JP5401801B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus including an electric motor that generates a steering assist torque applied to a steering shaft of a steering mechanism.

Conventionally, as a steering device, a driver calculates a current command value based on a steering torque for steering the steering wheel, and performs feedback control based on a deviation between the current command value and a detected drive current value of the electric motor to control the electric motor. 2. Description of the Related Art An electric power steering device that gives steering assist force to a steering mechanism by controlling driving is widely used.
In general, in a steering mechanism, when the steering wheel is continuously steered in the left or right steering direction from the neutral position and the steering wheel operation amount reaches a maximum steering angle corresponding to the maximum value, the steering mechanism is mechanically operated. A steering limit occurs at which the steering wheel cannot contact any further when it comes into contact with the stopper. It is called so-called end pad that such a steering limit is brought into contact with the mechanical stopper.

  In the electric power steering device, when the above-described end-contact state is entered in the steering assist state, the rotation of the electric motor suddenly stops and the back electromotive force of the electric motor rapidly disappears, and the motor current corresponding to the current command value is obtained. The current corresponding to the back electromotive force is added to cause overshoot. When overshoot occurs in this way, there is a risk of damaging the semiconductor elements constituting the inverter as the drive means of the electric motor.

  Therefore, as a countermeasure against this overshoot, in an electric power steering apparatus that calculates a current command value based on the steering torque, and proportionally / integratesly compensates for a deviation between the current command value and the actual motor current, thereby controlling the drive of the electric motor. It is known that when an overshoot of the current flowing through the electric motor is detected, the overshoot is suppressed by controlling at least one of the proportional sensitivity and integral gain of the proportional / integral compensation (for example, , See Patent Document 1).

  In addition, in the conventional electric power steering device, when the above-described end contact state is established in the steering assist state, a large impact (torque) is applied to the rack end mechanism to generate abnormal noise, components of the rack end mechanism, reduction gears, etc. The torque transmission system mechanical parts may be damaged or deformed. Therefore, in order to withstand such a large impact, high-performance mechanical parts are required, which increases costs.

Therefore, as edge contact protection control that implements edge contact countermeasures with a control function, the electric motor that controls the drive of an electric motor with a pulse width modulation signal is performed by proportionally / integrating compensating for the deviation between the current command value and the actual motor current. In a power steering device, there are a method of limiting the duty of a pulse width modulation signal used during normal control to a predetermined value or less, and a method of fixing the duty to a constant value and setting an electromagnetic brake mode.
Japanese Patent No. 3232030

  However, in the conventional end contact protection control, since the method of limiting the duty command value output from the current controller is adopted as the output limiting method, the feedback control is limited and the motor actual current is limited. Will cause the current controller to move unintentionally. As a result, the deviation between the current command value and the motor actual current increases, and in the current controller that receives the deviation, the past value of the integrator that is configured becomes unnecessarily large.

  Therefore, when the end-contact protection control is canceled in this state and the normal control state is restored, an unnecessarily large duty command value is output from the current controller due to the large past value of the integrator, and the actual motor current changes suddenly. However, there is a risk that abnormal noise may occur or the steering feeling may deteriorate. Moreover, depending on the case, an overcurrent will generate | occur | produce and will place a burden on a motor drive circuit.

  Therefore, an object of the present invention is to provide an electric power steering device that can suppress the generation of abnormal noise and the deterioration of steering feeling when the feedback restriction such as the end pad protection control is canceled.

In order to solve the above problems, an electric power steering apparatus according to claim 1 is based on a steering torque detecting means for detecting a steering torque input to a steering mechanism, and at least a steering torque detected by the steering torque detecting means. A current command value calculating means for calculating a current command value; an electric motor for generating a steering assist torque applied to a steering shaft of the steering mechanism; a current detecting means for detecting a drive current of the electric motor; and the current command value; Electric power comprising: current control means for performing feedback control based on a deviation from the detected drive current value and calculating a voltage command value; and motor control means for controlling drive of the electric motor based on the voltage command value A steering device,
When a predetermined condition is satisfied, a feedback restriction unit that restricts the feedback control of the current control unit, a restriction release unit that releases the restriction of the feedback control by the feedback restriction unit, and the restriction release by the restriction release unit Current suppression means for suppressing a sudden change in the drive current of the electric motor ,
The current control means includes an integrator that integrates a deviation between the current command value and the drive current detection value, and calculates the voltage command value using an integral value output from the integrator. Then, the current suppressing means fixes the past value of the integrator to zero while the feedback control is limited by the feedback limiting means .

The electric power steering apparatus according to claim 2 calculates a current command value based on steering torque detection means for detecting steering torque input to the steering mechanism and at least steering torque detected by the steering torque detection means. A current command value calculating means; an electric motor for generating a steering assist torque applied to a steering shaft of the steering mechanism; a current detecting means for detecting a drive current of the electric motor; the current command value and the drive current detected value; An electric power steering device comprising: current control means for performing feedback control based on the deviation of the current, and calculating a voltage command value; and motor control means for driving and controlling the electric motor based on the voltage command value,
When a predetermined condition is satisfied, a feedback restriction unit that restricts the feedback control of the current control unit, a restriction release unit that releases the restriction of the feedback control by the feedback restriction unit, and the restriction release by the restriction release unit Current suppression means for suppressing a sudden change in the drive current of the electric motor,
The current control means includes an integrator that integrates a deviation between the current command value and the drive current detection value, and calculates the voltage command value using an integral value output from the integrator. The current suppressing means sets the past value of the integrator to zero when the restriction is released by the restriction releasing means.

