JP2008260357A - Electric power steering device - Google Patents

Abstract

An electric power steering apparatus capable of reducing steering vibration without reducing responsiveness to a current command value is provided.
An electric motor for applying a steering assist force for reducing a driver's steering burden to a steering system is provided, and the electric motor is driven and controlled to generate at least a steering assist force according to a steering torque. At this time, when it is determined that the steering wheel 1 is in the steering holding state, a filter process is performed on the motor drive current I (or the deviation ΔI between the current command value It and the motor drive current I), and the current command value It and The electric motor 12 is feedback-controlled based on the deviation ΔI (or the deviation ΔI ′ after the filtering process) from the motor current I ′ after the filtering process.
[Selection] Figure 2

Description

  The present invention relates to an electric power steering apparatus including an electric motor that generates a steering assist torque to be applied to a steering system, and more particularly to an electric power steering apparatus that can reduce vibration and abnormal noise during steering.

  As a conventional electric power steering device, a motor that supplements the steering force based on the steering torque generated on the steering shaft, and the motor based on the deviation between the current command value determined based on the steering torque and the motor current flowing through the motor. There is known a motor control unit that performs feedback control, and changes the feedback response characteristic of the motor control unit in accordance with the rotational speed of the steering wheel (see, for example, Patent Document 1). As a result, the steering force is assisted without a delay in sudden steering during traveling, and the vibration of the steering wheel and the buzzing sound of the motor are suppressed during slow speed steering and steering while stopping.

Further, it is determined whether the steering means is in the steering holding state or the steering state based on the torque differential value that is the time change amount of the steering torque, and the control gain of the electric motor is changed based on the determination result. An electric power steering device is known (see, for example, Patent Document 2).
Furthermore, as an electric power steering apparatus having an electric motor control means for driving and controlling the electric motor by current feedback control, the crossing frequency in the loop transfer function of the current feedback loop is set to be equal to or higher than the primary natural frequency of the rotating system of the electric motor. Thus, it is known that steering feeling deterioration due to current vibration during steering of the steering wheel and noise due to mechanical vibration during high-speed rotation of the steering wheel are reduced (for example, see Patent Document 3).

Further, as an electric power steering apparatus having a control means for outputting a control signal for generating a steering assist force for the steering system based on the steering torque to the electric motor, the rotation direction of the electric motor is reversed and the motor current is set to a predetermined value. It is known that when it is determined that the current is less than or equal to one current threshold, the proportional gain of the control means is reduced (see, for example, Patent Document 4).
JP 2001-239947 A JP 2001-253358 A Japanese Patent Laid-Open No. 2002-59860 JP 2004-358985 A

However, in the electric power steering apparatus described in each of the above patent documents, since the response to the current command value is reduced to reduce the occurrence of vibration and abnormal noise during steering, When shifting to the steered state, the responsiveness to the current command value becomes discontinuous, resulting in a discontinuous feeling in the steering feeling.
In addition, by lowering the control gain at the time of steering, the influence of the vibration of the current detection value is reduced, thereby reducing the steering vibration. In this case, the amount of change in the current command value is also reduced along with the current detection value. Will do. Therefore, if the control gain is lowered too much, the responsiveness to the current command value is lowered, and as a contradiction, a sticking feeling and a ripple feeling are generated at the start of turning.

  Therefore, an object of the present invention is to provide an electric power steering device that can reduce the steering vibration without reducing the response to the current command value that impairs the steering feeling.

In order to solve the above-described problem, an electric power steering apparatus according to claim 1 calculates a current command value based on steering torque detection means for detecting steering torque and at least steering torque detected by the steering torque detection means. A current command value calculating means; an electric motor for generating a steering assist torque to be applied to the steering system; a drive current detecting means for detecting a motor drive current of the electric motor; and a deviation between the current command value and the motor drive current. An electric power steering device comprising: motor control means for feedback control of the electric motor based on
A steering holding state determining unit that determines whether or not the steering wheel is in a steering holding state; and a filter processing unit that performs a filter process on the motor drive current, wherein the motor control unit is configured to determine the steering holding state. When the means determines that the steering wheel is in the steering holding state, feedback control of the electric motor is performed based on a deviation between the motor drive current filtered by the filter processing means and the current command value. It is a feature.

