JP2007320429A - Electric power steering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering apparatus capable of restraining kickback more appropriately in releasing steering assist control. <P>SOLUTION: This electric power steering system is provided with a three-phase brushless motor 12 for providing a steering assist force relieving a driver from a steering burden to a steering system. To generate the steering assist force corresponding to at least a steering torque T, the motor 12 is drivingly controlled, referring to a motor rotational angle θ. At this time, when there is abnormality in the motor rotational angle θ detected by a rotational angle detection unit, a reference angle of the motor rotational angle θ is changed so that a rotational state of the motor 12 just before the abnormality occurs is maintained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that includes a steering assist mechanism having an electric motor that applies a steering assist force to a steering system, and suppresses the occurrence of a kickback phenomenon when the operation of the steering assist mechanism is stopped.

As a conventional electric power steering device, when the motor is stopped during the steering assist, a so-called kickback phenomenon in which the return force of the torsion of the steering system suddenly acts on the steering wheel by short-circuiting the terminals of the motor for a predetermined time. Is known to reduce the steering burden on the driver (for example, Patent Document 1).
Japanese Patent No. 3399226

However, the electric power steering device described in Patent Document 1 only suppresses a rapid steering wheel return caused by the torsional return force of the steering system when shifting from the steering assist state to the manual steering. The steering wheel is gradually returned to the neutral position, and the occurrence of the kickback phenomenon cannot be completely prevented.
Therefore, an object of the present invention is to provide an electric power steering device that more appropriately suppresses kickback when canceling steering assist control.

  In order to solve the above-described problem, an electric power steering apparatus according to claim 1 is an electric power steering apparatus including an electric motor that applies a steering assist force that reduces a steering burden on a driver to a steering system, and the electric power steering apparatus includes: Rotation angle detection means for detecting the motor rotation angle of the motor; steering torque detection means for detecting steering torque; Motor control means for controlling the drive of the motor, and abnormality detection means for detecting an abnormality in the motor rotation angle detected by the rotation angle detection means. Change of the reference angle of the motor rotation angle so as to maintain the rotation state of the electric motor immediately before the occurrence of abnormality It is characterized in that it comprises a stage.

According to a second aspect of the present invention, there is provided the electric power steering apparatus according to the first aspect of the invention, wherein when the reference angle changing means detects an abnormality in the motor rotation angle by the abnormality detecting means, the motor rotation immediately before the occurrence of the abnormality is detected. An angle is set to the reference angle.
Furthermore, the electric power steering apparatus according to a third aspect is the invention according to the second aspect, wherein the reference angle changing means uses the twisting force of the steering system immediately before the occurrence of the abnormality as a reference value, and the current twisting force of the steering system is When the reference value is the same as the reference value and less than or equal to the reference value, the reference angle at that time is maintained.

According to a fourth aspect of the present invention, there is provided the electric power steering apparatus according to the third aspect of the invention, wherein the reference angle changing means has the same sign as the reference value and larger than the reference value when the current torsional force of the steering system is The reference angle is changed in a direction opposite to the steering neutral direction with respect to the reference angle at that time.
Furthermore, in the electric power steering apparatus according to claim 5, in the invention according to claim 3 or 4, the reference angle changing unit is configured to perform the reference when the torsional force of the current steering system is different from the reference value. The angle is changed in a steering neutral direction with respect to the reference angle at that time.

An electric power steering apparatus according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein the reference angle changing means detects the abnormality of the motor rotation angle by the abnormality detecting means. The motor rotation angular velocity immediately before the occurrence of abnormality is set as a reference angular velocity, and the reference angle is set based on the reference angular velocity.
Furthermore, the electric power steering apparatus according to a seventh aspect is characterized in that, in the invention according to the sixth aspect, the reference angle changing means includes a reference angular velocity reducing means for gradually reducing the reference angular velocity.

An electric power steering apparatus according to an eighth aspect of the present invention is the invention according to any one of the first to seventh aspects, wherein the motor control unit detects an abnormality in the motor rotation angle by the abnormality detection unit. A gradual change processing means for gradually decreasing the output of the electric motor is provided.
Furthermore, the electric power steering apparatus according to a ninth aspect is the invention according to the eighth aspect, wherein the gradual change processing means determines a reduction rate of the output of the electric motor in accordance with a torsional force of a steering system. It is said.

  According to the electric power steering device of the present invention, when the abnormality of the motor rotation angle detected by the rotation angle detection means is detected, the rotation angle of the electric motor immediately before the occurrence of the abnormality is maintained as the reference angle of the motor rotation angle. Since the drive control of the motor is performed by changing, it is possible to prevent the motor from returning due to the reaction force and to suppress the occurrence of the kickback phenomenon.

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 an electric power steering apparatus according to the present invention.
In the figure, reference numeral 1 denotes a steering wheel, and a steering force applied to the steering wheel 1 from a driver is transmitted to a steering shaft 2 having an input shaft 2a and an output shaft 2b. The steering shaft 2 has one end of the input shaft 2a connected to the steering wheel 1 and the other end connected to one end of the output shaft 2b via a torque sensor 3 as steering torque detecting means.

  The steering force transmitted to the output shaft 2 b is transmitted to the lower shaft 5 via the universal joint 4 and further transmitted to the pinion shaft 7 via the universal joint 6. The steering force transmitted to the pinion shaft 7 is transmitted to the tie rod 9 via the steering gear 8 and steers steered wheels (not shown). Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8a connected to the pinion shaft 7 and a rack 8b meshing with the pinion 8a, and the rotational motion transmitted to the pinion 8a is linearly moved by the rack 8b. It has been converted to movement.

