JP2014000943A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which improves steering feeling of a driver.SOLUTION: An electric power steering device has a controller for controlling drive of a motor which provides an assist torque to a steering mechanism based on an assist command value Ta*. The controller calculates a first assist component Ta1 based on a steering torque Th and a vehicle velocity V, and in addition, calculates a steering angle command value θp* based on the steering torque Th and the first assist component Ta1, and calculates a second assist component Ta2 by executing feedback control for matching a steering angle θp to the steering angle command value θp*. Then, the controller adds the second assist component Ta2 to the first assist component Ta1, and calculates the assist command value Ta*. Herein, an axial force sensor for detecting an axial force F which applies to a rack shaft of a vehicle is provided. Based on the detected axial force F of the axial force sensor, a road surface state torque component Tar is calculated, and based on the road surface state torque component Tar, the assist command value Ta* is changed.

Description

  The present invention relates to an electric power steering device that assists a driver's steering operation.

  2. Description of the Related Art There is known an electric power steering device that assists a driver's steering operation by applying power of a motor to a steering mechanism of a vehicle. Conventionally, as this type of electric power steering apparatus, there is an apparatus described in Patent Document 1.

  The electric power steering apparatus described in Patent Document 1 includes a first reference model that determines a target steering torque based on a steering angle, and a second reference that determines a target steering angle (target turning angle) of a steering system based on the steering torque. Has a model. The drive of the motor is controlled based on both of these reference models (ideal models). That is, the steering torque can always be set to an optimum value by the first assist component obtained by executing the torque feedback control so that the actual steering torque follows the target steering torque. Further, the reverse input vibration from the steered wheels can be canceled by the second assist component obtained by executing the steered angle feedback control for causing the actual steered angle to follow the target steered angle.

Japanese Patent No. 4453012

  By the way, when the vehicle travels, vibration according to the road surface condition is generated in the steered wheels, and this vibration is transmitted to the steering wheel via the steering mechanism of the vehicle. Therefore, the driver can grasp the road surface condition (road information) by the vibration transmitted to the hand holding the steering wheel. However, in the power steering device described in Patent Document 1, vibration generated in the steering mechanism according to the road surface state is also suppressed by the turning angle feedback control, so that the driver feels steering feeling (responsiveness) corresponding to the road surface state. Can't get. This is one factor that causes a deterioration in steering feeling.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an electric power steering apparatus that improves a driver's steering feeling.

  In order to solve the above-described problem, an invention according to claim 1 includes an assist mechanism that applies an assist torque of a motor to a steering mechanism of a vehicle, and a control unit that controls driving of the motor based on an assist command value. The control unit includes a turning angle command value calculation unit that calculates a turning angle command value that is a target value of the turning angle of the turning wheel, and the turning angle of the turning wheel is set to the turning angle command value. A steering angle feedback control unit that calculates an assist component by executing a matching steering angle feedback control, an assist command value calculation unit that calculates the assist command value based on the assist component, and the road surface state And a road surface state compensation unit that calculates a road surface state torque component according to a reaction force acting on the steered wheels, and changing the assist command value based on the road surface state torque component.

  According to this configuration, since the steering angle of the steered wheels is controlled so as to coincide with the steering angle command value by applying the assist torque based on the assist command value to the steering mechanism, the steering mechanism caused by disturbance Can be accurately suppressed. In addition, when a reaction force according to the road surface condition acts on the steered wheels, the assist command value is changed by a road surface state torque component set based on the reaction force. As a result, the assist torque applied to the steering mechanism changes in accordance with the road surface state, so that the driver's steering feeling changes in accordance with the road surface state each time. Therefore, the driver can grasp the road surface condition from the change in the steering feeling, so that the driver's steering feeling is improved.

  According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, the control unit includes a basic assist component calculating unit that calculates a basic assist component based on a steering torque applied to the steering mechanism. Further, the assist command value calculation unit calculates the assist command value based on a value obtained by adding the basic assist component and the assist component.

  According to this configuration, the assist torque based on the assist component calculated by the turning angle feedback control unit is applied to the steering mechanism, so that the vibration of the steering mechanism can be accurately suppressed. Further, the assist torque based on the assist component calculated by the basic assist component calculation unit is applied to the steering mechanism, so that the driver's steering operation can be accurately assisted.