According to a second aspect of the present invention, there is provided an electric power steering apparatus comprising: steering torque detection means for detecting steering torque; and current command value calculation means for calculating a current command value based on at least the steering torque detected by the steering torque detection means. An electric motor for generating a steering assist torque to be applied to the steering system; drive current detecting means for detecting a motor drive current of the electric motor; and the electric motor based on a deviation between the current command value and the motor drive current An electric power steering device including motor control means for feedback control of
A steered state determining unit that determines whether or not the steering wheel is in a steered state; and a filter processing unit that performs a filtering process on the deviation, wherein the motor control unit is the steered state determining unit. When it is determined that the steering wheel is in the steering holding state, the electric motor is feedback-controlled based on the deviation filtered by the filter processing means.

  Furthermore, an electric power steering apparatus according to a third aspect is the invention according to the first or second aspect, wherein the vehicle speed detecting means for detecting the vehicle speed, the rotation angle detecting means for detecting the motor rotation angle of the electric motor, and the electric motor. It has at least one of motor angular velocity detecting means, and the steering state determining means is detected by the steering torque detected by the steering torque detecting means, the current command value calculated by the current command value calculating means, and the vehicle speed detecting means. It is determined whether or not the steering wheel is in a steered state based on at least one of the measured vehicle speed, the motor rotation angle detected by the rotation angle detection means, and the motor angular speed detected by the angular speed detection means. It is said.

  According to a fourth aspect of the present invention, there is provided the electric power steering apparatus according to any one of the first to third aspects, wherein the filter of the filter processing means is a low-pass filter.

  According to the electric power steering apparatus according to the present invention, when it is determined that the steering wheel is in the steered state, the current detection value is subjected to the filter process, and the current detection value and the current command value after the filter process are calculated. Since the electric motor is feedback-controlled based on the deviation, the influence of quantization error due to A / D conversion of the current detection value can be reduced, and the steering vibration can be reduced without reducing the responsiveness to the current command value. The steering feeling can be improved.

  In addition, when it is determined that the steering wheel is in the steered state, a filter process is performed on the deviation between the current command value and the current detection value, and the electric motor is feedback-controlled based on the deviation after the filter process. The influence of quantization error due to the current detection value and A / D conversion of the steering torque sensor can be reduced, and the steering vibration can be reduced without lowering the responsiveness to the current command value. The effect that it can be made is acquired.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an embodiment of an electric power steering apparatus according to the present invention.
In the figure, symbol SM is a steering mechanism. This steering mechanism SM has a steering shaft 2 having an input shaft 2a to which a steering force applied from a driver is transmitted to the steering wheel 1 and an output shaft 2b connected to the input shaft 2a via a torsion bar (not shown). It has. The steering shaft 2 is rotatably mounted on the steering column 3, one end of the input shaft 2a is connected to the steering wheel 1, and the other end is connected to a torsion bar (not shown).

The steering force transmitted to the output shaft 2b is transmitted to the intermediate shaft 5 via the universal joint 4 composed of the two yokes 4a and 4b and the cross connecting portion 4c for connecting them, It is transmitted to the pinion shaft 7 through a universal joint 6 composed of yokes 6a and 6b and a cross connecting portion 6c for connecting them.
The steering force transmitted to the pinion shaft 7 is transmitted to the left and right tie rods 9 via the steering gear 8, and steered wheels (not shown) are steered by these tie rods 9. Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8b connected to the pinion shaft 7 and a rack shaft 8c meshing with the pinion 8b in the gear housing 8a, and is transmitted to the pinion 8b. The rotational motion is converted into a straight motion by the rack shaft 8c.

