Electric power steering device

Abstract

The purpose of the present invention is to simply achieve both the responsiveness of control of an electric power steering device during normal steering and the suppression of noise effects in a state of keeping steering. An electric power steering device is provided with: a motor (20) for generating steering assist force applied to a steering system of a vehicle; a current command value calculation unit (40) that calculates a current command value for controlling the drive current of the motor (20); a current control unit (45) that outputs a first voltage command value on the basis of a current deviation between a measured value of a drive current of the motor and the current command value; a first gain setting unit (43) that sets a first gain corresponding to the rotational speed of the motor (20); a disturbance voltage suppression unit (47) that adds the output of the first delay element to a second voltage command value obtained by limiting the first voltage command value by a first gain, calculates a third voltage command value, and inputs the third voltage command value to the first delay element; and a drive circuit (48, 49) that drives the motor on the basis of the third voltage command value.

Description

Technical Field

[0001] The invention relates to an electric power steering device. Background Art

[0002] The electric power steering device described in Patent Document 1 below includes a steering assist motor that generates a steering assist force, sets a current command value based on a steering torque applied to a steering shaft of a vehicle, and controls the steering assist motor based on a current deviation between a detected value of a driving current of the steering assist motor and the current command value.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2010-47203 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In an electric power steering device that provides a steering assist force to a vehicle's steering system, noise, vibration, etc. may be generated due to noise contained in a control signal. In a state where the steering angle is kept unchanged, the generation of sound and vibration is likely to become noticeable, so it is preferable to suppress the influence of noise. For example, by configuring a noise reduction filter at the front stage and the rear stage of a feedback controller of the driving current of the steering assist motor, the influence of such noise can be suppressed.

[0008] On the other hand, during normal steering, the control responsiveness of the electric power steering device is required to be high. If a noise reduction filter such as the above is provided, it is necessary to switch the filter characteristics between normal steering and maintaining the steering state. As a result, the control becomes complicated, and the time and effort required for matching the filter characteristics increases.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to easily achieve both the responsiveness of control of an electric power steering device during normal steering and the suppression of the influence of noise while maintaining the steering state.

[0010] Means for solving problems

[0011] In order to achieve the above-mentioned purpose, an electric power steering device of one embodiment of the present invention comprises: a motor, which generates a steering assist force applied to a steering system of a vehicle; a current command value calculation unit, which calculates a current command value for controlling a driving current of the motor; a current control unit, which outputs a first voltage command value based on a current deviation of a measured value of the driving current of the motor relative to the current command value; a first gain setting unit, which sets a first gain corresponding to the rotational speed of the motor; an interference voltage suppression unit, which calculates a third voltage command value by adding an output of a first delay element to a second voltage command value obtained by limiting the first voltage command value with the first gain, and inputs the third voltage command value into the first delay element; and a drive circuit, which drives the motor based on the third voltage command value.

[0012] Effects of the Invention

[0013] According to the present invention, it is possible to easily achieve both the responsiveness of the control of the electric power steering device during normal steering and the suppression of the influence of noise while maintaining the steering state. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic structural diagram showing an example of an electric power steering device according to an embodiment.

[0015] Figure 2 Yes means Figure 1 A block diagram showing an example of the functional configuration of the controller described herein.

[0016] Figure 3 This is a block diagram showing an example of the functional configuration of a hold steering gain setting unit.

[0017] Figure 4 (a) and (b) are explanatory diagrams of an operation example of the steering gain setting unit.

[0018] Figure 5 This is a diagram showing an example of the characteristics of the rotation speed sensitive gain.

[0019] Figure 6 This is a block diagram showing an example of the functional configuration of the current control unit.

[0020] Figure 7 This is a block diagram showing an example of the functional configuration of the interference voltage suppression unit.

[0021] Figure 8 This is a flowchart of an example of a control method of the electric power steering device according to the embodiment.

[0022] Fig. 9 (a) and (b) are block diagrams showing an example of the functional configuration of a hold steering gain setting unit according to a modified example. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are described in detail with reference to the accompanying drawings. In addition, the embodiments of the present invention shown below illustrate devices and methods for implementing the technical ideas of the present invention, but the technical ideas of the present invention do not limit the structure and configuration of the components to the following contents. The technical ideas of the present invention can be modified in various ways within the technical scope specified by the technical solutions described in the claims.

[0024] (structure)

[0025] Figure 1 The schematic structural diagram of an example of an electric power steering device according to an embodiment is shown. A steering shaft (steering shaft, handle shaft) 2 of a steering wheel (steering handle) 1 is connected to steered wheels 8L, 8R via a reduction gear (worm gear) 3 constituting a reduction mechanism, universal joints 4a, 4b, a pinion rack mechanism 5, tie rods 6a, 6b, and further via hub units 7a, 7b.

[0026] The rack and pinion mechanism 5 includes a pinion 5a connected to a pinion shaft to which the steering force is transmitted from the universal joint 4b and a rack 5b meshing with the pinion 5a. The rack 5b converts the rotational motion transmitted to the pinion 5a into a linear motion in the vehicle width direction.

