JP2012020709A - Electric power steering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which does not consume excessive power more than necessary while satisfying a target command value.SOLUTION: When a motor current command value is limited so that the power consumption of a steering auxiliary motor may not exceed a power limit value, a predetermined power limit value Pmax expressing a power limit of a power source is applied as a power limit value when motor torque is in a prescribed range 0 to T1 or the number of revolutions of the motor is in a prescribed range N1 to N2, and a value smaller than the prescribed power limit value Pmax is applied as the power limit value when the motor torque is in a range T1 to T2 outside the prescribed range or the number of revolutions of the motor is in a range 0 to N1 outside the prescribed range.

Description

  The present invention relates to an electric power steering apparatus including a steering means and a steering assist motor that assists the steering means.

A steering assist motor (hereinafter simply referred to as a “motor”) used in an electric power steering apparatus has its motor torque controlled by energizing a stator winding in accordance with the rotation of the motor. The relationship between the motor rotation speed (also referred to as rotation speed) and motor torque is referred to as “motor output characteristics” in this specification.
The motor output characteristics include the power limit of the power source that drives the motor. By limiting the power of the motor based on the power limit of the power source, the current drawn from the power source can be suppressed below a certain level. Is prevented from malfunctioning due to overcurrent or overheating. FIG. 8 shows the relationship between the motor output characteristics and the power supply power limit. The horizontal axis of the graph indicates motor torque, and the vertical axis indicates the number of rotations.

  In a normal design, a target output is set in a range that does not exceed the power supply power limit in the motor output characteristics, and the rotation of the motor is controlled to be the target output. The target output is called “target command value”, and is indicated by “A” in FIG.

JP 2008-149910 A JP 2009-248838

  By the way, during the operation of the motor, the target state A may be exceeded due to the state of the motor. When the target command value A is close to the power supply power limit as indicated by reference numeral 100 in FIG. 8, the power of the motor is limited due to the power supply power limit. However, when the target command value A is far from the power supply power limit as indicated by reference numeral 101, the power supply power limit is not applied. For this reason, there has been a problem in that excessive output (steering assist) exceeds the target output, resulting in excessive power consumption of the power source.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering apparatus that satisfies a target command value and does not consume excessive power more than necessary.

  To achieve the above object, an electric power steering apparatus according to the present invention sets a power source for driving a steering assist motor, detection means for detecting the motor torque or motor rotation speed of the steering assist motor, and a motor current command value. And the control means for controlling the steering assist motor using the motor current command value and the steering assist motor based on the power limit value so that the power consumption of the steering assist motor does not exceed the power limit value. A power limiting unit that limits a motor current command value to be supplied, and the power limiting unit is a predetermined power representing a power limit of the power source as the power limit value according to the motor torque or the motor rotation speed. A value lower than the power limit value is applied.

With this configuration, there is a case where a value lower than the predetermined power limit value is applied as the power limit value, so that the power of the power source is not consumed excessively.
The value lower than the predetermined power limit value is selected from a range in which the predetermined power limit value is the upper limit and the power value corresponding to the motor current command value or a power value larger than that is the lower limit. preferable. According to this, when the motor current command value is going to be exceeded, the “decreased” power supply power limit is applied, so that the motor state does not exceed the target command value due to the event. Therefore, excessive steering assist is reduced, and excess power consumption can be eliminated.

  When the motor torque is within a predetermined range or when the motor rotation speed is within a predetermined range, the power limiting unit is configured to use a predetermined power limit value representing a power limit of the power source as the power limit value. The power limiting means applies the power limit value as the power limit value when the motor torque is outside the predetermined range or the motor rotation speed is outside the predetermined range. A reduced value may be applied.

  The upper limit of the predetermined range of the motor torque is increased along the motor output characteristic representing the relationship between the rotation speed of the motor and the motor torque, and the power consumption of the steering assist motor is the predetermined power. The motor torque value when the limit value is reached can be set (“T1” in FIG. 7). In this case, when the motor torque exceeds this upper limit, a power limit value lower than the predetermined power limit value is applied.

