JP2013074648A - Electrically-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrically-driven power steering device that holds a light steering feeling by weak field control, and at the same time avoids an event of ineffectual heat generation due to the weak field control becoming invalid, according to the driving state of a motor.SOLUTION: When q axis current Iq, which is torque current corresponding to the driving state of a motor, is set to Iq=Iq', a current vector i will not be set in a dotted area 135 where the rotation number of the motor does not increase but only heat generation increases, but it will be set to a current vector k, by which d axis current Id, which is weak field current, becomes the upper limit value Idlim of a usage area 134 in a usage area 134 indicated by hatching.

Description

  According to the present invention, when a vehicle is steered by an operation member such as a steering handle (steering wheel), the power of a motor (electric motor) is transmitted to the steering system (steering system) as a steering assist force (steering assist force), and the operation by the driver is performed. More particularly, the present invention relates to an electric power steering apparatus that performs field weakening control of the motor.

  The motor of the electric power steering device has a high torque and low rotation performance as when steering the steering wheel while the vehicle is stopped, and the steering wheel slides out of the rear wheel when oversteer occurs during driving. There is a demand for low torque and high rotation performance as when applying quick steering (also known as fast-turn steering) in the direction and applying counter-steer.

  In order to achieve both high-torque low-rotation performance and low-torque high-rotation performance, the electric power steering system is equipped with a high-torque low-rotation rated motor, and field-weakening control is performed on this high-torque low-rotation rated motor. In order to obtain low torque and high rotation performance.

  More specifically, according to the current flowing through the motor, in other words, according to the torque, on the low torque side, the motor field is weakened to increase the rotation speed, thereby ensuring low torque and high rotation performance. On the high torque side, the two fields of performance were achieved by ensuring high torque and low rotation performance without weakening the motor field.

  In a brushless motor, when attempting to increase the motor speed by field weakening control, the d-axis is set to the direction of the field component, and the q-axis is set to the direction of the torque component advanced by π / 2 with respect to this. When the field weakening control is not performed with the q-axis current Iq held at a predetermined value, control is performed to increase the value (absolute value) of the d-axis current Id (polarity is negative), which is zero. Is known (Patent Document 1).

JP 2010-64544 A ([0030], [0033]-[0035], [0037], [0044], FIG. 7, FIG. 10)

  By the way, in the invention according to Patent Document 1 made by the inventors of this application, as shown in FIG. 16 (FIG. 10 of Patent Document 1), even if the d-axis current Id is increased (the value of the d-axis current Id). Is a negative value, the absolute value increases. The same applies hereinafter.) In the region where the motor rotation speed Nm [rpm] does not increase, the d-axis current Id is controlled so as not to increase any further. Heat generation associated with an increase in Id is suppressed.

  In this case, the maximum value of the d-axis current Id depends on the battery voltage Vb that is the power supply voltage, that is, the motor voltage applied to the motor. For example, if the battery voltage Vb is Vb = 10 [V], the d-axis current Id It is disclosed that the current Id is limited to Id = −35 [A], and if the battery voltage Vb is Vb = 12 [V], the current Id is limited to Id = −57 [A].

  However, the control technology that simply limits the maximum value (absolute maximum value) that the d-axis current Id can take according to the battery voltage Vb is sufficient to suppress heat generation depending on the steering situation, that is, the motor driving situation. There is room for improvement, as the problem of not being able to obtain a certain effect is known.

  The present invention has been made in connection with such a technology, and while maintaining a light steering feeling by field weakening control, an event in which useless heat generation occurs because field weakening control becomes ineffective is generated. An object of the present invention is to provide an electric power steering apparatus that can be effectively avoided with a simple configuration according to a driving situation.

  An electric power steering apparatus according to the present invention is an electric power steering apparatus that drives and controls a steering assist motor in accordance with a steering input of a driver, and has the following features [1]-[5].

  [1] A steering input detection unit that detects the magnitude of the steering input, a torque current setting unit that sets a torque current of the motor based on a signal from the steering input detection unit, and a torque current setting unit A field weakening current setting unit for setting a field weakening current for weakening the field of the motor based on the torque current and the rotation speed of the motor, and the torque current setting unit. A motor drive control unit configured to drive and control the motor based on the torque field and the field weakening current set by the field weakening current setting unit; and field weakening configured to set the field weakening current to a limit value or less. A field limiting unit, wherein the field weakening current limiting unit sets the limit value of the field weakening current according to the torque current of the motor.

  According to the invention having the above feature [1], the limit value of the field weakening current is set according to the torque current set by the torque current setting unit, in other words, according to the driving state of the motor. Therefore, it is easy to set the limit value, and the event that the field-weakening control is not effective and wasteful heat generation occurs can be effectively avoided with a simple configuration according to the driving state of the motor.