[0027] The steering shaft 2 is provided with a torque sensor 10 for detecting a steering torque Th. In addition, the steering shaft 2 is provided with a steering angle sensor 14 for detecting a steering angle θh of the steering wheel 1 .

[0028] A motor 20 assisting the steering force of the steering wheel 1 is connected to the steering shaft 2 via a reduction gear 3. A controller 30 controlling an electric power steering (EPS) device is supplied with power from a battery 13 and receives an ignition key signal via an ignition key 11.

[0029] In addition, the unit for applying the steering assist force is not limited to the motor, and various actuators can be used.

[0030] The controller 30 is an electronic control unit (ECU) that calculates a current command value for an auxiliary control command based on the steering torque Th detected by the torque sensor 10, the vehicle speed Vh detected by the vehicle speed sensor 12, and the steering angle θh detected by the steering angle sensor 14, and controls the current supplied to the motor 20 by obtaining a voltage command value Vref by compensating the current command value.

[0031] The steering angle sensor 14 is not necessarily required, and the steering angle θh may be calculated by adding the torsion angle of the torsion bar of the torque sensor 10 to the rotation angle obtained from the rotation angle sensor that detects the rotation angle of the rotation shaft of the motor 20 .

[0032] In addition, the steering angle of the steered wheels 8L, 8R may be used instead of the steering angle θh. For example, the steering angle may be detected by detecting the displacement of the rack 5b.

[0033] The controller 30 may include, for example, a computer including a processor and peripheral components such as a storage device. The processor may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit).

[0034] The storage device may include any of a semiconductor storage device, a magnetic storage device, and an optical storage device. The storage device may include a register, a cache memory, a ROM (Read Only Memory) used as a main storage device, and a RAM (Random Access Memory) and other memories.

[0035] The functions of the controller 30 described below are implemented, for example, by a processor of the controller 30 executing a computer program stored in a storage device.

[0036] Alternatively, the controller 30 may be formed by dedicated hardware for executing each information processing described below.

[0037] For example, the controller 30 may include a functional logic circuit set in a general-purpose semiconductor integrated circuit. For example, the controller 30 may include a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

[0038] Next, refer to Figure 2 , an example of the functional structure of the steering assist function based on the controller 30 is described. The controller 30 includes a current command value calculation unit 40, filters 41, 44, an angular velocity conversion unit 42, a steering gain setting unit 43, a current control unit 45, a voltage command value limiter 46, a disturbance voltage suppression unit 47, a PWM (Pulse Width Modulation) control unit 48, and an inverter (INV) 49.

[0039] The current command value calculation unit 40 calculates a basic current command value Iref, which is a current command value for controlling the drive current of the motor 20 , based on at least the steering torque Th and the vehicle speed Vh.

[0040] The filter 41 performs filtering processing on the basic current command value Iref, and outputs a current command value Iref1 in which noise included in the basic current command value Iref is reduced. The filter 41 may be, for example, a low-pass filter.

[0041] The angular velocity converter 42 acquires the rotation angle θm from the rotation angle sensor 21 that detects the rotation angle of the rotation shaft of the motor 20. The angular velocity converter 42 calculates the rotation speed ω of the motor 20 based on the temporal change of the rotation angle θm.

[0042] The holding steering gain setting unit 43 sets the holding steering gain G1 based on the rotation speed ω of the motor 20, and outputs the holding steering gain G1 to the current control unit 45 and the voltage command value limiting unit 46. The holding steering gain G1 is an example of the "first gain" described in the claims.

[0043] Figure 3 1 is a block diagram showing an example of the functional configuration of the hold steering gain setting unit 43. The hold steering gain setting unit 43 includes an absolute value calculation unit (abs) 50, a hold steering determination unit 51, a gain setting unit 52, a change rate limiter 53, a rotation speed sensitive gain setting unit 54, and a selector 55.

[0044] The absolute value calculation unit 50 calculates the absolute value |ω| of the rotation speed of the motor 20 .

[0045] The steering hold determination unit 51 determines whether the steering system of the vehicle is in the steering hold state based on the absolute value |ω| of the rotation speed of the motor 20 .

[0046] The steering hold state refers to a state in which the steering angle θh of the steering wheel 1 and the steering shaft 2 is hardly changed. For example, the steering hold determination unit 51 may determine that the steering system is in the steering hold state when the absolute value |ω| of the rotation speed of the motor 20 is less than the determination threshold ωth, and may determine that the steering system is not in the steering hold state when the absolute value |ω| is greater than the determination threshold ωth. The rotation speed ω may be obtained by using the steering angle θh instead of the rotation angle θm of the motor 20.

[0047] The gain setting unit 52 sets a hold-steering determination gain G2 corresponding to the determination result of the hold-steering determination unit 51. The hold-steering determination gain G2 is an example of the "second gain" described in the claims.