A steering assist mechanism 10 for transmitting a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 10 includes a reduction gear 11 connected to the output shaft 2b, and an electric motor 12 composed of, for example, a brushless motor as an electric motor that generates a steering assist force connected to the reduction gear 11. .
A steering torque sensor 14 is disposed in a housing 13 connected to the steering wheel 1 side of the reduction gear 11. The steering torque sensor 14 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a. For example, a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The torsional angular displacement is converted into a torsional angular displacement, and this torsional angular displacement is detected by a non-contact magnetic sensor.

The steering torque detection value T output from the steering torque sensor 14 is input to the controller 15 as shown in FIG. In addition to the torque detection value T, the controller 15 includes a vehicle speed detection value V detected by the vehicle speed sensor 16, a motor current I flowing through the electric motor 12, an electric motor detected by a rotation angle detection unit 17 including a resolver, an encoder, and the like. The rotation angle θ of the motor 12 is also input, and a steering assist torque command value I _M ^* for causing the electric motor 12 to generate a steering assist force corresponding to the input torque detection value T and vehicle speed detection value V is calculated, and the calculated steering is calculated. Various compensation processes are performed on the auxiliary torque command value I _M ^* based on the motor angular velocity ω and the motor angular acceleration α calculated based on the rotation angle θ to calculate the current command value It. Then, feedback processing is performed on the drive current supplied to the electric motor 12 based on the current command value It and the motor current I, and the motor current I for driving and controlling the electric motor 12 is output.

That is, the controller 15 compensates the steering assist torque command value I _M ^*, which calculates the steering assist torque command value I _M ^* based on the steering torque T and the vehicle speed V, and the calculated steering assist torque command value I _M ^* . A command value compensation unit 22 and a motor current control unit 23 that generates a motor current I based on the current command value It compensated by the command value compensation unit 22 are provided.
Further, the controller 15 calculates the steering torque differential value T ′ based on the steering torque T, the steering torque differential value T ′, the vehicle speed V, the motor rotation angle θ, the motor angular speed ω, and the current command value It. The steering wheel 1 is determined whether or not the steering wheel 1 is in a steered state, and a steered state determining unit 52 that outputs a signal S is provided.

Here, the signal S output from the steered state determination unit 52 is output to a filter processing unit 61 described later, and a switch 61a described later is switched.
In the steering assist torque command value calculation unit 21, first, the torque command value calculation unit 41 refers to the steering assist torque command value calculation map shown in FIG. 3 based on the steering torque T and the vehicle speed V, and the steering assist torque command value. I _M ^* is calculated.

As shown in FIG. 3, the steering assist torque command value calculation map has a parabolic shape with the steering torque T on the horizontal axis, the steering assist torque command value I _M ^* on the vertical axis, and the vehicle speed V as a parameter. It is composed of a characteristic diagram represented by a curve, and the steering assist torque command value I _M ^* is maintained at “0” while the steering torque T is between “0” and a set value Ts1 in the vicinity thereof, and the steering torque T is When the set value Ts1 is exceeded, initially, the steering assist torque command value I _M ^* increases relatively slowly with respect to the increase in the steering torque T. However, when the steering torque T further increases, the steering assist torque command with respect to the increase. The value I _M ^* is set so as to increase steeply, and this characteristic curve is set so that the inclination becomes smaller as the vehicle speed increases.

Then, the phase compensator 42 performs phase compensation to the steering assist torque command value I _M ^*, and outputs a steering assist torque command value I _M ^* after phase compensation to the adder 36 to be described later. The differential compensation unit 43 compensates the steering torque T based on the steering torque differential value T ′ obtained by differentiating the steering torque T, and outputs this to the adder 36 described later.
The command value compensation unit 22 differentiates the motor rotation angle θ detected by the rotation angle detection unit 17 to calculate the motor angular velocity ω, and differentiates the motor angular velocity ω calculated by the angular velocity calculation unit 31. An angular acceleration calculation unit 32 for calculating the motor angular acceleration α, a convergence compensation unit 33 for compensating the convergence of the yaw rate based on the motor angular velocity ω and the vehicle speed V calculated by the angular velocity calculation unit 31, and an angular acceleration calculation. And at least an inertia compensation unit 34 that compensates for the torque equivalent generated by the inertia of the electric motor 12 based on the motor angular acceleration α and the vehicle speed V calculated by the unit 32 to prevent deterioration of the sense of inertia or control responsiveness. .

