including a rotor connected to a pinion gear 14 meshing with the steering rack 8, and the steering controller 10 that controls the steering motor 9. For example, the steering controller 10 receives the steering angle θ of the steering wheel 2 from the controller 7 in the steering device 1, determines a steering amount of the steerable wheels W, and controls the steering motor 9. Therefore, the steering system S can turn the steerable wheels W according to the steering of the steering wheel 2.

[0017] Hereinafter, each portion of the steering device 1 will be described in detail. First, the steering wheel 2 is rotatable with respect to the vehicle via a rotary shaft 11 and is installed in a vehicle compartment (not illustrated) of the vehicle. The reaction motor 3 is connected to the rotary shaft 11 via a speed reducer 12, and can apply the reaction torque to the steering wheel 2. The speed reducer 12 may be omitted if unnecessary, and the reaction motor 3 may be a geared motor including a speed reducer.

[0018] The rotary shaft 11 has one end connected to a rotation center of the steering wheel 2, and a worm wheel 12a is provided on an outer periphery of the other end of the rotary shaft 11. A worm 12b connected to a rotor (not illustrated) of the reaction motor 3 meshes with the worm wheel 12a. In the present embodiment, the speed reducer 12 includes the worm wheel 12a and the worm 12b meshing with the worm wheel 12a. When the reaction motor 3 is energized to drive the worm 12b, power of the reaction motor 3 can be transmitted to the rotary shaft 11 via the worm wheel 12a, so that the reaction motor 3 can apply the reaction torque opposing a steering force to the steering wheel 2 when a driver steers the steering wheel 2. Here, the speed reducer 12 includes the worm wheel 12a and the worm 12b. However, the speed reducer 12 may also have a configuration other than the above-described configuration as long as the torque generated by the reaction motor 3 can be increased and transmitted to the rotary shaft 11.

[0019] In the present embodiment, the reaction motor 3 includes an armature having coils of three phases (not illustrated) and the rotor (not illustrated), and includes an angle sensor 3a that detects a mechanical angle of the rotor because the mechanical angle of the rotor is required for driving.

[0020] The speed detection unit 4 is a vehicle speed sensor that detects the traveling speed v of the vehicle from a vehicle speed pulse generated by a pulse generator installed in a crankshaft of an engine (not illustrated), a transmission, or the like in the vehicle. The speed detection unit 4 may detect a rotation speed of vehicle wheels by a rotation speed sensor instead of the vehicle speed sensor, and detect the traveling speed v from the rotation speed of the vehicle wheels. In addition, the speed detection unit 4 may be a vehicle speed sensor installed in advance on a vehicle side, and may obtain information regarding the traveling speed v via an electronic control unit (ECU) of the vehicle or a controller area network (CAN) bus.

[0021] In the steering device 1 according to the present embodiment, the steering angle detection unit 5 includes the angle sensor 3a attached to the reaction motor 3 and used to detect a position of the rotor for controlling the reaction motor 3, and a steering angle calculation unit 70 that calculates the steering angle θ of the steering wheel 2 based on the mechanical angle of the rotor in the reaction motor 3, the mechanical angle being detected by the angle sensor 3a. The steering angle θ is a rotation angle from a neutral position at which the steering wheel 2 positions the steerable wheels W at an angle at which the vehicle travels straight with respect to a vehicle body (not illustrated) of the vehicle. In the present embodiment, the steering angle calculation unit 70 that calculates the steering angle θ of the steering wheel 2 is integrated with the controller 7. However, a calculation processing device that calculates the rotation speed based on the mechanical angle of the rotor may also be provided separately from the controller 7. In a case where the vehicle is provided with a sensor that detects the steering angle θ, the controller 7 may obtain the steering angle θ from the sensor.

[0022] The torque detection unit 6 is a torque sensor that detects a torsional angle of a torsion bar (not illustrated) provided partway in the rotary shaft 11 and detects the steering torque τ acting on the steering wheel 2 from the torsional angle. The torque detection unit 6 only needs to be able to detect the steering torque τ acting on the rotary shaft 11. Therefore, the torque detection unit 6 may be a torque sensor other than the above-described torque sensor. In a case where the vehicle is provided with a sensor that detects the steering torque τ, the controller 7 may obtain the steering torque τ from the sensor.

[0023] As illustrated in Fig. 2, the controller 7 includes the steering angle calculation unit 70, an angular velocity calculation unit 71 that calculates a steering angular velocity ω by differentiating the steering angle θ, a base torque calculation unit 72 that calculates a base torque τb for returning the steering wheel 2 to the neutral position based on the traveling speed v and the steering angle θ, a return torque calculation unit 73 that calculates a return torque τr for returning the steering wheel 2 to the neutral position based on the traveling speed v, the steering angle θ, and the steering torque τ, a friction torque calculation unit 74 that calculates a friction torque τf simulating a friction force generated in the steering system S due to operation of the steering wheel 2 based on the traveling speed v and the steering angular velocity ω, a damping torque calculation unit 75 that calculates a damping torque τd to be applied to the steering wheel 2 for the operation of the steering wheel 2 based on the traveling speed v, the steering angle θ, and the steering angular velocity ω, a reaction torque calculation unit 76 that calculates a reaction torque τref based on the base torque τb, the return torque τr, the friction torque τf, and the damping torque τd, and a reaction motor control unit 77 that controls the reaction motor 3 based on the reaction torque τref.

