Patent Application
20220009547
One aspect of the present invention relates to a steering device and a motor control method in steering device.
Automatic traveling control in the related art is known to calculate a target steering angle (target steering angle or target turning angle) for a vehicle to automatically travel along a target route set in a travel path and feedback-control a steering actuator so that an actual steering angle matches with the target steering angle (for example, see Patent Literature 1 below).
Further, automatic parking control is known to calculate a target steering angle to move a vehicle from a current position to an automatically detected parking position or a parking position designated by a driver and feedback-control a steering actuator so that an actual steering angle matches with the target steering angle (for example, see Patent Literature 2 below).
[Patent Literature 1] JP-A-2006-175940
[Patent Literature 2] JP-A-2008-80866
When the automatic parking control and the automatic traveling control are executed, it is conceivable to similarly execute angle feedback control in each of the automatic parking control and the automatic traveling control. However, it has been found that when the same angle feedback control as the automatic traveling control is applied to the automatic parking control, vibration occurs in an electric motor which is the steering actuator during the automatic parking control, which leads to a strange feeling to the driver.
An object of the present invention is to provide a steering device and a motor control method in steering device that can perform automatic traveling control and automatic parking control and prevent vibration during the automatic parking control.
According to the present invention, there is provided a steering device including: an electric motor configured to steer a steered wheel coupled to a steering wheel; and a control unit configured to control the electric motor and change a steering angle of the steered wheel. The control unit includes: an angle feedback control unit configured to execute automatic traveling control in which feedback control is performed so that an actual steering angle matches with a first target steering angle that is calculated for the vehicle to travel along a target route set in a travel path, and automatic parking control in which feedback control is performed so that an actual steering angle matches with a second target steering angle calculated for the vehicle to move from a current position to a parking position; and a gain setting unit configured to set a feedback gain in the automatic parking control to a value smaller than a feedback gain in the automatic traveling control.
With this configuration, it is possible to implement a steering device that can perform automatic traveling control and automatic parking control and prevent vibration during the automatic parking control.
In an embodiment of the present invention, the feedback control is proportional integral differential control, and the feedback gain includes a differential gain of the proportional integral differential control.
In an embodiment of the present invention, the feedback gain further includes a proportional gain of the proportional integral differential control.
In an embodiment of the present invention, the feedback gain further includes an integral gain of the proportional integral differential control.
In an embodiment of the present invention, the angle feedback control unit is configured to execute emergency avoidance support control in which, when a risk of collision with an obstacle in a vehicle traveling direction is detected, feedback control is performed so that an actual steering angle matches with a third target steering angle that is calculated to move the vehicle in a direction in which the obstacle is not present, and the gain setting unit sets a feedback gain in the emergency avoidance support control to a value larger than the feedback gain in the automatic traveling control.
According to the present invention, there is provided a motor control method in steering device. The steering device includes an electric motor configured to steer a steered wheel coupled to a steering wheel and is configured to execute automatic traveling control and automatic parking control. The automatic traveling control includes: calculating a first target steering angle for a vehicle to travel along a target route set in a travel path; and performing feedback control so that an actual steering angle matches with the first target steering angle. The automatic parking control includes: calculating a second target steering angle for the vehicle to move from a current position to a parking position; and performing feedback control so that an actual steering angle matches with the second target steering angle using a feedback gain set to a value smaller than a feedback gain in the automatic traveling control.
By this method, it is possible to perform automatic traveling control and automatic parking control and prevent vibration during the automatic parking control.
An electric power steering system 1 includes a steering wheel 2 serving as a steering member that steers a vehicle, a steering mechanism 4 that steers steered wheels 3 in conjunction with rotation of the steering wheel 2, and a steering assist mechanism 5 that assists steering by a driver. The steering wheel 2 and the steering mechanism 4 are mechanically coupled via a steering shaft 6 and an intermediate shaft 7. As a result, the steering wheel 2 and the steered wheels 3 are mechanically coupled.