The subtractor 35 subtracts the convergence compensation value Ic calculated from the convergence compensation unit 33 from the inertia compensation value Ii calculated from the inertia compensation unit 34 to calculate a command compensation value Icom. Icom is added to the steering assist torque command value I _M ^* output from the steering assist torque command value calculation unit 21 by the adder 36 to calculate the current command value It.
The motor current control unit 23 filters the motor current I according to the signal S input from the motor current detector 60 that detects the motor current I supplied to the electric motor 12 and the steered state determination unit 52. Filter processing unit 61 that outputs motor current I ′ and subtracter 62 that subtracts motor current I ′ from current command value It to obtain current deviation ΔI, and performs proportional-integral control on current deviation ΔI A PI control unit 63 for calculating the voltage command value Vt, and calculating a duty ratio by performing a duty calculation based on the voltage command value Vt, and performing a pulse width modulation based on the duty ratio and outputting a pulse width modulation signal And a inverter 65 that outputs a motor current I to the electric motor 12 based on the pulse width modulation signal.

  A signal S output from the steered state determination unit 52 is input to the filter processing unit 61. The switch 61a is in a state indicated by a solid line when a signal S having a logical value “0”, which means that the steering wheel 1 is not in the steered state, is input, and the steering wheel 1 is in the steered state. When a signal S having a logical value “1”, which means that the signal is input, is switched to the state indicated by the broken line.

With this configuration, the filter processing unit 61 outputs the motor current I detected by the motor current detection unit 60 as it is as the motor current I ′ when the signal S having the logical value “0” is input.
On the other hand, when the signal S having the logical value “1” is input, the filter processing unit 61 outputs the output value from the filter 61b that performs the filter process on the motor current I detected by the motor current detection unit 60 as the motor current. Output as I '.

Here, in the present embodiment, the filter 61b is an IIR low-pass filter.
Further, the differential calculation unit 51 differentiates the steering torque T detected by the steering torque sensor 14 to calculate a steering torque differential value (time change amount) T ′, and outputs this to the steered state determination unit 52.
The steered wheel state determination unit 52 receives the steering torque differential value T ′, the vehicle speed V, the motor rotation angle θ, the motor angular velocity ω, and the current command value It, respectively, and performs a steered wheel state determination process to be described later. The signal S which shows whether 1 is in a steering maintenance state is output.

FIG. 4 is a flowchart showing a steered state determination processing procedure executed by the steered state determination unit 52. First, in step S1, various data of the steering torque differential value T ′, the vehicle speed V, the motor rotation angle θ, the motor angular speed ω, and the current command value It are read, and the process proceeds to step S2.
In step S2, it is determined whether or not the following steering state determination condition is satisfied, that is, whether or not the steering state of the steering wheel 1 has been switched from the normal steering state to the steering state. Specifically, whether or not the steering torque differential value T ′ is smaller than the steering torque differential threshold T _TH ′ (for example, 4LSB in the amount of change between the steering torques 2 ms), the vehicle speed V is the vehicle speed threshold V _TH (for example, 8 km / h) whether the motor rotational speed Nm is smaller than the motor rotational speed threshold value Nm _TH, whether the motor angular speed ω is smaller than the motor angular speed threshold value ω _TH , and the current command value It is a current command value threshold value It is determined whether or not it is greater than It _TH (for example, 2A).