[0024] The steering angle calculation unit 70 calculates the steering angle θ, which is the rotation angle from the neutral position of the steering wheel 2, based on the mechanical angle of the rotor detected by the angle sensor 3a attached to the reaction motor 3 and a reduction ratio between the worm wheel 12a and the worm 12b. In a case where the current steering angle of the steering wheel 2 is not stored at the time of activation of the controller 7, the current steering angle may be obtained from a sensor capable of detecting the current steering angle of the steering wheel 2, and the steering angle of the steering wheel 2 may be calculated based on the mechanical angle of the rotor detected by the angle sensor 3a. The steering angle θ of the steering wheel 2 calculated by the steering angle calculation unit 70 is input to each of the angular velocity calculation unit 71, the base torque calculation unit 72, and the return torque calculation unit 73. The angular velocity calculation unit 71 calculates the steering angular velocity ω by differentiating the steering angle θ detected by the steering angle detection unit 5, and inputs the steering angular velocity ω to the friction torque calculation unit 74 and the damping torque calculation unit 75.

[0025] As illustrated in Fig. 3, the base torque calculation unit 72 includes a map calculation unit 72a that calculates a value of the base torque τb for returning the steering wheel 2 to the neutral position based on the traveling speed v detected by the speed detection unit 4 and the steering angle θ detected by the steering angle detection unit 5, a direction determination unit 72b that calculates a direction in which the base torque τb is to be applied to the steering wheel 2, and a multiplier 72c that calculates the base torque τb to be applied to the steering wheel 2 by multiplying the value of the base torque τb calculated by the map calculation unit 72a and an output of the direction determination unit 72b.

[0026] The map calculation unit 72a holds a map that defines a characteristic of the base torque τb for an absolute value of the steering angle θ. In the map, the characteristic of the base torque τb is defined for absolute values of the steering angles θ corresponding to several traveling speeds v. The map calculation unit 72a selects the characteristic corresponding to the traveling speed v and performs map calculation to calculate the value of the base torque τb corresponding to the absolute value of the detected steering angle θ.

[0027] As the characteristic, for example, characteristics corresponding to a plurality of different traveling speeds v such as a low speed, a medium speed, and a high speed are mapped. For example, the low speed is set to 25 km / h, the medium speed is set to 50 km / h, and the high speed is set to 75 km / h, but specific traveling speeds corresponding to the low speed, the medium speed, and the high speed can be arbitrarily set. In addition, four or more characteristics for calculating the base torque τb may be prepared by subdividing the traveling speed, or two characteristics may be prepared corresponding to the low speed and the high speed.

[0028] The map calculation unit 72a selects a characteristic corresponding to a traveling speed close to the detected traveling speed v, and calculates the value of the base torque τb by map calculation based on the absolute value of the steering angle θ by using the selected characteristic. In a case where there is no characteristic corresponding to the detected traveling speed v, it is sufficient if the map calculation unit 72a calculates the value of the base torque τb by performing linear interpolation using a characteristic corresponding to a high traveling speed close to the detected traveling speed v and a characteristic corresponding to a low traveling speed close to the detected traveling speed v. Specifically, in a case where the detected traveling speed v is a traveling speed between the low speed and the medium speed, the map calculation unit 72a calculates values of the base torque τb by using a characteristic corresponding to the medium speed that is a high traveling speed close to the detected traveling speed v and a characteristic corresponding to the low speed that is a low traveling speed close to the detected traveling speed v, and performs linear interpolation on the calculated values of the base torque τb to calculate the value of the base torque τb.

[0029] The base torque τb tends to increase as the traveling speed v increases, and tends to increase as the absolute value of the steering angle θ increases, and forms a part of the self-alignment torque generated when the steerable wheels W are turned to an angle for turning the vehicle. The characteristic for calculating the value of the base torque τb is a characteristic in which the value of the base torque τb is changed linearly with respect to the absolute value of the steering angle θ in the present embodiment, but design change can be made such that the ideal self-alignment torque can be applied to the steering wheel 2 according to a characteristic of the return torque τr described below.

[0030] In addition, the base torque calculation unit 72 grasps a direction in which the base torque τb is applied to the steering wheel 2 from a sign of the steering angle θ, and calculates the base torque τb. Therefore, the base torque calculation unit 72 includes the direction determination unit 72b. The direction determination unit 72b grasps the direction in which the base torque τb is applied to the steering wheel 2 from the sign of the steering angle θ, and outputs a value of 1 or -1 according to the direction.