According to a third aspect of the present invention, there is provided an electric power steering apparatus for calculating a current command value based on a steering torque detecting means for detecting a steering torque input to a steering mechanism and at least the steering torque detected by the steering torque detecting means. A current command value calculating means; an electric motor for generating a steering assist torque applied to a steering shaft of the steering mechanism; a current detecting means for detecting a drive current of the electric motor; the current command value and the drive current detected value; An electric power steering device comprising: current control means for performing feedback control based on the deviation of the current, and calculating a voltage command value; and motor control means for driving and controlling the electric motor based on the voltage command value,
When a predetermined condition is satisfied, a feedback restriction unit that restricts the feedback control of the current control unit, a restriction release unit that releases the restriction of the feedback control by the feedback restriction unit, and the restriction release by the restriction release unit Current suppression means for suppressing a sudden change in the drive current of the electric motor,
The current control means includes an integrator that integrates a deviation between the current command value and the drive current detection value, and calculates the voltage command value using an integral value output from the integrator. The current suppression means, when the restriction is released by the restriction release means, the past value of the integrator, the current command value at the time of the restriction release and the voltage command of the electric motor after the feedback control is restricted It is characterized by setting based on the value.
Furthermore, an electric power steering apparatus according to a fourth aspect is the invention according to any one of the first to third aspects, wherein the restriction release means starts restriction of feedback control by the feedback restriction means, The restriction is released after a predetermined time has elapsed.

According to a fifth aspect of the present invention, in the electric power steering apparatus according to the fourth aspect , the predetermined time is set based on at least one of a steering torque, a current command value, and a motor rotational speed. .
Furthermore, the electric power steering apparatus according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein the motor control means sends the pulse width modulation signal to the electric motor based on the voltage command value. The feedback limiting means limits the feedback control by setting an upper limit on the duty of the pulse width modulation signal and limiting the duty when the predetermined condition is satisfied. It is characterized by.

An electric power steering apparatus according to a seventh aspect is the invention according to any one of the first to fifth aspects, wherein the motor control means transmits a pulse width modulation signal to the electric motor based on the voltage command value. The feedback limiting means limits the feedback control by fixing a duty of the pulse width modulation signal to a constant value when the predetermined condition is satisfied. .

Furthermore, the electric power steering apparatus according to an eighth aspect of the present invention is the invention according to the seventh aspect , wherein the motor control means includes an inverter that is driven by the pulse width modulation signal and supplies a drive current to the electric motor. The feedback limiting means is characterized in that when the predetermined condition is satisfied, either one of the upper arm and the lower arm of the inverter is simultaneously turned on to control the electromagnetic brake mode.

An electric power steering apparatus according to a ninth aspect is the invention according to any one of the first to eighth aspects, wherein the motor control means sends a pulse width modulation signal to the electric motor based on the voltage command value. The feedback limiting means determines the duty of the pulse width modulation signal between the steering shaft and the steered wheels of the steering mechanism when determining that the steering mechanism has reached the steering limit. Control is performed so as to suppress the torque transmitted to the torque transmission member.

  According to the electric power steering apparatus of the present invention, when a predetermined condition is satisfied, the feedback control in the current controller is temporarily limited, and the past value of the integrator of the current controller is limited during the limitation of the feedback control. Since the past value of the current controller integrator is reset to a constant value when the limit of feedback control is released, the past value of the integrator of the current controller must be large when the limit is released. Can be prevented. As a result, when the restriction is released, it is possible to prevent the drive current of the electric motor from changing suddenly due to the influence of a large past value of the integrator, and it is possible to prevent the generation of abnormal noise and the deterioration of the steering feeling.

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

The steering force transmitted to the output shaft 2b is transmitted to the intermediate shaft 5 via the universal joint 4 composed of the two yokes 4a and 4b and the cross connecting portion 4c for connecting them, It is transmitted to the pinion shaft 7 through a universal joint 6 composed of yokes 6a and 6b and a cross connecting portion 6c for connecting them.
The steering force transmitted to the pinion shaft 7 is transmitted to the left and right tie rods 9 via the steering gear 8, and the steered wheels WR and WL are steered by these tie rods 9. Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8b coupled to the pinion shaft 7 and a rack shaft 8c meshing with the pinion 8b in the gear housing 8a, and is transmitted to the pinion 8b. The rotational motion is converted into a straight motion by the rack shaft 8c.

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

The steering torque detection value T output from the steering torque sensor 14 is input to the controller 15 as shown in FIG. In addition to the torque detection value T, the controller 15 detects the vehicle speed detection value V detected by the vehicle speed sensor 16, the motor currents Iu to Iw flowing through the electric motor 12, and a rotation angle sensor 17 constituted by a resolver, an encoder, and the like. The rotation angle θ of the electric motor 12 is also input, and the steering assist torque command value I _M ^* for causing the electric motor 12 to generate a steering assist force corresponding to the input torque detection value T and vehicle speed detection value V is calculated and calculated. The steering assist torque command value I _M ^{* is} subjected to various compensation processes based on the motor angular velocity ω and the motor angular acceleration α calculated based on the motor rotation angle θ, and then the dq-axis current command value Id ^* , Convert to Iq ^* .

