JP2013244798A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of inhibiting generation of vibration and noise.SOLUTION: A control gain setting section 58 variably sets a gain (proportional gain) Kof a proportional element 55a and a gain (integral gain) Kof an integral element 55b in a PI control section 55 on the basis of steering torque Th, a mechanical angle θand a q-axis detection current Ito thereby vary control responsiveness. Specifically, the control gain setting section 58 determines whether or not in a transmission error occurring region and, when determining to be in the transmission error occurring region, deteriorates control responsiveness of an electric motor 19. With this, generation of vibration and noise in the transmission error occurring region is inhibited.

Description

  The present invention relates to an electric power steering apparatus.

As an electric power steering device (EPS), there is a dual pinion type electric power steering device (DP-EPS). The dual pinion type electric power steering apparatus includes a steering member such as a steering wheel, a steering mechanism that steers the steered wheels in conjunction with rotation of the steering member, and a steering assist mechanism that assists the driver's steering. It has.
The steered mechanism includes a first pinion shaft that rotates according to the rotation of the steering member, and a rack shaft that extends along the left-right direction of the automobile. A steered wheel is connected to each end of the rack shaft via a tie rod and a knuckle arm. A first pinion is connected to the tip of the first pinion shaft. A first rack that meshes with the first pinion is formed on the rack shaft. The rotation of the pinion shaft is converted into the axial movement of the rack shaft by the first rack and pinion mechanism including the first pinion and the first rack. The steered wheels are steered by moving the rack shaft in the axial direction.

  The steering assist mechanism is coupled to a steering assist electric motor, a second pinion shaft to which torque of the electric motor is transmitted via a coupling (shaft coupling) and a speed reduction mechanism, and a tip of the second pinion shaft. A second pinion and a second rack provided on the rack shaft and meshing with the second pinion. The coupling is for connecting the drive shaft of the electric motor and the input shaft of the speed reduction mechanism. When the second pinion is rotated by the electric motor, the rotation of the pinion shaft is converted into the axial movement of the rack shaft by the second rack and pinion mechanism including the second pinion and the second rack. Thereby, a steered wheel is steered.

Japanese Patent Laid-Open No. 08-91236

  In the conventional dual pinion type electric power steering device as described above, a power transmission device such as a coupling, a speed reduction mechanism, and a second rack and pinion mechanism is interposed between the electric motor and the rack shaft. Each of these power transmission devices has play (backlash). For this reason, when the rotation of the electric motor is started from a state where the steering member such as the steering wheel is not operated, a rotation angle region in which the motor torque is not accurately transmitted to the rack shaft occurs immediately after the rotation is started. In this rotation angle region, vibration and abnormal noise are likely to occur. In particular, if the control responsiveness of the electric motor is increased in order to improve the performance of the electric power steering device, sensor noise and the like are easily amplified, and thus vibration and abnormal noise are likely to occur in the rotation angle region.

  An object of the present invention is to provide an electric power steering apparatus capable of suppressing the occurrence of vibration and abnormal noise.

  In order to achieve the above object, the invention according to claim 1 is characterized in that the turning shaft (15) is driven from the electric motor (19) via at least one power transmission device (20; 21; 23, 24) having play. An electric power steering device (1) for applying a steering assist force to the electric motor, a current command value setting means (51) for setting a current command value of the electric motor, and a current for detecting a motor current flowing in the electric motor Detection means (33, 53) and feedback control means for feedback-controlling the electric motor so that the detected current value detected by the current detection means approaches the current command value set by the current command value setting means (54, 55) and a rotation angle change amount calculation for calculating a rotation angle change amount of the electric motor from the most recent non-steering state in which the steering member (2) is not operated. When the absolute value of the rotation angle change amount calculated by the stage (52, 58) and the rotation angle change amount calculation means is equal to or less than a predetermined rotation amount (α) set in advance, the control of the feedback control means An electric power steering apparatus including responsiveness reducing means (55, 58; 59, 60) for reducing responsiveness. In addition, although the alphanumeric character in parentheses represents a corresponding component in an embodiment described later, of course, the scope of the present invention is not limited to the embodiment. The same applies hereinafter.