  Thereby, it is possible to avoid performing field-weakening control that is useless (invalid and unnecessary) when the torque current is changed. That is, it is possible to avoid a reduction in the number of rotations of the motor due to an increase in the field weakening current (invalid and unnecessary) and unnecessary heat generation.

  [2] In the invention having the above-mentioned feature [1], the field weakening current limiting unit may set the torque current when setting the limit value of the field weakening current according to the torque current of the motor. For each value, when the value of the field weakening current is increased while holding the value of the torque current, the field weakening current value when the motor rotation speed is reduced by a predetermined number of rotations from the maximum rotation speed is It is characterized by setting a limit value.

  According to the invention having the above feature [2], the maximum number of revolutions, which is a peak value at which the number of revolutions of the motor decreases when the field weakening is further strengthened, is set as the reference value of the limit value, and errors are taken into consideration. Since the field weakening current value when the predetermined number of rotations is reduced from the maximum number of rotations is set as the limit value, it is easy to set the limit value when there is an error or variation in each function unit such as the steering input detection unit. . In other words, the degree of freedom in design when selecting components, sensors, and the like constituting the electric power steering apparatus is large, and the cost can be reduced.

  [3] In the invention having the feature of the above [2], the field weakening current limiting unit sets the limit value of the field weakening current according to the torque current of the motor. For each value, when the value of the field weakening current is increased while holding the value of the torque current, the limit value is set to the value of the field weakening current at which the motor rotation speed becomes the maximum rotation speed. It is characterized by doing.

  According to the invention having the above feature [3], if the field weakening is further increased, the motor rotation speed is decreased, and the value of the field weakening current that becomes the peak value of the motor rotation speed is set as the limit value. Until the limit value is reached, the motor rotation speed increases as the field weakening current increases, and the amount of heat loss can be suppressed while maintaining a light steering feeling. That is, unnecessary heat generation accompanying an increase in unnecessary field weakening current can be avoided.

  [4] In the invention having any one of the above features [1] to [3], a phase current limiting unit for setting an upper limit value of the phase current of the motor, and a phase of the motor by the phase current limiting unit When the upper limit value of the current is changed, according to the change of the upper limit value, the current limit circle representing the magnitude of the vector determined by the value of the torque current and the value of the field weakening current is changed, In the current limit circle after the change, a use region setting unit after field weakening current limitation for setting a use region after limitation limited by the limit value of the field weakening current is provided, .

  According to the invention having the above feature [4], the field weakening current limiting section can be easily constructed.

  [5] In the invention having any one of the above features [1] to [4], the field weakening current limiting unit is configured to reduce the field current of the field weakening current based on a power supply voltage value of the electric power steering apparatus. The limiting value is changed.

  According to the invention having the above feature [5], since the limit value is further changed based on the power supply voltage value, more effective heat generation suppression is possible.

  According to the present invention, the limit value of the field weakening current is set according to the torque current set by the torque current setting unit, in other words, according to the driving condition of the motor. The event that the setting is easy and the field-weakening control becomes ineffective and wasteful heat generation occurs can be effectively avoided with a simple configuration according to the driving state of the motor.

  Thereby, it is possible to avoid performing field-weakening control that is useless (invalid and unnecessary) when the torque current is changed. That is, it is possible to avoid a reduction in the number of rotations of the motor due to an increase in the field weakening current (invalid and unnecessary) and unnecessary heat generation.

  Therefore, while maintaining a light steering feeling by the field weakening control, the phenomenon in which the field weakening control becomes ineffective and wasteful heat generation occurs as described above is effective with a simple configuration according to the motor driving situation. Can be avoided.