The motor currents Iu to Iw are converted into three-phase / two-phase to calculate the dq-axis motor currents Id and Iq, and the dq-axis current command values Id ^* and Iq ^* and the dq-axis motor current Id are calculated. , Iq based on feedback processing of the drive current supplied to the electric motor 12, the result is subjected to two-phase / three-phase conversion, and motor currents Iu, Iv, and Iw for controlling the drive of the electric motor 12 are output.
That is, the controller 15 compensates the steering assist torque command value I _M ^*, which calculates the steering assist torque command value I _M ^* based on the steering torque T and the vehicle speed V, and the calculated steering assist torque command value I _M ^* . Based on the command value compensation unit 22 and the torque command value Ir compensated by the command value compensation unit 22, dq-axis current command values Id ^* and Iq ^* are calculated, and the motor currents Iu˜ And a motor current control unit 23 that generates Iw.

  Further, the controller 15 determines whether the rack shaft 8c of the steering gear 8 reaches the rack stroke end based on the q-axis current Iq, or whether the tire has reached a steering limit at which no further turning is possible due to contact with the curb or the like. Based on the determination result by the end contact determination unit 51 and the end contact determination unit 51 for determining whether or not (at the time of end contact), the operation / non-operation of the end contact protection control for taking the end contact countermeasure is shown. And a protection control determination unit 52 that outputs an end contact protection control flag FL1.

The protection control flag FL1 output from the protection control determination unit 52 is output to a later-described current control unit 63 and duty calculation unit 65 of the motor current control unit 23.
In the steering assist torque command value calculation unit 21, first, the torque command value calculation unit 41 refers to the steering assist torque command value calculation map shown in FIG. 3 based on the steering torque T and the vehicle speed V to obtain a current command value. A steering assist torque command value I _M ^* is calculated.

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

Then, the phase compensator 42 performs phase compensation to the steering assist torque command value I _M ^*, and outputs a steering assist torque command value I _M ^* after phase compensation to the adder 38 to be described later. Further, the torque differentiation circuit 43 calculates a compensation value for the steering torque T based on the steering torque change rate Td obtained by differentiating the steering torque T, and outputs this to an adder 38 described later.
The command value compensator 22 differentiates the motor rotation angle θ detected by the rotation angle sensor 17 to calculate the motor angular velocity ω, and differentiates the motor angular velocity ω calculated by the angular velocity calculator 31. The angular acceleration calculation unit 32 that calculates the motor angular acceleration α, the convergence compensation unit 33 that compensates for the convergence of the yaw rate based on the motor angular velocity ω calculated by the angular velocity calculation unit 31, and the angular acceleration calculation unit 32 Based on the motor angular acceleration α, the inertia compensator 34 that compensates for the torque equivalent generated by the inertia of the electric motor 12 to prevent the deterioration of the feeling of inertia or control responsiveness, and the self-aligning torque (SAT) are estimated. And at least a SAT estimation feedback unit 35.

Here, the convergence compensation unit 33 receives the motor angular velocity ω calculated by the angular velocity calculation unit 31 and applies a brake to the operation in which the steering wheel 1 swings in order to improve the yaw convergence of the vehicle. Thus, the convergence compensation value Ic is calculated.
The SAT estimation feedback unit 35 receives the steering torque T, the motor angular velocity ω, the motor angular acceleration α, and the steering assist torque command value I _M ^* calculated by the steering assist torque command value calculation unit 21, and based on these, the SAT estimation feedback unit 35 The aligning torque SAT is estimated and calculated.

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 1, a steering torque T is generated, and the electric motor 12 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, torque serving as a steering resistance of the steering wheel 1 is generated by the inertia J and friction (static friction) Fr of the electric motor 12. Considering the balance of these forces, the following equation of motion can be obtained:

J · α + Fr · sign (ω) + 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 (ω (s)) (2)
As can be seen from the above equation (2), the inertia J and static friction Fr of the electric motor 12 are obtained in advance as constants, so that the self-aligning torque is obtained from the motor angular velocity ω, motor angular acceleration α, assist torque Tm, and steering torque T. The SAT can be estimated. Here, the assist torque Tm is proportional to the steering assist torque command value I _M ^*, to apply a steering assist torque command value I _M ^* in place of the assist torque Tm.

Then, the inertia compensation value Ii calculated by the inertia compensation unit 34 and the self-aligning torque SAT calculated by the SAT estimation feedback unit 35 are added by the adder 36, and the addition output of the adder 36 and the convergence compensation unit 33 are added. Is added by the adder 37 to calculate a command compensation value Icom, and this command compensation value Icom is output from the steering assist torque command value calculation unit 21. _The compensated torque command value Ir is calculated by adding to _M ^* by the adder 38, and this torque command value Ir is output to the motor current control unit 23.

