JP5066993B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus in which steering wheel return control is performed when a steering state of a steering system is returned to a neutral position.

As this type of electric power steering apparatus, there is known a steering wheel return control that detects an angular velocity of an electric motor that applies a steering assist force to a steering system and returns a steering wheel to a neutral position based on the angular velocity. In this case, when the frictional force and the steering assist force are balanced, the angular velocity becomes zero, so the handle cannot be returned to the neutral position.
For this reason, it is conventionally known to use a steering angle sensor and perform steering wheel return control based on the absolute steering angle detected by the steering angle sensor (see, for example, Patent Document 1).

In the case where the steering wheel return control is performed based on the absolute steering angle detected by the steering angle sensor in this way, it is necessary to equip the steering angle sensor that is not normally required in the electric power steering apparatus, and thus the manufacturing cost increases. Therefore, an inexpensive electric power steering device cannot be provided.
For this reason, conventionally, the steering wheel return state is detected without a steering angle sensor by detecting the steering wheel return state from the steering torque and rotation information of the steering system and performing the steering wheel return control based on the difference between the left and right wheel speeds of the front wheels. An electric power steering device has been proposed (see, for example, Patent Document 2).
JP 2002-145100 A Japanese Patent Laid-Open No. 2000-238652

  However, in the conventional example described in Patent Document 2, the steering torque sensor detects the steering torque detected by the torque sensor and the motor rotational angular velocity estimation means without using the steering angle sensor, and the motor terminal of the power assist motor. A return correction control means for detecting a steering wheel return state based on the motor rotation angular velocity estimated based on the inter-voltage and generating a return correction signal for causing the power assist motor to perform proper return steering when in the steering wheel return state. Although it is provided, the steering wheel return control detected by the steering wheel return detection means performs the steering wheel return control in a situation other than the situation where the steering wheel return is originally required, and the driver feels uncomfortable that the steering wheel is returned unnecessarily. There is an unsolved problem of giving.

  Therefore, the present invention has been made paying attention to the above-mentioned unsolved problems of the conventional example, and the handle return control is performed unnecessarily by performing the handle return control only in the steering state requiring the handle return control. It is an object of the present invention to provide an electric power steering device that can reliably prevent the failure.

To achieve the above object, an electric power steering apparatus according to claim 1, an electric motor for applying a steering assist force to vehicles of the steering system, a steering torque sensor for detecting steering torque of the steering system, at least A current command value calculation unit that calculates a current command value based on a steering torque detected by the steering torque sensor; and a motor control unit that controls the electric motor based on a current command value generated by the current command value calculation unit; An electric power steering apparatus comprising: a self-aligning torque estimating unit that estimates a self-aligning torque of the vehicle; a steering direction detecting unit that detects a steering direction of the steering system; and left and right front wheels in the vehicle A front wheel speed detector for detecting the wheel speed of the vehicle, a wheel speed of the left and right front wheels detected by the front wheel speed detector, and an operation detected by the steering direction detector. And a steering wheel return control unit performs steering wheel return control for the current command value based on the direction, the steering wheel return control unit, the frictional force between the road surface and Fr, estimated by the self aligning torque estimating unit Self When the absolute value of the aligning torque is set to | SAT | , the steering wheel return control is performed when 0 ≦ | SAT | ≦ Fr.

In the first aspect of the invention, the self-aligning torque estimating unit estimates the self-aligning torque, and sets the range for performing the steering wheel return control based on the estimated self-aligning torque and the steering direction. It is possible to reliably prevent the handle returning control from being performed unnecessarily by appropriately performing the control.
According to the first aspect of the present invention, when the absolute value | SAT | of the self-aligning torque estimated by the self-aligning torque estimating unit is not less than zero and not more than the frictional force Fr, the handle returning control is performed. Control can be performed more appropriately.
According to a second aspect of the present invention, there is provided an electric power steering device that is detected by an electric motor that applies a steering assist force to a steering system of a vehicle, a steering torque sensor that detects a steering torque of the steering system, and at least the steering torque sensor. An electric power steering apparatus comprising: a current command value calculation unit that calculates a current command value based on a steering torque; and a motor control unit that controls the electric motor based on a current command value generated by the current command value calculation unit A self-aligning torque estimating unit that estimates a self-aligning torque of the vehicle, a steering direction detecting unit that detects a steering direction of the steering system, and a front wheel that detects wheel speeds of left and right front wheels in the vehicle. Based on the wheel speed detection unit, the wheel speeds of the left and right front wheels detected by the front wheel speed detection unit, and the steering direction detected by the steering direction detection unit And a steering wheel return control unit performs the restoration control with respect to the current command value, the steering wheel return control unit, the frictional force between the road surface and Fr, the self aligning torque estimated by the self aligning torque estimating unit S A When T is set, when the left steering direction is detected by the steering direction detection unit, it is within the range of 0 ≦ S A T ≦ Fr , and when the right steering direction is detected, −Fr ≦ when in the range of SAT ≦ 0, it is characterized by being configured to perform handle return control.