[0048] For example, the gain setting unit 52 may set the steering holding determination gain G2 to be smaller when it is determined that the steering system is in the steering holding state than when it is determined that the steering system is not in the steering holding state. That is, the gain setting unit 52 may set the steering holding determination gain G2 to a first value G21 when it is determined that the steering system is in the steering holding state, and set the steering holding determination gain G2 to a second value G22 greater than the first value G21 when it is determined that the steering system is not in the steering holding state. For example, the gain setting unit 52 sets the steering holding determination gain G2 to a value of "0" when it is determined that the steering system is in the steering holding state, and sets the steering holding determination gain G2 to a value of "1" when it is determined that the steering system is not in the steering holding state.

[0049] In addition, the gain setting unit 52 may delay the change of the steering hold determination gain G2 relative to the change in the state of the steering system when the state changes from the state determined that the steering system is not in the steering hold state to the state determined that the steering system is in the steering hold state. In addition, when the state changes from the state determined that the steering system is in the steering hold state to the state determined that the steering system is not in the steering hold state, the steering hold determination gain G2 may be changed immediately when the state of the steering system changes.

[0050] For example, when a predetermined delay time T0 has passed from the time when the state in which the steering system is determined not to be in the steering holding state changes to the time in which the steering system is determined to be in the steering holding state, the steering holding determination gain G2 may be changed from the second value G22 to the first value G21. In addition, when the state in which the steering system is determined to be in the steering holding state changes to the state in which the steering system is determined not to be in the steering holding state, the steering holding determination gain G2 may be immediately changed from the first value G21 to the second value G22.

[0051] The change rate limiter 53 limits the change rate of the steering hold determination gain G2. For example, the change rate limiter 53 limits the change rate so that the absolute value of the change rate of the steering hold determination gain G2 becomes less than a predetermined upper limit value. The change rate limiter 53 inputs the steering hold determination gain G2a with the limited change rate to the selector 55.

[0052] Reference Figure 4 (a) and Figure 4 (b) is used to illustrate an example of maintaining the steering determination gain G2a. Figure 4 (a) is a timing chart showing the temporal change of the rotation speed ω of the motor 20. Figure 4 The one-dot chain line in (b) is a timing chart showing the time change of the steering determination gain G2a.

[0053] During the period before time t1, the rotation speed ω of the motor 20 is greater than the determination threshold ωth, so the steering hold determination unit 51 determines that the steering system is not in the steering hold state. Therefore, the gain setting unit 52 sets the steering hold determination gain G2 to a value of "1". As a result, the steering hold determination gain G2a is also set to a value of "1".

[0054] When the rotation speed ω changes to be less than the determination threshold ωth at time t1, the steering hold determination unit 51 determines that the steering system is in the steering hold state. The gain setting unit 52 maintains the steering hold determination gain G2 at a value of "1" until the arrival of time t2 after a predetermined delay time T0 has passed from time t1, and changes the steering hold determination gain G2 to a value of "0" at time t2. The steering hold determination gain G2a, whose change rate is limited, starts to decrease from time t2, decreases at a limited change rate, and reaches a value of "0" at time t3.

[0055] When the rotation speed ω changes to be greater than the determination threshold ωth at time t4, the steering hold determination unit 51 determines that the steering system is not in the steering hold state. The gain setting unit 52 immediately sets the steering hold determination gain G2 to a value of "1". The steering hold determination gain G2a, whose change rate is limited, starts to increase from time t4, increases at a limited change rate, and reaches a value of "1" at time t5.

[0056] As described above, the gain setting unit 52 changes the steering holding determination gain G2 from the value "1" to the value "0" after the delay time T0 has passed, so the steering holding determination gain G2a changes with a delay relative to the change in the rotation speed of the motor 20. In addition, the change rate limiter 53 limits the change speed of the steering holding determination gain G2a, thereby the steering holding determination gain G2a changes with a delay relative to the change in the rotation speed of the motor 20. Therefore, the steering holding determination gain G2a is an example of the "first component that changes with a delay relative to the change in the rotation speed of the motor" described in the technical solution.

[0057] Reference Figure 3 The rotation speed sensitive gain setting unit 54 sets the rotation speed sensitive gain G3 that changes according to the absolute value |ω| of the rotation speed of the motor 20. The rotation speed sensitive gain G3 is an example of the “third gain” described in the claims.

[0058] Figure 5 Schematic diagram of an example of the characteristics of the speed-sensitive gain G3. The speed-sensitive gain G3 has a characteristic that it becomes smaller when the absolute value |ω| is small compared to when the absolute value |ω| is large. For example, the speed-sensitive gain G3 may have a characteristic that it becomes smaller as the absolute value |ω| is smaller. For example, the speed-sensitive gain G3 may have a characteristic that it maintains a constant value within a range where the absolute value |ω| is greater than the determination threshold value ωth.