  Since the steering assist force is applied from the electric motor to the steered shaft via at least one power transmission device having play, when the rotation of the electric motor is started from the state where the steering member is not operated, immediately after the rotation starts In this case, a rotation angle region (transmission error generation region) is generated in which the motor torque is not accurately transmitted to the steering shaft. In the present invention, when the amount of change in the rotation angle of the electric motor from the most recent non-steering state where the steering member is not operated is equal to or less than a predetermined rotation amount set in advance, the control responsiveness of the feedback control means is reduced. Can do. Thereby, since it becomes possible to reduce the control responsiveness of the electric motor in the transmission error occurrence region, it is possible to suppress the occurrence of vibration and noise.

  According to a second aspect of the present invention, the predetermined rotation amount is a rotation amount of the electric motor corresponding to a total amount of play of the power transmission device existing between the electric motor and the steered shaft. The electric power steering apparatus according to Item 1. According to this configuration, since the control response of the electric motor can be lowered in the transmission error occurrence region, it is possible to suppress the occurrence of vibration and abnormal noise.

According to a third aspect of the present invention, the responsiveness reducing means is configured to reduce the responsiveness of the feedback control means by changing a control gain (K _P , K _I ) of the feedback control means. The electric power steering apparatus according to claim 1 or 2.
According to a fourth aspect of the present invention, the responsiveness reducing means has an absolute value of the rotation angle change amount calculated by the rotation angle change amount calculation means being equal to or less than a predetermined rotation amount (α) set in advance. 2. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is configured to reduce responsiveness of the feedback control unit when a motor torque of the electric motor is equal to or less than a predetermined torque (β).

It is a mimetic diagram showing a schematic structure of an electric power steering device concerning one embodiment of the present invention. FIG. 2 is a schematic diagram showing an electrical configuration of the ECU as the motor control device. FIG. 3 is an illustrative view for explaining the configuration of the electric motor. FIG. 4 is a graph showing a setting example of the q-axis current command value with respect to the detected steering torque. FIG. 5 is a graph schematically showing an example of a change in the handle torque with respect to the handle rotation angle obtained by the experiment. FIG. 6 is a flowchart showing the operation of the control gain setting unit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention.
The electric power steering apparatus 1 includes a steering wheel 2 as a steering member, a steering mechanism 4 that steers the steered wheels 3 in conjunction with the rotation of the steering wheel 2, and steering assistance for assisting the driver's steering. And a mechanism 5. The steering wheel 2 and the steering mechanism 4 are mechanically coupled via a steering shaft 6 and an intermediate shaft 7.

  The steered mechanism 4 includes a first pinion shaft 14 and a rack shaft 15 as a steered shaft. The steered wheel 3 is connected to each end of the rack shaft 15 via a tie rod 16 and a knuckle arm (not shown). The first pinion shaft 14 includes an input shaft 8 connected to the intermediate shaft 7 and an output shaft 9 connected to the input shaft 8 via a torsion bar 10. A first pinion 17 is connected to the tip of the output shaft 9 (the lower end in FIG. 1). When the steering wheel 2 is rotated, the input shaft 8 and the output shaft 9 rotate in the same direction while rotating relative to each other.

A torque sensor 11 is disposed around the first pinion shaft 14. The torque sensor 11 detects the steering torque applied to the steering wheel 2 based on the relative rotational displacement amount of the input shaft 8 and the output shaft 9. The steering torque detected by the torque sensor 11 is input to an ECU (Electronic Control Unit) 13.
The rack shaft 15 extends linearly along the left-right direction of the automobile (direction orthogonal to the straight-ahead direction). A first rack 18 that meshes with the first pinion 17 is formed on the first end side in the axial direction of the rack shaft 15. The first pinion 17 and the first rack 18 constitute first rack and pinion mechanisms 17 and 18. The first rack and pinion mechanisms 17 and 18 convert the rotation of the first pinion shaft 14 into the axial movement of the rack shaft 15. The steered wheels 3 can be steered by moving the rack shaft 15 in the axial direction.