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 a three-phase brushless motor 12 as an electric motor that is connected to the reduction gear 11 and generates a steering assist force for the steering system. Yes.
The torque sensor 3 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a, and a torsional angle displacement of 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 detected by, for example, a potentiometer.

  Further, as shown in FIG. 2, the three-phase brushless motor 12 is connected to one end of the U-phase coil Lu, the V-phase coil Lv and the W-phase coil Lw to form a star connection, and each of the coils Lu, Lv and Lw The other end is connected to the steering assist control device 20, and motor drive currents Iu, Iv, and Iw are individually supplied. In addition, the three-phase brushless motor 12 includes a rotor position detection circuit 13 as a rotation angle detection unit that includes a resolver, an encoder, and the like that detect the rotation position of the rotor.

  The rotor position detection circuit 13 supplies a carrier wave signal sin ωt having a predetermined frequency to a resolver, and a sine wave signal (sin ωt · sin θ) having a waveform obtained by amplitude-modulating the carrier wave signal sin ωt with a sine wave sin θ and the carrier wave signal sin ωt. A cosine wave signal (sin ωt · cos θ) having a waveform modulated with the cosine wave cos θ is generated. Then, the sine wave signal (sin ωt · sin θ) and the cosine wave signal (sin ωt · cos θ) are A / D converted and, for example, a positive peak time (peak detection pulse Pp) of the carrier wave sin ωt is detected, and the peak detection pulse Pp Each time is detected, a motor rotation angle calculation process (not shown) is executed to calculate sin θ and cos θ, and a motor rotation angle (rotor rotation angle) θ is calculated from the calculated sin θ and cos θ.

  As shown in FIG. 2, the steering assist control device 20 receives the steering torque T detected by the torque sensor 3 and the vehicle speed detection value Vs detected by the vehicle speed sensor 21 and is detected by the rotor position detection circuit 13. Is output from the motor current detection circuit 22 that detects the motor drive currents Iu, Iv, and Iw supplied to the phase coils Lu, Lv, and Lw of the three-phase brushless motor 12. Drive current detection values Iud, Ivd, and Iwd are input.

  The steering assist control device 20 calculates a steering assist target current value based on the steering torque T, the vehicle speed detection value Vs, and the rotor rotation angle θ, and outputs motor voltage command values Vu, Vv, and Vw, for example. The control arithmetic device 23 configured, a motor drive circuit 24 configured by a field effect transistor (FET) that drives the three-phase brushless motor 12, and phase voltage command values Vu, Vv, and Vw output from the control arithmetic device 23. And an FET gate drive circuit 25 for controlling the gate current of the field effect transistor of the motor drive circuit 24. This steering assist control device 20 corresponds to a motor control means.

As shown in FIG. 3, the control arithmetic unit 23 determines the current command values of the vector control d and q components using the excellent characteristics of vector control, and then sends the current command values to the respective excitation coils Lu to Lw. A vector control phase command value calculation circuit 30 that converts and outputs the corresponding phase current command values Iu ^* , Iv ^*, and Iw ^* , and each phase current command value Iu that is output from the vector control device command value calculation circuit 30 ^* , Iv ^* and Iw ^*, and a current control circuit 40 that performs current feedback processing using the motor current detection values Iud, Ivd, and Iwd detected by the motor current detection circuit 22.

As shown in FIG. 3, the vector phase command value calculation circuit 30 receives the steering torque T detected by the torque sensor 3 and the vehicle speed Vs detected by the vehicle speed sensor 21, and based on these, the steering assist current command value I _M A steering assist current command value calculation unit 31 for calculating ^* and a control angle (electrical angle θe and electrical angular velocity ωe) and a control amount (steering assist current command) based on the rotor rotation angle θ detected by the rotor rotation angle detection circuit 13. The d-axis command current Id ^* is calculated based on the control signal output unit 32 that outputs the current limit value of the value I _M ^* ), the steering auxiliary current command value I _M ^* limited by the control amount, and the electrical angular velocity ωe. A d-axis command current calculator 34, a d-q-axis voltage calculator 35 that calculates a d-axis voltage ed (θ) and a q-axis voltage eq (θ) based on the electrical angle θe, and a d-axis voltage ed (θ ) And q-axis voltage eq (θ) and d-axis command current Id ^* And q-axis command current calculation unit 36 for calculating q-axis command current Iq ^* based on steering assist current command value I _M ^*, and d-axis command current Id ^* and q output from d-axis command current calculation unit 34 A two-phase / three-phase conversion unit 37 that converts the q-axis command current Iq ^* output from the axis command current calculation unit 36 into three-phase current command values Iu ^* , Iv ^*, and Iw ^* is provided.

The steering assist current command value calculation unit 31 described above calculates the steering assist current command value I _M ^* with reference to the steering assist current command value calculation map shown in FIG. 4 based on the steering torque T and the vehicle speed Vs. Here, as shown in FIG. 4, the steering assist current command value calculation map takes the steering torque T on the horizontal axis, the steering assist command value I _M ^* on the vertical axis, and the vehicle speed detection value V as a parameter. It is composed of a characteristic diagram represented by a parabolic curve, and the steering assist command value I _M ^* maintains “0” during the period from the steering torque T to “0” to a set value Ts1 in the vicinity thereof. When T exceeds the set value Ts1, initially, the steering assist 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 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.