The invention according to claim 2 can also be appropriately performed by the steering wheel return control similarly to the invention according to claim 1 . Et al is, the electric power steering apparatus according to claim 3 is the invention according to claim 1 or 2, wherein the steering wheel return control unit, said steering wheel return current command value set by the steering wheel return control the front wheel speed detected Is set to zero when the absolute value of the wheel speed difference between the left and right front wheels detected by the vehicle is equal to or greater than the slip determination threshold, and when the absolute value of the wheel speed difference is less than the slip determination threshold, When the wheel speed difference from the vehicle speed exceeds a straight traveling determination threshold, the constant current value that opposes the frictional force is set .

In the invention according to claim 3, it is possible to prevent a malfunction in a one-wheel slip state on a split μ road, etc., and to perform a handle return control in an actual turning state, and to perform an appropriate handle return control. Can do.
Furthermore, the electric power steering apparatus according to claim 4 is the invention according to claim 1 or 2, wherein the steering wheel return control unit detects the steering wheel return current command value set in the steering wheel return control by detecting the front wheel speed. Is set to zero when the absolute value of the wheel speed difference between the left and right front wheels detected by the head is less than the straight travel determination threshold, and is increased in proportion to the increase of the absolute value of the wheel speed difference when the absolute value is greater than or equal to the straight travel determination threshold. It is characterized by that.

In the invention according to claim 4, the wheel speed difference between the left and right front wheels detected by the front wheel speed detector corresponds to the turning angle of the steered wheels, so the steering wheel return current command value is based on the wheel speed difference between the left and right front wheels. By setting this, it is possible to perform an appropriate steering wheel return control corresponding to the steering angle.
Still further, according to a fifth aspect of the present invention, in the electric power steering device according to any one of the first to fourth aspects, the front wheel speed detection values of the front left and right wheels detected by the front wheel speed detecting unit are averaged. A vehicle speed detection unit that detects the vehicle speed of the vehicle, and the front wheel speed detection unit time-integrates each front wheel speed detection value when the vehicle speed is equal to or lower than a threshold value for determining a low vehicle speed region . The time integral value is configured to be set as the front wheel speed.

In the invention according to claim 5, since the time integral value of the front wheel speed detection value is set as the front wheel speed in the low vehicle speed region, the wheel speed detection is performed in the low vehicle speed region where an accurate wheel speed detection value cannot be obtained. The value can be low pass filtered to ensure a stable front wheel speed.
According to a sixth aspect of the present invention, there is provided the electric power steering device according to the fifth aspect of the invention, wherein the vehicle speed detection is performed by averaging the front wheel speed detection values of the left and right front wheels detected by the front wheel speed detecting unit. A vehicle speed detection unit that detects the vehicle speed of the vehicle, and the front wheel speed detection unit decreases the integration time of the front wheel speed detection value as the vehicle speed detected by the vehicle speed detection unit increases. It is characterized by being comprised.

  In the invention according to claim 6, the integration time of the front wheel speed detection value is changed according to the vehicle speed detected by the vehicle speed detection unit, so that the integration time is lengthened as the detection accuracy of the wheel speed detection value decreases. Thus, a value corresponding to the actual wheel speed can be set.

  According to the present invention, the self-aligning torque estimation unit estimates the self-aligning torque, and determines whether to perform the steering wheel return control based on the estimated self-aligning torque. It is possible to surely prevent the return control from being performed and perform an appropriate steering wheel return control to prevent the driver from feeling uncomfortable.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a steering device. The steering device 1 includes a steering shaft 3 on which a steering wheel 2 is mounted, and the steering shaft 3. A rack and pinion mechanism 4 connected to the opposite side of the steering wheel 2 and left and right steered wheels 6 connected to the rack and pinion mechanism 4 via a connecting mechanism 5 such as a tie rod.

  An electric motor 8 is connected to the steering shaft 3 via a speed reduction mechanism 7 constituted by, for example, a worm gear. The electric motor 8 is composed of, for example, a brushless motor, and operates as a steering assist force generation motor that generates a steering assist force of the electric power steering apparatus. The electric motor 8 is driven and controlled by a control device 14 to which a battery voltage Vb output from a battery 11 mounted on the vehicle is supplied via an ignition switch 12 and a fuse 13.

The control device 14 receives a steering torque T input to the steering wheel 2 detected by a steering torque sensor 16 disposed on the steering shaft 3 and is detected by a vehicle speed sensor 17 as a vehicle speed detection unit. The vehicle speed detection value Vs detected is detected by the wheel speed sensors 18FL and 18FR for detecting the wheel speeds of the left and right front wheels 6L and 6R used in the antilock brake control system and the traction control system, for example. _FL and V _FR are input, and the motor rotation angle θm detected by the motor rotation angle sensor 20 that detects the rotation angle of the electric motor 8 is input.