[0059] exist Figure 5 In the example of the speed sensing gain G3, when the absolute value |ω| of the speed is "0", the speed sensing gain G3 is set to the value "0", and when the absolute value |ω| is greater than the value "0", the speed sensing gain G3 is set to a value greater than "0". In the range where the absolute value |ω| is greater than "0" and less than the determination threshold ωth, the larger the absolute value |ω| is, the larger the speed sensing gain G3 is.

[0060] The rotation speed sensitive gain G3 may change nonlinearly with respect to the change in the absolute value |ω|, or may change in proportion to the absolute value |ω| (that is, may change linearly).

[0061] In the range where the absolute value |ω| is equal to or greater than the determination threshold value ωth, it is maintained at a constant value "1".

[0062] The rotation speed sensitive gain G3 is an example of the “second component that changes in accordance with changes in the rotation speed of the motor” described in the claims.

[0063] The speed-sensitive gain G3 is not given a delay time T0 like the steering hold determination gain G2a, and the change speed is not limited by the change rate limiter. Therefore, the change of the speed-sensitive gain G3 has a very small delay (ideally no delay) relative to the change of the speed of the motor 20. Therefore, the speed-sensitive gain G3 changes with a delay smaller than the delay of the steering hold determination gain G2a in accordance with the change of the speed ω of the motor 20.

[0064] Reference Figure 3 The selector 55 selects the larger one of the steering hold determination gain G2a and the rotation speed sensing gain G3 and outputs it as the steering hold gain G1.

[0065] Figure 4 The dotted line in (b) represents the speed-sensitive gain G3, and the solid line represents the steering holding gain G1. Immediately after the speed ω of the motor 20 changes from a state above the determination threshold ωth to a state below the determination threshold ωth, the steering holding determination gain G2a is larger than the speed-sensitive gain G3 until a certain length of time has passed, and therefore the steering holding determination gain G2a is output as the steering holding gain G1.

[0066] Therefore, until a certain length of time has passed since the rotation speed ω of the motor 20 changes to a state smaller than the determination threshold ωth, the steering gain G1 is maintained to change with a delay relative to the change in the rotation speed of the motor 20. Therefore, even if the rotation speed ω temporarily becomes smaller than the determination threshold ωth, the steering gain G1 can be maintained at a certain level.

[0067] In the hold steering state, the speed ω is maintained to be less than the determination threshold ωth. Therefore, the hold steering determination gain G2a gradually decreases following the value "0" of the hold steering determination gain G2 set by the gain setting unit 52. When the hold steering determination gain G2a is less than the speed sensing gain G3, the speed sensing gain G3 is output as the hold steering gain G1. Thus, the hold steering gain G1 changes with a small delay relative to the change in the speed ω (or changes without delay relative to the speed ω). Therefore, when the driver starts steering and the speed ω increases, the hold steering gain G1 increases immediately.

[0068] Reference Figure 2 The filter 44 performs a filtering process on the measurement value Im of the drive current of the motor 20 detected by the motor current detector 22, and outputs a measurement value Im1 in which noise included in the measurement value Im is reduced. The filter 44 may be, for example, a low-pass filter.

[0069] The current control unit 45 calculates the basic voltage command value Vref0 based on the current deviation ΔI=( Iref1 − Im1 ) of the measured value Im1 of the drive current with respect to the current command value Iref1 .

[0070] For example, the current control unit 45 calculates the basic voltage command value Vref0 by at least one of proportional control (P control), integral control (I control) and differential control (D control) based on the current deviation ΔI or a combination thereof. That is, the current control unit 45 calculates the basic voltage command value Vref0 by feedback control based on the current deviation ΔI. The basic voltage command value Vref0 is an example of the "first voltage command value" described in the technical claim.

[0071] Figure 6 This is a block diagram showing an example of the functional configuration of the current control unit 45 when the basic voltage command value Vref0 is calculated by proportional integral derivative (PID) control. The current control unit 45 includes a subtractor 45a, gain multipliers 45b, 45d, 45f, an approximate differential unit 45c, an integrator 45e, and an adder 45g.

[0072] The subtractor 45 a calculates a current deviation ΔI=( Iref1 −Im1 ) of the measured value Im1 of the drive current with respect to the current command value Iref1 .

[0073] The gain multiplication unit 45b outputs the multiplication result of the current deviation ΔI and the proportional gain Kp to the adder 45g.

[0074] The approximate differential unit 45c calculates the differential value of the current deviation ΔI. For example, the approximate differential unit 45c can calculate the differential value by multiplying the current deviation ΔI by the transfer function s / (Ts+1) which is a combination of differential operation and low-pass filter. The gain multiplication unit 45d outputs the multiplication result of the differential value of the current deviation ΔI and the differential gain Kd to the adder 45g.

[0075] The integrator 45e calculates the integrated value of the current deviation ΔI. The gain multiplication unit 45f outputs the multiplication result of the integrated value of the current deviation ΔI and the integral gain Ki to the adder 45g. The integral gain Ki is an example of the "fourth gain" described in the claims.