Further, a limit value is provided for the steering assist command value I _M ^* , and this current limit value is normally set to the normal limit value I _MAX0 . The current limit value can be changed by the control signal output unit 32 and is output from the control signal output unit 32 as a control amount.
In the present embodiment, the control amount output from the control signal output unit 32 is such that the torsional force of the steering system generated by the motor is reduced by reducing the control amount. Here, the current limit value of the motor However, a gain (assist control gain) that multiplies the torsional force of the steering system can also be used.

Further, the current control circuit 40 is a motor that flows in the phase coils Lu, Lv, Lw detected by the current detection circuit 22 from the current command values Iu ^* , Iv ^* , Iw ^* supplied from the vector control phase command value calculation unit 30. Subtractors 41u, 41v, and 41w for subtracting phase current detection values Iud, Ivd, and Iwd to obtain phase current errors ΔIu, ΔIv, and ΔIw, and proportional-integral control for the obtained phase current errors ΔIu, ΔIv, and ΔIw To calculate the command voltages Vu, Vv, Vw, and pulse width modulation (corresponding to the field effect transistors Qua to Qwb of the motor drive circuit 24 based on the calculated command voltages Vu, Vv, Vw ( PWM) 43 that forms signals PWMua to PWMwb.

Then, the pulse width modulation signals PWMua to PWMwb output from the PWM control unit 43 are supplied to the FET gate drive circuit 25.
In this way, steering assist force control is performed in which the motor is driven and controlled with reference to the rotor rotation angle θ in order to generate the steering assist force according to the steering torque T and the vehicle speed detection value Vs. The reference angle of the rotor rotation angle θ is output as a control angle from the control signal output unit 32. In this embodiment, the control signal output unit 32 executes a control signal output process to be described later to control steering assist force. If the release condition is not satisfied, the control angle is set to the normal angle, and the motor is controlled based on this control angle. On the other hand, when the cancellation condition of the steering assist force control is satisfied, the control angle is changed with respect to the normal angle, and the abnormality occurrence control for controlling the drive of the motor based on the changed control angle is performed.

  FIG. 5 is a flowchart showing a control signal output processing procedure executed by the control signal output unit 32. This control signal output process is executed as a timer interrupt process at predetermined time intervals. First, in step S1, the control signal output unit 32 determines whether or not a condition for canceling the steering assist force control is satisfied. Here, it is determined whether or not the abnormality occurrence control flag FL is set to “1” which means that the abnormality occurrence control is performed. If FL = 0 and the release condition is not satisfied, the process proceeds to step S2. If FL = 1 and the release condition is satisfied, the process proceeds to step S13 described later.

In step S <b> 2, the control signal output unit 32 performs an abnormality detection process for detecting an abnormality in the rotor position detection circuit 13. Specifically, a sine wave sin θ and a cosine wave cos θ calculated by a motor rotation angle calculation process (not shown) are read to determine whether sin θ and cos θ are normal. Here, (sin θ) ² + (cos θ) ² is calculated, and when (sin θ) ² + (cos θ) ² ≠ 1, it is determined that there is an abnormality, or an abnormality determination map stored in advance is referred to, When the combination of sin θ and cos θ does not exist within a predetermined normal region, it is determined that there is an abnormality.

Next, the process proceeds to step S3, and the control signal output unit 32 determines whether or not the rotor position detection circuit 13 is normal based on the determination result of step S2. Then, when it is determined to be normal, the process proceeds to step S4, and when it is determined to be abnormal, the process proceeds to step S10 described later.
In step S4, the control signal output unit 32 stores in the memory the rotor rotation angle θ detected by the rotor position detection circuit 13 and the rotor rotation angular velocity θ ′ obtained by differentiating the rotor rotation angle θ.

Next, in step S5, the control signal output unit 32 performs abnormality detection processing other than the rotor position detection circuit 13 (torque sensor 3, vehicle speed sensor 15, etc.), and proceeds to step S6.
In step S6, the control signal output unit 32 determines whether other than the rotor position detection circuit 13 is normal based on the determination result in step S5. When it is determined that the steering assist force control is normal, the process proceeds to step S7 on the assumption that the condition for canceling the steering assist force control is not satisfied, and the control angle and the control amount for performing the normal steering assist force control are set. . Specifically, the current rotor rotation angle θ stored in the memory in the step S4 is converted into an electrical angle θe, and the electrical angle θe is differentiated to calculate an electrical angular velocity ωe, which is used as a control angle (normal angle). ). In addition, a preset normal limit value I _MAX0 is set as a control amount.

Next, the process proceeds to step S8, where the control signal output unit 32 outputs the set control angle and control amount, and ends the control signal output process.
On the other hand, if it is determined in step S6 that the control signal output unit 32 has an abnormality other than the rotor position detection circuit 13, the process proceeds to step S9, where an abnormality has occurred other than the rotor position detection circuit 13. After the steering assist force control (other abnormal process) is executed, the control signal output process is terminated.

In step S10, the control signal output unit 32 sets the abnormality occurrence time control flag FL to “1” which means that the steering assist force control is performed when the abnormality occurs, and the process proceeds to step S11.
In step S11, the control signal output unit 32 converts the rotor rotation angle θ stored in the memory in step S4 into an electrical angle θe, and differentiates the electrical angle θe to calculate an electrical angular velocity ωe, which is abnormally detected. The initial control angle of the on-occurrence control is set, and the process proceeds to step S12.

In step S12, the control signal output unit 32 sets the normal limit value I _MAX0 as the initial control amount for the abnormality occurrence control, and _proceeds to step S8.
In step S13, the control signal output unit 32 performs an abnormality detection process for the torque sensor 3, and proceeds to step S14.
In step S14, the control signal output unit 32 determines whether or not the torque sensor 3 is normal based on the determination result in step S13. If it is determined that the torque sensor 3 is abnormal, the process proceeds to step S15. Then, after the steering assist force control is performed when the torque is abnormal, the control signal output process is terminated.