  The invention according to claim 3 is the electric power steering apparatus according to claim 1 or 2, further comprising a road surface reaction force detection unit that detects a road surface reaction force acting on the steered wheels from the road surface, and the road surface condition compensation The gist is to calculate the road surface state torque component by extracting a reaction force belonging to a predetermined frequency band from the detected road surface reaction force of the road surface reaction force detection unit.

  The detected road surface reaction force of the road surface reaction force detection unit includes various disturbances other than the reaction force that acts on the steered wheels due to the road surface condition, but the type of disturbance can be roughly determined by frequency. . Therefore, according to the said structure, the torque component which reflected the road surface state more appropriately can be calculated.

  According to a fourth aspect of the present invention, in the electric power steering apparatus according to the third aspect, the predetermined frequency band is set to a frequency band excluding the frequency of the natural vibration of the vehicle body.

  The largest disturbance included in the road surface reaction force detected by the road surface reaction force detection unit is the natural vibration of the vehicle body, but the frequency can be easily measured in advance through experiments or the like. Therefore, if the predetermined frequency band is set to a frequency band excluding the frequency of the natural vibration of the vehicle body as in the above configuration, disturbance caused by the natural vibration of the vehicle body can be removed from the detected road surface reaction force. Thereby, the road surface state torque component can be easily calculated.

  According to a fifth aspect of the present invention, in the electric power steering apparatus according to the third or fourth aspect of the invention, the road surface state compensation unit steers a reaction force acting on the steered wheel when the steered wheel steers. The gist of the present invention is to perform a process of removing the steering reaction force from the detected road surface reaction force, and calculate the road surface state torque component based on the detected road surface reaction force after the process.

  The detected road surface reaction force of the road surface reaction force detector includes a steering reaction force. Therefore, if the processing for removing the steering reaction force from the detected road surface reaction force is performed as in the above configuration, and the road surface state torque component is calculated based on the detected road surface reaction force after the processing, torque that more appropriately reflects the road surface state The component can be calculated.

  In the electric power steering apparatus according to any one of claims 1 to 5, as in the invention according to claim 6, the turning angle command value calculation unit is a steering provided to the steering mechanism. The turning angle command value is calculated based on an ideal model obtained by modeling ideal turning angles of steered wheels according to input information including torque, and the control unit performs the assist based on the road surface state torque component. It is effective to adopt a configuration in which input information to the ideal model is changed based on the road surface state torque component in order to change the command value. Thus, the assist command value can be easily changed according to the road surface condition.

  According to the electric power steering apparatus of the present invention, the driver's steering feeling is improved.

The block diagram which shows the structure about one Embodiment of the electric power steering apparatus of this invention. The block diagram which shows the structure of the control apparatus about the electric power steering apparatus of embodiment. The control block diagram which shows the structure of the control apparatus about the electric power steering apparatus of embodiment. The graph which shows the relationship between steering torque, vehicle speed, and a 1st assist component. The control block diagram which shows the structure of a road surface state compensation part about the electric power steering apparatus of embodiment. (A) is a graph which shows the example of transition of the detected axial force of an axial force sensor. (B) is a graph showing an output example of a low-pass filter. (C) is a graph which shows the example of transition of the difference value of the detection axial force of an axial force sensor, and the output of a low-pass filter. The graph which shows an example of the pass frequency band of a band pass filter about the electric power steering device of an embodiment.

Hereinafter, an embodiment of an electric power steering apparatus according to the present invention will be described with reference to FIGS.
As shown in FIG. 1, the electric power steering apparatus includes a steering mechanism 1 for turning the steered wheels 15 based on an operation of the driver's steering wheel 10 and an assist mechanism 2 for assisting the driver's steering operation. ing.

  The steering mechanism 1 includes a steering wheel 10 that is operated by a driver, and a steering shaft 11 that serves as a rotating shaft of the steering wheel 10. The steering shaft 11 includes a column shaft 11a connected to the center of the steering wheel 10, an intermediate shaft 11b connected to the lower end portion of the column shaft 11a, and a pinion shaft 11c connected to the lower end portion of the intermediate shaft 11b. . A rack shaft 13 is connected to a lower end portion of the pinion shaft 11c via a rack and pinion mechanism 12. As a result, when the steering shaft 11 rotates as the driver operates the steering wheel 10, the rotational motion is converted into a reciprocating linear motion in the axial direction of the rack shaft 13 via the rack and pinion mechanism 12. The reciprocating linear motion of the rack shaft 13 is transmitted to the steered wheels 15 via tie rods 14 connected to both ends thereof, whereby the steered angle θp of the steered wheels 15 is changed, and the traveling direction of the vehicle is changed.