When T ′ <T _TH ′, V <V _TH , Nm <Nm _TH , ω <ω _TH , and It> It _TH, it is determined that the steering wheel 1 is in the steering-holding state. The process proceeds to S3. Otherwise, it is determined that the steering wheel 1 is in the non-steering state, and the process proceeds to Step S4.
Thus, when the vehicle speed V is high, in order to ensure the steering performance during traveling, the filter function by the filter processing unit 61 is turned off to ensure the current control state during normal steering.

Note that, as the steering holding condition determination condition, a condition such as whether or not the steering torque T belongs to a predetermined range (whether T1 <T <T2) or the like can be added to each of the above conditions.
In step S3, the signal S having the logical value “1” is output to the filter processing unit 61, and then the steered state determination process is terminated. In step S4, the signal S having the logical value “0” is filtered. After the output to the unit 61, the steered state determination process is terminated.

  In FIG. 2, the steering torque sensor 14 corresponds to the steering torque detection means, the vehicle speed sensor 16 corresponds to the vehicle speed detection means, and the steering assist torque command value calculation unit 21 and the command value compensation unit 22 correspond to the current command value calculation means. , The motor current control unit 23 corresponds to the motor control unit, the steered state determination unit 52 corresponds to the steered state determination unit, the rotation angle detection unit 17 corresponds to the rotation angle detection unit, and the angular velocity calculation unit 31 corresponds to the angular velocity detection means, the motor current detection unit 60 corresponds to the drive current detection means, and the filter processing unit 61 corresponds to the filter processing means.

Next, the operation in the first embodiment of the present invention will be described.
Assuming that the ignition switch IG is turned on to start traveling of the vehicle, the controller 15 is turned on to start execution of the steering assist control process, and the steering torque T detected by the steering torque sensor 14 is started. The vehicle speed V detected by the vehicle speed sensor 16, the motor current I detected by the motor current detection unit 60, and the motor rotation angle θ detected by the rotation angle detection unit 17 are supplied to the controller 15.

Therefore, the steering assist torque command value calculation unit 21 calculates the steering assist torque command value I _M ^* based on the steering torque T and the vehicle speed V with reference to the steering assist command value calculation map shown in FIG. On the other hand, the motor rotation angle θ detected by the rotation angle detector 17 is input to the angular velocity calculator 31 to calculate the motor angular velocity ω, and the motor angular velocity ω is input to the angular acceleration calculator 32 to calculate the motor angular acceleration α. Is done.

Then, the convergence compensation unit 33 calculates the convergence compensation value Ic based on the motor angular velocity ω, and the inertia compensation unit 34 calculates the inertia compensation value Ii based on the motor angular acceleration α. These are input to the subtractor 35. Then, the command value compensation value Icom is calculated, and this is added to the steering assist torque command value I _M ^* by the adder 36 to calculate the current command value It.
At this time, when the vehicle is in a traveling state, a steering assist torque command value I _M ^* based on the steering torque T detected by the steering torque sensor 14 and the vehicle speed V detected by the vehicle speed sensor 16 is calculated. The compensation value calculated by the command value compensation unit 22 is compensated for the steering assist torque command value I _M ^* , and the current command value It is calculated.

Here, if the vehicle enters a curved road and the steering torque differential value T ′ is equal to or greater than the steering torque differential threshold value T _TH ′, the steering state determination unit 52 determines No in step S2 of FIG. Therefore, the process proceeds to step S4, and the signal S having the logical value “0” is output to the filter processing unit 61, assuming that the steering wheel 1 is in the non-steering state. Therefore, the electric motor 12 is driven and controlled by current feedback control based on the motor current I detected by the motor drive current detector 60 and the current command value It without filtering the motor current I. . As a result, a steering assist force that reduces the driver's steering burden is generated.

  From this state, when the steering wheel 1 is in the steered state, for example, when the vehicle enters a straight path, the steered state determination unit 52 determines Yes in step S2 of FIG. 4 and proceeds to step S3. A signal S having a value “1” is output to the filter processing unit 61. Therefore, the filter processing unit 61 controls the drive of the electric motor 12 by current feedback control based on the motor current I ′ obtained by performing the filter process on the motor current I and the current command value It.