  The lower limit of the predetermined range of the rotational speed is reduced along the motor output characteristic representing the relationship between the rotational speed of the motor and the motor torque, and the power consumption of the steering assist motor is reduced to the predetermined power. The value of the number of revolutions when the limit value is reached can be set (see “N1” in FIG. 7). In this case, when the motor rotation speed falls below this lower limit, the power limit value lower than the predetermined power limit value is applied.

  As described above, according to the present invention, it is possible to eliminate excessive power consumption of the power source, and thus it is possible to reduce the power load of the vehicle.

1 is a block diagram for explaining an electrical configuration of an electric power steering apparatus according to a first embodiment of the present invention. It is an illustration figure for demonstrating the structure of a motor. Is a graph showing the a relationship _| T M | absolute value of the power limit value P_lim and the motor torque. 4 is a flowchart showing the operation of the power limiting unit 22. It is a block diagram for demonstrating the electrical structure of the 2nd Embodiment of this invention. It is a graph which shows the relationship between electric power limiting value P_lim and absolute value | N | of motor rotation speed. It is the graph which drew the motor output characteristic and the power supply power limit set by the present invention in an overlapping manner. It is the graph which drew the motor output characteristic and the power supply power limit in a superimposed manner.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram for explaining an electrical configuration of an electric power steering device (an example of a vehicle steering device) to which the motor control device according to the first embodiment of the present invention is applied.
This electric power steering device includes a torque sensor 1 for detecting a steering torque T applied to a steering wheel 10 as an operation member for steering a vehicle, and a steering assist force via a speed reduction mechanism 8 to a steering mechanism 2 of the vehicle. A motor 3 (steering assist motor) that gives power, a power supply 30 for driving the motor 3 through the drive circuit 12, and a rotation angle sensor (for example, a motor resolver) 5 for detecting the rotation angle (electrical angle) of the motor 3. The motor control device 6 that controls the motor 3 and the vehicle speed sensor 7 that detects the speed of the vehicle on which the electric power steering device is mounted are provided. The above-described rotation angle sensor 5, torque sensor 1 and vehicle speed sensor 7 are connected to the motor control device 6.

The motor control device 6 drives the motor 3 according to the steering torque detected by the torque sensor 1 and the vehicle speed detected by the vehicle speed sensor 7, thereby realizing appropriate steering assistance according to the steering situation and the vehicle speed.
In this embodiment, the motor 3 is a three-phase motor. As schematically illustrated in FIG. 2, the U phase and the V phase are arranged in a rotor 50 as a field and a stator 55 facing the rotor 50. And W-phase stator windings 51, 52, 53. The motor 3 may be of an inner rotor type in which a stator is disposed facing the outside of the rotor, or may be of an outer rotor type in which a stator is disposed facing the inside of a cylindrical rotor.

Three-phase fixed coordinates (UVW coordinate system) are defined in which the U, V, and W axes are taken in the direction of the stator windings 51, 52, and 53 of each phase. Further, a two-phase rotational coordinate system (dq coordinate) in which the d axis (magnetic pole axis) is taken in the magnetic pole direction of the rotor 50 and the q axis (torque axis) is taken in the direction perpendicular to the d axis in the rotation plane of the rotor 50. System (real rotating coordinate system).
The dq coordinate system is a rotating coordinate system that rotates with the rotor 50. In the dq coordinate system, since only the q-axis current contributes to the torque generation of the rotor 50, the d-axis current may be set to zero and the q-axis current may be controlled according to the desired torque. The rotation angle θ _M of the rotor 50 is the rotation angle of the d axis with respect to the U axis. d-q coordinate system is an actual rotating coordinate system that rotates in accordance with the rotor angle theta _M. With the use of the rotor angle theta _M, coordinate conversion may be made between the UVW coordinate system and the d-q coordinate system.