On the other hand, when the control signal output unit 32 determines in step S14 that the torque sensor 3 is normal, the process proceeds to step S16 to detect the steering torque T.
Next, in step S <b> 17, the control signal output unit 32 performs control angle update processing according to the torsional force of the steering system. In this embodiment, based on the twisting force of the steering system at the time when the condition for canceling the steering assist force control is satisfied, the control angle is updated according to the deviation and sign of the reference value and the current twisting force. To do.

When the reference value and the current twisting force have the same sign and the current twisting force is larger than the reference value, the control angle is advanced in the direction opposite to the neutral direction of the handle. Further, when the reference value and the current twisting force have the same sign and the current twisting force is smaller than the reference value, the control angle is held.
In addition, when the torsional force of the steering system becomes zero even once after the release condition of the steering assist force control is satisfied, the reference value is changed to “0”, and thereafter the reference value “0” is changed. The control angle is updated based on the original. At this time, if the sign of the torsional force of the steering system is reversed with respect to the sign of the reference value when an abnormality occurs, the control angle is advanced in the neutral direction of the steering wheel.

Here, the speed at which the control angle is advanced is determined as shown in FIG. 6 according to the deviation between the current twisting force and the reference value. That is, the greater the deviation between the current twisting force and the reference value, the greater the speed at which the control angle is advanced. A predetermined limiter is provided for the speed at which the control angle is advanced.
Next, in step S18, the control signal output unit 32 performs a control amount update (decrease) process. The reduction rate of the control amount is determined as shown in FIG. 7 according to the absolute value of the deviation between the current twisting force and the reference value. Here, the larger the absolute value of the deviation between the current torsional force and the reference value, the smaller the control rate reduction rate, and the longer the control time for control when an abnormality occurs.

The method for reducing the reduction ratio can be determined by various functions such as a straight line and a quadratic curve. In addition, the reduction rate of the control amount can be always constant.
This control amount reduction process is not executed when the steering system is turned up so that the torsional force of the steering system becomes larger than the reference value, and during steering, and the control amount is maintained.

Next, in step S19, the control signal output unit 32 determines whether or not the control amount is greater than a predetermined control end determination threshold value (for example, 0). Then, when the control amount is larger than “0”, it is determined that the control at the time of occurrence of the abnormality is continued, and the process proceeds to the step S8. When the control amount is “0” or less, the control signal output process is finished as it is.
In FIG. 5, the processes in steps S2 and S3 correspond to the abnormality detecting means, the processes in steps S11 and S17 correspond to the reference angle changing means, and the processes in steps S12 and S18 correspond to the gradual change processing means.

Next, the operation of the first embodiment will be described based on the time chart shown in FIG. In FIG. 8, A is the torsional force of the steering system, and B is the control angle.
Now, it is assumed that the host vehicle is turning on a right curve road while being steered, no abnormality has occurred in the torque sensor 3 or the like, and the release condition for the steering assist force control is not satisfied. In this case, the control signal output unit 32 determines that the rotor position detection circuit 13 is normal in step S3 of FIG. 5 and proceeds to step S4, and stores the rotor rotation angle θ and the rotor rotation angular velocity θ ′ in the memory. save. Further, since the torque sensor 3 and the vehicle speed sensor 15 are also normal, the routine proceeds from step S6 to step S7, so that normal steering assist force control is executed.

Therefore, the steering arithmetic unit 23 determines each phase current command value Iu ^* based on the steering torque T detected by the torque sensor 3, the vehicle speed Vs detected by the vehicle speed sensor 15, and the rotor rotation angle θ detected by the rotor position detection circuit 13 ^. , Iv ^* and Iw ^* are calculated, and current feedback processing is performed using the phase current command values Iu ^* , Iv ^* and Iw ^* and the motor current detection values Iud, Ivd and Iwd detected by the motor current detection circuit 22. The phase voltage commands Vu, Vv and Vw are calculated. Then, PWM signals PWMua to PWMwb calculated based on the phase voltage commands Vu, Vv and Vw are output to the FET gate drive circuit 25.
The FET gate drive circuit 25 controls the gate current of the field effect transistor of the motor drive circuit 24 based on the PWM signal. As a result, the torque generated by the three-phase brushless motor 12 is converted into the rotational torque of the steering shaft 2 via the reduction gear 11, and the driver's steering force is assisted.

From this state, it is assumed that an abnormality has occurred in the rotor position detection circuit 13 at time t1 in FIG. 8 and the release condition for the steering assist force control is satisfied. In this case, the steering arithmetic unit 13 determines that an abnormality has occurred in the rotor position detection circuit 13 in step S3 of FIG. 5, and proceeds to step S10 to set the abnormality occurrence control flag FL = 1. To do. Then, the electrical angle θe and the electrical angular velocity ωe obtained based on the rotor rotation angle θ stored in the memory in the previous sampling process are set as the initial control angle, and the current limit value I _MAX0 is set as the initial control amount. Is output. Thus, steering assist force control is performed based on the electrical angle θe and the electrical angular velocity ωe calculated based on the rotor rotation angle θ immediately before the occurrence of the abnormality.