By the way, as shown in FIG. 5, when feedback control using a current detection value is adopted as the drive control method of the electric motor 100, if the current detection value vibrates, the output from the PI controller 110. The (duty command value) also vibrates under the influence.
It is known that the rudder vibration occurs due to limit cycle vibration caused by A / D quantization, and A / D quantization occurs at two locations, that is, a current detection signal and a torque signal.

  Therefore, it is considered that the influence of the limit cycle can be reduced by providing the LSB filter 120 and the steering gain 130 in the previous stage of the PI controller 110 as shown in FIG. Here, by lowering the steering gain, the amount of change in the signal is reduced, and the influence of vibration of the current detection value is reduced. The LSB filter 120 is provided in front of the steering holding gain 130 to play a role of improving the resolution of the signal, and is configured so that the filter function is turned on when the motor rotation speed is lower than the predetermined rotation speed. Has been.

This countermeasure reduces steering vibration, but also reduces the amount of change in the current command value along with the detected current value. Therefore, if the steering gain is reduced too much, the response of the duty command value to the current command value is reduced. As a result, a feeling of sticking at the start of turning occurs as a contradiction.
For example, in an engine specification vehicle, the engine always rotates and constantly vibrates, so that it is possible to achieve the steering vibration performance with a relatively high steering gain, and to achieve both a feeling of sticking. However, in a vehicle with high engine quietness, such as a hybrid specification vehicle, it is not possible to achieve the steering vibration performance with the same steering gain as the engine specification vehicle, and the steering gain is reduced to a relatively low value. Although it is necessary to lower it, a feeling of sticking occurs at the steering gain. As described above, it is difficult for the conventional vehicle to satisfy both of the steering vibration performance and the sticking feeling.

  By the way, when comparing the steered vibration in the feedforward control in which the current detection value is not fed back and the steered vibration in the feedback control, as shown in FIG. 7, the feedforward control that is not affected by the vibration of the current detection value is more It can be seen that the steering vibration is reduced. That is, it can be understood that the influence of the limit cycle on the steering vibration is the current detection signal, and the steering vibration is reduced by reducing the vibration of the current detection signal.

  Therefore, as in the present embodiment, during steering, the current detection value is subjected to low-pass filter processing to reduce vibration of the current detection value, and as a result, the response to the current command value is not deteriorated. Vibration and noise during steering can be reduced. That is, even if the steering gain is set in a range where the feeling of sticking does not occur, the steering vibration can be reduced, and both the steering vibration performance and the sticking feeling can be achieved.

Here, an IIR low-pass filter is employed as a filter used in the present embodiment. In order to reduce the steering vibration, it is estimated that the frequency band (around 250 Hz) of the steering vibration included in the signal may be reduced. Therefore, the filter is designed so that the signal in the frequency range of the steering holding vibration is reduced.
FIG. 8 is a diagram illustrating the frequency characteristics of the filter used in the present embodiment. As shown in FIG. 8A, it can be seen that the steering vibration performance is achieved by sufficiently reducing the signal at 250 Hz which is the frequency band of the steering vibration.

As described above, when the steering wheel 1 is in the steering-holding state, the steering vibration is effectively reduced by performing the filtering process using the IIR low-pass filter designed as described above on the current detection value. be able to.
Incidentally, the steering wheel holding determination is generally performed based on the motor rotation speed. However, if the steering determination is performed based only on the motor rotation speed, the steering wheel is determined to be in the steering holding state when the motor rotation speed instantaneously becomes 0, such as during a sudden reverse.

When it is determined that the steering state is maintained, a signal S having a logical value “1” is output from the steering state determination unit 52 to the filter processing unit 61, and the filter function is turned on. Since the filter has low responsiveness, the detected current value becomes discontinuous and abnormal noise may occur as shown in FIG.
Therefore, in the present embodiment, the steering torque differential value T ′ is used for the steering wheel holding determination, and the amount of change in the steering torque is larger at the time of sudden reversal than when turning from the steered state to the held state. However, when the change amount of the steering torque is equal to or larger than the threshold value, the steering holding state is not determined.