[0076] The adder 45g outputs the sum of the multiplication result of the current deviation ΔI and the proportional gain Kp, the multiplication result of the differential value of the current deviation ΔI and the differential gain Kd, and the multiplication result of the integral value of the current deviation ΔI and the integral gain Ki as the basic voltage command value Vref0.

[0077] The integrator 45e includes a delay element 45e1, an adder 45e2, and a gain multiplication unit 45e3.

[0078] The delay element 45e1 delays the output of the integrator 45e and inputs it to the adder 45e2. That is, the delay element 45e1 inputs the past value (previous value) of the output of the integrator 45e to the adder 45e2. The delay element 45e1 is an example of the "second delay element" described in the claims.

[0079] The adder 45e2 outputs the sum of the current deviation ΔI and the output of the delay element 45e1. The gain multiplication unit 45e3 calculates the multiplication result of the gain corresponding to the hold steering gain G1 and the output of the adder 45e2 as the output of the integrator 45e.

[0080] The gain of the gain multiplication unit 45e3 multiplied by the output of the adder 45e2 may be, for example, a gain having a smaller value when the steering gain G1 is kept small than when the steering gain G1 is kept large. For example, the gain may be a gain having a smaller value as the steering gain G1 is kept small. For example, the gain multiplication unit 45e3 may multiply the output of the adder 45e2 by the steering gain G1 itself.

[0081] Reference Figure 2 The voltage command value limiting unit 46 calculates the intermediate voltage command value Vref1 by limiting the basic voltage command value Vref0 using the steering gain G1. For example, when the steering gain G1 is small, the voltage command value limiting unit 46 calculates a smaller intermediate voltage command value Vref1 than when the steering gain G1 is large.

[0082] For example, the voltage command value limiter 46 may be a multiplier that calculates the product of the basic voltage command value Vref0 and the steering gain G1 as the intermediate voltage command value Vref1. The intermediate voltage command value Vref1 is an example of the "second voltage command value" described in the claims.

[0083] The disturbance voltage suppression unit 47 suppresses the influence of the back electromotive force and other disturbance voltages on the intermediate voltage command value Vref1 to calculate the voltage command value Vref. The voltage command value Vref is an example of the "third voltage command value" described in the claims.

[0084] Figure 7 4 is a block diagram showing an example of the functional configuration of the interference voltage suppressing unit 47. The interference voltage suppressing unit 47 includes an adder 47a, a filter 47b, and a delay element 47c. The delay element 47c is an example of the "first delay element" described in the claims.

[0085] The adder 47a outputs the sum of the intermediate voltage command value Vref1 and the output of the delay element 47c.

[0086] The filter 47b reduces noise by filtering the sum of the intermediate voltage command value Vref1 and the output of the delay element 47c. For example, the filter 47b may be a low-pass filter. The output of the filter 47b is output from the interference voltage suppression unit 47 as the voltage command value Vref and input to the delay element 47c.

[0087] The delay element 47c delays the output of the filter 47b (ie, the voltage command value Vref) and inputs the delayed output to the adder 47a. That is, the delay element 47c inputs the past value (previous value) of the voltage command value Vref to the adder 47a.

[0088] Reference Figure 2 The voltage command value Vref is input to the PWM control unit 48 , and the motor 20 is PWM-driven via the inverter 49 . The drive current of the motor 20 is detected by the motor current detector 22 , and fed back to the subtractor 45 a of the current control unit 45 via the filter 44 .

[0089] In addition, the controller 30 can calculate the q-axis current command value as the torque generating component and the d-axis current command value as the magnetic field generating component as the current command value Iref1, and perform vector control to generate a voltage command value based on the deviation between the q-axis motor current detection value and the q-axis current command value, and the deviation between the d-axis motor current detection value and the d-axis current command value.

[0090] (effect)

[0091] Next, the operation of the electric power steering device according to the embodiment will be described. Figure 4 As shown in (b), the steering gain G1 set by the steering gain setting unit 43 has a characteristic that the steering gain G1 becomes smaller when the absolute value |ω| of the rotation speed of the motor 20 is small than when the absolute value |ω| of the rotation speed of the motor 20 is large. Therefore, the steering gain G1 is set to a smaller value in the steering state than in the normal steering. The voltage command value limiting unit 46 calculates the intermediate voltage command value Vref1 by limiting the basic voltage command value Vref0 using the steering gain G1.

[0092] Therefore, in the steering hold state, the intermediate voltage command value Vref1 becomes smaller. Therefore, it is possible to suppress the influence of the noise contained in the intermediate voltage command value Vref1 on the voltage command value Vref. As a result, in the steering hold state, it is possible to suppress the influence of the noise contained in the control signal of the electric power steering device. Thus, even if the filter characteristics of the filter 41 and the filter 44 are not switched between the normal steering and the steering hold state, it is possible to suppress the influence of the noise in the steering hold state.