Returning to FIG. 1, the motor control device 6 includes a current detection unit 13 and a drive circuit 12.
The current detector 13 detects the current flowing through the stator windings 51, 52, 53 (see FIG. 2) of the motor 3. More specifically, the current detection unit 13 includes current detectors that detect phase currents in the three-phase (U-phase, V-phase, and W-phase) stator windings 51, 52, and 53, respectively.
The portions other than the current detection unit 13 and the drive circuit 12 of the motor control device 6 are configured by a microcomputer including a CPU and a memory (ROM, RAM, etc.), and a plurality of functions are executed by executing a predetermined program. Functions as a processing unit.

The plurality of function processing units include a target motor torque generation unit 20, a current command value generation unit 21, a power limiting unit 22, a current deviation calculation circuit 23, a PI (proportional integration) control unit 24, a dq / A UVW converter 25, a PWM (Pulse Width Modulation) controller 26, a UVW / dq converter 27, a rotation angle calculator 31, and a motor torque calculator 37 are included.
The rotation angle calculation unit 31 calculates the rotation angle (electrical angle; hereinafter referred to as “rotation angle θ1”) of the rotor 50 of the motor 3 based on the output signal of the rotation angle sensor 5. The rotation angle θ1 is output as the transformation angle theta _S for coordinate transformation.

The target motor torque generator 20 generates the target motor torque T _M ^* based on the steering torque (detected steering torque) detected by the torque sensor 1 and the vehicle speed detected by the vehicle speed sensor 7. Specifically, the target motor torque generation unit 20 is based on the detected vehicle speed and the target motor torque T according to the detected steering torque based on the relationship of the target motor torque T _M ^* to the detected steering torque set in advance for each vehicle speed. Generate _M ^* .

For the detected steering torque, for example, the torque for steering in the left direction is a positive value, and the torque for steering in the right direction is a negative value. The target motor torque T _M ^* is a positive value when a steering assist force for steering leftward from the motor 3 is to be generated, and when a steering assist force for steering rightward from the motor 3 is to be generated. Negative value.
The target motor torque T _M ^* generated by the target motor torque generation unit 20 is given to the current command value generation unit 21.

The current command value generation unit 21 generates a current to be passed through the coordinate axes of the dq coordinate system as a current command value. Specifically, the d-axis current command value I _d ^* and the q-axis current command value I _q ^* are generated. More specifically, the current command value generation unit 21 sets the q-axis current command value I _q ^* to a significant value, and sets the d-axis current command value I _d ^* to zero or a negative value (negative value). This is the case when field-weakening control is performed). More specifically, the current command value generation unit 21 divides the target motor torque T _M ^* generated by the target motor torque generation unit 20 by the torque constant K _T of the motor 3 to obtain a q-axis current command value. _Find I _q ^* . This q-axis current command value may be referred to as “motor current command value” in this specification. The motor current command value I _q ^* generated by the current command value generation unit 21 is given to the current deviation calculation circuit 23 via the power limiting unit 22.

The current detection unit 13 includes the U-phase current I _U , the V-phase current I _V , and the W-phase current I _W (hereinafter, collectively referred to as “three-phase detection current I _UVW ”) of the motor 3 in the drive circuit 12. To detect. The three-phase detection current I _UVW detected by the current detection unit 13 is given to the UVW / dq conversion unit 27.
The UVW / dq conversion unit 27 converts the three-phase detection current I _UVW into a d-axis current I _d and a q-axis current I _q (hereinafter collectively referred to as the two-phase rotation coordinate system (dq coordinate system)). The coordinates are converted to “two-phase detection current I _dq ”. For this coordinate conversion, the conversion angle θ _S obtained by the rotation angle calculation unit 31 is used.

The motor torque calculator 37 calculates a motor torque (motor torque) T _M based on the two-phase detection current I _dq obtained by the UVW / dq converter 27. Specifically, the motor torque calculation unit 37 calculates the motor torque T _M by multiplying the q-axis detection current I _q obtained by the UVW / dq conversion unit 27 by the torque constant K _T of the motor 3. Motor torque T _M calculated by the motor torque computing unit 37 is supplied to the power limiting portion 22.