The motor current control unit 23 includes a motor current detector 60 that detects motor currents Iu, Iv, and Iw supplied to the phase coils Lu, Lv, and Lw of the electric motor 12, and a dq axis current from the torque command value Ir. A current command value calculation unit 61 for calculating the command values Id ^* and Iq ^* , a three-phase / two-phase conversion unit 62 for converting the motor currents Iu, Iv and Iw into dq-axis motor currents Id and Iq, and d− The subtractors 61d and 61q for obtaining the respective phase current deviations ΔId and ΔIq by individually subtracting the dq-axis motor currents Id and Iq from the q-axis current command values Id ^* and Iq ^* and the respective phase current deviations ΔId and ΔIq. A current control unit 63 for performing feedback control for performing proportional integral control to calculate the voltage command values Vd and Vq, and the voltage command values Vd and Vq are input, and three-phase voltage command values Vu, Vv, Vw is calculated Duty calculation for calculating the duty Du, Dv, and Dw of each phase that becomes the drive command value of the electric motor 12 by performing duty calculation based on the phase / three-phase conversion unit 64 and these voltage command values Vu, Vv, and Vw Part 65.

Further, the motor current control unit 23 performs pulse width modulation based on the duty output from the duty calculation unit 65 to obtain a pulse width modulation signal, and based on the pulse width modulation signal, the three-phase motor currents Iu, Iv, and An inverter 66 that outputs Iw to the electric motor 12 is provided.
The protection control flag FL1 output from the protection control determination unit 52 is input to the current control unit 63 and the duty calculation unit 65.

FIG. 5 is a diagram showing the current control unit 63 as a discrete digital signal processing system. In the present embodiment, when the protection control flag FL1 having the logical value “1” is input, the switch unit 63a is switched to the state indicated by the broken line, and the past value of the integrator is reset to a constant value (for example, “0”). It is like that.
Further, as shown in FIG. 6, the duty calculator 65 calculates the duty of each phase calculated based on the voltage command values Vu, Vv, and Vw according to the protection control flag FL1 output from the protection control determination unit 52. du _B, and Dv _B and Dw _B, the duty du _B, a predetermined value Dv _B and Dw _B (e.g., 3%) limit duty du _L was limited below, selects one Dv _L and Dw _L Tonouchi In addition, duty calculation / restriction calculation units 65u, 65v, and 65w that output the final duty Du, Dv, and Dw of each phase are provided.

Here, the duty calculation / limit calculation unit 65u includes a phase duty operation section 65a for calculating the sign of the duty Du _B based on voltage command value Vu, the duty Du _B calculated in this phase duty operation unit 65a And a limiter 65b limited to a predetermined value (for example, 3%) or less.
Further, the duty ratio / limit calculation section 65u receives the duty ratio Du _B and the limit duty Du _L , and the protection control flag FL1 is a logical value “0” which means that the steering mechanism has not reached the steering limit. When the duty Du _B is selected and the protection control flag FL1 is a logical value “1” meaning that the steering limit has been reached, the limit duty Du _L is selected and output as the duty Du. It has. The other duty calculation / limit calculation units 65v and 65w have the same configuration as the duty calculation / limit calculation unit 65u.

  That is, in the present embodiment, when the protection control flag FL1 having a logical value “1”, which means that the steering mechanism has reached the steering limit, is output from the protection control determination unit 52, the duty calculation is performed as the end pad protection control. By performing duty limit control that limits the duty to a certain value or less by the unit 65, the feedback control in the current control unit 63 is limited, and while the duty limit control is being performed, the current control unit 63 uses the integrator. Is continuously reset to “0”.

The end contact determination unit 51 receives the q-axis motor current Iq output from the three-phase / two-phase conversion unit 62, and first calculates the current change rate Iq ′ by differentiating the q-axis motor current Iq.
Next, the calculated current change rate Iq ′ occurs when the rack shaft 8c of the steering gear 8 reaches the rack stroke end or when the tire comes into contact with a curb or the like and reaches a steering limit where no further turning is possible. It is determined whether or not a threshold value ΔIth (for example, 3500 A / sec) or more for determining a large gradient current that does not occur in normal steering.

When Iq ′ <Iqth, it is determined that the steering limit has not been reached, and when Iq ′ ≧ Iqth, it is determined that the steering limit has been reached.
FIG. 7 is a q-axis motor current waveform when the steering mechanism reaches the steering limit.
When the rack shaft 8c reaches the rack stroke end at the time t1, the movement of the rack shaft 8c in the vehicle width direction is stopped. Since the rotation of the electric motor 12 is stopped via 2b and further via the speed reducer 11, the motor currents Iu to Iw supplied to the electric motor 12 increase rapidly. As a result, the q-axis current Iq increases with a large slope that does not occur in normal steering (in the example of FIG. 7, about 4000 A / sec), and then the motor currents Iu to Iw gradually decrease due to the operation of the overcurrent protection circuit. As a result, the q-axis current Iq gradually decreases.