As a result, it is possible to prevent the steering state from being determined at the time of sudden reversal.
As described above, in the first embodiment, when it is determined that the steering wheel is in the steered state, the current detection value is subjected to the filter process, and the deviation between the current detection value after the filter process and the current command value is determined. Since the electric motor is feedback-controlled based on this, the influence of quantization error due to A / D conversion of the detected current value can be avoided, and the steering feeling can be improved by reducing vibration and noise during steering. Can do. Further, at this time, since the responsiveness to the current command value is not lowered, for example, it is possible to prevent the sticking feeling from occurring at the start of the turning.

  In addition, since the steering wheel holding determination is performed based on at least one of the steering torque, the current command value, the vehicle speed, the motor rotation angle, and the motor angular velocity, the steering wheel holding state can be reliably determined. In addition, when the amount of change in the steering torque is greater than or equal to a predetermined value, it is not determined that the steering state is maintained. It can be avoided that the rudder state is determined. As a result, it can be avoided that the current detection value becomes discontinuous due to the filter function being turned on, and the generation of abnormal noise can be prevented.

Furthermore, since the filter process using the IIR low-pass filter is adopted as the filter process, it is possible to reduce the steering vibration and the feeling of sticking.
Next, a second embodiment of the present invention will be described.
In the second embodiment, when the steering wheel 1 is determined to be in the steering-holding state in the first embodiment described above, the current detection value is filtered, whereas the current command value And the detected current value are subjected to filter processing.

  That is, as shown in FIG. 10 for the configuration of the controller in the second embodiment, the filter processing unit 61 in FIG. 2 is deleted, a filter processing unit 66 is added in front of the PI control unit 63, and the steered state determination unit Except for the fact that the signal S output from 52 is input to the filter processing unit 66, the configuration is the same as in FIG.

  A signal S output from the steered state determination unit 52 is input to the filter processing unit 66. The switch 66a is in a state indicated by a solid line when a signal S of a logical value “0”, which means that the steering wheel 1 is not in the steered state, is input, and the steering wheel 1 is in the steered state. When a signal S having a logical value “1”, which means that the signal is input, is switched to the state indicated by the broken line.

Accordingly, when the signal S having the logical value “0” is input, the filter processing unit 66 outputs the current deviation ΔI calculated by the subtractor 62 as it is as the current deviation ΔI ′.
On the other hand, when the signal S having the logical value “1” is input, the filter processing unit 66 outputs the output value from the filter 66 b that performs the filter process on the current deviation ΔI calculated by the subtractor 62 as the current deviation ΔI ′. Output as.

Here, the filter 66b is an IIR low-pass filter designed in the same manner as in the first embodiment described above.
With such a configuration, when the steering wheel 1 shifts from the normal steering state to the steered state, the steered state determination unit 52 determines Yes in step S2 of FIG. 4 and proceeds to step S3, and the logical value “1”. The signal S is output to the filter processing unit 66. Therefore, the filter processing unit 66 outputs the current deviation ΔI ′ obtained by performing the filtering process on the current deviation ΔI to the PI control unit 63. The electric motor 12 is driven and controlled by current feedback control based on the filtered current deviation ΔI ′.

As described above, the rudder vibration occurs in the limit cycle vibration due to A / D quantization, and the A / D quantization occurs in two places, the current detection signal and the torque signal. Therefore, by applying a filter process to the deviation ΔI between the current command value It and the motor current I, it is possible to avoid the influence of the quantization error due to the current detection value and the A / D conversion of the steering torque sensor.
As described above, in the second embodiment, when it is determined that the steering wheel is in the steering-holding state, the filter process is performed on the deviation between the current command value and the current detection value, and the deviation is calculated based on the deviation after the filter process. Since the electric motor is feedback controlled, the influence of the quantization error due to the current detection value and the A / D conversion of the steering torque sensor can be avoided, and the influence of the limit cycle in the steering vibration is reduced and more effective. In addition, vibration and noise during steering can be reduced, and the steering feeling can be improved.