[0031] Specifically, assuming that the sign of the steering angle θ when the steering wheel 2 is rotated counterclockwise from the neutral position is positive and the sign of the steering angle θ when the steering wheel 2 is rotated clockwise from the neutral position is negative, when the sign of the steering angle θ of the steering wheel 2 is positive, a direction in which the base torque τb is to be applied to the steering wheel 2 is a direction for rotating the steering wheel 2 clockwise. Therefore, the direction determination unit 72b outputs a value of -1 indicating a clockwise direction. On the other hand, when the sign of the steering angle θ of the steering wheel 2 is negative, a direction in which the base torque τb is to be applied to the steering wheel 2 is a direction for rotating the steering wheel 2 counterclockwise. Therefore, the direction determination unit 72b outputs a value of 1 indicating a counterclockwise direction.

[0032] The multiplier 72c multiplies the value of the base torque τb calculated based on the absolute value of the steering angle θ by a value output from the direction determination unit 72b to calculate the base torque τb to be applied to the steering wheel 2. Therefore, the base torque calculation unit 72 outputs the base torque τb having a negative value to return the steering wheel 2 to the neutral position in a case where the sign of the steering angle θ of the steering wheel 2 is positive, and outputs the base torque τb having a positive value to return the steering wheel 2 to the neutral position in a case where the sign of the steering angle θ of the steering wheel 2 is negative. In this manner, the base torque τb is applied to the steering wheel 2 so as to return the steering wheel 2 to the neutral position when the steering wheel 2 is rotated from the neutral position.

[0033] The return torque calculation unit 73 calculates the return torque τr for returning the steering wheel 2 to the neutral position based on the traveling speed v calculated by the speed calculation unit 71, the steering angle θ detected by the steering angle detection unit 5, and the steering torque τ detected by the torque detection unit 6. As illustrated in Fig. 4, the return torque calculation unit 73 includes the map calculation unit 73a that calculates a value of the return torque τr for returning the steering wheel 2 to the neutral position based on the traveling speed v calculated by the speed calculation unit 71 and the steering angle θ detected by the steering angle detection unit 5, a direction determination unit 73b that calculates a direction in which the return torque τr is to be applied to the steering wheel 2, a gain calculation unit 73c that calculates a return torque gain Gr to be multiplied by the value of the return torque τr calculated by the map calculation unit 73a based on the steering torque τ, and a multiplier 73d that calculates the final return torque τr to be applied to the steering wheel 2 by multiplying the value of the return torque τr, an output of the direction determination unit 73b, and the return torque gain Gr.

[0034] The map calculation unit 73a holds a map that defines a characteristic of the return torque τr for the absolute value of the steering angle θ. In the map, the characteristic of the return torque τr is defined for the absolute values of the steering angles θ corresponding to several traveling speeds v. The return torque calculation unit 73 selects the characteristic corresponding to the traveling speed v and performs map calculation to calculate the value of the return torque τr corresponding to the absolute value of the detected steering angle θ. The return torque τr calculated based on the steering angle θ is hereinafter referred to as a return torque τr before correction.

[0035] As the characteristic, for example, characteristics corresponding to a plurality of different traveling speeds v such as a low speed, a medium speed, and a high speed are mapped. For example, the low speed is set to 25 km / h, the medium speed is set to 50 km / h, and the high speed is set to 75 km / h, but specific traveling speeds corresponding to the low speed, the medium speed, and the high speed can be arbitrarily set. In addition, four or more characteristics for calculating the return torque τr may be prepared by subdividing the traveling speed, or two characteristics may be prepared corresponding to the low speed and the high speed.

[0036] The map calculation unit 73a selects a characteristic corresponding to a traveling speed close to the detected traveling speed v, and calculates the value of the return torque τr by map calculation based on the absolute value of the steering angle θ by using the selected characteristic. In a case where there is no characteristic corresponding to the detected traveling speed v, it is sufficient if the map calculation unit 73a calculates the value of the return torque τr by performing linear interpolation using a characteristic corresponding to a high traveling speed close to the detected traveling speed v and a characteristic corresponding to a low traveling speed close to the detected traveling speed v. Specifically, in a case where the detected traveling speed v is a traveling speed between the low speed and the medium speed, the map calculation unit 73a calculates values of the return torque τr by using a characteristic corresponding to the medium speed that is a high traveling speed close to the detected traveling speed v and a characteristic corresponding to the low speed that is a low traveling speed close to the detected traveling speed v, and performs linear interpolation on the calculated values of the return torque τr to calculate the value of the return torque τr.

[0037] The return torque τr before correction tends to increase as the traveling speed v increases, and tends to increase as the absolute value of the steering angle θ increases, and forms the self-alignment torque together with the base torque τb. In the present embodiment, the characteristic for calculating the value of the return torque τr before correction is a characteristic in which the value of the return torque τr is changed linearly with respect to the absolute value of the steering angle θ, but design change can be made such that ideal self-alignment torque can be applied to the steering wheel 2 according to the characteristic of the base torque τb.