For this reason, the steering limit can be reliably detected by setting the threshold value Iqth of the current change rate Iq ′ to a predetermined value (for example, about 3500 A / sec).
The end control determination result of the end contact determination unit 51 is input to the protection control determination unit 52. When the end contact determination unit 51 determines that the steering mechanism has not reached the steering limit, the protection control flag FL1 having a logical value “0” is output. On the other hand, when the end contact determination unit 51 determines that the steering mechanism has reached the steering limit, it determines that the end contact protection control is to be performed, and starts outputting the protection control flag FL1 having the logical value “1”.

Further, in this embodiment, when a predetermined time (for example, about 20 msec) has elapsed since the output of the protection control flag of FL1 = 1, it is determined that the end contact protection control is to be released, and the logical value “ It is assumed that a protection control flag FL1 of “0” is output.
At this time, the predetermined time is calculated from a combination of the steering torque T detected by the steering torque sensor 14, the rotation angle θ of the electric motor 12 detected by the rotation angle sensor 17, and the torque command value Ir.

Specifically, the predetermined time is set longer as the transmission torque transmitted to the intermediate shaft 5 when the steering mechanism reaches the steering limit is larger. That is, the predetermined time is set longer as the steering torque T, the motor rotation angle θ, and the torque command value Ir are larger.
In FIG. 2, the steering torque sensor 14 corresponds to the steering torque detection means, the steering assist torque command value calculation unit 21 and the command value compensation unit 22 correspond to the current command value calculation means, and the motor current detector 60 corresponds to the current. Corresponding to the detection means, the current control unit 63 corresponds to the current control means, the duty calculation unit 65 and the inverter 66 correspond to the motor control means, the end contact determination unit 51 and the duty calculation unit 65 (switch unit 65c in FIG. 6). ) Corresponds to the feedback restriction means, and the protection control determination unit 52 corresponds to the restriction release means. In FIG. 5, the switch part 63a of the current control part 63 corresponds to the current suppressing means.

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

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

Then, the convergence compensation unit 33 calculates the convergence compensation value Ic based on the motor angular velocity ω, the inertia compensation unit 34 calculates the inertia compensation value Ii based on the motor angular acceleration α, and the SAT estimation feedback unit 35 further. The self-aligning torque SAT is calculated based on the motor angular velocity ω and the motor angular acceleration α, and these are added by the adders 36 and 37 to calculate the command value compensation value Icom. The adder 38 calculates the steering assist torque command value. A torque command value Ir after compensation is calculated by adding to I _M ^* .

At this time, when the vehicle is stopped and the steering wheel 1 is not steered, the torque command value Ir is “0”.
Further, since the electric motor 12 is also stopped, the motor currents Iu to Iw detected by the motor current detector 60 are also “0”, and the motor currents Iu to Iw are converted by the three-phase / two-phase axis conversion unit 62. Since the q-axis current Iq is also “0”, the current change rate Iq ′ is also “0”. For this reason, the end contact determination unit 51 determines that the steering mechanism has not reached the steering limit, and receives the protection control flag FL1 having the logical value “0” from the protection control determination unit 52 as the current control unit 63 and the duty calculation unit 65. Is output.

Therefore, the current control unit 63 performs normal proportional-integral control while maintaining the switch unit 63a in FIG. 5 in the state indicated by the solid line, and the duty calculation unit 65 sets the switch unit 65c in FIG. 6 in the state indicated by the solid line. The duty Du _B , Dv _B and Dw _B of each phase is maintained and outputted as the duty Du, Dv and Dw as they are. And the electric motor 12 is drive-controlled based on these duties Du, Dv, and Dw. At this time, since the duty Du _B , Dv _B and Dw _B are 0%, the motor currents Iu to Iw output from the inverter 66 are also “0”, and the electric motor 12 continues to be stopped.

Assuming that the vehicle starts from this state and normal steering is performed by the driver, the steering assist torque command value calculation unit 21 detects the steering torque T detected by the steering torque sensor 14 and the vehicle speed sensor 16. A steering assist torque command value I _M ^* based on the vehicle speed V is calculated. Then, the compensation for the steering assist torque command value I _M ^* is performed by each compensation value calculated by the command value compensation unit 22, and the compensated torque command value Ir is calculated.

At this time, if the rack shaft 8c does not reach the rack stroke end, since Iq ′ <Iqth, the protection control determination unit 52 continues to output FL1 = 0, and the duty calculation unit 65 supplied to the inverter 66 as it is as the duty Du~Dw duty Du _B ~Dw _B. Therefore, the motor currents Iu to Iw are output from the inverter 66, and the electric motor 12 is rotationally driven. As a result, steering assist torque corresponding to the steering torque T and the vehicle speed V is generated and transmitted to the output shaft 2b of the steering shaft 2 via the speed reducer 11, so that the driver's steering burden can be reduced. .

  If it is assumed that the steering limit is reached by quickly operating the steering wheel 1 from such a normal steering state and the tire contacting a curbstone or the like, the q-axis current Iq increases rapidly as shown in FIG. The change rate Iq ′ is equal to or greater than the threshold value Iqth. Therefore, upon receiving this result, the protection control determination unit 52 outputs a protection control flag FL1 having a logical value “1” to the current control unit 63 and the duty calculation unit 65.