  In each of the above embodiments, the electric motor 12 may be a single-phase motor or a three-phase motor. Further, in the case of a three-phase motor, the motor current control is a three-phase control. It goes without saying that the effects of the present invention can be obtained even with dq control.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the controller in 1st Embodiment. It is a steering assist torque command value calculation map. It is a flowchart which shows the steering holding | maintenance state determination processing procedure performed in a steering holding state determination part. It is a block diagram which shows the structure of electric current feedback control. It is a block diagram which shows the existing steering holding vibration countermeasure function. It is the figure which compared the steering vibration in feedforward control, and the steering vibration in feedback control. It is a figure which shows the frequency characteristic of the filter used by this embodiment. It is a figure which shows the change of the electric current detection value at the time of sudden inversion. It is a block diagram which shows the structure of the controller in 2nd Embodiment.

Explanation of symbols

  SM ... steering mechanism, 1 ... steering wheel, 2 ... steering shaft, 3 ... steering column, 4, 6 ... universal joint, 5 ... intermediate shaft, 8 ... steering gear, 10 ... steering assist mechanism, 11 ... reduction gear, 12 ... Electric motor, 14 ... steering torque sensor, 15 ... controller, 16 ... vehicle speed sensor, 17 ... rotation angle detection unit, 21 ... steering assist torque command value calculation unit, 22 ... command value compensation unit, 23 ... motor current control unit, 51 ... differentiation calculation unit, 52 ... steering state determination unit, 61 ... filter processing unit

Claims (4)

Steering torque detecting means for detecting steering torque, current command value calculating means for calculating a current command value based on at least the steering torque detected by the steering torque detecting means, and electric motor for generating steering assist torque to be applied to the steering system Electric power comprising: a motor; drive current detection means for detecting a motor drive current of the electric motor; and motor control means for feedback-controlling the electric motor based on a deviation between the current command value and the motor drive current. A steering device,
A steering holding state determining unit that determines whether or not the steering wheel is in a steering holding state; and a filter processing unit that performs a filter process on the motor drive current, wherein the motor control unit is configured to determine the steering holding state. When the means determines that the steering wheel is in the steering holding state, feedback control of the electric motor is performed based on a deviation between the motor drive current filtered by the filter processing means and the current command value. An electric power steering device. Steering torque detecting means for detecting steering torque, current command value calculating means for calculating a current command value based on at least the steering torque detected by the steering torque detecting means, and electric motor for generating steering assist torque to be applied to the steering system Electric power comprising: a motor; drive current detection means for detecting a motor drive current of the electric motor; and motor control means for feedback-controlling the electric motor based on a deviation between the current command value and the motor drive current. A steering device,
A steered state determining unit that determines whether or not the steering wheel is in a steered state; and a filter processing unit that performs a filtering process on the deviation, wherein the motor control unit is the steered state determining unit. When it is determined that the steering wheel is in the steering-holding state, the electric power steering device is configured to perform feedback control of the electric motor based on the deviation filtered by the filter processing unit.   It has at least one of vehicle speed detection means for detecting vehicle speed, rotation angle detection means for detecting the motor rotation angle of the electric motor, and motor angular speed detection means for the electric motor, and the steered state determination means includes the steering torque Steering torque detected by the detection means, current command value calculated by the current command value calculation means, vehicle speed detected by the vehicle speed detection means, motor rotation angle detected by the rotation angle detection means, and motor detected by the angular velocity detection means 3. The electric power steering apparatus according to claim 1, wherein it is determined whether or not the steering wheel is in a steered state based on at least one of angular velocities. 4.   The electric power steering apparatus according to any one of claims 1 to 3, wherein the filter of the filter processing means is configured by a low-pass filter.

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