  The assist mechanism 2 includes a motor 20 that applies assist torque to the column shaft 11a. The motor 20 is a three-phase AC motor. The rotation of the motor 20 is transmitted to the column shaft 11a via the gear mechanism 21, whereby a motor torque is applied to the steering shaft 11 and the steering operation is assisted.

  In addition, the power steering device includes various sensors that detect the operation amount of the steering wheel 10 and the state amount of the vehicle. For example, the column shaft 11a is provided with a torque sensor (torque detector) 4 that detects torque (steering torque) Th applied to the steering shaft 11 when the driver performs a steering operation. The rack shaft 13 is provided with an axial force sensor 5 that detects a force (axial force) F acting in the axial direction. Since there is a correlation between the axial force F of the rack shaft 13 and the road surface reaction force acting on the steered wheel 15, the axial force sensor 5 is used as a road surface reaction force detection unit in this embodiment. The vehicle is provided with a vehicle speed sensor 6 for detecting the traveling speed V thereof. The motor 20 is provided with a rotation angle sensor 7 for detecting the rotation angle θm. Outputs of these sensors are taken into a control device (control unit) 3. The control device 3 controls the drive of the motor 20 based on the output of each sensor.

  As shown in FIG. 2, the control device 3 is an inverter that converts a DC voltage supplied from a power source (power supply voltage “+ Vcc”) such as an in-vehicle battery into an AC voltage of three phases (U phase, V phase, W phase). The microcomputer 30 which drives the circuit 30 and the inverter circuit 30 by PWM (pulse width modulation) is provided.

  The inverter circuit 30 converts the DC voltage from the power source into a three-phase AC voltage based on the PWM drive signal output from the microcomputer 31. The converted three-phase AC voltage is supplied to the motor 20 via the UL line, the VL line, and the WL line.

  The UL line, the VL line, and the WL line are respectively provided with current sensors 21u, 21v, and 21w that detect the phase current values Iu, Iv, and Iw flowing through them. The outputs of the current sensors 21u, 21v, 21w are taken into the microcomputer 31.

  The microcomputer 31 also captures outputs of the torque sensor 4, the axial force sensor 5, the vehicle speed sensor 6, and the rotation angle sensor 7. The microcomputer 31 generates a PWM drive signal based on the steering torque Th detected by each sensor, the axial force F of the rack shaft 13, the vehicle speed V, the motor rotation angle θm, and the phase current values Iu, Iv, and Iw. Then, the microcomputer 31 outputs this PWM drive signal to the inverter circuit 30 to drive the inverter circuit 30 by PWM and control the drive of the motor 20.

Next, drive control of the motor 20 by the microcomputer 31 will be described in detail with reference to the control block of FIG.
As shown in FIG. 3, the microcomputer 31 includes an assist command value calculation unit 40 that calculates an assist command value Ta * based on the vehicle speed V, the steering torque Th, the axial force F, and the motor rotation angle θm.

  The assist command value calculation unit 40 includes a basic assist component calculation unit 41 that calculates a first assist component Ta1 that is a basic component of the assist command value Ta * based on the vehicle speed V and the steering torque Th. For example, as shown in FIG. 4, the basic assist component calculation unit 41 sets the absolute value of the first assist component Ta <b> 1 to a larger value as the absolute value of the steering torque Th increases and as the vehicle speed V decreases. The basic assist component calculation unit 41 calculates a first assist component Ta1 from the vehicle speed V and the steering torque Th using a map as shown in FIG. 4, and turns the calculated first assist component Ta1 as shown in FIG. It outputs to the angle command value calculation unit 44.

  In addition to the first assist component Ta1 from the basic assist component calculation unit 41, the steering torque Th is input to the turning angle command value calculation unit 44. The turning angle command value calculation unit 44 calculates the basic driving torque by adding the first assist component Ta1 and the steering torque Th, and determines the turning angle θp of the turning wheel 15 based on the ideal model from the obtained basic driving torque. A turning angle command value θp * that is a target value is calculated. The ideal model is obtained by modeling an ideal turning angle according to the basic driving torque in advance through experiments or the like. The turning angle command value calculation unit 44 outputs the calculated turning angle command value θp * to the turning angle feedback control unit 45.