The steering shaft 6 includes an input shaft 8 coupled to the steering wheel 2 and an output shaft 9 coupled to the intermediate shaft 7. The input shaft 8 and the output shaft 9 are coupled via a torsion bar 10 to be rotatable relative to each other. In the vicinity of the torsion bar 10 is disposed a torque sensor 12. The torque sensor 12 detects a steering torque Td applied to the steering wheel 2 based on a relative rotational displacement amount between the input shaft 8 and the output shaft 9. In the present embodiment, the steering torque Td detected by the torque sensor 12 is, for example, a positive value as a torque for steering to left and a negative value as a torque for steering to right, and the magnitude of the steering torque Td increases as an absolute value thereof increases.
The steering mechanism 4 is a rack-and-pinion mechanism including a pinion shaft 13 and a rack shaft 14 serving as a steering shaft. The rack shaft 14 includes end portions coupled to corresponding steered wheels 3 via tie rods 15 and knuckle arms (not shown).
The pinion shaft 13 is coupled to the intermediate shaft 7. The pinion shaft 13 rotates in conjunction with steering of the steering wheel 2. The pinion shaft 13 includes a distal end coupled to a pinion 16.
The rack shaft 14 extends linearly along a left-right direction of the vehicle. At an intermediate portion of the rack shaft 14 in the axial direction, a rack 17 meshes with the pinion 16. The pinion 16 and the rack 17 convert the rotation of the pinion shaft 13 into an axial movement of the rack shaft 14. By moving the rack shaft 14 in the axial direction, the steered wheels 3 can be steered.
When the steering wheel 2 is steered (rotated), the rotation is transmitted to the pinion shaft 13 via the steering shaft 6 and the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14 by the pinion 16 and the rack 17. As a result, the steered wheels 3 are steered.
The steering assist mechanism 5 includes an electric motor 18 that generates a steering assist force (assist torque) and a speed reducer 19 that amplifies an output torque of the electric motor 18 and transmits the amplified output torque to the steering mechanism 4. The speed reducer 19 is a worm gear mechanism including a worm gear 20 and a worm wheel 21 that meshes with the worm gear 20.
The speed reducer 19 is accommodated in a gear housing 22 serving as a transmission mechanism housing. In the following description, a speed reduction ratio (gear ratio) of the speed reducer 19 may be represented by N. The speed reduction ratio N is defined as a ratio ωwg/ωww of an angular velocity ωwg of the worm gear 20 to an angular velocity ωww of the worm wheel 21.
The worm gear 20 is rotationally driven by the electric motor 18. The worm wheel 21 is coupled to the output shaft 9 to be rotatable together with the output shaft 9.
When the worm gear 20 is rotationally driven by the electric motor 18, the worm wheel 21 is rotationally driven, a motor torque is applied to the steering shaft 6, and the steering shaft 6 (output shaft 9) is rotated. The rotation of the steering shaft 6 is transmitted to the pinion shaft 13 via the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into axial movement of the rack shaft 14. As a result, the steered wheels 3 are steered. As the steering shaft 6 rotates, the steering wheel 2 also rotates.
That is, by rotationally driving the worm gear 20 by the electric motor 18, steering assistance by the electric motor 18 and steering of the steered wheels 3 can be performed. The electric motor 18 is provided with a rotation angle sensor 23 that detects a rotation angle of a rotor of the electric motor 18.