As a result, the current control unit 63 switches the switch unit 63a in FIG. 5 to the state indicated by the broken line and performs proportional integration control in a state where the past value of the integrator is reset to “0”. The switch unit 65c in FIG. 6 is switched to a state indicated by a broken line, and the low duty limiting duties Du _{L to} Dw _L output from the limiter 65b are output as the duties Du to Dw. And the electric motor 12 is drive-controlled based on these duties Du-Dw.

  Thus, by limiting the duties Du to Dw, the motor currents Iu to Iw output from the inverter 66 are reduced, and the steering assist torque generated by the electric motor 12 is reduced and transmitted to the intermediate shaft 5. The peak value of the transmission torque is suppressed as compared with the case where the duty limit control is not performed, and the durability of the torque transmission member such as the intermediate shaft can be improved.

  Thereafter, when a predetermined time for continuing the duty limit control elapses, the protection control determination unit 52 outputs a protection control flag FL1 having a logical value “0”. Thereby, the current control unit 63 returns the switch unit 63a of FIG. 5 to the state indicated by the solid line, cancels the reset process of the past value of the integrator and returns to the normal proportional integration control, and the duty calculation unit 65 The switch unit 65c in FIG. 6 is returned to the state indicated by the solid line, and the duty limit control is released.

At this time, since the past value of the integrator is reset to “0” by the current control unit 63 during the duty limit control, the past value of the integrator becomes “0” when the duty limit control is canceled. ing.
By the way, when the end contact protection control is performed by the duty limit control, when the end contact protection control functions, the actual motor current moves unintentionally by the current controller. Therefore, if the past value reset process of the integrator in the current control unit 63 is not performed as in the present embodiment, the deviation between the current command value and the actual motor current becomes large, and the current controller that receives the deviation as input is used. The past value of the integrator becomes unnecessarily large.

Therefore, when the end-contact protection control is canceled and the normal control state is restored in that state, an unnecessarily large duty is output from the current controller due to the large past value of the integrator, and the actual motor current changes suddenly. There is a possibility that abnormal noise occurs or the steering feeling deteriorates. In some cases, an overcurrent occurs, which places a burden on the motor drive circuit.
On the other hand, in this embodiment, while the end contact protection control is functioning, the past value of the integrator is continuously reset to “0” by the current control unit 63. Therefore, as described above, the end contact protection control is performed. It is possible to prevent the past value of the integrator of the current controller from becoming large at the time when is released and the normal control state is restored.

  As described above, in the first embodiment, when it is determined that the steering mechanism has reached the steering limit, the duty of the pulse width modulation signal is limited. Therefore, the intermediate shaft inserted between the steering shaft and the steering gear, etc. It is possible to achieve end contact protection control that limits the steering assist torque generated by the electric motor before excessive torque is transmitted to the torque transmission member, and reduces the impact force transmitted to the torque transmission member.

  In addition, during duty limit control, the past value of the integrator of the current controller is reset to a constant value (for example, 0), preventing the past value of the integrator of the current controller from increasing when control is released. can do. As a result, when the control is canceled, it is possible to prevent the drive current of the electric motor from changing suddenly due to the influence of a large past value of the integrator, and it is possible to prevent the generation of abnormal noise and the deterioration of the steering feeling.

Furthermore, since the duty limit control is canceled after a predetermined time has elapsed, the duty limit control is continued for a time sufficient to reduce the peak of the transmission torque generated in the torque transmission member such as the intermediate shaft, and the long time limit control is performed. It is possible to suppress the driver's uncomfortable feeling due to the continuation of the vehicle.
At this time, since the duration of the duty limit control is set based on at least one of the steering torque, the current command value, and the motor rotation speed, an appropriate duration according to the magnitude of the impact load applied to the torque transmission member is set. Can be set.

Next, a second embodiment of the present invention will be described.
In the second embodiment, while the end pad protection control is functioning in the first embodiment described above, the current controller 63 resets the past value of the integrator to a constant value. The past value of the integrator is reset to a constant value when the end pad protection control is released.

  That is, as shown in FIG. 8, the controller 15 in the second embodiment deletes the output of the protection control flag FL1 from the protection control determination unit 52 to the current control unit 63 in the controller 15 shown in FIG. The configuration is the same as that shown in FIG. 2 except that a control cancellation determination unit 53 that outputs a control cancellation flag FL2 to the current control unit 63 is added based on the determination result of the control determination unit 52.

The protection control determination unit 52 performs the duty limit control as the end contact protection control for a predetermined time after the end contact determination unit 51 determines that the steering mechanism has reached the steering limit, and protects the logical value “1”. The control flag FL1 is output to the duty calculator 65.
The control release determination unit 53 performs current control on the control release flag FL2 having the logical value “1” in synchronization with the release timing of the end pad protection control, that is, the timing at which the protection control determination unit 52 switches from FL1 = 1 to FL1 = 0. The data is output to the unit 63. In other cases, a control release flag FL 2 having a logical value “0” is output to the current control unit 63.

FIG. 9 is a diagram showing the current control unit 63 in the second embodiment as a discrete digital signal processing system. In this embodiment, when the control release flag FL2 having the logical value “1” is input, the switch unit 63a is switched to a state indicated by a broken line, and the past value of the integrator is reset to a constant value (for example, “0”). It is like that.
As described above, in the second embodiment, when the duty limit control is canceled, the past value of the integrator of the current controller is reset to a constant value (for example, 0), so that it is the same as in the first embodiment described above. In addition, it is possible to prevent the past value of the integrator of the current controller from increasing when the control is released, and to prevent the drive current of the electric motor from changing suddenly due to the influence of the large past value of the integrator.