  On the other hand, as shown in FIG. 1, since the motor 20 is connected to the column shaft 11 a via the gear mechanism 21, there is a correlation between the motor rotation angle θm and the rotation angle of the steering shaft 11. Therefore, there is also a correlation between the motor rotation angle θm and the turning angle θp of the steered wheels 15. As shown in FIG. 3, the assist command value calculation unit 40 uses this correlation to calculate the actual turning angle (actual turning angle) θp of the steered wheels 15 from the motor rotation angle θm. A portion 43 is provided. The turning angle calculation unit 43 outputs the calculated actual turning angle θp to the turning angle feedback control unit 45.

  The turning angle feedback control unit 45 performs feedback control based on the deviation so as to make the actual turning angle θp coincide with the turning angle command value θp *, and generates the second assist component Ta2.

  The assist command value calculation unit 40 calculates the assist command value Ta * by adding the second assist component Ta2 to the first assist component Ta1, and outputs the assist command value Ta * to the current command value calculation unit 50. .

  Current command value calculation unit 50 calculates current command value Iq * on the q axis in the d / q coordinate system based on assist command value Ta *, and outputs this current command value Iq * to PWM drive signal generation unit 60. To do. In the present embodiment, the current command value Id * on the d-axis is “0”, and the current command value calculation unit 50 also outputs this current command value Id * to the PWM drive signal generation unit 60.

  In addition to the current command values Iq * and Id * from the current command value calculation unit 50, the PWM drive signal generation unit 60 receives information on each phase current value Iu, Iv, Iw and the motor rotation angle θm. The PWM drive signal generation unit 60 converts each phase current value Iu, Iv, Iw into a d-axis current value Id and a q-axis current value Iq in the d / q coordinate system using the motor rotation angle θm. The PWM drive signal generation unit 60 performs feedback control based on the deviation so that the q-axis current value Iq becomes the current command value Iq * and the d-axis current value Id becomes the current command value Id *. Is generated. As a result, the inverter circuit 30 is PWM-driven, assist torque corresponding to the assist command value Ta * is applied from the motor 20 to the steering shaft 11, and assist control for assisting steering operation is executed.

  According to such a configuration, since the second assist component Ta2 generated by the turning angle feedback control is included in the assist command value Ta *, an assist torque based on the assist command value Ta * is applied to the steering shaft 11. Thus, the actual turning angle θp of the steered wheels 15 is controlled to coincide with the turning angle command value θp *. Since the reverse input from the steered wheels 15 can be effectively canceled by this steered angle feedback control, the vibration of the steering mechanism 1 due to disturbance can be suppressed accurately. In addition, by appropriately adjusting the ideal model of the turning angle command value calculation unit 44, an arbitrary characteristic can be formed by the control regardless of the actual characteristic of the mounted vehicle. That is, a desired steering feeling can be realized.

  By the way, the driver obtains a lot of road information related to the traveling vehicle such as the road surface condition and the grip force of the steered wheels 15 from the reverse input transmitted from the steered wheels 15 to the steering wheel 10 via the steering mechanism 1. For this reason, if all the reverse inputs from the steered wheels 15 are canceled by the steered angle feedback control, the driver cannot obtain the road information from the steering wheel 10, and the steering feeling may be deteriorated.

  Here, the axial force F of the rack shaft 13 detected by the axial force sensor 5 shown in FIG. 1 includes information on the axial force acting on the steered wheels 15 in accordance with the road surface condition. Therefore, in this embodiment, the axial force resulting from the road surface state is extracted from the detected axial force F of the axial force sensor 5. Then, by changing the assist command value Ta * based on the axial force resulting from the road surface state, the driver's steering feeling is changed according to the road surface state each time. Details will be described below.

  As shown in FIG. 3, the assist command value calculation unit 40 includes a road surface state compensation unit 42 that calculates a road surface state torque component Tar from the detected axial force F of the axial force sensor 5. As shown in the control block of FIG. 5, the road surface compensation unit 42 includes a low-pass filter 42 a that performs a filtering process on the detected axial force F.