Motor power limiting portion 22, as shown in the inverter power limit value (referred to simply as "power limit value") graph showing the relationship between P_lim and the motor torque T _M (FIG. 3), which is calculated by the motor torque calculating section 37 When the torque T _M is in the predetermined range T1 to T2, the power limit value P_lim is lowered from the predetermined power limit value Pmax.
The reduced power limit value P_lim has the predetermined power limit value Pmax as an upper limit, and corresponds to a power value corresponding to the motor current command value I _q ^* or a power value larger than that (for example, equivalent to the motor current command value I _q ^*) . (A value obtained by adding or multiplying a certain margin to a power value to be performed) is a value selected from a range having a lower limit.

  Here, the predetermined value T1 is a torque corresponding to the intersection Q1 between the curve of the power source power limit Pmax and the motor output characteristic h in FIG. The number of motor revolutions at this intersection Q1 is N1. The rotational speed of the motor corresponds to the steering speed of the steering means including the steering wheel 10. The predetermined value T2 is a torque corresponding to the intersection Q2 of the motor output characteristic h and the torque coordinate axis T in FIG. The motor speed at this intersection Q2 is zero. In a range T1 to T2 defined by these torques T1 and T2, the power limit value P_lim is lowered from a predetermined power limit value Pmax.

Specifically, as shown in FIG. 3, it is equal to the default power limit value Pmax if the motor torque T _M is less torque T1, reduce the power limit value P_lim with increasing the torque T1, the torque T2 The minimum power limit value Pdown. The power limit minimum value Pdown corresponds to the power of the power line such as the power source when the torque is T2 and the motor speed is 0 (see FIG. 7).
The power limit value P_lim after the adjustment is expressed by the following linear expression, for example (see FIG. 3).

P_lim = aT _M + b (T1 <T _M <T2) (1) Formula
P_lim = Pmax (0 <T _M <= T1) (2) The coefficient a is expressed by (Pmax−Pdown) / (T1−T2) and takes a negative value. The coefficient b is expressed by (Pmax / T1−Pdown / T2) · T1 · T2 / (T2−T1) and takes a positive value.
Listed above (1) In the formula, although power limit value P_lim is an example which varies linearly in the range T1~T2 the motor torque T _M, the control of the power limiting portion 22 of the present invention is not limited thereto It is not something. For example, the power limit value P_lim may change in a curved line in the range T1 to T2 (secondary curve, exponential curve, sine wave curve, etc.). The power limit value P_lim is calculated by calculation based on the torque T. A memory is prepared in advance, and the power limit value P_lim corresponding to each torque value is stored in a table (referred to as a power limit table) in this memory. You can write it in and use it.

Further, as indicated by a two-dot chain line P_lim ′ in FIG. 3, the power limit value may be decreased in a region where the motor torque is close to zero.
The power limiting unit 22 adjusts the motor current command value I _q ^* input from the current command value generating unit 21 so that the power consumption of the motor does not exceed the power limit value P_lim. That is, the motor current command value I _q ^* , the d-axis command voltage value V _d ^*, and the q-axis command voltage value V _q ^* input from the current command value generation unit 21 are determined by applying the following equation (3). If the power consumption of the motor is equal to or less than the power limit value P_lim, the motor current command value I _q ^* is output as it is. Motor determined by applying the motor current command value I _q ^* , the d-axis command voltage value V _d ^* and the q-axis command voltage value V _q ^* input from the current command value generation unit 21 to the following equation (3) If the power consumption exceeds the power limit value P_lim, the motor current command value I _q ^* is reduced and output so that the power consumption of the motor is equal to or less than the power limit value P_lim.

Here, the relational expression between the motor power consumption, the motor current, and the voltage is
I _q ^* = (P_lim−V _d ^* × I _d ^* ) / V _q ^* (3)
In the case of a motor with a brush, if I _q ^* is replaced with the motor current command value I _m ^* and V _q ^* is replaced with the voltage V _m between the motor terminals,
I _m ^* = P_lim / V _m (4) The power can be limited by the motor current as in the brushless motor.