In the following description, automatic traveling control refers to control in which feedback control is performed so that an actual steering angle matches with a target steering angle (hereinafter, referred to as a “first target steering angle”). The target steering angle is calculated for the vehicle to travel along a target route set in a travel path. The automatic traveling control includes, for example, lane keeping control in which feedback control is performed by setting the target route by continuously setting a target traveling position in a predetermined position in the lane width direction within a lane in order to maintain traveling in the predetermined position in the lane width direction within the lane, and preceding vehicle travel trajectory following control in which feedback control is performed by setting a travel trajectory of a preceding vehicle as the target route of a given vehicle. In addition to the above control, the automatic traveling control further includes, for example, automatic driving control in which feedback control is performed by setting a travel route from a current position to a destination, and automatic overtaking control in which feedback control is performed by setting a travel route for overtaking the preceding vehicle having a traveling speed lower than that of the given vehicle. In addition to the above control, the automatic traveling control further includes overall control in which feedback control is performed by setting a target travel route on a travel path (road) so that the actual steering angle matches with the target steering angle that is calculated for the vehicle to travel along the target route. The present embodiment will describe an aspect in which the lane keeping control is performed as the automatic traveling control. In the automatic parking control, feedback control is performed so that the actual steering angle matches with the target steering angle (hereinafter referred to as a “second target steering angle”) that is calculated for the vehicle to move from a current position to a parking position. In the present embodiment, the “target steering angle” is a target rotation angle relative to the output shaft 9.
The electric power steering system 1 further includes a motor control ECU (control unit) 102. The steering torque Td detected by the torque sensor 12 and an output signal of the rotation angle sensor 23 are input to the motor control ECU 102. The motor control ECU 102 controls the electric motor 18 based on these received signals and information received from a host ECU 101 on a vehicle side.
The host ECU 101 has a function of generating a first target steering angle θad1 for the vehicle to automatically travel along the target route and providing the first target steering angle θad1 to the motor control ECU 102 during the lane keeping control, and a function of generating a second target steering angle θad2 for the vehicle to move to a predetermined parking position and providing the second target steering angle θad2 to the motor control ECU 102 during the automatic parking control. Processing of generating the first target steering angle θad1 and the second target steering angle θad2 is well known and thus detailed description thereof will be omitted here. The host ECU 101 further has a function of providing a control mode signal Smode indicating a control mode set by the driver to the motor control ECU 102. The control mode includes a normal control mode performed during normal traveling, a lane keeping control mode for the lane keeping control, and an automatic parking control mode for the automatic parking control.
The first target steering angle θad1, the second target steering angle θad2, and the control mode signal Smode generated by the host ECU 101 are provided to the motor control ECU 102 via, for example, an in-vehicle network.
The motor control ECU 102 includes a microcomputer 40, a drive circuit (inverter circuit) 31 that is controlled by the microcomputer 40 and supplies electric power to the electric motor 18, and a current detection circuit 32 that detects a current (hereinafter referred to as a “motor current I”) flowing through the electric motor 18.
The microcomputer 40 includes a CPU and a memory (ROM, RAM, nonvolatile memory, and the like), and functions as a plurality of functional processing units by executing predetermined programs. The plurality of functional processing units include a current command value setting unit 41, an angle deviation calculation unit 43, a proportional-integral-derivative (PID) control unit 44 (angle feedback control unit), a command value switching unit 45, a current deviation calculation unit 46, a proportional-integral (PI) control unit 47, a PWM control unit 48, a rotation angle calculation unit 49, a speed reduction ratio division unit 50, and a gain setting unit 51.
The current command value setting unit 41 calculates a current command value Ias for the electric motor 18 in the normal control mode based on the steering torque Td. The current command value Ias is positive for the positive value of the steering torque Td, and generates a steering assist force for steering to the left from the electric motor 18. The current command value Ias is negative for the negative value of the steering torque Td, and generates a steering assist force for steering to the right from the electric motor 18. The current command value Ias is set such that an absolute value of the current command value Ias increases as the absolute value of the steering torque Td increases. The current command value Ias calculated by the current command value setting unit 41 is input to the command value switching unit 45.