  Here, the detected axial force F of the axial force sensor 5 acts on the steered wheel 15 when the steered wheel 15 steers, for example, in response to a steering operation, in addition to the reaction force acting on the steered wheel 15 according to the road surface condition. Reaction force (steering reaction force) is also included. Of these, the temporal waveform of the former reaction force has a higher frequency than the temporal waveform of the latter reaction force. For this reason, the detection axial force F changes in a waveform as shown in FIG. 6A, for example, in which a waveform having a high frequency and a waveform having a low frequency are synthesized. When a filtering process is performed on the waveform of the detected axial force F through the low-pass filter 42a, a waveform of the steering reaction force as shown in FIG. 6B is extracted as an output of the low-pass filter 42a. Therefore, if the output of the low-pass filter 42a is removed from the detected axial force F, the steering reaction force can be removed from the detected axial force F as shown in FIG. As shown in FIG. 5, the corrected detected axial force F 'from which the steering reaction force has been removed is input to the bandpass filter 42b.

  On the other hand, the detected axial force F of the axial force sensor 5 includes various disturbances other than the axial force acting on the rack shaft 13 due to the road surface state. is there. Of these disturbances, the largest influence is the natural vibration of the vehicle body such as the vibration of the suspension and the vibration caused by the shimmy phenomenon and the flutter phenomenon. In the present embodiment, the frequencies of various natural vibrations of the vehicle body are measured in advance by experiments or the like. As shown in FIG. 7, the pass frequency band of the bandpass filter 42b is set to a frequency band centered on a predetermined frequency fa so as to exclude the frequency of the natural vibration of the vehicle body. As a result, as shown in FIG. 5, by passing the corrected detected axial force F ′ through the bandpass filter 42b, the disturbance caused by the natural vibration of the vehicle is removed from the detected axial force F ′, resulting in the road surface condition. Thus, the axial force Fr acting on the rack shaft 13 is extracted. The output of the band pass filter 42b is input to the axial force / torque converter 42c.

  The axial force / torque converter 42c calculates the road surface state torque component Tar based on the axial force Fr resulting from the road surface state. The road surface state torque component Tar can be calculated by a known method such as multiplying the axial force Fr caused by the road surface state by the radius of the pinion shaft 11c. The calculated road surface state torque component Tar becomes the output of the road surface state compensation unit 42.

  As shown in FIG. 3, the road surface state torque component Tar and the first assist component Ta <b> 1 output from the road surface state compensation unit 42 are added and input to the turning angle command value calculation unit 44. Therefore, the turning angle command value calculation unit 44 calculates the turning angle command value θp * based on the ideal model from the sum of the added value of the first assist component Ta1 and the road surface state torque component Tar and the steering torque Th.

Next, an operation example (action) of the power steering apparatus of the present embodiment will be described with reference to FIGS. 1 and 3.
In the power steering apparatus shown in FIG. 1, for example, when vibration occurs in the steered wheels 15 due to a change in road surface condition, an axial force corresponding to the vibration acts on the rack shaft 13, and a detected axial force F of the axial force sensor 5 changes. To do. At this time, as shown in FIG. 3, in the assist command value calculation unit 40, when the detected axial force F of the axial force sensor 5 changes, the road surface state torque component Tar changes. Therefore, since the value of the first assist component Ta1 that is input information of the turning angle command value calculation unit 44 changes, the turning angle command value θp * calculated by the turning angle command value calculation unit 44 changes. Therefore, the second assist component Ta2 calculated by the turning angle feedback control unit 45 changes, and the magnitude of the assist command value Ta * changes. As a result, the assist torque applied to the steering shaft 11 changes according to the road surface state, so that the driver's steering feeling also changes according to the road surface state. For this reason, the driver can feel the road information due to the change in the steering feeling, which improves the steering feeling.

As described above, according to the electric power steering apparatus of the present embodiment, the following effects can be obtained.
(1) The control device 3 is provided with a basic assist component calculation unit 41 that calculates the first assist component Ta1 based on the steering torque Th and the vehicle speed V. Further, a turning angle command value calculation unit 44 for calculating a turning angle command value θp * based on an ideal model from the steering torque Th and the first assist component Ta1, and an actual turning angle θp as a turning angle command value θp *. A turning angle feedback control unit 45 that calculates the second assist component Ta2 by executing the turning angle feedback control to be matched is provided. Then, the assist command value calculation unit 40 calculates the assist command value Ta * based on a value obtained by adding the first assist component Ta1 and the second assist component Ta2. Thus, vibration of the steering mechanism 1 can be accurately suppressed through the turning angle feedback control while accurately assisting the driver's steering operation.