FIG. 4 is a flowchart showing the operation of the power limiting unit 22. Power limiting unit 22 obtains a motor current command value _I ^{q *} from the current command value generating section 21 (step S1), and obtains the motor torque _{T M} from the motor torque calculating section 37 (step S2). Then, the power limit value P_lim is calculated using the above-described equations (1) and (2), or obtained from the power limit table, and the power limit value P_lim is set (step S3). Further, a motor current (motor current limit value Ilim) obtained by applying the power limit value P_lim to the above-described expression (3) or (4) is set (step S4). The motor current command value I _q ^* and the motor current limit value Ilim are compared in absolute value. If the motor current command value I _q ^* is larger than the motor current limit value Ilim (Yes in step S5), the motor current command value I _q ^* is rewritten so as to be the same value as the motor current limit value Ilim (step S6). If the motor current command value I _q ^* is equal to or less than the motor current limit value Ilim (No in step S5), the motor current command value I _q ^* is used without being rewritten. The motor current command value I _q ^* is provided to the current deviation calculation circuit 23.

The current deviation calculation circuit 23 calculates a deviation between the motor current command value I _q ^* and the d-axis current command value I _d ^* and the two-phase detection current I _dq given from the UVW / dq conversion unit 27. These deviations are given to the PI control unit 24.
The PI control unit 24 performs a PI calculation on the current deviation calculated by the deviation calculation unit 23, so that the two-phase instruction voltage V _dq ^* (d-axis instruction voltage V _d ^* and q-axis instruction voltage to be applied to the motor 3 is obtained. V _q ^* ) is generated. The two-phase instruction voltage V _dq ^* is given to the dq / UVW converter 25.

The dq / UVW conversion unit 25 converts the two-phase instruction voltage V _dq ^* into the three-phase instruction voltage V _UVW ^* . For this coordinate conversion, the conversion angle θ _S obtained by the rotation angle calculation unit 31 is used. The three-phase command voltage V _UVW ^* includes a U-phase command voltage V _U ^* , a V-phase command voltage V _V ^*, and a W-phase command voltage V _W ^* . The three-phase instruction voltage V _UVW ^* is given to the PWM control unit 26.
The PWM control unit 26 includes a U-phase PWM control signal, a V-phase PWM control signal, and a W-phase PWM having a duty corresponding to the U-phase instruction voltage V _U ^* , the V-phase instruction voltage V _V ^*, and the W-phase instruction voltage V _W ^* , respectively. A control signal is generated and supplied to the drive circuit 12.

The drive circuit 12 includes a three-phase converter circuit corresponding to the U phase, the V phase, and the W phase. The power elements constituting the inverter circuit are controlled by a PWM control signal supplied from the PWM control unit 26, so that a voltage corresponding to the three-phase instruction voltage V _UVW ^* becomes a stator winding 51, 52 for each phase of the motor 3. , 53.
In such a configuration, when a steering torque is applied to the steering wheel 10, this is detected by the torque sensor 1. Then, the target motor torque T _M ^* corresponding to the steering torque detected by the torque sensor 1 and the vehicle speed detected by the vehicle speed sensor 7 is generated by the target motor torque generator 20. Then, a current command value I _dq ^* corresponding to the target motor torque T _M ^* is generated by the current command value generation unit 21.

If the power consumption of the motor corresponding to the motor current command value I _q ^* corresponding to the target motor torque T _M ^* exceeds the power limit value P_lim, the power limit unit 22 reduces the power consumption of the motor to the power limit value P_lim. The motor current command value I _q ^* is reduced and output so as to be as follows.
A deviation between the motor current command value I _dq ^* and the two-phase detection current I _dq is obtained by the current deviation calculation circuit 23. PI calculation is performed by the PI control unit 24 so as to lead this deviation to zero, and a two-phase instruction voltage V _dq ^* corresponding to the calculation result is output from the PI control unit 24. This two-phase command voltage V _dq ^* is converted into a three-phase command voltage V _UVW ^* by the dq / UVW converter 25.