[0093] Here, the disturbance voltage suppression unit 47 provided at the subsequent stage of the voltage command value limiting unit 46 has an integration function for accumulating the intermediate voltage command value Vref1 by adding the intermediate voltage command value Vref1 to the past value of the voltage command value Vref. Therefore, even if the intermediate voltage command value Vref1 decreases due to the state change of the steering system to the steering holding state, the voltage command value Vref for generating the steering assist force required for steering holding can be maintained by the integration function of the disturbance voltage suppression unit 47.

[0094] Furthermore, if the steering gain G1 is simply reduced when the absolute value |ω| of the rotation speed of the motor 20 decreases, the intermediate voltage command value Vref1 decreases every time the absolute value |ω| of the rotation speed becomes 0 during normal steering, so the steering assist force decreases and the driver may feel a sense of stuttering.

[0095] Therefore, if Figure 4 As shown in (b), even if the rotation speed ω of the motor 20 changes to be less than the determination threshold ωth, the magnitude of the steering gain G1 is maintained until a certain length of time has passed immediately after the change. This can prevent the occurrence of a stuttering feeling during the back-steering.

[0096] After that, the hold steering gain G1 is changed with a small delay relative to the change in the rotation speed ω. Thus, the hold steering gain G1 can be increased according to the steering of the steering wheel 1 and the steering shaft 2. As a result, the steering assist force can be output even when a small steering is performed during the hold steering. In addition, the output of the steering assist force can be immediately restarted when returning from the hold steering state to the normal steering state.

[0097] In addition, if Figure 6 As shown, when the feedback control of the current control unit 45 includes integral control, the basic voltage command value Vref0 output by the current control unit 45 is limited by the steering gain G1, thereby leaving the current deviation ΔI. Therefore, the integral value of the current deviation ΔI output from the integrator 45e increases (accumulates).

[0098] Therefore, the gain multiplication unit 45e3 multiplies the integrated value of the current deviation ΔI by a gain corresponding to the maintained steering gain G1 (or the maintained steering gain G1 itself). This can suppress an increase (accumulation) in the integrated value of the integrator 45e.

[0099] (action)

[0100] Figure 8 This is a flowchart of an example of a control method of the electric power steering device according to the embodiment.

[0101] In step S1 , the torque sensor 10 , the vehicle speed sensor 12 , the motor current detector 22 , and the rotation angle sensor 21 detect the steering torque Th, the vehicle speed Vh, the drive current Im, and the rotation angle θm of the motor 20 , respectively.

[0102] In step S2, the current command value calculation unit 40 calculates the basic current command value Iref. The filter 41 outputs the current command value Iref1 by reducing the noise of the basic current command value Iref.

[0103] In step S3 , the angular velocity converter 42 calculates the rotation speed ω of the motor 20 based on the temporal change in the rotation angle θm.

[0104] In step S4 , the holding steering gain setting unit 43 sets the holding steering gain G1 based on the rotation speed ω of the motor 20 .

[0105] In step S5, filter 44 calculates measured value Im1 of drive current by reducing noise included in measured value Im of drive current of motor 20. Current control unit 45 calculates basic voltage command value Vref0 based on current deviation ΔI of measured value Im1 of drive current with respect to current command value Iref1.

[0106] In step S6 , the voltage command value limiting unit 46 calculates the intermediate voltage command value Vref1 by limiting the basic voltage command value Vref0 by maintaining the steering gain G1 .

[0107] In step S7 , the disturbance voltage suppression unit 47 calculates the voltage command value Vref by suppressing the influence of the disturbance voltage on the intermediate voltage command value Vref1 .

[0108] In step S8 , the PWM control unit 48 and the inverter 49 drive the motor 20 based on the voltage command value Vref. Thereafter, the process ends.

[0109] (Variation Example)

[0110] Fig. 9 (a) and Fig. 9 (b) is a block diagram showing an example of the functional structure of the maintenance steering gain setting unit 43 of the modified example. The maintenance steering gain setting unit 43 can compare the delayed speed signal after delaying the speed ω of the motor 20 with the speed ω of the motor 20, and set the gain corresponding to the higher speed among these speeds as the maintenance steering gain G1.

[0111] For example Fig. 9 The steering gain setting unit 43 of (a) includes an absolute value calculation unit (abs) 50 , a low-pass filter (LPF) 60 , a selector 61 , and a rotation speed sensitive gain setting unit 62 .

[0112] The absolute value calculation unit 50 calculates the absolute value |ω| of the rotation speed of the motor 20 , and inputs the absolute value to the low-pass filter 60 and the selector 61 .

[0113] The low-pass filter 60 performs low-pass filtering on the absolute value |ω| of the rotation speed. The low-pass filter 60 inputs the rotation speed signal ω1 after the filtering process to the selector 61. The low-pass filter 60 functions as a delay element that delays the absolute value |ω| of the rotation speed.

[0114] The selector 61 selects the larger one of the absolute value |ω| of the rotation speed and the rotation speed signal ω1 and inputs the larger one to the rotation speed sensitive gain setting unit 62 .