  (2) The electric power steering apparatus is provided with an axial force sensor 5 that detects an axial force F acting on the rack shaft 13. Further, the control device 3 calculates the axial force Fr acting on the rack shaft 13 due to the road surface state from the detected axial force F of the axial force sensor 5, and calculates the road surface state torque component Tar based on this axial force Fr. A road surface condition compensation unit 42 is provided. The assist command value calculation unit 40 changes the assist command value Ta * based on the road surface state torque component Tar. As a result, the assist torque applied to the steering shaft 11 changes according to the road surface condition, so that the driver's steering feeling changes according to the road surface condition each time. For this reason, a driver | operator's steering feeling improves.

  (3) The road surface state compensation unit 42 calculates the road surface state torque component Tar by extracting the axial force belonging to the frequency band centered on the frequency fa from the detected axial force F of the axial force sensor 5. Thereby, the torque component Tar more appropriately reflecting the road surface condition can be calculated.

  (4) The road surface state compensation unit 42 performs a process of removing the steering reaction force from the detected axial force F of the axial force sensor 5 and calculates a road surface state torque component Tar based on the detected axial force F after the processing. did. Thereby, the torque component Tar more appropriately reflecting the road surface condition can be calculated.

  (5) In the control device 3, the value of the first assist component Ta1, which is input information of the turning angle command value calculation unit 44, is changed based on the road surface state torque component Tar. Thereby, the assist command value Ta * can be easily changed according to the road surface condition.

In addition, the said embodiment can also be implemented with the following forms which changed this suitably.
The ideal model of the turning angle command value calculation unit 44 is not limited to the one that sets the turning angle command value θp * based on the sum of the first assist component Ta1 and the steering torque Th. For example, the turning angle command value θp * may be set based only on the steering torque Th.

  In the above embodiment, the road surface state torque component Tar and the first assist component Ta1 are added and input to the turning angle command value calculation unit 44. Instead, the road surface state torque component Tar and the first assist component Ta1 are separately input to the turning angle command value calculation unit 44. The turning angle command value calculation unit 44 calculates the sum of the steering torque Th, the first assist component Ta1, and the road surface state torque component Tar, and calculates the turning angle command value θp * based on the calculation result. Good. Instead of inputting the road surface state torque component Tar to the turning angle command value calculation unit 44, for example, the second assist component Ta2 output from the turning angle feedback control unit 45 is changed based on the road surface state torque component Tar. You may let them. The point is that the assist command value Ta * may be changed based on the road surface state torque component Tar. In any configuration, since the assist command value Ta * changes according to the road surface condition, the driver can feel road information based on the change in steering feeling.

  -The turning angle command value calculating part 44 is not restricted to calculating the turning angle command value (theta) p * using an ideal model. For example, like the basic assist component calculation unit 41, the turning angle command value θp * may be calculated by map calculation.

  In the above embodiment, the pass frequency band of the bandpass filter 42b is set so that the disturbance caused by the natural vibration of the vehicle body can be removed from the detected axial force F of the axial force sensor 5. However, when it is desired to remove a disturbance other than the disturbance caused by the natural vibration of the vehicle body from the detected axial force F, the pass frequency band of the bandpass filter 42b may be adjusted as appropriate. Further, when the influence of the natural vibration of the vehicle body is small, the frequency band of the bandpass filter 42b may be set to a band including the frequency of the natural vibration of the vehicle body.

Depending on the type of disturbance to be removed from the detected axial force F, the road surface state compensation unit 42 may be provided with an appropriate filter circuit other than the low-pass filter 42a and the band-pass filter 42b.
In the above embodiment, the axial force sensor 5 is used as the road surface reaction force detection unit that detects the road surface reaction force of the steered wheels 15, but a sensor that can directly detect the road surface reaction force may be used. Examples of this type of sensor include a tire load sensor provided on a tire hub.

  The torque sensor 4 may be provided at an appropriate place of the steering mechanism 1 such as the intermediate shaft 11b and the pinion shaft 11c as long as the steering torque Th can be detected.

  In the above embodiment, the rotation angle sensor 7 and the turning angle calculation unit 43 are used as sensors for detecting the actual turning angle of the steered wheels 15, but the present invention is not limited to such a configuration. For example, a sensor that detects the rotation angle of the steering shaft 11 or a sensor that directly detects the turning angle of the steered wheels 15 may be used.