The drive circuit 12 operates with a duty ratio corresponding to the three-phase instruction voltage V _UVW ^* by the action of the PWM control unit 26, so that the motor 3 is driven and corresponds to the final current command value I _dq ^* . The motor torque (assist torque) thus applied is given to the steering mechanism 2. Thus, steering assistance can be performed according to the steering torque and the vehicle speed.
Next, an electric power steering device to which a motor control device according to a second embodiment of the present invention is applied will be described.

FIG. 5 is a block diagram for explaining the electrical configuration of the second embodiment. Parts corresponding to the respective parts in FIG. 1 are denoted by the same reference numerals as in FIG.
In this embodiment, the motor torque calculator 37 is not provided. Instead, the rotation speed θ1 of the rotor 50 of the motor 3 output from the rotation angle calculator 31 is used (for example, by differential calculation) to rotate the motor speed. A rotation speed calculation unit 38 is provided.

As shown in the graph of FIG. 6, the power limiting unit 22 reduces the power limiting value P_lim when the motor rotation number N calculated by the rotation number calculation unit 38 is in a predetermined range 0 to N1.
The reduced power limit value P_lim has the predetermined power limit value Pmax as an upper limit, and corresponds to a power value corresponding to the motor current command value I _q ^* or a power value larger than that (for example, equivalent to the motor current command value I _q ^*) . A value selected from a range having a lower limit of a value obtained by adding or multiplying a certain margin to a power value to be performed.

  Here, the predetermined value N1 is the motor rotation speed N1 corresponding to the intersection Q1 between the curve of the power source power limit Pmax and the motor output characteristic h in FIG. The motor torque at the intersection Q1 is T1. In FIG. 7, the number of rotations when the motor torque is 0 is N2. In FIG. 7, the torque corresponding to the intersection Q2 between the motor output characteristic h and the torque coordinate axis T is defined as T2. The motor speed at this intersection Q2 is zero. In the range 0 to N1 defined by the motor rotation speed N1, the power limit value P_lim is lowered from the predetermined power limit value Pmax. Specifically, as shown in FIG. 6, if the motor speed N is equal to or greater than N1, it is equal to the predetermined power limit value Pmax. However, as the speed N decreases, the power limit value P_lim is decreased and = 0, the power limit minimum value Pdown. The power limit minimum value Pdown corresponds to a power line such as a power source when the torque is T2 and the motor speed is 0 (see FIG. 7).

The power limit value P_lim after the adjustment is expressed by, for example, the following formula (see FIG. 6).
P_lim = Pmax (N> = N1) (5)
P_lim = cN + d (0 <N <N1) (6) The coefficient c is expressed by (Pmax−Pdown) / N1 and takes a positive value. The coefficient b is equal to Pdown.
In the above formula (6), an example is shown in which the power limit value P_lim changes linearly in the motor rotation speed range 0 to N1, but the control of the power limiter 22 of the present invention is limited to this. It is not a thing. For example, the power limit value P_lim may change in a curved line in the range 0 to N1 (secondary curve, exponential curve, sine wave curve, etc.). The power limit value P_lim is calculated by calculation based on the rotation speed N, but a memory is prepared in advance, and the power limit value P_lim corresponding to each rotation value is stored in a table in this memory (referred to as a power limit table). ) And use it.

Further, as indicated by a two-dot chain line P_lim ′ in FIG. 6, the power limit value may be decreased in the region where the motor rotation speed is the maximum rotation speed N2 and the vicinity thereof.
The power limiting unit 22 adjusts the motor current command value I _q ^* input from the current command value generating unit 21 so that the power consumption of the motor does not exceed the power limit value P_lim. That is, if the motor power consumption corresponding to the motor current command value I _q ^* input from the current command value generation unit 21 is equal to or less than the power limit value P_lim, the motor current command value I _q ^* is output as it is. If the power consumption of the motor corresponding to the motor current command value I _q ^* input from the current command value generation unit 21 exceeds the power limit value P_lim, the power consumption of the motor becomes equal to or less than the power limit value P_lim. The motor current command value I _q ^* is reduced and output.