Here, the steering torque sensor 16 detects the steering torque applied to the steering wheel 2 and transmitted to the steering shaft 3. For example, the torsion bar in which the steering torque is interposed between an input shaft and an output shaft (not shown). The torsional angular displacement is converted into an electrical signal, and the torsional angular displacement is detected with a magnetic signal and converted into an electrical signal.
The control device 14 is constituted by, for example, a microcomputer, and the configuration is shown in FIG. 2 in a functional block diagram. That is, the control device 14 receives the steering torque T detected by the steering torque sensor 16 and the vehicle speed Vs detected by the vehicle speed sensor 17, and calculates the three-phase current command values I _{Aref to} I _Cref for the electric motor 8 based on these. Current command value calculation unit 21 to perform, three-phase current command values I _{Aref to} I _Cref calculated by the current command value calculation unit 21 and three-phase motor current Im (Ima to Imc) detected by the motor current detection unit 19 And a current feedback control unit 22 that calculates a three-phase voltage command value Vref by performing current feedback processing based on the above, and the three-phase voltage command value Vref calculated by the current feedback control unit 22 is input to control the electric motor 8. An electric angle θe and a motor angular velocity ω based on the motor rotation angle θm input from the motor drive circuit 23 for driving control and the motor rotation angle sensor 20. An angular velocity calculation unit 24 serving as a steering direction detection unit that calculates m, and a differentiation circuit 25 that calculates the motor angular acceleration α by differentiating the motor angular velocity ωm calculated by the angular velocity calculation unit 24 are provided.

Here, the current command value calculation unit 21 refers to the current command value calculation map shown in FIG. 3 based on the steering torque T and the vehicle speed Vs, and calculates a current command value I _ref . The d-axis current command value I _dref and the q-axis current command value I are based on the current command value I _ref output from the current command value generation unit 21a, the electrical angle θe calculated by the angular velocity calculation unit 24, and the motor angular velocity ωm. _{The dq} -axis current command value generation unit 21b that generates _qref, and the d-axis current command value I _dref and the q-axis current command value I _qref generated by the dq-axis current command value generation unit 21b are _subjected to angular velocity calculation. A two-phase / three-phase conversion unit 21c that converts to three-phase current command values I _Aref , I _Bref, and I _Cref corresponding to the electric motor 8 based on the electrical angle θe calculated by the unit 24.

Further, the control device 14 controls the steering torque T detected by the steering torque sensor 16, the current command value I _ref generated by the current command value generation unit 21 a of the current command value calculation unit 21, and the motor output from the angular velocity calculation unit 24. A self-aligning torque estimation unit 31 is provided that receives the angular velocity ωm and the motor angular acceleration α output from the differentiation circuit 25 and estimates the self-aligning torque SAT based on the angular velocity ωm.

  The principle of calculating the self-aligning torque SAT will be described with reference to FIG. 4 showing the state of torque generated between the road surface and the steering. That is, when the driver steers the steering wheel 2, a steering torque T is generated, and the electric motor 8 generates an assist torque Tm according to the steering torque T. As a result, the wheel W is steered and a self-aligning torque SAT is generated as a reaction force. Further, at that time, a torque serving as a steering resistance of the steering wheel 2 is generated by the inertia J and the friction (static friction) Fr of the electric motor 8. Considering the balance of these forces, the following equation of motion can be obtained:

J ・ α + Fr ・ sign (ωm) + SAT = Tm + T (1)
Here, when the above equation (1) is Laplace transformed with the initial value zero and the self-aligning torque SAT is solved, the following equation (2) is obtained.
SAT (s) = Tm (s) + T (s) − J ・ α (s) − Fr ・ sign (ωm (s)) (2)
As can be seen from the above equation (2), the inertia J and static friction Fr of the electric motor 8 are obtained in advance as constants, so that the self-aligning torque is obtained from the motor angular velocity ωm, the rotational angular acceleration α, the assist torque Tm, and the steering torque T. The SAT can be estimated.

Here, since the assist torque Tm is proportional to the current command value Iref, the current command value Iref is applied instead of the assist torque Tm.
Further, the control device 14 performs the steering wheel return control based on the wheel speeds V _FL and V _FR input from the wheel speed sensors 18FL and 18FR and the self-aligning torque SAT estimated by the self-aligning torque estimation unit 31. When the steering wheel return control is performed, the steering wheel returning state from the right-turning state to the neutral position or the steering wheel returning state from the left-turning state to the neutral position is determined based on the sign of the motor angular velocity ωm. A handle for outputting a steering wheel return control current command value I _comp consisting of current values −I _fri and + I _fri to counter the positive and negative frictional force Fr to the adder 32 provided on the output side of the current command value generation unit 21a. A return control unit 33 is provided.

Here, the handle return control unit 33 executes the handle return control process shown in FIG.
In the steering wheel return control process, first, in step S1, the wheel speed detection values V _FL and V _FR , the motor angular speed ωm, and the self-aligning torque SAT are read. Then, the process proceeds to step S2, and the wheel speed detection value V _FL and The average value of V _FR is calculated as the vehicle speed Vs (= (V _FL + V _FR ) / 2).