Next, a third embodiment of the present invention will be described.
In the third embodiment, in the second embodiment described above, the past value of the integrator of the current control unit 63 is reset to a constant value when the end pad protection control is released. The reset value is set based on the current command value when the protection control is released and the duty after the duty limit control.

FIG. 10 is a diagram showing the current control unit 63 in the third embodiment as a discretized digital signal processing system. In this embodiment, when the control release flag FL2 having the logical value “1” is input, the switch unit 63a is switched to the state indicated by the broken line, and the past value of the integrator is calculated by the reset past value calculation unit 63b. It resets to the value.
The reset past value calculation unit 63b calculates the reset past value z ⁻¹ by, for example, the following calculation.

z ⁻¹ = {b0 / (a1 · b0−b1)} u− {1 / (a1 · b0−b1)} y (1)
Here, u is a current command value output from the current command value calculation unit 61, and y is a duty output from the duty calculation unit 65.
As described above, in the third embodiment, when the duty limit control is released, the past value of the integrator of the current controller is changed to the current command value when the duty limit control is released and the duty after the duty limit control is performed. Therefore, it is possible to prevent the past value of the integrator of the current controller from increasing when the control is released, and to prevent the transition from the contact protection control to the normal control. This can be done without causing continuity.

In each of the above embodiments, the case where the duty limit control for limiting the duty to a certain value or less has been described as the end pad protection control. However, the duty is fixed to a constant value (for example, 3%). May be.
At this time, the duty of the pulse width modulation signal for the three switching elements constituting the upper arm (or lower arm) of the inverter 66 is set to 0%, and the three constituting the lower arm (or upper arm) are configured. The duty of the pulse width modulation signal with respect to the switching element is fixed to 100%, and each coil of the electric motor 12 is set to a closed circuit in a short-circuit state, so that the electromagnetic brake mode is established, and the inertia force of the rotor of the electric motor 12 is changed to the intermediate shaft. 5 may be prevented from being transmitted.

Further, in each of the above embodiments, the case has been described in which the end contact determination unit 51 determines whether or not the steering mechanism has reached the steering limit based on the current change rate Iq ′ of the q-axis current Iq. Based on the torque change rate, the motor angular acceleration, the motor torque change rate, or a combination thereof, it can also be determined whether or not the steering limit is reached.
In each of the above embodiments, when the integral control is performed by the current control unit 63 with respect to the deviation between the d-axis current Id and q-axis current Iq and the d-axis target current Id ^* and q-axis target current Iq ^*. The three-phase / two-phase conversion unit is provided on the output side of the current command value calculation unit 61 to convert the current command values Iu ^* , Iv ^* and Iw ^* , and the current command value Iu ^{* is} calculated by the three subtraction units ^. Proportional integral control can also be performed with respect to the deviation between ~ Iw ^* and motor currents Iu ~ Iw.

Further, in each of the above embodiments, in the duty calculation unit 65, the duty Du _B is calculated by each phase duty calculation unit 65a, the limit duty Du _L is calculated by the limiter 65b, and these are selected by the selection switch unit 65c. As described above, the voltage command values Vu to Vw are limited to predetermined values by a limiter, the voltage command values Vu to Vw and the limit voltage command values Vu _{L to} Vw _L are selected by the selection switch unit, and the selected command is selected. It is also possible to calculate the duties Du to Dw based on the values.

Further, in each of the above embodiments, the case where the end contact protection function is used as a function for temporarily limiting the feedback control has been described. However, for example, when an overcurrent exceeding the rated current flows, the feedback control is temporarily performed. Further, by limiting the duty of the pulse width modulation signal, it can be applied to a protection function for protecting the motor drive circuit.
Still further, in each of the above embodiments, the case where a three-phase brushless motor is applied as the electric motor has been described, but a brush motor system can also be applied. In this case, for example, the motor angular velocity ω may be estimated from the back electromotive force of the motor.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the controller in 1st Embodiment. It is a steering assist torque command value calculation map. It is a schematic diagram with which it uses for description of the self-aligning torque. It is a block diagram which shows the specific structure of the electric current control part in 1st Embodiment. It is a block diagram which shows the specific structure of a duty calculating part. It is a signal waveform diagram which shows the q-axis motor current change at the time of a steering limit reaching. It is a block diagram which shows the structure of the controller in 2nd Embodiment. It is a block diagram which shows the specific structure of the electric current control part in 2nd Embodiment. It is a block diagram which shows the specific structure of the electric current control part in 3rd Embodiment.