When the steering wheel 2 is steered (rotated), this rotation is transmitted to the first pinion shaft 14 via the steering shaft 6 and the intermediate shaft 7. The rotation of the first pinion shaft 14 is converted into axial movement of the rack shaft 15 by the first rack and pinion mechanisms 17 and 18. Thereby, the steered wheel 3 is steered.
The steering assist mechanism 5 includes a steering assist electric motor 19, a coupling (shaft coupling) 20, a speed reduction mechanism 21, a second pinion shaft 22, a second pinion 23, and a second rack 24. Including. The coupling 20 connects the drive shaft of the electric motor 19 and the input shaft (worm shaft) of the speed reduction mechanism 21. The speed reduction mechanism 21 includes a worm shaft connected to the drive shaft of the electric motor 19 by the coupling 20 and a worm wheel that is rotatably connected to the second pinion shaft 22 and meshes with the worm shaft. The second pinion 23 is connected to the tip (the lower end in FIG. 1) of the second pinion shaft 22. The second rack 24 is provided on the second end side in the axial direction of the rack shaft 15 and meshes with the second pinion 23. Second rack and pinion mechanisms 23 and 24 are configured by the second pinion 23 and the second rack 24. In this embodiment, the electric motor 19 is a three-phase brushless motor.

  When the electric motor 19 is driven to rotate, the rotation of the electric motor 19 is transmitted to the second pinion shaft 22 via the coupling 20 and the speed reduction mechanism 21. The rotation of the second pinion shaft 22 is converted into the axial movement of the rack shaft 15 by the second rack and pinion mechanisms 23 and 24. Thereby, the steered wheel 3 is steered. In other words, the steered wheels 3 are steered by rotating the second pinion shaft 22 by the electric motor 19.

The rotation angle of the rotor of the electric motor 19 is detected by a rotation angle sensor 25 such as a resolver. An output signal of the rotation angle sensor 25 is input to the ECU 13.
The electric motor 19 is controlled by the ECU 13 as a motor control device. The ECU 13 controls the electric motor 19 based on the output signal of the rotation angle sensor 25 and the steering torque detected by the torque sensor 11.

FIG. 2 is a schematic diagram showing an electrical configuration of the ECU 13 as a motor control device.
The ECU 13 drives the electric motor 19 according to the output signal of the rotation angle sensor 25 and the steering torque Th detected by the torque sensor 11, thereby realizing appropriate steering assistance according to the steering situation.
The ECU 13 detects a current flowing in the microcomputer 31, a drive circuit (three-phase inverter circuit) 32 that is controlled by the microcomputer 31 and supplies electric power to the electric motor 19, and a stator winding of each phase of the electric motor 19. Current detecting section 33 for performing the above operation.

As schematically shown in FIG. 3, the electric motor 19 includes a rotor 41 as a magnetic field and a stator 42 including U-phase, V-phase, and W-phase field windings 19U, 19V, and 19W. . Three-phase fixed coordinates (UVW coordinate system) are defined with the U, V, and W axes in the direction of the field windings 19U, 19V, and 19W of each phase. Also, a two-phase rotational coordinate system (dq coordinate system) in which the d axis (magnetic pole axis) is taken in the magnetic pole direction of the rotor 41 and the q axis (torque axis) is taken in the direction perpendicular to the d axis in the rotation plane of the rotor 41. The actual rotating coordinate system) is defined. The dq coordinate system is a rotating coordinate system that rotates with the rotor 41. In the dq coordinate system, since only the q-axis current contributes to the torque generation of the rotor 41, the d-axis current may be set to zero and the q-axis current may be controlled according to the desired torque. A rotation angle (rotor angle (electrical angle)) θ _E of the rotor 41 is a rotation angle of the d axis with respect to the U axis. The dq coordinate system is an actual rotating coordinate system according to the rotor angle θ. With the use of the rotor angle theta _E, coordinate conversion may be made between the UVW coordinate system and the dq coordinate system.

The drive circuit 32 is composed of a three-phase inverter circuit including a plurality of switching elements. The current detection unit 33 detects the U-phase current I _U , the V-phase current I _V, and the W-phase current I _W (hereinafter collectively referred to as “three-phase detection current I _UVW ”) of the electric motor 19. To do.
The microcomputer 31 includes a CPU and a memory (ROM, RAM, etc.), and functions as a plurality of function processing units by executing a predetermined program. The plurality of function processing units include a current command value setting unit 51, a rotation angle calculation unit 52, a UVW / dq conversion unit 53, a current deviation calculation unit 54, a PI (proportional integration) control unit 55, and a dq. A / UVW conversion unit 56, a PWM control unit 57, and a control gain setting unit 58 are included.