Next, the process proceeds to step S3, and whether or not the vehicle speed Vs calculated in step S2 is equal to or less than a threshold value Vs _L for determining a low vehicle speed region in which the preset wheel speed detection values V _FL and V _FR are unstable. If Vs ≦ Vs _L , it is determined that the vehicle is in the low vehicle speed region, and the process proceeds to step S4, where the wheel speed detection values V _FL and V _FR are time-integrated with a preset set time V _FL ′ and After setting V _FR ′ as the wheel speeds V _WL and V _WR , the process proceeds to step S6.

On the other hand, the determination result in the step S3, Vs> when a Vs _L, the process proceeds to step S5 it is determined that the wheel speed detected value V _FL and V _FR are high vehicle speed region is stable, the wheel speed detected value the transition from set to V _FL and V _FR directly as the wheel speed V _WL and V _WR to step S6.
In this step S6, it is determined whether or not the absolute value | ΔV _W | of the wheel speed difference ΔV _W obtained by subtracting the wheel speed V _WR from the set wheel speed V _WL is less than the slip determination threshold ΔV _{E. When W} | ≧ ΔV _E , for example, by traveling on a so-called split μ road where the road surface to which one of the front left and right wheels contacts is a low friction coefficient road surface and the road surface to which the other wheel contacts is a high friction coefficient road surface, low friction is achieved. If the front wheel on the road surface slips, or if one of the front left and right wheels slips on a slippery road surface such as a manhole in a front-wheel drive vehicle, slip occurs on one of the front left and right wheels. When it is determined that the wheel speed is not reached, the process proceeds to step S15, which will be described later, the handle return control current command value I _comp is set to "0" and output to the adder 32, and then the process returns to step S1 described above.

If the absolute value | ΔV _W | of the wheel speed difference ΔV _W is less than the slip determination threshold ΔV _{E as a} result of the determination in step S6, it is determined that there is no slip on one of the front left and right wheels. Then, the process proceeds to step S7.
In step S7, it is determined whether or not the motor angular velocity ωm is a negative value equal to or less than zero and the vehicle is in a left-turned state. If ωm> 0 and the vehicle is in the right steering state, the process proceeds to step S8, It is determined whether or not the lining torque SAT is less than zero and the friction force between the steered wheels 6 and the road surface is greater than or equal to −Fr. When −Fr ≦ SAT ≦ 0, the self-returning state is returned from the left steering state to the neutral position. When the absolute value of the aligning torque SAT is smaller than the frictional force Fr, it is determined that the torque for returning the steering wheel 2 to the neutral position is insufficient and the steering wheel return control is required, and the routine proceeds to step S9.

In this step S9, it is determined whether or not the wheel speed difference ΔV _W obtained by subtracting the front wheel left wheel speed V _WL from the front wheel right wheel speed V _WR is equal to or greater than the straight travel determination threshold value ΔV _e for determining the straight travel state. , ΔV _W > ΔVe, it is determined that the steering wheel is in the steered state and the steering wheel is being returned from the left steering state to the neutral position, and the process proceeds to step S10, where the current value + I _fri against the frictional force Fr is _handled . The return current command value I _comp is set, and then the process proceeds to step S11 to output the set handle return current command value I _comp to the adder 32 and then return to step S1.

On the other hand, when the determination result of step S7 is ω ≦ 0 and the vehicle is in the left steering state, the process proceeds to step S12, and the steering wheel return control in which the self-aligning torque SAT is equal to or less than the frictional force + Fr and equal to or greater than zero. It is determined whether or not it is a necessary region. When 0 ≦ SAT ≦ Fr, it is determined that the steering wheel return control is necessary, and the process proceeds to step S13, where the front left wheel speed V _{WL is changed} to the front right wheel speed. It is determined whether or not the wheel speed difference ΔV _W obtained by subtracting the wheel speed V _WR exceeds a straight traveling determination threshold value ΔV _e for determining a straight traveling state. If ΔV _W > ΔV _e, it is determined that the vehicle is in a steered state. Then, the process proceeds to step S14, where the current value −I _fri that opposes the frictional force Fr is set as the handle return current command value I _{comp and then the process proceeds} to step S11.

When the determination result of step S8 is SAT> 0 or SAT <−Fr, the determination result of step S9 is that when the wheel speed difference ΔV _W is less than the straight travel determination threshold value ΔV _e , When the determination result is SAT <0 or SAT> Fr, and when the determination result of step S13 is that the wheel speed difference ΔV _W is less than the straight travel determination threshold value ΔV _e, it is determined that it is not necessary to perform the steering wheel return control. Then, the process proceeds to step S15, the handle return control current command value I _comp is set to “0”, and this is output to the adder 32, and then the process returns to step S1.