Explanation of symbols

  SM ... steering mechanism, 1 ... steering wheel, 2 ... steering shaft, 3 ... steering column, 4, 6 ... universal joint, 5 ... intermediate shaft, 8 ... steering gear, 10 ... steering assist mechanism, 11 ... speed reducer, 12 ... Electric motor, 14 ... steering torque sensor, 15 ... control unit, 16 ... vehicle speed sensor, 17 ... rotation sensor, 21 ... steering assist torque command value calculation unit, 22 ... command value compensation unit, 23 ... motor current control unit, 51 ... End contact determination unit, 52 ... protection control determination unit, 53 ... control release determination unit

Claims (9)

Steering torque detection means for detecting steering torque input to the steering mechanism, current command value calculation means for calculating a current command value based on at least the steering torque detected by the steering torque detection means, and a steering shaft of the steering mechanism An electric motor that generates a steering assist torque applied to the electric motor, current detection means that detects a drive current of the electric motor, feedback control based on a deviation between the current command value and the drive current detection value, and a voltage command value An electric power steering device comprising: current control means for calculating the motor; and motor control means for driving and controlling the electric motor based on the voltage command value,
When a predetermined condition is satisfied, a feedback restriction unit that restricts the feedback control of the current control unit, a restriction release unit that releases the restriction of the feedback control by the feedback restriction unit, and the restriction release by the restriction release unit Current suppression means for suppressing a sudden change in the drive current of the electric motor ,
The current control means includes an integrator that integrates a deviation between the current command value and the drive current detection value, and calculates the voltage command value using an integral value output from the integrator. The electric current steering device fixes the past value of the integrator to zero while the feedback control by the feedback limiting device is limited . Steering torque detection means for detecting steering torque input to the steering mechanism, current command value calculation means for calculating a current command value based on at least the steering torque detected by the steering torque detection means, and a steering shaft of the steering mechanism An electric motor that generates a steering assist torque applied to the electric motor, current detection means that detects a drive current of the electric motor, feedback control based on a deviation between the current command value and the drive current detection value, and a voltage command value An electric power steering device comprising: current control means for calculating the motor; and motor control means for driving and controlling the electric motor based on the voltage command value,
When a predetermined condition is satisfied, a feedback restriction unit that restricts the feedback control of the current control unit, a restriction release unit that releases the restriction of the feedback control by the feedback restriction unit, and the restriction release by the restriction release unit Current suppression means for suppressing a sudden change in the drive current of the electric motor,
The current control means includes an integrator that integrates a deviation between the current command value and the drive current detection value, and calculates the voltage command value using an integral value output from the integrator. Te, the current suppressing section, the restriction at restriction release by the releasing means, said integrator past value set to that electric power steering device, characterized in that the zero. Steering torque detection means for detecting steering torque input to the steering mechanism, current command value calculation means for calculating a current command value based on at least the steering torque detected by the steering torque detection means, and a steering shaft of the steering mechanism An electric motor that generates a steering assist torque applied to the electric motor, current detection means that detects a drive current of the electric motor, feedback control based on a deviation between the current command value and the drive current detection value, and a voltage command value An electric power steering device comprising: current control means for calculating the motor; and motor control means for driving and controlling the electric motor based on the voltage command value,
When a predetermined condition is satisfied, a feedback restriction unit that restricts the feedback control of the current control unit, a restriction release unit that releases the restriction of the feedback control by the feedback restriction unit, and the restriction release by the restriction release unit Current suppression means for suppressing a sudden change in the drive current of the electric motor,
The current control means includes an integrator that integrates a deviation between the current command value and the drive current detection value, and calculates the voltage command value using an integral value output from the integrator. The current suppression means, when the restriction is released by the restriction release means, the past value of the integrator, the current command value at the time of the restriction release and the voltage command of the electric motor after the feedback control is restricted The electric power steering device is set based on the value. Wherein the restriction releasing means, the electric power according to any one of claim 1 to 3 from the start of the restriction of the feedback control by the feedback limiting means, characterized in that for releasing the restriction after a predetermined time has elapsed Steering device. The electric power steering apparatus according to claim 4 , wherein the predetermined time is set based on at least one of a steering torque, a current command value, and a motor rotation speed. The motor control means controls driving of the electric motor with a pulse width modulation signal based on the voltage command value, and the feedback limiting means is configured to output the pulse width modulation signal when the predetermined condition is satisfied. of limiting the duty an upper limit to the duty, the electric power steering apparatus according to any one of claim 1 to 5, characterized in that to limit the feedback control. The motor control means controls driving of the electric motor with a pulse width modulation signal based on the voltage command value, and the feedback limiting means is configured to output the pulse width modulation signal when the predetermined condition is satisfied. of by fixing the duty to a predetermined value, the electric power steering apparatus according to any one of claim 1 to 5, characterized in that to limit the feedback control. The motor control means has an inverter that is driven by the pulse width modulation signal and supplies a drive current to the electric motor, and the feedback limiting means has an upper arm and a lower arm of the inverter when the predetermined condition is satisfied. 8. The electric power steering apparatus according to claim 7 , wherein one of the arms is simultaneously turned on to control the electromagnetic brake mode. The motor control means controls driving of the electric motor by a pulse width modulation signal based on the voltage command value, and the feedback restriction means determines that the steering mechanism has reached a steering limit. , the duty of the pulse width modulated signal, any one of claims 1-8, wherein a control that to suppress the torque transmitted to the torque transmitting member between the steering shaft and the steering wheel of the steering mechanism The electric power steering apparatus according to Item 1.

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