Therefore, the rotor rotation angle is fixed to the rotor rotation angle immediately before the occurrence of the abnormality, and the rotation state of the rotor is maintained at the rotation state of the rotor immediately before the occurrence of the abnormality.
After that, the driver increased the steering angle to the right and steered, and between time t1 and time t2, the torsional force of the steering system became the same value as the torsional force at time t1 as the reference value and was larger than the reference value. If it is assumed, in step S17, the control signal output unit 32 advances the control angle at the speed shown in FIG. 6 according to the deviation between the current twisting force of the steering system and the reference value. That is, as shown in FIG. 8, the control angle gradually increases between time t1 and time t2. Further, since the driver is turning and steering, the control amount reduction process is not performed in step S18. Then, the control assisting force control at the time of occurrence of an abnormality is continued based on the control angle and the control amount updated in this way.

  If the torsional force of the steering system becomes the same sign as the reference value and less than or equal to the reference value between time t2 and time t3, the control signal output unit 32 controls the control at time t2 in step S17. Hold the angle. In step S18, the control signal output unit 32 decreases the current limit value, which is the control amount, at the decreasing rate shown in FIG. 7 according to the absolute value of the deviation between the current twisting force of the steering system and the reference value. . Then, the control assisting force control at the time of occurrence of an abnormality is continued based on the control angle and the control amount set in this way.

In this manner, the steering angle changing process and the control amount reducing process according to the torsional force of the steering system are repeated, and the reference value is changed to 0 when the torsional force of the steering system becomes 0 at time t4. Thereafter, when the sign of the torsional force of the steering system is reversed and becomes different from the reference value at time t1, the control angle is changed at the speed shown in FIG. 6 according to the deviation between the current torsional force and the reference value “0”. Will be advanced in the neutral direction of the handle.
When the control amount becomes equal to or less than the control end determination threshold, it is determined No in step S19, the steering assist force control at the time of occurrence of abnormality is ended, and the process proceeds to manual steering.

Incidentally, as shown in FIG. 9, when the steering assist force control is canceled at time t0 due to an abnormality occurring in the steering assist mechanism 10 while the steering wheel is being steered, the abnormality as in this embodiment is performed. If the occurrence control is not performed, as shown in FIG. 9 (b), the steering assist torque by the motor is suddenly lost, so that this is applied to the steering shaft by the return force of the elastic deformation of the steering system such as tire twisting. A so-called kickback phenomenon occurs in which a force is applied to return the valve to the neutral position. At this time, when the manual input torque by the driver is small as shown by the solid line in FIG. 9A, a sudden steering return occurs as shown by the solid line in FIG. 9C. Further, in order to avoid this sudden steering wheel return and secure a steered state as shown by the broken line in FIG. 9C, a large hand by the driver as shown by the broken line in FIG. 9A. Input torque is required rapidly, and the steering burden on the driver increases.
Therefore, in order to reduce the driver's steering burden, it is known that when the motor is stopped during the steering assist, the occurrence of the kickback phenomenon is suppressed by short-circuiting the terminals of the motor for a predetermined time. Yes.

However, in this case, when an abnormality occurs in the steering assist mechanism 10 at time t0 in FIG. 10 and it is necessary to stop the motor, it is only necessary to suppress a rapid steering wheel return caused by the return force of the torsion of the steering system. Therefore, if correction steering by the driver is not performed, the steering wheel is gradually returned to the neutral position as shown by the solid line in FIG. Therefore, in order to avoid this steering wheel return and to secure a steered state as shown by the broken line in FIG. 10C, manual input torque by the driver is indispensable. At this time, as shown in FIG. 10 (b), the steering assist torque gradually decreases, and as shown by the broken line in FIG. 10 (a), a rapid manual input torque is not required. As in the case of 9, a large manual input torque is required.
In contrast, in the present embodiment, when normal steering assist force control is canceled when an abnormality occurs, the motor rotation angle is maintained so as to maintain the motor rotation angle immediately before the occurrence of the abnormality according to the twisting force of the steering system. Therefore, the occurrence of the kickback phenomenon can be effectively suppressed.

FIG. 11 is a time chart for explaining the effect in the present embodiment. In FIG. 11, (a) is a manual input torque by the driver, (b) is a steering assist torque, (c) is a motor control angle, (d) is an assist control amount, and (e) is a steering angle.
As shown in FIG. 11, when some abnormality occurs at time t11 and the normal steering assist force release condition is satisfied, the steering assist force control when the abnormality occurs is performed until time t12. At this time, the control angle immediately before the occurrence of the abnormality is set as the initial control angle, and when the twisting force of the steering system has the same sign as the reference value and smaller than the reference value, the control angle at that time is maintained and the rotor rotation angle is set. Since it is fixed at the rotor rotation angle immediately before the occurrence of the abnormality, it is possible to obtain an effect of preventing a sudden change in the handle angle.

Also, if the torsional force of the steering system has the same sign as the reference value and is greater than the reference value, the control angle is advanced in the direction opposite to the steering neutral direction, so the steering burden required for shifting to manual steering is required. Is reduced, and a large manual input torque for maintaining the steered state as shown in FIGS. 9 and 10 becomes unnecessary.
Further, after the occurrence of abnormality, after the torsional force of the steering system becomes zero, the control angle is advanced in the steering neutral direction to stop the energization of the motor, so that it is possible to promptly shift to manual steering.

Thus, even after the occurrence of an abnormality, the steering assist torque can be applied according to the twisting force of the steering system (manual input torque by the driver). As a result, it is possible to prevent the steering assist torque from suddenly disappearing when an abnormality occurs, and it is possible to reliably prevent sudden steering wheel return.
Therefore, in the first embodiment, when the abnormality of the motor rotation angle detected by the rotation angle detection means is detected, the reference angle of the motor rotation angle is changed so as to maintain the rotation state of the electric motor immediately before the occurrence of the abnormality. Thus, the motor drive control is performed, so that the motor can be prevented from returning due to the reaction force, and the occurrence of the kickback phenomenon can be suppressed. In particular, the effect is greater as the vehicle has a greater torsional force in the steering system during manual steering due to heavy vehicle weight.