Next, the operation of the above embodiment will be described.
Assuming that the vehicle is stopped and the ignition switch 12 is in an off state, the battery voltage Vb from the battery 11 is not supplied to the control device 14 in this state, so that the control device 14 is in a stopped state. The steering assist control process executed based on the steering torque T and the vehicle speed Vs shown in the functional block diagram of FIG. 2 is in an execution stop state, and the electric motor 8 is stopped and the steering assist force is transmitted to the steering shaft 3. Absent.

  When the ignition switch 12 is turned on from the vehicle stop state, the battery voltage Vb is supplied to the control device 14, whereby the control device 14 is activated, and the motor current detection unit 19 in FIG. Execution of the steering assist control process by the value calculation unit 21, the current feedback control unit 22, the motor drive circuit 23, the self-aligning torque estimation unit 31, the steering wheel return control unit 33, and the steering wheel return control process shown in FIG. 5 is started.

In this state, since the vehicle is stopped, the wheel speeds V _FL and V _FR detected by the wheel speed sensors 18FL and 18FR are “0”.
In this state, when the steering torque from the driver is not transmitted to the steering wheel 2, the steering torque T detected by the steering torque sensor 16 is substantially “0”. The current command value I _ref calculated by the value generator 21a is also “0”, and the d-axis current command value I _dref and the q-axis current command value I generated by the dq-axis current command value generator 21b. _{qref is} also “0”, and the three-phase current command values I _Aref , I _Bref and I _Cref output from the current command value calculation unit 21 are also “0”.

  Since the electric motor 8 is stopped, the motor currents Ima, Imb and Imc detected by the motor current detection unit 19 are also “0”, and the three-phase voltage command value output from the current feedback control unit 22 Vref also becomes “0”, the three-phase currents Ima, Imb, and Imc output from the motor drive circuit 23 also become “0”, and the electric motor 8 continues to be stopped.

In the non-steering state when the vehicle is stopped, the motor angular velocity ωm calculated by the angular velocity calculating unit 24 and the motor angular acceleration α calculated by the differentiating circuit 25 are both “0”, so that the self-aligning torque estimating unit 31 Thus, the self-aligning torque SAT estimated based on the equation (2) is also “0”, and when the handle return control unit 33 executes the handle return control process shown in FIG. The calculated vehicle speed Vs becomes “0”, and it is determined that the vehicle speed is in the low vehicle speed range. The process proceeds to step S4, where the wheel speed detection values V _FL and V _FR are integrated with respect to time integral values V _FL ′ and V _FR ′. Although set as V _WL and V _WR , since the wheel speed detection values V _FL and V _FR are “0”, the wheel speeds V _WL and V _WR are also naturally “0”.

Therefore, in the process of FIG. 5, the wheel speed difference ΔV _W = V _WR −V _WL ≦ ΔV _e when the process proceeds from step S 6 to steps S 7 and S 8 to step S 9, the steering wheel return control current command value The control returns to step S1 without generating I _comp , and the handle return control current command value I _comp is not added to the current command value I _ref but is input to the dq axis current command value generation unit 21b. The current command value I _ref maintains “0”.

When the driver steers the steering wheel 2 while the vehicle is stopped, so-called stationary is performed, the steering torque T detected by the steering torque sensor 16 correspondingly increases. The current command value I _ref generated by the current command value generation unit 21a of the command value calculation unit 21 becomes a large value, which is supplied to the dq axis command value generation unit 21b, and d-axis current command values I _dref and q The shaft current command value I _qref is generated, and these are converted into the three-phase current command values I _Aref , I _Bref and I _Cref by the two-phase / three-phase conversion unit 21 c and output to the current feedback control unit 22.

At this time, since the electric motor 8 is in the stopped state, the motor currents Ima to Imc detected by the motor current detection unit 19 are maintained at “0”. The phase voltage command value Vref is output to the motor drive circuit 23, and a relatively large value of the motor drive current Im is output from the motor drive circuit 23 to the electric motor 8.
For this reason, the electric motor 8 is rotationally driven to generate a relatively large steering assist force, and this steering assist force is transmitted to the steering shaft 3 via the speed reduction mechanism 7, so that the steering wheel 2 is lightly steered. Can do.

In this state, since the motor angular velocity ωm and the motor angular acceleration α are relatively large values, the self-aligning torque estimation unit 31 calculates a relatively large self-aligning torque SAT. In the process of FIG. 5, since the wheel speed difference ΔV _W obtained by subtracting the wheel speed V _WR from the wheel speed V _WL is “0”, the process returns from step S9 to step S1 as it is to return the steering wheel return control current command value I _comp. Will continue to be calculated and not output.

In this state, when the vehicle is started, this wheel speed detection value V _FL and V _FR detected by the wheel speed sensors 18FL and 18FR is increased in accordance with, the straight running condition, the wheel speed detected value V _FL and V _FR is substantially the same value, but the wheel speed detection value V _FL (or V _FR ) on the outer ring side becomes larger than the wheel speed detection value V _FR (or V _FL ) on the inner ring side when the vehicle is turning, and both wheel speeds are The difference ΔV _W increases as the turning radius decreases.