The rotation angle calculation unit 49 calculates a rotor rotation angle θm of the electric motor 18 based on the output signal of the rotation angle sensor 23. The speed reduction ratio division unit 50 divides the rotor rotation angle Om calculated by the rotation angle calculation unit 49 by the speed reduction ratio N to convert the rotor rotation angle θm into a rotation angle (actual steering angle) θ of the output shaft 9. The actual steering angle θ calculated by the speed reduction ratio division unit 50 is provided to the angle deviation calculation unit 43.
The angle deviation calculation unit 43 calculates a deviation Δθ(=(θad1−θ) or (θad2−θ)) between the first target steering angle θad1 or the second target steering angle θad2 output from the host ECU 101 and the actual steering angle θ. The PID control unit 44 calculates a current command value Iad by performing PID calculation on the angle deviation Δθ calculated by the angle deviation calculation unit 43. Specifically, the PID control unit 44 includes a proportional processing unit 61, an integral processing unit 62, a differential processing unit 63, a proportional gain multiplication unit 64, an integral gain multiplication unit 65, a differential gain multiplication unit 66, and an addition unit 67.
The proportional gain multiplication unit 64 multiplies the angle deviation Δθ after being proportionally processed by the proportional processing unit 61 by a proportional gain KP provided by the gain setting unit 51. The integral gain multiplication unit 65 multiplies the angle deviation Δθ after being integrally processed by the integral processing unit 62 by an integral gain K1 provided by the gain setting unit 51. The differential gain multiplication unit 66 multiplies the angle deviation Δθ after being differentially processed by the differential processing unit 63 by a differential gain KD provided by the gain setting unit 51. Details of the operation of the gain setting unit 51 will be described later.
The addition unit 67 adds multiplication results of the proportional gain multiplication unit 64, the integral gain multiplication unit 65, and the differential gain multiplication unit 66, thereby calculating the current command value Iad for the electric motor 18 in the lane keeping control mode or the automatic parking control mode. The current command value Iad calculated by the PID control unit 44 is input to the command value switching unit 45.
The command value switching unit 45 selects and outputs the current command value Ias when the control mode signal Smode is a signal indicating the normal control mode, and selects and outputs the current command value Iad when the control mode signal Smode is a signal indicating the lane keeping control mode or a signal indicating the automatic parking control mode. The output of the command value switching unit 45 is provided to the current deviation calculation unit 46.
The current deviation calculation unit 46 calculates a deviation ΔI (=(Ias−I) or (Iad−I)) between the current command value Ias or Iad received from the command value switching unit 45 and the motor current I detected by the current detection circuit 32.
The PI control unit 47 performs proportional-integral calculation (PI calculation) on the current deviation ΔI calculated by the current deviation calculation unit 46, thereby generating a drive command value for leading the motor current I flowing through the electric motor 18 to the current command value Ias or Iad. The PWM control unit 48 generates a PWM control signal having a duty ratio corresponding to the drive command value, and provides the PWM control signal to the drive circuit 31. As a result, electric power corresponding to the drive command value is supplied to the electric motor 18.
In the above-described configuration, when the control mode is set to the normal control mode, the current command value Ias set by the current command value setting unit 41 is output from the command value switching unit 45. Accordingly, an assist torque corresponding to the steering torque Td is generated from the electric motor 18.
When the control mode is set to the lane keeping control mode, the host ECU 101 provides the first target steering angle θad1 to the motor control ECU 102. Then, the PID control unit 44 performs PID calculation on the angle deviation Δθ(=θad1−θ) between the first target steering angle θad1 and the actual steering angle θ. As a result, the current command value Iad for the lane keeping control is calculated. Since the current command value Iad is output from the command value switching unit 45, the drive circuit 31 is driven and controlled so that the motor current I matches with the current command value Iad. As a result, the electric motor 18 is controlled so that the actual steering angle θ matches with the first target steering angle θad1.