  In the basic assist component calculation unit 41, the first assist component Ta1 is set based on the steering torque Th and the vehicle speed V. However, for example, the first assist component Ta1 may be set based only on the steering torque Th. Further, so-called phase compensation control for changing the phase of the detected steering torque Th of the torque sensor 4 based on the assist gradient may be executed. Furthermore, so-called torque differential control may be executed in which the first assist component Ta1 is increased as the differential value of the first assist component Ta1 is increased.

  The basic assist component calculation unit 41 may be omitted, and the assist command value Ta * may be set based only on the second assist component Ta2 calculated by the turning angle feedback control unit 45. In this case, for example, if the steering torque Th input to the turning angle command value calculation unit 44 is changed based on the road surface state torque component Tar, the assist torque applied to the steering shaft 11 changes according to the road surface state. Thus, the driver's steering feeling changes according to the road surface condition.

  The turning angle feedback control may be performed using a rotation angle of an appropriate rotation shaft that can be converted into the turning angle θp, such as the rotation angle of the intermediate shaft 11b and the rotation angle of the pinion shaft 11c. Specifically, the turning angle command value calculation unit 44 calculates the rotation angle command value of the pinion shaft 11c based on the first assist component Ta1 and the steering torque Th. Further, the turning angle feedback control unit 45 performs feedback control based on the deviation so that the actual rotation angle of the pinion shaft 11c becomes the rotation angle command value, and generates the second assist component Ta2. Even with such a configuration, it is possible to obtain an effect equivalent to the effect of the above embodiment.

  In the above embodiment, the present invention is applied to an electric power steering device that applies assist torque to the column shaft 11a. Instead of this, for example, the present invention may be applied to an electric power steering apparatus that applies assist torque to the pinion shaft 11 c or applies assist torque to the rack shaft 13.

  DESCRIPTION OF SYMBOLS 1 ... Steering mechanism, 2 ... Assist mechanism, 3 ... Control apparatus (control part), 5 ... Axial force sensor (road surface reaction force detection part), 15 ... Steered wheel, 20 ... Motor, 40 ... Assist command value calculating part, 41 ... basic assist component calculation unit, 42 ... road surface condition compensation unit, 44 ... turning angle command value calculation unit, 45 ... turning angle feedback control unit.

Claims (6)

An assist mechanism for applying a motor assist torque to a vehicle steering mechanism;
A control unit for controlling the driving of the motor based on an assist command value,
The controller is
A turning angle command value calculation unit for calculating a turning angle command value that is a target value of the turning angle of the turning wheel;
A turning angle feedback control unit for calculating an assist component by executing turning angle feedback control for matching the turning angle of the steered wheels with the turning angle command value;
An assist command value calculation unit for calculating the assist command value based on the assist component;
A road surface state compensation unit that calculates a road surface state torque component according to a reaction force acting on the steered wheels due to a road surface state,
The electric power steering device, wherein the assist command value is changed based on the road surface state torque component. The electric power steering apparatus according to claim 1, wherein
The controller is
A basic assist component calculation unit for calculating a basic assist component based on a steering torque applied to the steering mechanism;
The assist command value calculator is
The electric power steering apparatus, wherein the assist command value is calculated based on a value obtained by adding the basic assist component and the assist component. In the electric power steering apparatus according to claim 1 or 2,
A road surface reaction force detection unit for detecting a road surface reaction force acting on the steered wheels from the road surface;
The road surface compensation unit is
The electric power steering apparatus, wherein the road surface state torque component is calculated by extracting a reaction force belonging to a predetermined frequency band from a detected road surface reaction force of the road surface reaction force detection unit. In the electric power steering device according to claim 3,
The electric power steering apparatus according to claim 1, wherein the predetermined frequency band is set to a frequency band excluding a natural vibration frequency of a vehicle body. In the electric power steering apparatus according to claim 3 or 4,
The road surface compensation unit is
When a reaction force acting on the steered wheel when the steered wheel is steered is a steering reaction force, a process of removing the steering reaction force from the detected road surface reaction force is performed, and a detected road surface reaction force after the process is performed. The electric power steering apparatus characterized by calculating the road surface state torque component based on In the electric power steering device according to any one of claims 1 to 5,
The turning angle command value calculation unit is
The steering angle command value is calculated based on an ideal model that models an ideal turning angle of a steered wheel according to input information including steering torque applied to the steering mechanism,
The controller is
An electric power steering device, wherein input information to the ideal model is changed based on the road surface state torque component in order to change the assist command value based on the road surface state torque component.