For this reason, when the vehicle is traveling in the low vehicle speed region, in the steering wheel return control process of FIG. 5 executed by the steering wheel return control unit 33, the process proceeds from step S3 to step S4 to detect the wheel speed detection value V. _{by FL} and V _FR of time integrating the time-integrated value V _FL 'and V _FR' is set as the wheel speed V _WL and V _WR, the wheel speed detection detected by the wheel speed sensors 18FL and 18FR especially at low vehicle speed It is possible to obtain stable wheel speeds V _WL and V _WR by compensating that the values V _FL and V _FR are not accurate values.

  When the vehicle is traveling in the low vehicle speed range, the self-aligning torque SAT estimated by the self-aligning torque estimating unit 31 is a small value, and therefore the handle returning control unit 33 performs the handle returning shown in FIG. When the control process is executed, for example, when the steering wheel 2 is turned to the right from the neutral position, as shown in FIG. 6, the motor angular velocity ωm calculated by the angular velocity calculating unit 24 becomes positive and self The self-aligning torque SAT estimated by the aligning torque estimation unit 33 is also a positive value.

Therefore, in the handle return control process of FIG. 5, the process proceeds from step S7 to step S8, but since SAT> 0, the process proceeds to step S15, and the handle return control current command value I _comp is set to “0”. The process of outputting this to the adder 32 and then returning to step S1 is repeated.
After that, when the driver turns the steering wheel 2 leftward (left steering) after the steering wheel 2 is turned from the steering state to the steered state, the motor angular velocity ωm calculated by the angular velocity calculation unit 24 is a negative value indicating the left steering direction. It becomes.

Assuming that the self-aligning torque SAT estimated by the self-aligning torque estimation unit 33 at this time is a positive value and larger than the frictional force Fr as shown in FIG. 6, the steering wheel return control process of FIG. Then, the process proceeds from step S7 to step S12. However, since SAT> Fr, the process proceeds to step S15, the handle return control current command value I _comp is set to “0”, and this is output to the adder 32. Returning to step S1, the handle return control continues to be suspended.

Thereafter, when the steering angle of the steering wheel 2 is reduced and the estimated self-aligning torque SAT becomes equal to or less than the frictional force Fr, the process proceeds from step S12 to step S13 in the process of FIG. Therefore, the wheel speed detection value V _FL of the front left wheel becomes larger than the wheel speed detection value V _{FR of the} front right wheel, and the wheel speed difference ΔV _{W that} is the difference between the two exceeds the straight travel determination threshold value ΔV _e . Then, the process proceeds from step S13 to step S14, and a negative current command value -I _fri that opposes the frictional force Fr is set as the steering wheel return control current command value I _comp . Next, the steering wheel return control current command value I _comp set in step S11 is output to the adder 32, whereby the steering wheel return control current is added to the current command value I _ref output from the current command value generation unit 21a. The command value I _comp is added.

At this time, since the steering wheel return control current command value I _comp is a negative value, the steering angle is small, and the steering torque is substantially “0”, the current command value I _ref is substantially “0”. The current command value input to the q-axis current command value generation unit 21b is a negative value, and a d-axis current command value I _dref and a q-axis current command value I _{qref corresponding to this} are calculated, Since the conversion unit 21c converts the three-phase current command values I _Aref , I _Bref and I _Cref to output to the current feedback control unit 22, the electric motor 8 generates a steering assist force against the frictional force Fr, and the steering It becomes easy for the wheel 2 to return to the neutral position. For the driver, since the steering torque does not increase, it is easy to drive.

Similarly, when the steering wheel 2 is turned leftward from the neutral position to increase the steering wheel 2 and then right steering is performed to return the steering wheel 2 to the neutral position, the motor angular velocity ωm calculated by the angular velocity calculator 24 becomes a positive value. The self-aligning torque SAT estimated by the self-aligning torque estimating unit 31 is a negative value. At this time, when the self-aligning torque SAT is smaller than the negative frictional force −Fr (SAT <−Fr), the process proceeds from step S8 to step S15, and the handle return control current command value I _comp is set to “0”. Is output to the adder 32, the process returns to step S1 to stop the handle return control. However, when the estimated self-aligning torque SAT is in the range of −Fr ≦ SAT ≦ 0, the process proceeds to step S10 through steps S8 and S9, and the positive current command value + I _fri is the steering wheel return control current. Since the command value I _comp is set and output to the adder 32, the steering assist force against the frictional force -Fr is generated by the electric motor 8 in the same manner as the steering wheel returning state from the right turn state described above. The steering wheel 2 can be easily returned to the neutral position.