Based on the detected steering torque Th detected by the torque sensor 11, the current command value generation unit 51 sets a current command value that is a command value of a current that should flow through the electric motor 19. Specifically, the current command value setting unit 51 refers to a d-axis current command value I _d ^* and a q-axis current command value I _q ^* (hereinafter referred to as “two-phase current command value I _dq ^* ”). ) Is generated. More specifically, the current command value generation unit 51 sets the q-axis current command value I _q ^* to a significant value and sets the d-axis current command value I _d ^* to zero.

More specifically, the current command value setting unit 51 based on the map storing the relationship between the detected steering torque and q-axis current command value I _q ^*, setting a q-axis current command value I _q ^*. FIG. 4 is a graph showing a setting example of the q-axis current command value I _q ^* with respect to the detected steering torque.
For the detected steering torque Th, for example, the torque for steering in the left direction is a positive value, and the torque for steering in the right direction is a negative value. The q-axis current command value I _q ^* is a positive value when assist torque for leftward steering is generated by the electric motor 19, and when assist torque for rightward steering is generated by the electric motor 19. Negative value.

The q-axis current command value I _q ^* takes a positive value for a positive value of the detected steering torque Th and takes a negative value for a negative value of the detected steering torque Th. When the detected steering torque Th is a minute value in the range of -Th1 to Th1, the q-axis current command value _Iq ^* is set to zero. In a region where the detected steering torque T is outside the range of -Th1 to Th1, the q-axis current command value I _q ^* is set such that the absolute value thereof increases as the absolute value of the detected steering torque T increases. ing. The two-phase current command value I _dq ^* set by the current command value setting unit 51 is given to the current deviation calculation unit 54.

The rotation angle calculation unit 52 calculates the rotation angle of the rotor of the electric motor 19 (the electrical angle θ _-E and the mechanical angle θ _{M based} on the neutral position) based on the output signal of the rotation angle sensor 25.
The UVW / dq converter 53 converts the three-phase detection current I _UVW (U-phase current I _U , V-phase current I _V and W-phase current I _W ) in the UVW coordinate system detected by the current detection unit 33 into the dq coordinate system. _Are converted into two-phase detection currents I _d and I _q (hereinafter collectively referred to as “two-phase detection current I _dq ”). These are supplied to the current deviation calculation unit 54. The coordinate transformation in UVW / dq converter 53, computed by the rotation angle calculation unit 52 an electrical angle theta _E is used.

The current deviation calculation unit 54 calculates a deviation between the two-phase current command value I _dq ^* set by the current command value setting unit 51 and the two-phase detection current I _dq given from the UVW / dq conversion unit 53. More specifically, the current deviation calculation unit 54 calculates the deviation of the d-axis detection current I _d with respect to the d-axis current command value I _d ^* and the deviation of the q-axis detection current I _q with respect to the q-axis current command value I _q ^* . To do. These deviations are given to the PI control unit 55.

The PI control unit 55 performs a PI calculation for each current deviation calculated by the current deviation calculation unit 54, thereby performing a two-phase voltage command value V _dq ^* (d-axis voltage command value V _d ^*) to be applied to the electric motor 19 ^. And q-axis voltage command value V _q ^* ). The two-phase voltage command value V _dq ^* is given to the dq / UVW conversion unit 56.
More specifically, the PI control unit 55 includes a proportional element 55a, an integral element 55b, and an adder 55c. However, _{K P} is a proportional gain, _{K I} is an integral gain, 1 / s is an integration operator. The calculation results of the proportional element 55a and the integral element 55b are added by the adder 55c, whereby the two-phase voltage command value V _dq ^* is obtained.

The dq / UVW conversion unit 56 converts the two-phase voltage command value V _dq ^* into a three-phase voltage command value V _UVW ^* . The coordinate transformation, computed by the rotation angle calculation unit 52 an electrical angle theta _E is used. The three-phase voltage command value V _UVW ^* includes a U-phase voltage command value V _U ^* , a V-phase voltage command value V _V ^*, and a W-phase voltage command value V _W ^* . This three-phase voltage command value V _UVW ^* is given to the PWM control unit 57.