[0038] In addition, the return torque calculation unit 73 grasps a direction in which the return torque τr is applied to the steering wheel 2 from a sign of the steering angle θ, and calculates the return torque τr. Therefore, the return torque calculation unit 73 includes the direction determination unit 73b. Specifically, when the sign of the steering angle θ of the steering wheel 2 is positive, a direction in which the return torque τr is to be applied to the steering wheel 2 is a direction for rotating the steering wheel 2 clockwise. Therefore, the direction determination unit 73b outputs a value of -1 indicating a clockwise direction. On the other hand, when the sign of the steering angle θ of the steering wheel 2 is negative, a direction in which the return torque τr is to be applied to the steering wheel 2 is a direction for rotating the steering wheel 2 counterclockwise. Therefore, the direction determination unit 73b outputs a value of 1 indicating a counterclockwise direction.

[0039] Further, as described above, the return torque calculation unit 73 calculates the final return torque τr by multiplying the value of the return torque τr calculated based on the absolute value of the steering angle θ by the return torque gain Gr calculated based on the steering torque τ. Therefore, the return torque calculation unit 73 includes the gain calculation unit 73c. The gain calculation unit 73c holds a map that defines a characteristic of the return torque gain Gr for the absolute value of the steering torque τ. The return torque gain Gr is characterized so as to take a maximum value when the absolute value of the steering torque τ is 0, and take a smaller value as the absolute value of the steering torque τ increases.

[0040] The multiplier 73d multiplies the value of the return torque τr before correction calculated based on the absolute value of the steering angle θ, the value output by the direction determination unit 73b, and the return torque gain Gr calculated by the gain calculation unit 73c to calculate the final return torque τr to be applied to the steering wheel 2. Therefore, the return torque calculation unit 73 outputs the return torque τr having a negative value to return the steering wheel 2 to the neutral position in a case where the sign of the steering angle θ of the steering wheel 2 is positive, and outputs the return torque τr having a positive value to return the steering wheel 2 to the neutral position in a case where the sign of the steering angle θ of the steering wheel 2 is negative. In this manner, the return torque τr is applied to the steering wheel 2 so as to return the steering wheel 2 to the neutral position when the steering wheel 2 is rotated from the neutral position.

[0041] Therefore, the final return torque τr output from the return torque calculation unit 73 tends to decrease as the traveling speed v increases, tends to increase as the absolute value of the steering angle θ increases, and tends to decrease as the steering torque τ increases.

[0042] Subsequently, the friction torque calculation unit 74 calculates the friction torque τf simulating the friction force generated in the steering system S due to operation of the steering wheel 2 based on the traveling speed v and the steering angular velocity ω. Specifically, as illustrated in Fig. 5, the friction torque calculation unit 74 includes a map calculation unit 74a that calculates a value of the friction torque τf based on the traveling speed v of the vehicle by map calculation, a dead zone processing unit 74b that executes dead zone processing on the steering angular velocity ω, a direction determination unit 74c that determines a rotation direction of the steering wheel 2 based on the steering angular velocity ω after dead zone processing and outputs a value corresponding to the rotation direction, a multiplier 74d that multiplies the value of the friction torque τf and the value output from the direction determination unit 74c, a low-pass filter 74e that filters an output of the multiplier 74d, and a limiter 74f that clamps an output of the low-pass filter 74e to an upper limit value.

[0043] The map calculation unit 74a holds a map that defines a characteristic of the friction torque τf for the traveling speed v, and calculates the value of the friction torque τf based on the traveling speed v by the map calculation. The friction torque τf is a torque applied to the steering wheel 2 as a reaction force in a direction opposite to a steering direction by simulating the friction force generated in the steering system S, which includes friction between the steerable wheels W and a road surface and friction generated in the steering system S when the steerable wheels W are driven. In addition, the friction torque τf is mapped as a characteristic so as to take a maximum value when the traveling speed v of the vehicle is 0 and take a smaller value as the value of the traveling speed v increases. The map calculation unit 74a calculates the value of the friction torque τf based on the traveling speed v by the map calculation using the map characterized as described above. In the present embodiment, the characteristic for calculating the value of the friction torque τf is a characteristic in which the value of the friction torque τf is linearly changed with respect to the traveling speed v, but design change can be made such that the ideal friction torque can be simulated.

[0044] The dead zone processing unit 74b obtains the steering angular velocity ω calculated by the angular velocity calculation unit 71, and outputs 0 in a case where the steering angular velocity ω is within a predetermined dead zone range set including 0, and outputs the steering angular velocity ω as it is in a case where the steering angular velocity ω is outside the dead zone range. In a case where the steering angular velocity ω takes a value close to 0, when noise is superimposed on a signal of the steering angular velocity ω, it is not possible to determine a correct direction in the determination of the rotation direction subsequent to the dead zone processing. Therefore, the correct rotation direction can be determined by executing the dead zone processing in the dead zone processing unit 74b.