In addition, since the motor rotation angle immediately before the occurrence of the abnormality is set as the reference angle, by fixing the rotor rotation angle to the rotor rotation angle immediately before the occurrence of the abnormality, an effect of preventing a sudden change in the handle angle can be obtained. The occurrence of the kickback phenomenon can be suppressed.
Furthermore, when the torsional force of the steering system immediately before the occurrence of the abnormality is set as a reference value, and the current torsional force of the steering system has the same sign as the reference value and is equal to or less than the reference value, the reference angle at that time is maintained. Steering wheel return can be appropriately suppressed while maintaining the motor rotation angle immediately before the occurrence.

Further, when the current torsional force of the steering system has the same sign as the reference value and is larger than the reference value, the reference angle is changed to the direction opposite to the steering neutral direction with respect to the reference angle at that time. It is possible to reduce the burden of a person's additional steering and to eliminate the need for a large manual input torque when shifting to manual steering.
Furthermore, when the current torsional force of the steering system is different from the reference value, the reference angle is changed to the steering neutral direction with respect to the reference angle at that time. Then, the energization of the electric motor can be continued, the energization of the electric motor can be released after the manual input torque of the driver is lost, and the appropriate abnormality occurrence control can be performed.

In addition, when the abnormality detecting means detects an abnormality in the motor rotation angle, the output of the electric motor is gradually reduced, so that the steering assist force can be prevented from suddenly becoming zero.
Further, since the reduction rate of the output of the electric motor is determined according to the torsional force of the steering system, the decrease rate is decreased as the torsional force of the steering system is increased, and the duration of the control when the abnormality occurs is set longer. be able to.
In the first embodiment, the case where the desired control angle is set based on the rotor rotation angle immediately before the occurrence of the abnormality has been described. However, based on the average value of the rotor rotation angle for a predetermined time before the occurrence of the abnormality. The desired control angle can also be set.

Next, a second embodiment of the present invention will be described.
In the second embodiment, the control angle is changed so as to maintain the motor rotational angular velocity immediately before the occurrence of the abnormality.
FIG. 12 is a flowchart showing a control signal output processing procedure executed by the control signal output unit 32 in the second embodiment. In the control signal output processing of FIG. 5 described above, the rotor rotational angular velocity θ ′ after step S10. Step S31 for determining whether or not is greater than a predetermined threshold value, and Step S32 for setting an initial control angle according to the rotor rotational angular velocity θ ′ immediately before the occurrence of abnormality when YES in Step S31, are added. Step S33 for determining whether the rotor rotational angular velocity θ ′ is greater than a predetermined threshold later, Step S34 for performing motor angular velocity subtraction processing when YES in Step S33, and the control angle based on the result of the motor angular velocity subtraction processing. Except for the addition of step S35 to be updated, the same processing is performed to perform the same processing as in FIG. Min denoted by the same reference numerals will be described mainly different parts of the process.

In step S31, the control signal output unit 32 determines whether or not the rotor rotational angular velocity θ ′ stored in step S4 is greater than a predetermined angular velocity threshold θ ′ _{TH, and} if θ ′ ≦ θ ′ _TH , The process proceeds to S11, and if θ ′> θ ′ _TH , the process proceeds to Step S32. Here, the angular velocity threshold value θ ′ _TH is set to a value at which it is possible to determine that the driver is in the steered state.
In step S32, the control signal output unit 32 sets the rotor angular velocity θ ′ stored in step S4 as the reference angular velocity, sets the electrical angle θe and the electrical angular velocity ωe based on this, and proceeds to step S12. Specifically, the electrical angle θe is set so that the rotor rotational angular velocity matches the rotor rotational angular velocity θ ′ immediately before the occurrence of abnormality stored in step S4.

In step S33, the control signal output unit 32 determines whether or not the rotor rotational angular velocity θ ′ (reference angular velocity) is greater than a predetermined angular velocity threshold θ ′ _TH, and when θ ′ ≦ θ ′ _TH , The process proceeds to S17, and if θ ′> θ ′ _TH , the process proceeds to Step S34.
In step S34, the control signal output unit 32 performs a motor angular velocity subtraction process for decreasing the reference angular velocity. In this motor angular velocity subtraction process, the reduction rate of the reference angular velocity is calculated with reference to the reduction rate calculation map shown in FIG. 13 based on the torsional force of the steering system, and the reference angular velocity is reduced by the reduction rate.

  The reduction rate calculation map shown in FIG. 13 has the steering system torsional force on the horizontal axis and the reference angular velocity reduction rate on the vertical axis, and the direction of the steering system torsional force at the start of steering assist force control when an abnormality occurs is The reduction rate is set to be smaller as the torsional force of the steering system is larger. Note that the method of reducing the reduction rate can be determined by various functions such as a straight line and a quadratic curve. Further, the reduction rate can be made constant.

  In the present embodiment, the case of calculating the reduction rate of the reference angular velocity with reference to the reduction rate calculation map shown in FIG. 13 has been described, but a reduction rate calculation map as shown in FIG. 14 can also be referred to. The reduction rate calculation map of FIG. 14 is set so that the vehicle speed Vs is taken on the horizontal axis and the reference angular velocity reduction rate is taken on the vertical axis, and the reference angular speed reduction rate increases as the vehicle speed Vs increases.