The PWM controller 57 is a U-phase PWM (Pulse Width Modulation) control signal having a duty corresponding to the U-phase voltage command value V _U ^* , the V-phase voltage command value V _V ^*, and the W-phase voltage command value V _W ^* , V A phase PWM control signal and a W phase PWM control signal are generated. Further, the PWM control unit 57 performs on / off control of each switching element in the drive circuit 32 based on these PWM control signals. As a result, a voltage corresponding to the three-phase voltage command value V _UVW ^* is applied to the field windings 19U, 19V, 19W of each phase of the electric motor 19.

The current deviation calculation unit 54 and the PI control unit 55 constitute a current feedback control unit. By the action of the current feedback control means, the current flowing through the electric motor 19 is controlled so as to approach the two-phase current command value I _dq ^* set by the current command value setting unit 51.
The control gain setting unit 58 receives the steering torque Th detected by the torque sensor 11, the mechanical angle θ _M calculated by the rotation angle calculation unit 52, and the q-axis detection current I _q obtained by the UVW / dq conversion unit 53. To do. The mechanical angle θ _M is the rotation amount (rotation angle) of the rotor in both forward and reverse directions with respect to the neutral position. The rotation amount from the neutral position to the left steering direction is a positive value, and the right steering is performed from the neutral position. The amount of rotation in the direction is a negative value. Control gain setting unit 58, the steering torque Th, based on the mechanical angle theta _M and q-axis detected current _{I q,} the gain of the proportional element 55a in the PI control unit 55 (proportional gain) _{K P} and integral element 55b of the gain ( the integral gain) K _I variably set, thereby changing the control response.

  The concept of gain control by the control gain setting unit 58 will be described. As shown in FIG. 1, a power transmission device such as a coupling 20, a speed reduction mechanism 21, and second rack and pinion mechanisms 23 and 24 are interposed between the electric motor 19 and the rack shaft 15. These power transmission devices have play (backlash). For this reason, when the rotation of the electric motor 19 is started from a state where the steering wheel 2 is not operated (hereinafter referred to as “non-steering state”), the motor torque is not accurately transmitted to the rack shaft 15 immediately after the rotation is started. A rotation angle region (hereinafter referred to as “transmission error generation region”) occurs. This transmission error generation region corresponds to the amount of rotation of the electric motor 19 corresponding to the total amount of play of the power transmission device interposed between the electric motor 19 and the rack shaft 15.

  In the transmission error occurrence region, vibration and noise are likely to occur. In particular, if the control responsiveness of the electric motor is increased in order to improve the performance of the electric power steering apparatus, sensor noise and the like are easily amplified, so that vibration and abnormal noise are likely to occur in the transmission error occurrence region. Therefore, the control gain setting unit 58 determines whether or not it is a transmission error generation region, and when it is determined that it is a transmission error generation region, the control responsiveness of the electric motor 19 is reduced. This suppresses the occurrence of vibration and abnormal noise in the transmission error occurrence region.

  In order to determine whether or not it is a transmission error generation region, the rotation amount (rotation angle) of the rotor corresponding to the transmission error generation region (hereinafter referred to as “first threshold value α”) and the transmission error generation region are overcome. The minimum required motor torque (hereinafter referred to as “second threshold value β”) is obtained in advance through experiments, for example, and set in the control gain setting unit 58. This experiment is performed as follows, for example.

  The electric motor 19 is removed from the electric power steering device 1. As a tool for rotating the worm shaft of the speed reduction mechanism 21, a handle having the same type of member as one member of the coupling 20 attached to the drive shaft of the electric motor 19 is prepared. With the rack shaft 15 fixed so as not to move in the axial direction, the worm shaft of the speed reduction mechanism 21 is rotated, for example, in the left steering direction using the handle. At this time, the rotation angle of the handle and the rotation torque of the handle (hereinafter referred to as “handle torque”) are measured. Continue measuring until you can no longer rotate the handle. A similar experiment is performed when the steering wheel is rotated in the right steering direction.

  FIG. 5 is a graph schematically showing an example of a change in the handle torque with respect to the handle rotation angle obtained by the experiment. Assuming that the rotation angle position of the handle at the start of the experiment is the reference position Ps, in FIG. 5, the horizontal axis indicates the rotation amount (handle rotation angle) [deg] of the handle from the reference position Ps, and the vertical axis indicates the handle torque. Represents. A broken line L in FIG. 5 represents a change in the handle torque with respect to the steering wheel rotation angle when the handle is rotated in the left steering direction from the reference position Ps. A broken line R in FIG. 5 represents the handle in the right steering direction from the reference position Ps. A change in handle torque with respect to the handle rotation angle when the handle is rotated is shown.