[0045] The direction determination unit 74c grasps the direction in which the friction torque τf is applied to the steering wheel 2 from a sign of the steering angular velocity ω, and outputs a value corresponding to the grasped direction. Specifically, when the sign of the steering angular velocity ω of the steering wheel 2 is positive, the rotation direction of the steering wheel 2 is the counterclockwise direction, and a direction in which the friction torque τf is to be applied to the steering wheel 2 is a direction for rotating the steering wheel 2 clockwise. Therefore, the direction determination unit 74c outputs a value of -1 indicating the clockwise direction. On the other hand, when the sign of the steering angular velocity ω of the steering wheel 2 is negative, the rotation direction of the steering wheel 2 is the clockwise direction, and a direction in which the friction torque τf is to be applied to the steering wheel 2 is a direction for rotating the steering wheel 2 counterclockwise. Therefore, the direction determination unit 74c outputs a value of 1 indicating the counterclockwise direction.

[0046] The multiplier 74d multiplies the value of the friction torque τf calculated based on the traveling speed v by a value output from the direction determination unit 74c to calculate the friction torque τf to be applied to the steering wheel 2. Therefore, in a case where the sign of the steering angular velocity ω of the steering wheel 2 is positive, the friction torque calculation unit 74 outputs the friction torque τf having a negative value indicating the clockwise direction so as to apply a resistance to the operation of the steering wheel 2 in the counterclockwise direction. Conversely, in a case where the sign of the steering angular velocity ω of the steering wheel 2 is negative, the friction torque calculation unit 74 outputs the friction torque τf having a positive value indicating the counterclockwise direction so as to apply a resistance to the operation of the steering wheel 2 in the clockwise direction. In this manner, the friction torque τf is applied to the steering wheel 2 in a direction opposite to the rotation direction of the steering wheel 2.

[0047] The friction torque τf output from the multiplier 74d is processed by the low-pass filter 74e to reduce a sudden change and remove noise, and then input to the limiter 74f and clamped to the upper limit value. The limiter 74f outputs the value of the friction torque τf as it is in a case where the friction torque τf does not reach the upper limit value set for the friction torque τf, and outputs the upper limit value with the value of the friction torque τf as the upper limit value when the friction torque τf reaches a predetermined upper limit value.

[0048] The friction torque τf takes the maximum value when the traveling speed v of the vehicle is 0 and takes a smaller value as the value of the traveling speed v increases, and is applied as the reaction force for the steering wheel 2 by simulating friction between tires and the road surface, which is changed according to the traveling speed v.

[0049] The damping torque calculation unit 75 calculates the damping torque τd to be applied to the steering wheel 2 for the operation of the steering wheel 2 based on the traveling speed v and the steering angular velocity ω. Specifically, as illustrated in Fig. 6, the damping torque calculation unit 75 includes a damping coefficient calculation unit 75a that calculates a damping coefficient C based on the steering angular velocity ω, a gain calculation unit 75b that calculates a speed gain Gv based on the traveling speed v, a multiplier 75c that calculates the damping torque τd by multiplying the steering angular velocity ω, the damping coefficient C, and the speed gain Gv, a low-pass filter 75d that filters the damping torque τd calculated by the multiplier 75c, and a limiter 75e that clamps the damping torque τd to an upper limit value.

[0050] The damping coefficient calculation unit 75a holds a map that defines a characteristic of the damping coefficient C for an absolute value of the steering angular velocity ω, and calculates a value of the damping coefficient C based on the absolute value of the steering angular velocity ω by map calculation. Further, two maps including a map used when the steering wheel 2 is steered so as to increase the current rotation speed and a map used when the steering wheel 2 is steered so as to decrease the current rotation speed are prepared. Therefore, the damping coefficient calculation unit 75a determines whether the rotation of the steering wheel 2 is accelerated or decelerated based on signs of the steering torque τ and the steering angular velocity ω, selects one of the two maps based on the determination result, and calculates the damping coefficient C based on the absolute value of the steering angular velocity ω by using the selected map. As described above, by selectively using the map used when the rotation speed of the steering wheel 2 is increased and the map used when the rotation speed of the steering wheel 2 is decreased, an appropriate damping torque can be applied for the steering of the steering wheel 2, and fine tuning can be performed. However, in a case where the damping coefficient C is changed only for the absolute value of the steering angular velocity ω regardless of whether the rotation speed of the steering wheel 2 is increased or decreased, the damping coefficient calculation unit 75a may calculate the damping coefficient C using only one map.

[0051] The damping coefficient C gradually decreases as the absolute value of the steering angular velocity ω increases, and is set such that the damping torque τd applied to the steering wheel 2 in a case where a speed at which the steering wheel 2 is steered by the driver increases does not become excessive and does not hinder the steering. The characteristic for calculating the value of the damping coefficient C can be changed by design such that the ideal damping torque τd can be calculated.