Further, when the vehicle speed Vs exceeds the low vehicle speed threshold value Vs _L , the process proceeds from step S3 to step S5 in the process of FIG. 5, and the wheel speed detection values V _FL and V _FR are directly used as the wheel speed V _WL and Except for setting as V _WR , the same effects as those in the low vehicle speed region described above can be obtained.
When the vehicle travels, traveling on a split μ road, manhole, etc. causes one wheel to slip, and the absolute value | ΔV _W | of the wheel speed difference ΔV _W is greater than or equal to the slip determination threshold ΔV _E. When the value is reached, in the process of FIG. 5, the process proceeds from step S6 to step S15, the handle return control current command value I _comp is set to “0” and output to the adder 32, and then the process returns to step S1 to handle Since the return control is stopped, it is possible to reliably prevent the handle return control from being performed unnecessarily when a slip occurs.

As described above, according to the present embodiment, the self-aligning torque estimator 33 estimates the self-aligning torque SAT, and the absolute value | SAT | of the self-aligning torque SAT exceeds the frictional force Fr. Counteracts the frictional force Fr when the absolute value | SAT | of the self-aligning torque SAT is less than the frictional force Fr by returning the steering wheel 2 to the neutral position by the self-aligning torque actually acting on the vehicle. Since the handle return control is performed by calculating the handle return control current command value I _comp and adding it to the current command value I _ref , the handle return control is performed only in a state where the handle return control is required, and unnecessary handle return control is performed. It is possible to reliably prevent the vehicle from being performed, and to reliably prevent the driver from feeling uncomfortable.

Moreover, in the low vehicle speed range where the wheel speed detected value V _FL and V _FR to be detected by the wheel speed sensors 18FL and 18FR becomes unstable, the wheel speed detected value V _FL and V wheel speed time integral value of the _FR V _WL and V by employing as _WR, the wheel speed detection value V _FL and V _FR low pass filter to be able to obtain a stable wheel speed V _WL and V _WR, it is possible to perform stable wheel return control in the low vehicle speed range it can.

  Incidentally, in the case of the conventional example in which the judgment based on the self-aligning torque SAT is not applied to determine whether or not to perform the steering wheel return control, the above-described self-aligning torque SAT in FIG. 6 is larger than the frictional force Fr, and the steering wheel return control is unnecessary. The steering wheel return control is performed even in such a region, and the steering assist force for returning the steering wheel 2 to the neutral position becomes too large, which gives the driver a sense of incongruity. However, in the present invention, the steering wheel return control is performed as described above. Handle return control can be performed only when necessary.

In the above-described embodiment, the case where the current value I _{fri serving} as the steering wheel return control current command value I _comp is set to a constant value has been described. However, the present invention is not limited to this, and as illustrated in FIG. When the speed difference ΔV _W is smaller than the straight traveling determination threshold value ΔV _e , the current value I _fri is “0”. As the straight _traveling determination threshold value ΔV _e increases, the current value I _fri increases, and the wheel speed difference ΔV _W becomes the set value ΔV _WS. Applying a current value calculation map in which the current value I _fri becomes a constant value when the value is equal to or greater than the current value according to the wheel speed difference ΔV _W with reference to the current value calculation map based on the wheel speed difference ΔV _W I _fri may be set. In this case, since the steering wheel return control current command value I _comp becomes smaller as the turning state approaches the straight traveling state, it is possible to prevent overshooting when the steering wheel 2 returns to the neutral position. .

In the above embodiment, the case where the wheel speed detection values V _FL and V _FR are time-integrated with the set time in the low vehicle speed region to calculate the time integration values V _VL ′ and V _FR ′ has been described. However, the set time may be set to be shorter as the vehicle speed Vs increases.
Furthermore, although the case where the angular velocity calculation unit 24 is applied as the steering direction detection unit has been described in the above embodiment, the present invention is not limited to this, and the rotation is based on the motor rotation angle θm detected by the rotation angle sensor 20. The direction may be detected, or the steering direction may be detected based on the steering torque T detected by the steering torque sensor 16.

  Furthermore, in the above embodiment, the case where a brushless motor is applied as the electric motor 8 has been described. However, the present invention is not limited to this, and a brushed motor can also be applied. In this case, dq The shaft current command value generation unit 21b and the two-phase / three-phase conversion unit 21c are omitted, and instead of the case where the motor current detection unit 19 detects the three-phase motor current, the DC motor current is detected, and the current feedback control unit 22 may be fed back.