The motor angular velocity subtraction process in step S34 is not executed when the manual input torque is equal to or greater than a certain value, and the reference angular velocity is maintained.
In step S35, the control signal output unit 32 updates the electrical angle θe and the electrical angular velocity ωe based on the reference angular velocity updated in the motor angular velocity subtraction process in step S34, and proceeds to step S8.
In FIG. 12, the process of step S34 corresponds to the reference angular velocity reducing means.

Next, the operation of the second embodiment will be described based on the time chart of FIG. In FIG. 15, (a) is a manual input torque by the driver, (b) is a steering assist torque, (c) is a motor control angular velocity, (d) is an assist control amount, and (e) is a steering angle.
When the driver is steering relatively suddenly, if any abnormality occurs at time t21 and the normal steering assist force release condition is satisfied, the control signal output unit 32 performs step S31 in FIG. From Step S32, the rotor rotational angular velocity θ ′ immediately before the occurrence of the abnormality is set as the reference angular velocity, and the electrical angle θe and the electrical angular velocity ωe are set so as to maintain this reference angular velocity. Then, steering assist force control at the time of occurrence of abnormality is started based on the electrical angle θe and the electrical angular velocity ωe.

As described above, since the control angle is set based on the rotor rotational angular velocity immediately before the occurrence of the abnormality, it is possible to suppress a sudden change in the angular velocity of the motor control when the abnormality occurs, and a sudden change in the angular acceleration of the handle occurs. Can be suppressed.
Thereafter, the reference angular velocity is decreased at the reduction rate shown in FIG. 13 in the motor angular velocity subtraction process in step S34, and steering is performed when an abnormality occurs at the electrical angle θe and the electrical angular velocity ωe that are updated based on the sequentially decreased reference angular velocity. Auxiliary force control is continued.

When the manual input torque becomes equal to or greater than the constant value α at time t22, the reference angular velocity is maintained. Accordingly, the motor control angular velocity is maintained as shown in FIG. 15 (c), and the steering angle is increased at a constant velocity as shown in FIG. 15 (e).
When the steering angle approaches the angle intended by the driver, the driver weakens the manual input torque at time t23, and when the manual input torque becomes smaller than the constant value α at time t24, the motor angular velocity subtraction process in step S34 is performed. The reference angular velocity reduction control is resumed.

Thereafter, when the rotor rotational angular velocity θ ′ (reference angular velocity) becomes equal to or smaller than the predetermined angular velocity threshold θ ′ _TH , the control signal output unit 32 determines No in step S33, and performs control angle update processing in step S17 and control in step S18. Apply volume reduction processing. Accordingly, as shown in FIG. 15 (d), the assist control amount gradually decreases. Along with this, as shown in FIG. 15B, the steering assist torque gradually decreases, and when the steering assist torque (control amount) becomes zero at time t25, the control shifts completely to manual steering.

As described above, in the second embodiment, the motor rotation angular velocity immediately before the occurrence of the abnormality is set as the reference angular velocity, and the reference angle of the motor rotation angle is set based on the reference angular velocity, so that the normal steering assist force control is canceled. It is possible to suppress a sudden change in angular acceleration of the steering wheel when it occurs.
In addition, since the reference angular velocity is gradually reduced, the rate of change of the steering angle can be gradually reduced, a sense of incongruity in steering can be suppressed, and the running stability of the vehicle can be improved.
In the second embodiment, the case where the intended control angle is set based on the rotor rotational angular velocity immediately before the occurrence of the abnormality has been described. However, based on the average value of the rotor rotational angular velocity for a predetermined time before the occurrence of the abnormality. The desired control angle can also be set.

Next, a third embodiment of the present invention will be described.
In the third embodiment, the control angle is fixed so that the motor rotation angle immediately before the occurrence of abnormality is maintained for a predetermined time.
That is, in the control signal output unit 32 of the third embodiment, the control angle update process of step S17 is deleted in the control signal output process of FIG. A similar process is executed.
In the present embodiment, an assist control gain is applied as the control amount instead of the above-described current limit value.

  This assist control gain is, for example, a gain that is multiplied with the proportional-integral control in the PI control unit 42, and is normally set to gain = 1, and is controlled to decrease to a value smaller than 1 in the control amount subtraction process in step S18. It shall be. Here, the reduction rate of the assist control gain can be determined by various functions such as a straight line and a quadratic curve as shown in FIG.

Next, the operation of the third embodiment will be described based on the time chart shown in FIG. In FIG. 16, (a) is an assist torque, (b) is a motor control angle, (c) is an assist control gain, and (d) is a steering angle.
If any abnormality occurs at time t31 and the normal steering assist force control cancellation condition is satisfied, the control signal output unit 32 determines the electrical angle θe and the electrical angle θe based on the motor rotation angle θ immediately before the abnormality occurs in step S11. The electrical angular velocity ωe is set, and the steering assist force control when an abnormality occurs is started. Thereby, the motor rotation angle θ immediately before the occurrence of the abnormality is held.

After that, the control angle update process is not performed until the steering assist force control at the time of occurrence of the abnormality is terminated, so that the motor control angle is set to the motor rotation angle θ immediately before the occurrence of the abnormality as shown in FIG. The control angle is fixed based on the control angle.
On the other hand, after time t31, the control signal output unit 32 executes a control amount reduction process in step S18, and decreases the control amount at the reduction rate shown in FIG. Therefore, as shown in FIG. 10C, the assist control gain gradually decreases from time t31, and accordingly, the steering assist force also gradually decreases. Thus, the steering angle is gradually returned to the neutral position as shown in FIG. 10 (d) as the assist control gain decreases.