[0052] The gain calculation unit 75b holds a map that defines a characteristic of the speed gain Gv for the traveling speed v, and calculates a value of the speed gain Gv based on the traveling speed v by the map calculation. Further, two maps including a map used when the steering wheel 2 is steered so as to increase the current rotation speed and a map used when the steering wheel 2 is steered so as to decrease the current rotation speed are prepared. Therefore, the gain calculation unit 75b determines whether the rotation of the steering wheel 2 is accelerated or decelerated based on the signs of the steering torque τ and the steering angular velocity ω, selects one of the two maps based on the determination result, and calculates the speed gain Gv based on the traveling speed v by using the selected map. As described above, by selectively using the map used when the rotation speed of the steering wheel 2 is increased and the map used when the rotation speed of the steering wheel 2 is decreased, an appropriate damping torque can be applied for the steering of the steering wheel 2, and fine tuning can be performed. However, in a case where the speed gain Gv is changed only for the traveling speed v regardless of whether the rotation speed of the steering wheel 2 is increased or decreased, the gain calculation unit 75b may calculate the speed gain Gv using only one map.

[0053] The speed gain Gv increases as the traveling speed v increases, and is set such that the damping torque τd applied to the steering wheel 2 for the steering of the steering wheel 2 by the driver increases when the traveling speed v increases, so that sudden operation of the steering wheel 2 can be suppressed. The characteristic for calculating the value of the speed gain Gv can be changed by design such that the ideal damping torque τd can be calculated.

[0054] In the determination of whether the rotation speed of the steering wheel 2 is increased or decreased in the damping coefficient calculation unit 75a and the gain calculation unit 75b, processing similar to that in the dead zone processing unit 74b in the friction torque calculation unit 74 may be executed on the steering angular velocity ω so that the rotation direction of the steering wheel 2 with respect to the neutral position can be accurately determined. In the damping coefficient calculation unit 75a and the gain calculation unit 75b, instead of calculating the damping torque τd based on whether the rotation speed of the steering wheel 2 is increased or decreased, in a case where the value of the damping torque τd is made to depend on whether the rotation direction of the steering wheel 2 is a direction of returning to the neutral position or a direction of moving away from the neutral position, it is sufficient if a map corresponding to the rotation direction of the steering wheel 2 is prepared, and the map to be used is selected by determining the direction based on the sign of the steering angle θ and the sign of the steering angular velocity ω.

[0055] The multiplier 75c multiplies the steering angular velocity ω, the damping coefficient C, and the speed gain Gv to calculate the damping torque τd to be applied to the steering wheel 2. Therefore, the damping torque calculation unit 75 applies, to the steering wheel 2, the damping torque τd that applies a resistance to the operation of the steering wheel 2.

[0056] The damping torque τd output from the multiplier 75c is processed by the low-pass filter 75d to reduce a sudden change and remove noise, and then input to the limiter 75e and clamped to an upper limit value. The limiter 75e outputs the value of the damping torque τd as it is in a case where the damping torque τd does not reach the upper limit value set for the damping torque τd, and outputs the upper limit value with the value of the damping torque τd as the upper limit value when the damping torque τd reaches a predetermined upper limit value.

[0057] The damping torque τd tends to decrease as the steering angular velocity ω increases, and tends to increase as the traveling speed v increases. The damping torque τd is applied as the reaction force for the steering wheel 2, which suppresses sudden operation of the steering wheel 2 according to the traveling speed v of the vehicle.

[0058] The reaction torque calculation unit 76 calculates the reaction torque τref based on the base torque τb, the return torque τr, the friction torque τf, and the damping torque τd. As illustrated in Fig. 7, the reaction torque calculation unit 76 includes an adder 76a that adds the value of the base torque τb, the value of the final return torque τr, the value of the friction torque τf, and the value of the damping torque τd, a multiplier 76b that multiplies a value output from the adder 76a by an adjustment gain Ge, and a limiter 76c that clamps a value output from the multiplier 76b to an upper limit value and outputs a value output from the limiter 76c as the reaction torque τref.

[0059] The adjustment gain Ge is a gain that can be arbitrarily set, and is set such that the reaction torque τref output from the reaction torque calculation unit 76 is optimal for the vehicle to which the steering device 1 is applied. In the calculation of the reaction torque τref, the multiplier 76b may be omitted if gain adjustment is unnecessary. The limiter 76c outputs the value of the reaction torque τref as it is in a case where the target reaction torque τref does not reach the upper limit value set for the reaction torque τref, and outputs the upper limit value with the value of the damping torque τd as the upper limit value when the damping torque τd reaches a predetermined upper limit value.

[0060] As illustrated in Fig. 8, the reaction motor control unit 77 includes a current command calculation unit 77a that generates a current command indicating a target current to be supplied to the reaction motor 3 from the reaction torque τref, and a driver 77b that supplies a current to the reaction motor 3 by receiving the current command generated by the current command calculation unit 77a.