1 is an overall configuration diagram showing a first embodiment of the present invention. It is a functional block diagram which shows the control apparatus in 1st Embodiment. It is a characteristic diagram showing the relationship between the steering torque and current command value showing the current command value calculation map. It is a schematic diagram explaining the estimation principle of a self-aligning torque. It is a flowchart which shows an example of the handle | steering-wheel return control processing procedure performed with a handle | steering-wheel return control part. FIG. 6 is a characteristic diagram showing a relationship between a steering angle, a self-aligning torque, and a steering assist force for explaining the operation of the present invention. It is a characteristic diagram which shows the map for electric current value calculation used as a steering wheel return control electric current command value.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering device, 2 ... Steering wheel, 3 ... Steering shaft, 7 ... Deceleration mechanism, 8 ... Electric motor, 14 ... Control device, 16 ... Steering torque sensor, 17 ... Vehicle speed sensor, 18FL, 18FR ... Wheel speed sensor, 19 DESCRIPTION OF SYMBOLS ... Motor current detection part, 20 ... Motor rotation angle sensor, 21 ... Current command value calculation part, 21a ... Current command value generation part, 21b ... dq-axis current command value generation part, 21c ... Two-phase / 3-phase conversion part , 22 ... current feedback control unit, 23 ... motor drive circuit, 24 ... angular velocity calculation unit, 25 ... differentiation circuit, 31 ... self-aligning torque estimation unit, 32 ... adder, 33 ... handle return control unit

Claims (6)

An electric motor that applies a steering assist force to a steering system of a vehicle, a steering torque sensor that detects a steering torque of the steering system, and a current command that calculates a current command value based on at least the steering torque detected by the steering torque sensor An electric power steering apparatus comprising: a value calculation unit; and a motor control unit that controls the electric motor based on a current command value generated by the current command value calculation unit,
A self-aligning torque estimating unit for estimating a self-aligning torque of the vehicle; a steering direction detecting unit for detecting a steering direction of the steering system; and a front wheel speed detecting unit for detecting wheel speeds of left and right front wheels in the vehicle. A steering wheel return control unit that performs steering wheel return control on the current command value based on the wheel speeds of the left and right front wheels detected by the front wheel speed detection unit and the steering direction detected by the steering direction detection unit,
When the frictional force with the road surface is Fr and the absolute value of the self-aligning torque estimated by the self-aligning torque estimating unit is | SAT |, the steering wheel return control unit satisfies 0 ≦ | SAT | ≦ Fr. An electric power steering apparatus configured to perform a steering wheel return control when it is within a range . An electric motor that applies a steering assist force to a steering system of a vehicle, a steering torque sensor that detects a steering torque of the steering system, and a current command that calculates a current command value based on at least the steering torque detected by the steering torque sensor An electric power steering apparatus comprising: a value calculation unit; and a motor control unit that controls the electric motor based on a current command value generated by the current command value calculation unit,
A self-aligning torque estimating unit for estimating a self-aligning torque of the vehicle; a steering direction detecting unit for detecting a steering direction of the steering system; and a front wheel speed detecting unit for detecting wheel speeds of left and right front wheels in the vehicle. A steering wheel return control unit that performs steering wheel return control on the current command value based on the wheel speeds of the left and right front wheels detected by the front wheel speed detection unit and the steering direction detected by the steering direction detection unit,
The steering wheel return control unit detects the left steering direction by the steering direction detection unit when the frictional force with the road surface is Fr and the self-aligning torque estimated by the self-aligning torque estimation unit is S AT. when you are, in the range of 0 ≦ S a T ≦ Fr, performs when it is in the range of -Fr ≦ SAT ≦ 0, handle return control when and detects the right steering direction it characterized by being composed electrostatic power steering apparatus as. The steering wheel return control unit sets the steering wheel return current command value set in the steering wheel return control to zero when the absolute value of the wheel speed difference between the left and right front wheels detected by the front wheel speed detection unit is equal to or greater than a slip determination threshold. When the absolute value of the wheel speed difference is less than the slip judgment threshold, the constant current value is set to oppose the frictional force when the wheel speed difference between the turning outer wheel speed and the turning inner wheel speed exceeds the straight running judgment threshold. the electric power steering apparatus according to claim 1 or 2, characterized in that it is configured to. The steering wheel return control unit sets the steering wheel return current command value set in the steering wheel return control to zero when the absolute value of the wheel speed difference between the left and right front wheels detected by the front wheel speed detection unit is less than a straight travel determination threshold value. set, the electric power steering apparatus according to claim 1 or 2, wherein Rukoto characterized increases in proportion to the increase of the absolute value of the wheel speed difference when it straight determination threshold value or higher. It has a vehicle speed detection unit that detects the vehicle speed of the vehicle by averaging the front wheel speed detection values of the front left and right wheels detected by the front wheel vehicle speed detection unit, and the front wheel speed detection unit determines whether the vehicle speed is in a low vehicle speed region. 5. The system according to claim 1 , wherein a time integration value obtained by time-integrating each detected front wheel speed detection value is set as a front wheel speed when the threshold value is equal to or less than a threshold value. The electric power steering device described in 1. The vehicle has a vehicle speed detection unit that detects the vehicle speed of the vehicle by averaging the front wheel speed detection values of the front left and right wheels detected by the front wheel vehicle speed detection unit, the vehicle speed detection unit that detects the vehicle speed of the vehicle, and the front wheel speed detection unit, the electric power according to claim 5, characterized in that vehicle speed integration time detected by the vehicle speed detecting section of the front wheel speed detected value is configured so that a short enough to increase steering apparatus.

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