  When the handle is rotated in the left steering direction from the reference position Ps, first, an area where the handle torque does not increase with respect to an increase in the rotation angle of the handle appears due to the play of the coupling 20. Next, an area where the handle torque does not increase with respect to the increase in the rotation angle of the handle appears due to the play of the speed reduction mechanism 21. Next, an area where the handle torque does not increase with respect to an increase in the rotation angle of the handle appears due to the influence of the second rack and pinion mechanisms 23 and 24. Next, after a region where the handle torque increases linearly with respect to the increase in the rotation angle of the handle appears, the handle stops rotating.

The value of the rotation angle of the steering wheel (the amount of rotation of the steering wheel from the reference position Ps) at the time when the region where the steering torque increases linearly with respect to the increase in the rotation angle of the steering wheel is set as the first threshold value α. Is set as the second threshold value β.
The change in the handle torque relative to the handle rotation angle when the handle is rotated in the right steering direction from the reference position Ps is the same as that in the case where the handle is rotated in the right steering direction from the reference position Ps. To do.

FIG. 6 is a flowchart showing the operation of the control gain setting unit. The process of FIG. 6 is repeatedly executed at every predetermined calculation cycle.
The control gain setting unit 58 acquires the steering torque Th detected by the torque sensor 11, the mechanical angle θ _M calculated by the rotation angle calculation unit 52, and the q-axis detection current I _q obtained by the UVW / dq conversion unit 53. (Step S1). Hereinafter, it represents the currently acquired mechanical angle theta _M in theta _Mn, the mechanical angle theta _M obtained in the previous time to be represented by θ _{M (n-1).} The rotation angle of the electric motor 19 in most recent non-steering state (mechanical angle) is called a reference rotation angle, to be represented by the variable theta _S. The initial value of theta _S is set to, for example, zero.

Next, in order to determine whether or not the control gain setting unit 58 is in the non-steering state, the control gain setting unit 58 determines whether or not the first condition represented by the following equation (1) is satisfied (step S2).
| Θ _M −θ _{M (n−1)} | ≦ A and Th ≦ B (1)
In the equation (1), | θ _M −θ _{M (n−1)} | is the rotor angular velocity (absolute value) of the electric motor 19. A (A> 0) is a predetermined value set in advance, and is set to a value corresponding to, for example, 1.0 [deg / sec]. B (B> 0) is a predetermined value set in advance, and is set to 0.25 [Nm], for example.

If the first condition is satisfied (step S2: YES), the control gain setting unit 58 determines that the vehicle is in the non-steering state, and sets the mechanical angle θ _Mn acquired this time as the reference rotation angle θ _S. (Step S3). That is, the reference rotation angle θ _S is updated. Further, the control gain setting unit 58 sets the proportional gain K _P in the PI control unit 54 to a relatively small first proportional gain K _P 1 and the integral gain K _I to a relatively small first integral gain K. _I is set to 1 (step S6). Then, the control gain setting unit 58 ends the process in the current calculation cycle.

If it is determined in step S2 that the first condition is not satisfied (step S2: NO), the control gain setting unit 58 determines that the steering wheel 2 is being operated, and the motor Torque Tm is calculated based on the following equation (2) (step S4).
Tm = I _q · K _T (2)
In Equation (2), I _q is the q-axis detection current acquired this time, and _KT is the torque constant of the electric motor 19.

Next, the control gain setting unit 58 determines whether or not the second condition represented by the following equation (3) is satisfied in order to determine whether or not the transmission error generation region is satisfied (step S5).
| Θ _Mn −θ _S | ≦ α and | Tm | ≦ β (3)
In the formula (3), | θ _Mn −θ _S | represents the rotation amount (absolute value) of the rotor from the most recent non-steering state. | Tm | is the absolute value of the motor torque Tm calculated in step S4. α is the aforementioned first threshold value, and β is the aforementioned second threshold value.