[0061] Although not illustrated in detail, the current command calculation unit 77a generates the current command indicating a value of the current to be applied to the reaction motor 3 based on the reaction torque τref by using a map obtained by mapping a characteristic of the reaction motor 3 for the reaction torque τref. The configuration of the current command calculation unit 77a is an example, and it is sufficient if the current command calculation unit 77a is configured to be able to cause the reaction motor 3 to generate the reaction torque τref.

[0062] The driver 77b includes a drive circuit that drives the reaction motor 3 by using pulse width modulation (PWM) based on the current command generated by the current command calculation unit 77a, and also includes a current sensor (not illustrated) that detects a current flowing through the reaction motor 3. The driver 77b supplies, to the reaction motor 3, a current amount corresponding to a target current indicated by the current command by current feedback. The driver 77b grasps a mechanical angle of the reaction motor 3 from the angle sensor 3a of the reaction motor 3, and energizes the coils of the three phases (not illustrated) at an energization timing suitable for the mechanical angle of the reaction motor 3 to drive the reaction motor 3.

[0063] Next, processing in the steering device 1 will be described with reference to the flowchart illustrated in Fig. 9. First, during the traveling of the vehicle, the steering device 1 detects the traveling speed v, the steering angle θ, and the steering torque τ, and obtains the steering angular velocity ω from the steering angle θ (step S1).

[0064] Subsequently, the controller 7 processes the obtained traveling speed v, steering angle θ, steering torque τ, and steering angular velocity ω to calculate the base torque τb, the return torque τr, the friction torque τf, and the damping torque τd (step S2).

[0065] Furthermore, the controller 7 calculates the reaction torque τref based on the base torque τb, the return torque τr, the friction torque τf, and the damping torque τd (step S3).

[0066] Then, the controller 7 generates the current command based on the reaction torque τref (step S4) and controls the reaction motor 3 (step S5).

[0067] The controller 7 repeatedly executes the processing procedure, detects the traveling speed v, the steering angle θ, the steering torque τ, and the steering angular velocity ω, processes the pieces of information, calculates the current command, and controls the reaction motor 3.

[0068] As described above, in the steering device 1, the base torque τb that forms a part of the self-alignment torque and acts so as to return the steering wheel 2 to the neutral position is calculated based on the traveling speed v and the steering angle θ, the return torque τr that forms a part of the self-alignment torque and acts so as to return the steering wheel 2 to the neutral position is calculated based on the traveling speed v, the steering angle θ, and the steering torque τ, and the reaction torque τref including the base torque τb and the return torque τr acts on the steering wheel 2. Since the return torque τr takes a large value when the steering torque τ is small and takes a small value when the steering torque τ is large, in the breakdown of the reaction torque τref, the base torque τb becomes relatively smaller than the return torque τr when the steering torque τ is small, and the base torque τb becomes relatively larger than the return torque τr when the steering torque τ is large.

[0069] When the reaction torque τref is calculated including the base torque τb and the return torque τr in this manner, in a situation in which the driver is steering the steering wheel 2, the return torque τr tends to decrease and the reaction torque τref tends to decrease. However, since the base torque τb does not decrease, it is possible to prevent a resistance from becoming excessive while applying an appropriate resistance for the steering of the steering wheel 2 by the driver with the base torque τb. In addition, when the reaction torque τref is calculated including the base torque τb and the return torque τr in this manner, in a situation in which the driver is not steering the steering wheel 2 or the steering torque τ is small, the return torque τr tends to increase, and thus, the reaction torque τref tends to increase. Accordingly, a torque for returning the steering wheel 2 to the neutral position increases, and the steering wheel 2 can be returned to the neutral position even when the steering angle θ is small. Therefore, even in the steering device 1 adopting the steer-by-wire system, the reaction torque to be applied to the steering wheel 2 is appropriately adjusted according to a steering condition of the steering wheel 2 by the driver while applying an appropriate resistance to the steering wheel 2 according to the vehicle speed v and the steering angle θ, so that a steering feel equivalent to that of a system in which the steering wheel and the steering system are mechanically connected to each other can be obtained, and the steering feel of the steering wheel 2 can be improved.

[0070] Although not illustrated, hardware resources of the controller 7 in the steering device 1 may specifically include, for example, except for the drive circuit in the driver 77b, an interface for fetching signals output from the angle sensor 3a, the speed detection unit 4, the steering angle detection unit 5, and the torque detection unit 6, a storage device such as a read only memory (ROM) in which a program used for processing necessary for fetching the rotation speed and the torque and controlling the reaction motor 3 is stored, an arithmetic device such as a central processing unit (CPU) that executes processing based on the program, and a storage device such as a random access memory (RAM) that provides a storage area for the CPU. Each portion in the controller 7 can be realized through execution of the program of the CPU. The controller 7 may be implemented by an analog electronic circuit instead of being implemented by the CPU executing the program.