At this time, the reduction rate of the assist control gain is set to be smaller as the absolute value of the deviation between the twisting force of the steering system and the reference value (the torsional force of the steering system when an abnormality occurs) is larger. Therefore, even if the vehicle has a large twisting force of the steering system due to, for example, a heavy vehicle weight, the steering wheel return can be effectively suppressed.
Then, when the control amount (assist control gain) becomes 0 at time t32, the steering assist force control at the time of occurrence of abnormality is terminated, and the process shifts to manual steering.

Thus, in the third embodiment, when an abnormality occurs, the reference angle of the motor rotation angle is fixed to the reference angle immediately before the occurrence of the abnormality, and the output of the electric motor is gradually reduced according to the torsional force of the steering system. Therefore, it is possible to prevent the handle from being suddenly returned with a relatively simple configuration.
In each of the above embodiments, the case where the control angle at the time of occurrence of an abnormality is set to the initial control angle has been described, but it may be set to an arbitrary angle set in advance.

Further, in each of the above embodiments, when the assist torque at the time of occurrence of abnormality is near 0, it is possible to determine that the influence of kickback is small and not to perform control at the time of occurrence of abnormality.
Furthermore, in each said embodiment, although the case where a three-phase brushless motor was applied as an electric motor was demonstrated, a brush motor system can also be applied. In this case, the motor rotation angle and the motor rotation angular velocity may be calculated from the detection value of the steering angle sensor, or the motor rotation angle and the motor rotation angular velocity may be estimated from the back electromotive force of the motor.

1 is a schematic configuration diagram of a vehicle in an embodiment of the present invention. It is a block diagram which shows an example of a steering assistance control apparatus. It is a block diagram which shows the specific structure of the control arithmetic unit of FIG. It is a characteristic diagram which shows a steering auxiliary current command value calculation map. It is a flowchart of the control signal output process performed in the control signal output part in 1st Embodiment. It is a map for calculating the speed which advances a control angle. It is a map for calculating the decreasing rate of control amount. It is a time chart explaining operation | movement of 1st Embodiment. It is a time chart explaining operation | movement of a conventional apparatus. It is a time chart explaining operation | movement of a conventional apparatus. It is a time chart explaining the effect of a 1st embodiment. It is a flowchart of the control signal output process performed in the control signal output part in 2nd Embodiment. It is a map for calculating the decreasing rate of motor angular velocity. It is a map for calculating the decreasing rate of motor angular velocity. It is a time chart explaining operation | movement of 2nd Embodiment. It is a time chart explaining operation | movement of 3rd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Torque sensor, 10 ... Steering assistance mechanism, 11 ... Reduction gear, 12 ... Three-phase brushless motor, 13 ... Rotor position detection circuit, 20 ... Steering assistance control device, 21 ... Vehicle speed Sensors 31... Steering auxiliary current command value calculation unit 32... Control signal output unit 34... D axis command current calculation unit 35... Dq axis voltage calculation unit 36 36 q axis command current calculation unit 37. Phase / 3-phase converter, 42 ... PI controller, 43 ... PWM controller

Claims (9)

An electric power steering apparatus including an electric motor that applies a steering assist force to reduce a steering burden on a driver to a steering system,
Rotation angle detection means for detecting the motor rotation angle of the electric motor, steering torque detection means for detecting steering torque, and at least referring to the motor rotation angle to generate a steering assist force corresponding to the steering torque. Motor control means for driving and controlling the electric motor; and abnormality detection means for detecting an abnormality in the motor rotation angle detected by the rotation angle detection means. The motor control means is configured to detect the motor rotation angle by the abnormality detection means. An electric power steering apparatus comprising reference angle changing means for changing a reference angle of the motor rotation angle so as to maintain the rotation state of the electric motor immediately before the occurrence of the abnormality when the abnormality is detected.   2. The electric power according to claim 1, wherein when the abnormality detection unit detects an abnormality in the motor rotation angle, the reference angle changing unit sets the motor rotation angle immediately before the occurrence of the abnormality to the reference angle. Steering device.   The reference angle changing means uses the torsional force of the steering system immediately before the occurrence of an abnormality as a reference value. The electric power steering apparatus according to claim 2, wherein the electric power steering apparatus is held.   When the torsional force of the current steering system has the same sign as the reference value and greater than the reference value, the reference angle changing means sets the reference angle in a direction opposite to the steering neutral direction with respect to the reference angle at that time. The electric power steering apparatus according to claim 3, wherein the electric power steering apparatus is changed.   The reference angle changing means changes the reference angle in a steering neutral direction with respect to the reference angle at that time when a torsional force of a current steering system is different from the reference value. Item 5. The electric power steering device according to Item 3 or 4.   When the abnormality detection unit detects an abnormality in the motor rotation angle, the reference angle change unit sets the reference angle based on the reference angular velocity, with the motor rotation angular velocity immediately before the occurrence of the abnormality as a reference angular velocity. The electric power steering apparatus according to any one of claims 1 to 5.   The electric power steering apparatus according to claim 6, wherein the reference angle changing unit includes a reference angular velocity reducing unit that gradually decreases the reference angular velocity.   The said motor control means is equipped with the gradual change process means to reduce gradually the output of the said electric motor, when the abnormality of the said motor rotation angle is detected by the said abnormality detection means. The electric power steering device according to claim 1.   9. The electric power steering apparatus according to claim 8, wherein the gradual change processing means determines a reduction rate of the output of the electric motor in accordance with a twisting force of a steering system.

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