When the control mode is set to the automatic parking control mode, the host ECU 101 provides the second target steering angle θad1 to the motor control ECU 102. Then, the PID control unit 44 performs PID calculation on the angle deviation Δθ(=θad2−θ) between the second target steering angle θad2 and the actual steering angle θ. As a result, the current command value Iad for the automatic parking control is calculated. Since the current command value Iad is output from the command value switching unit 45, the drive circuit 31 is driven and controlled so that the motor current I matches with the current command value Iad. As a result, the electric motor 18 is controlled so that the actual steering angle θ matches with the second target steering angle θad2.
Hereinafter, the operation of the gain setting unit 51 will be described in detail. The gain setting unit 51 sets the proportional gain KP, the integral gain KI, and the differential gain KD in accordance with the control mode signal Smode provided by the host ECU 101. A more specific description will be given below. The proportional gain KP, the integral gain KI, and the differential gain KD that are set when the control mode is the lane keeping control mode are referred to as a first proportional gain KP1, a first integral gain KI1, and a first differential gain KD1, respectively. In contrast, the proportional gain KP, the integral gain KI, and the differential gain KD that are set when the control mode is the automatic parking control mode are referred to as a second proportional gain KP2, a second integral gain KI2, and a second differential gain KD2, respectively.
The second proportional gain KP2, the second integral gain KI2, and the second differential gain KD2 are set to values smaller than the first proportional gain KP1, the first integral gain KI1, and the first differential gain KD2, respectively. A reason for this will be described below.
The vehicle speed during the lane keeping control is usually higher than the vehicle speed during the automatic parking control, and thus higher responsiveness is required in the lane keeping control than in the automatic parking control. For this reason, the first proportional gain KP1, the first integral gain KI1, and the first differential gain KD1 during the lane keeping control are set to relatively large values. In this way, it has been found that, when the feedback gains KP1, KI1, and KD1 of the lane keeping control are set to relatively large values and then the feedback gains KP2, KI2, and KD2 of the automatic parking control are set to the same values as the feedback gains KP1, KI1, and KD1 of the lane keeping control, the responsiveness to the vehicle speed during the automatic parking control is excessively high, and thus vibration occurs to the electric motor 18 during the automatic parking control, which leads to a strange feeling to the driver.
In the present embodiment, in order to prevent vibration of the electric motor 18 that occurs during the automatic parking control, the second proportional gain KP2, the second integral gain KI2, and the second differential gain KD2 are set to values smaller than the first proportional gain KP1, the first integral gain KI1, and the first differential gain KD1, respectively. As a result, it is possible to prevent vibration of the electric motor 18 that occurs during the automatic parking control.
In this way, when the feedback gains KP2, KI2, and KD21 of the automatic parking control are set to values smaller than the feedback gains KP1, KI1, and KD1 of the lane keeping control, the responsiveness during the automatic parking control is reduced. The automatic parking control is not hindered since high responsiveness is not required for the automatic parking control compared to the lane keeping control.
Further, among the second proportional gain KP2, the second integral gain KI2, and the second differential gain KD2, only the second differential gain KD2 may be set to a value smaller than the first differential gain KD1. Further, among the second proportional gain KP2, the second integral gain KI2, and the second derivative gain KD2, the second derivative gain KD2 and the second proportional gain KP2 other than the second integral gain KI2 may be set to values smaller than the first derivative gain KD1 and the first proportional gain KP1, respectively.
That is, among the second proportional gain KP2, the second integral gain KI2, and the second differential gain KD2, at least the second differential gain KD2 is set to a value smaller than the first differential gain KD1 so that vibration of the electric motor 18 during the automatic parking control can be prevented. However, it is preferable that the second differential gain KD2 and the second proportional gain KP2 are set to values smaller than the first differential gain KD1 and the first proportional gain KP1, respectively. As a result, vibration of the electric motor 18 during the automatic parking control can be prevented more effectively than in a case where only the second differential gain KD2 is set to a value smaller than the first differential gain KD1.