[0115] The rotation speed sensitive gain setting unit 62 sets the holding steering gain G1 corresponding to the output of the selector 61. The characteristics of the holding steering gain G1 set by the rotation speed sensitive gain setting unit 62 may be, for example, Figure 5 The same characteristics as described above are obtained for the speed sensing gain G3.

[0116] In addition, for example Fig. 9 The hold steering gain setting unit 43 of (b) includes an absolute value calculation unit (abs) 50 , a hold steering determination unit 51 , a delay element 63 , a change rate limiter 64 , a selector 61 , and a rotation speed sensitive gain setting unit 62 .

[0117] The steering hold determination unit 51 determines whether the steering system of the vehicle is in the steering hold state based on whether the absolute value |ω| of the rotation speed of the motor 20 is smaller than a determination threshold value ωth.

[0118] When the state in which the steering system is determined not to be in the steering holding state changes to the state in which the steering system is determined to be in the steering holding state, the delay element 63 outputs the rotation speed signal ω2 in which the absolute value |ω| of the rotation speed is delayed.

[0119] For example, when the steering system changes from being determined not to be in the steering holding state to being determined to be in the steering holding state, the delay element 63 may maintain the output value at the time when the state of the steering system changes to the steering holding state for a predetermined delay time T0.

[0120] The change rate limiter 64 limits the change rate of the rotation speed signal ω2. For example, the change rate limiter 53 limits the change rate so that the absolute value of the change rate of the rotation speed signal ω2 becomes less than a predetermined upper limit. The change rate limiter 53 inputs the rotation speed signal ω3 with the limited change rate to the selector 61.

[0121] The selector 61 selects the larger one of the absolute value |ω| of the rotation speed and the rotation speed signal ω3 and inputs the larger one to the rotation speed sensitive gain setting unit 62 .

[0122] The rotation speed sensitive gain setting unit 62 sets the holding steering gain G1 corresponding to the output of the selector 61. The characteristics of the holding steering gain G1 set by the rotation speed sensitive gain setting unit 62 may be, for example, Figure 5 The same characteristics as described above are obtained for the speed sensing gain G3.

[0123] (Effects of Embodiments)

[0124] (1) It comprises: a motor that generates a steering assist force applied to a steering system of a vehicle; a current command value calculation unit that calculates a current command value for controlling a drive current of the motor; a current control unit that outputs a first voltage command value based on a current deviation of a measured value of the drive current of the motor relative to the current command value; a first gain setting unit that sets a first gain corresponding to a rotation speed of the motor; an interference voltage suppression unit that calculates a third voltage command value by adding an output of a first delay element to a second voltage command value obtained by limiting the first voltage command value by the first gain, and inputs the third voltage command value into the first delay element; and a drive circuit that drives the motor based on the third voltage command value.

[0125] Thus, by limiting the first voltage command value by the first gain in the steering hold state, the influence of the noise contained in the first voltage command value on the steering assist force can be suppressed. Therefore, the control responsiveness of the electric power steering device during normal steering and the suppression of the influence of noise in the steering hold state can be easily achieved at the same time.

[0126] Furthermore, the disturbance voltage suppression unit has a function of integrating the second voltage command value, thereby being able to maintain the steering assist force required to maintain the steering.

[0127] (2) The first gain setting unit may set the first gain based on a larger component of a first component that changes with a delay relative to a change in the rotational speed of the motor and a second component that changes in response to a change in the rotational speed of the motor. For example, the second component may be a component that changes with a delay smaller than that of the first component in response to a change in the rotational speed of the motor.

[0128] Thus, it is possible to prevent a sense of stuttering during the return steering and to output a steering assist force for a small steering during the steering maintenance. In addition, when returning to the normal steering state from the steering maintenance state, the output of the steering assist force can be immediately restarted.

[0129] (3) The first gain setting unit may include: a second gain setting unit that sets the second gain based on the rotation speed of the motor and whether the steering system is in a steering hold state; and a change rate limiter that limits a change rate of the second gain and outputs the second gain as the first component.

[0130] Thereby, it is possible to generate the first component that changes with a delay relative to the change in the rotation speed of the motor.

[0131] (4) The second gain setting unit may delay the change of the second gain when the state of the steering system changes from a state not in the steering hold state to the steering hold state.

[0132] Thereby, it is possible to generate the first component that changes with a delay relative to the change in the rotation speed of the motor.

[0133] (5) The first gain setting unit may include a low-pass filter that performs low-pass filtering on the rotation speed of the motor to output the first component.

[0134] Thereby, it is possible to generate the first component that changes with a delay relative to the change in the rotation speed of the motor.

[0135] (6) The first gain setting unit may include: a third gain setting unit that sets a third gain corresponding to the rotation speed of the motor; and a selector that selects a larger one of the first component and the third gain as the first gain.