When the second condition is satisfied (step S5: YES), the control gain setting unit 58 determines that the rotation amount of the rotor from the latest non-steering state is within the transmission error occurrence region, and the PI control unit 54 and it sets the proportional gain _{K P} to relatively small first proportional gain _{K P} 1 of the inner sets the integral gain _{K I} relatively small first integral gain _{K I} 1 (step S6). Thereby, since the control responsiveness of the electric motor 19 can be reduced in a transmission error occurrence region where vibration and noise are likely to occur, the occurrence of vibration and noise can be suppressed. Then, the control gain setting unit 58 ends the process in the current calculation cycle.

When it is determined in step S5 that the second condition is not satisfied (step S5: NO), it is determined that the rotation amount of the rotor from the most recent non-steering state has exceeded the transmission error occurrence region, and the PI control unit proportional with gain _K set _P of relatively large second proportional gain _{K P} 2 in 54, integral gain _{K I} to be set to a relatively large second integral gain _{K I} 2 (step S7). Thereby, since the control responsiveness of the electric motor 19 can be improved in areas other than the transmission error generation area, the performance of the electric power steering apparatus 1 can be improved. Then, the control gain setting unit 58 ends the process in the current calculation cycle.

  According to the embodiment, since the control responsiveness of the electric motor 19 can be reduced in a transmission error occurrence region where vibration and noise are likely to occur, the occurrence of vibration and noise can be suppressed. On the other hand, in a region other than the transmission error generation region, the control responsiveness of the electric motor 19 can be improved, so that the performance of the electric power steering device 1 can be improved.

As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above-described embodiment, the condition for determining whether or not it is a transmission error occurrence region is | θ _Mn −θ _S | ≦ α and | Tm | ≦ β, but | θ _Mn −θ _The condition may be that only _S | is equal to or less than the first threshold value α (| θ _Mn −θ _S | ≦ α).
Further, as indicated by a broken line in FIG. 1, in addition to or instead of the control gain setting unit 58, a phase compensation process is performed on the output signal of the torque sensor 11 between the torque sensor 11 and the current command value setting unit. In addition to providing the phase compensation processing unit 59 to be applied, a phase compensation characteristic setting unit 60 for changing and setting the phase compensation characteristic (transfer function) of the phase compensation processing unit 59 may be provided. The phase compensation characteristic setting unit 60 determines whether or not it is a transmission error occurrence region by a method similar to that of the control gain setting unit 58. The phase compensation characteristic of the unit 59 may be changed.

  In addition, various design changes can be made within the scope of matters described in the claims.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering wheel, 5 ... Steering assist mechanism, 11 ... Torque sensor, 13 ... ECU, 15 ... Rack shaft, 19 ... Electric motor, 20 ... Coupling, 21 ... Deceleration mechanism, 23 ... First 2 pinions, 24 ... second rack, 25 ... rotation angle sensor, 31 ... microcomputer, 33 ... current detection unit, 51 ... current command value setting unit, 52 ... rotation angle calculation unit, 54 ... current deviation calculation unit, 55 ... PI control unit, 58 ... control gain setting unit, 59 ... phase compensation processing unit, 90 ... phase compensation characteristic setting unit

Claims (4)

An electric power steering device that applies a steering assist force from an electric motor to a steered shaft via at least one power transmission device having play,
Current command value setting means for setting a current command value of the electric motor;
Current detecting means for detecting a motor current flowing in the electric motor;
Feedback control means for feedback-controlling the electric motor so that the detected current value detected by the current detection means approaches the current command value set by the current command value setting means;
A rotation angle change amount calculating means for calculating a rotation angle change amount of the electric motor from the most recent non-steering state in which the steering member is not operated;
Responsiveness reducing means for reducing the control responsiveness of the feedback control means when the absolute value of the rotational angle change amount calculated by the rotational angle change amount calculating means is equal to or less than a predetermined rotation amount set in advance. Including an electric power steering apparatus.   The electric power steering according to claim 1, wherein the predetermined rotation amount is a rotation amount of the electric motor corresponding to a total amount of play of the power transmission device existing between the electric motor and the steered shaft. apparatus.   The electric power steering apparatus according to claim 1 or 2, wherein the responsiveness reducing means is configured to reduce the responsiveness of the feedback control means by changing a control gain of the feedback control means.   The responsiveness lowering means has an absolute value of the rotation angle change amount calculated by the rotation angle change amount calculation means being equal to or less than a predetermined rotation amount set in advance and a motor torque of the electric motor being equal to or less than a predetermined torque. 2. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is configured to reduce responsiveness of the feedback control means.

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