It is more preferable that the second proportional gain KP2, the second integral gain KI2, and the second differential gain KD2 are set to values smaller than the first proportional gain KP1, the first integral gain KI1, and the first differential gain KD1, respectively. This can improve the stability of the PID control system.
Accordingly, it is most preferable that all of the second proportional gain KP2, the second integral gain KI2, and the second differential gain KD2 are set to values smaller than the first proportional gain KP1, the first integral gain KI1, and the first differential gain KD1, respectively. Next, it is preferable that two of the second differential gain KD2 and the second proportional gain KP2 are set to values smaller than the first differential gain KD1 and the first proportional gain KP1, respectively. However, as long as at least the second differential gain KD2 is set to a value smaller than the first differential gain KD1, it is possible to achieve an effect of preventing vibration of the electric motor 18 during the automatic parking control.
Although one embodiment of the present invention has been described above, the present invention can be implemented by other embodiments. For example, in the above-described embodiment, the host ECU 101 has a function of generating the first target steering angle θad1 for the lane keeping control and the second target steering angle θad2 for the automatic parking control and providing the first target steering angle θad1 and the second target steering angle θad2 to the motor control ECU 102. However, the host ECU 101 may have a function of generating a third target steering angle θad3 for emergency avoidance support control and providing the third target steering angle θad3 to the motor control ECU 102 in addition to the above function, as is shown by two-dot chain lines in
The emergency avoidance support control refers to control in which feedback control is performed by, when a risk of collision with an obstacle in the vehicle traveling direction is detected, calculating the target steering angle (third target steering angle) θad3 for moving the vehicle in a direction in which the obstacle is not present so that the actual steering angle matches with the third target steering angle θad3. In this case, an emergency avoidance support control mode for the emergency avoidance support control is added to the normal control mode, the lane keeping control mode, and the automatic parking control mode described above as types of the control mode.
When the control mode is the emergency avoidance support control mode, the third target steering angle θad3 from the host ECU 101 is input to the angle deviation calculating unit 43. When the control mode is the emergency avoidance support control mode, the gain setting unit 51 sets the proportional gain KP, the integral gain KI, and the differential gain KD to a third proportional gain KP3, a third integral gain KI3, and a third differential gain KD3, respectively. In this case, the third proportional gain KP3, the third integral gain KI3, and the third differential gain KD3 are set to values larger than the first proportional gain KP1, the first integral gain KI1, and the first differential gain KD1, respectively. This is because higher responsiveness is required in the emergency avoidance support control than in the lane keeping control.
Further, among the third proportional gain KP3, the third integral gain KI3, and the third differential gain KD3, only the third differential gain KD3 may be set to a value larger than the first differential gain KD1. Further, among the third proportional gain KP3, the third integral gain KI3, and the third derivative gain KD3, the third derivative gain KD3 and the third proportional gain KP3 other than the third integral gain KI3 may be set to values larger than the first derivative gain KD1 and the first proportional gain KP1, respectively.
In addition, the above-described embodiment described an example in which the present invention is applied to a column type EPS, and the present invention can also be applied to an EPS other than the column type EPS. The present invention can also be applied to a steer-by-wire system.
In addition, various design changes can be made to the present invention within the scope of the matters described in the claims.
The present application is based on a Japanese Patent Application (No. 2018-217608) filed on Nov. 20, 2018, contents of which are incorporated herein by reference.
1 electric power steering device
3 steering wheel
4 steering mechanism
18 electric motor
40 microcomputer
41 current command value setting unit
43 angle deviation calculation unit
44 proportional-integral-derivative (PID) control unit
45 command value switching unit
46 current deviation calculation unit
47 proportional-integral (PI) control unit
48 PWM control unit
49 rotation angle calculation unit
50 reduction ratio division unit
51 gain setting unit
101 host ECU
102 motor control ECU
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-217608 | Nov 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/045224 | 11/19/2019 | WO | 00 |