[0071] As described above, the steering device 1 according to the present embodiment includes: the reaction motor 3 that can apply the reaction torque to the steering wheel 2 that is not mechanically connected to the steering system S including the steerable wheels W and the steering rack 8 connected to the steerable wheels W in the vehicle; and the controller 7 that controls the reaction motor 3, in which the controller 7 includes the base torque calculation unit 72 that calculates the base torque τb for returning the steering wheel 2 to the neutral position, the return torque calculation unit 73 that calculates the return torque τr for returning the steering wheel 2 to the neutral position according to the steering condition, and the reaction motor control unit 77 that controls the reaction motor 3 based on the base torque τb and the return torque τr, the base torque calculation unit 72 calculates the base torque τb based on the traveling speed v of the vehicle and the steering angle θ of the steering wheel 2, and the return torque calculation unit 73 calculates, based on the traveling speed v, the steering angle θ, and the steering torque τ acting on the steering wheel 2, the return torque τr that takes a small value when the steering torque τ is large.

[0072] In the steering device 1 configured as described above, since the return torque τr tends to decrease in a situation in which the driver is steering the steering wheel 2, the reaction torque τref tends to decrease. However, since the base torque τb does not decrease, it is possible to prevent a resistance from becoming excessive while applying an appropriate resistance for the steering of the steering wheel 2 by the driver, and in a situation in which the driver is not steering the steering wheel 2 or the steering torque τ is small, the return torque τr tends to increase, and thus, the reaction torque τref tends to increase. Accordingly, the torque for returning the steering wheel 2 to the neutral position increases, and the steering wheel 2 can be returned to the neutral position even when the steering angle θ is small. Therefore, with the steering device 1 configured as described above, the steering feel equivalent to that of a system in which the steering wheel 2 and the steering system S are mechanically connected to each other can be obtained, and the steering feel of the steering wheel 2 can be improved.

[0073] Further, in the steering device 1 according to the present embodiment, the controller 7 further includes the friction torque calculation unit 74 that calculates the friction torque τf simulating the friction force generated in the steering system S due to operation of the steering wheel 2 based on the traveling speed v and the rotation direction of the steering wheel 2, and the reaction motor control unit 77 controls the reaction motor 3 in consideration of the friction torque τf.

[0074] With the steering device 1 configured as described above, the friction force generated in the steering system S due to the steering of the steering wheel 2 can be simulated, so that a more natural steering feel can be obtained, and the steering feel can be further improved.

[0075] Further, in the steering device 1 according to the present embodiment, the controller 7 further includes the damping torque calculation unit 75 that calculates the damping torque τd to be applied to the steering wheel 2 for the steering of the steering wheel 2 based on the traveling speed v and the steering angular velocity ω, and the reaction motor control unit 77 controls the reaction motor 3 in consideration of the damping torque τd.

[0076] With the steering device 1 configured as described above, a vibration input to the steering wheel 2 can be suppressed, so that it is possible to avoid discomfort to the driver, and the steering feel can be further improved.

[0077] Although the preferred embodiment of the present invention has been described in detail above, modifications, variations, and changes can be made thereto without departing from the claims.

[0078] 1 Steering device 2 Steering wheel 3 Reaction motor 7 Controller 8 Steering rack 72 Base torque calculation unit 73 Return torque calculation unit 74 Friction torque calculation unit 75 Damping torque calculation unit 77 Reaction motor control unit S Steering system W Steerable wheel

Claims

1. A steering device comprising: a reaction motor that is configured to apply a reaction torque to a steering wheel that is not mechanically connected to a steering system including steerable wheels and a steering rack connected to the steerable wheels in a vehicle; and a controller that controls the reaction motor, wherein the controller includes a base torque calculation unit that calculates a base torque for returning the steering wheel to a neutral position, a return torque calculation unit that calculates a return torque for returning the steering wheel to the neutral position according to a steering condition, and a reaction motor control unit that controls the reaction motor based on the base torque and the return torque, the base torque calculation unit calculates the base torque based on a traveling speed of the vehicle and a steering angle of the steering wheel, and the return torque calculation unit calculates, based on the traveling speed, the steering angle, and a steering torque acting on the steering wheel, the return torque that takes a small value when the steering torque is large.

2. The steering device according to claim 1, wherein the controller further includes a friction torque calculation unit that calculates a friction torque simulating a friction force generated in the steering system due to operation of the steering wheel based on the traveling speed and a rotation direction of the steering wheel, and the reaction motor control unit controls the reaction motor in consideration of the friction torque.

3. The steering device according to claim 1 or 2, wherein the controller further includes a damping torque calculation unit that calculates a damping torque to be applied to the steering wheel for steering of the steering wheel based on the traveling speed and a steering angular velocity, and the reaction motor control unit controls the reaction motor in consideration of the damping torque.

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