FIG. 4 described above can be applied to the flowchart showing the operation of the power limiting unit 22. However, in step S2, instead of obtaining the motor torque T _M from the motor torque calculating section 37, it is different the place to get the motor rotation speed N from the rotational speed calculator 38.
Thereafter, the power limit value P_lim is calculated using the above-described equations (5) and (6), or obtained and set from the power limit table (step S3), and a motor corresponding to the power limit value P_lim is obtained. Current limit value Ilim is set (step S4), motor current command value _Iq ^* and motor current limit value Ilim are compared in absolute value, and if motor current command value _Iq ^* is greater than motor current limit value Ilim, the motor current instruction value I _q ^*, rewritten to be the same value as the motor current limit value Ilim, the motor current command value I _q ^* can not rewrite the motor current command value I _q ^* equal to or less than the motor current limit value Ilim Use as is. The motor current command value I _q ^* is provided to the current deviation calculation circuit 23.

  Unlike the first embodiment in which the power limit value P_lim is calculated based on the motor torque T, the second embodiment calculates the power limit value P_lim based on the motor speed N. However, since the relationship between the motor rotation speed N and the torque T is related to the motor output characteristic, the power limit value P_lim calculated based on the motor torque T is also based on the motor rotation speed N. The calculated power limit value P_lim is also the same. In this respect, it can be said that the first embodiment and the second embodiment are substantially the same invention. In addition, various modifications can be made within the scope of the present invention.

  DESCRIPTION OF SYMBOLS 3 ... Steering auxiliary motor, 22 ... Electric power limiting part, 30 ... Power supply, 37 ... Motor torque calculating part, 38 ... Rotational speed calculating part

Claims (6)

A steering assist motor for generating a steering assist force, a power source for driving the steering assist motor, detection means for detecting the motor torque or the motor speed of the steering assist motor, and a motor current command value are set, and the motor Control means for controlling the steering assist motor using a current command value; and power limiting means for preventing the power consumption of the steering assist motor from exceeding the power limit value based on the power limit value;
The electric power limiting means applies a value lower than a predetermined electric power limit value representing the electric power limit of the power source as the electric power limit value according to the motor torque or the motor rotation speed. Steering device.   2. The electric power according to claim 1, wherein the power limiting means limits a motor current command value supplied to the steering assist motor so that power consumption of the steering assist motor does not exceed a power limit value. Steering device.   The value lower than the predetermined power limit value is a value selected from a range in which the predetermined power limit value is the upper limit and the power value corresponding to the motor current command value or a power value larger than that is the lower limit. The electric power steering apparatus according to claim 2, wherein When the motor torque is within a predetermined range or when the motor rotation speed is within a predetermined range, the power limiting unit is configured to use a predetermined power limit value representing a power limit of the power source as the power limit value. Apply,
The power limiting means is a value that is lower than the predetermined power limit value as the power limit value when the motor torque is outside the predetermined range or the motor rotation speed is outside the predetermined range. The electric power steering device according to any one of claims 1 to 3, to which is applied.   The lower limit of the predetermined range of the absolute value of the motor torque is 0, and the upper limit of the absolute value of the motor torque increases along the motor output characteristic representing the relationship between the motor rotation speed and the motor torque. The electric power steering device according to claim 4, wherein the electric power steering device is a motor torque value when the power consumption of the steering assist motor reaches the predetermined power limit value.   The upper limit of the predetermined range of the absolute value of the rotational speed is the rotational speed when the motor torque is 0, and the lower limit of the predetermined range of the absolute value of the rotational speed is the relationship between the rotational speed of the motor and the motor torque. 5. The electric power according to claim 4, wherein the rotational speed decreases along the motor output characteristic that is expressed, and is the value of the rotational speed when the power consumption of the steering assist motor reaches the predetermined power limit value. Steering device.

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