[0136] Alternatively, the first gain setting unit may include: a selector that selects and outputs a larger one of the first component and the second component; and a gain setting unit that sets a gain corresponding to the output of the selector as the first gain.

[0137] Thus, the first gain can be set based on the larger component of the first component that changes with a delay relative to the change in the rotation speed of the motor and the second component that changes in accordance with the change in the rotation speed of the motor.

[0138] (7) The current control unit may output a first voltage command value including an integral component proportional to the integral of the current deviation, and the integral component may be suppressed by a first gain. For example, the current control unit may include: an integrator that multiplies the sum of the current deviation and the output of the second delay element by a gain corresponding to the first gain to calculate the integral value of the current deviation, and inputs the integral value to the second delay element; and a multiplier that multiplies the output of the integrator by a fourth gain to calculate the integral component.

[0139] Thus, even if a current deviation of the measured value of the motor drive current relative to the current command value remains due to the first voltage command value output by the current control unit being limited by the first gain, an increase (accumulation) in the integrated value of the integrator can be suppressed.

[0140] Description of Reference Numerals

[0141] 1…steering wheel, 2…steering shaft, 3…reduction gear, 4a, 4b…universal joint, 5…pinion-rack mechanism, 5a…pinion, 5b…rack, 6a, 6b…tie rod, 7a, 7b…hub unit, 8L, 8R…steering wheel, 10…torque sensor, 11…ignition key, 12…vehicle speed sensor, 13…battery, 14…steering angle sensor, 20…motor, 21…rotation angle sensor, 22…motor current detector, 30…controller, 40…current command value calculation unit, 41, 44, 47b…filter, 42…angular velocity conversion unit, 43…steering gain setting unit, 45…current control unit, 45a…subtractor, 45b, 45d, 45e3, 45f…gain multiplication unit, 45c…approximate differential unit, 45e…integrator, 45e1, 47c, 63…delay element, 45e2, 45g, 47a…adder, 46…voltage command value limiting unit, 47…interference voltage suppression unit, 48…PWM control unit, 49…inverter, 50…absolute value operation unit, 51…steering direction holding determination unit, 52…gain setting unit, 53, 64…rate of change limiter, 54, 62…speed sensing gain setting unit, 55, 61…selector, 60…low-pass filter.

Claims

1. An electric power steering device, characterized in that: The electric power steering device comprises: a motor that generates a steering assist force applied to a steering system of the vehicle; a current command value calculation unit for calculating a current command value for controlling a drive current of the motor; a current control unit that outputs a first voltage command value based on a current deviation of a measured value of a drive current of the motor relative to the current command value; a first gain setting unit configured to set a first gain corresponding to a rotation speed of the motor; a disturbance voltage suppression unit that adds an output of the first delay element to a second voltage command value obtained by limiting the first voltage command value by the first gain to calculate a third voltage command value, and inputs the third voltage command value to the first delay element; as well as A drive circuit drives the motor based on the third voltage command value.

2. The electric power steering device according to claim 1, characterized in that: The first gain setting unit sets the first gain based on a larger component of a first component that changes with a delay relative to a change in the rotation speed of the motor and a second component that changes in accordance with a change in the rotation speed of the motor.

3. The electric power steering device according to claim 2, characterized in that: The second component changes in accordance with a change in the rotation speed of the motor with a delay smaller than a delay of the first component.

4. The electric power steering device according to claim 2, characterized in that: The first gain setting unit comprises: a second gain setting unit that sets a second gain based on the rotation speed of the motor and in accordance with whether the steering system is in a steering hold state; and A change rate limiter limits a change speed of the second gain and outputs the second gain as the first component.

5. The electric power steering device according to claim 4, characterized in that: The second gain setting unit delays a change in the second gain when the state of the steering system changes from a state that is not in the steering hold state to the steering hold state.

6. The electric power steering device according to claim 2, characterized in that: The first gain setting unit includes a low-pass filter that performs low-pass filtering on the rotation speed of the motor to output the first component.

7. The electric power steering device according to any one of claims 2 to 6, characterized in that: The first gain setting unit comprises: a third gain setting unit that sets a third gain corresponding to the rotation speed of the motor; and A selector selects a larger one of the first component and the third gain as the first gain.

8. The electric power steering device according to any one of claims 2 to 6, characterized in that: The first gain setting unit comprises: A selector that selects and outputs a larger one of the first component and the second component; and A gain setting unit sets a gain corresponding to the output of the selector as the first gain.

9. The electric power steering device according to claim 1, characterized in that: The current control unit outputs the first voltage command value including an integral component proportional to an integral of the current deviation, and the integral component is suppressed by the first gain.

10. The electric power steering device according to claim 9, characterized in that: The current control unit comprises: an integrator that multiplies a sum of the current deviation and an output of the second delay element by a gain corresponding to the first gain to calculate an integrated value of the current deviation, and inputs the integrated value into the second delay element; as well as A multiplier is provided for multiplying the output of the integrator by a fourth gain to calculate the integral component.

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