It is a lineblock diagram of the electric power steering device concerning one embodiment of this invention. It is a block diagram of a motor control system provided with a control apparatus and a motor drive control apparatus in the electric power steering apparatus of the example of FIG. It is a functional block diagram of a d-axis current setting / limiting unit including a d-axis current setting unit and a field weakening current limiting unit. It is explanatory drawing of the q-axis command voltage corresponding | compatible map stored in a q-axis command voltage corresponding | compatible process part. It is explanatory drawing of the q-axis actual current corresponding | compatible map stored in a q-axis actual current corresponding | compatible process part. It is explanatory drawing of the motor rotational speed corresponding | compatible map stored in a motor rotational speed corresponding | compatible process part. It is explanatory drawing which shows the use area | region after the limitation of the d-axis current which concerns on a comparative example. FIG. 8A is an explanatory diagram according to an embodiment for explaining a region in which only heat generation increases in the use region shown in FIG. 7. FIG. 8B is an explanatory diagram illustrating a setting example after limiting the d-axis current according to the embodiment. It is explanatory drawing which shows the change of the rotation speed when the torque current is maintained at a predetermined value, and the field weakening current is increased (increase in absolute value) and the change in the heat generation amount. FIG. 10 is an explanatory diagram of a d-axis current limit line that does not use a region in which only heat generation increases when the torque current is changed under the conditions of the example in FIG. 9. It is explanatory drawing explaining the example of the limit value of the field weakening current before a limit, and the limit value of the field weakening current after a limit. FIG. 12A and FIG. 12B are explanatory diagrams for changing the use region of the field weakening current when the size of the current vector limiting circle is changed. FIG. 13A and FIG. 13B are explanatory diagrams illustrating an example of the limit value of the field weakening current when the size of the current vector limit circle is changed. FIG. 14A and FIG. 14B are explanatory diagrams for changing the use region of the field weakening current when the power supply voltage is changed. FIG. 15A and FIG. 15B are explanatory diagrams illustrating examples of limit values of the field weakening current when the power supply voltage is changed. FIG. 10 is an explanatory diagram of the relationship between field weakening current and motor rotation speed using the power supply voltage disclosed in Patent Document 1 as a parameter.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram of an electric power steering apparatus 10 according to an embodiment of the present invention.

  An electric power steering device 10 mounted on a vehicle (not shown) is configured to give a torque (auxiliary torque) for assisting a steering torque given by a driver to a steering shaft 14 connected to a steering handle 12. Is done.

  An upper end of the steering shaft 14 is connected to the steering handle 12, and a pinion 16 is attached to the lower end. A rack shaft 20 provided with a rack 18 that meshes with the pinion 16 is disposed. A rack and pinion mechanism 22 is formed by the pinion 16 and the rack 18. Tie rods 24 are provided at both ends of the rack shaft 20, and front wheels (steered wheels) 26 are attached to the outer ends of the tie rods 24.

  A motor (brushless motor) 30 is provided for the steering shaft 14 via a power transmission mechanism 28 that is a speed reduction mechanism. The motor 30 outputs a rotational force for assisting the steering torque. This rotational force is increased as the auxiliary torque via the power transmission mechanism 28 and is given to the steering shaft 14.

  A steering torque sensor 32 is also provided on the steering shaft 14. The steering torque sensor 32 detects the magnitude and direction of the steering torque applied to the steering shaft 14 when the steering torque generated by the driver operating the steering handle 12 is applied to the steering shaft 14, and the detected steering torque is detected. The steering torque Tq, which is an electrical signal corresponding to the magnitude of the torque, is output. The steering torque sensor 32 is configured using, for example, a torsion bar.

  The steering shaft 14 further includes a steering angle sensor 34 that detects a steering angle by the rotation of the steering shaft 14, that is, a steering angle including a steering direction, and outputs a steering angle θs that is an electrical signal corresponding to the detected steering angle. Is provided.

  A vehicle equipped with the electric power steering device 10 is provided with a vehicle speed sensor 36 that detects and outputs a vehicle speed Vs that is an electric signal corresponding to the traveling speed of the vehicle.

  Furthermore, the electric power steering device 10 includes a motor drive control device 42 including a control device 40. The above-described steering torque sensor 32, rudder angle sensor 34, vehicle speed sensor 36, motor 30, and rotation angle sensor 38 to be described later are electrically connected to a motor drive control device 42 including the control device 40.

  FIG. 2 is a configuration diagram of a motor control system 50 including a motor drive control device 42 including a control device (motor control device) 40 that controls the drive of the motor 30 of the electric power steering device 10 shown in FIG.

  The control device 40 is an ECU (Electronic Control Unit), and the ECU includes a CPU, a ROM, a RAM, a microcomputer having an input / output interface such as an A / D converter and a D / A converter, a timer, and the like. The CPU of the microcomputer operates as various functional units (various functional means) by executing programs stored in the ROM based on various inputs.

  The motor 30 is driven and controlled by the motor drive control device 42 by vector control based on the dq-axis current component.

  The motor 30 detects a rotation angle of the rotor of the motor 30, and detects and outputs a rotor rotation angle, which is an electric signal, that is, a state quantity related to the rotation angle of the magnetic pole of the rotor from a predetermined reference rotation position. The rotation angle sensor 38 is provided.

  An RD (resolver / digital) converter 46 in the control device 40 outputs the rotor rotation angle θm of the motor 30 and the rotation speed of the motor 30 from the output of the rotation angle sensor 38 (also referred to as motor rotation speed, motor rotation speed, or rotation speed). Nm is output as a digital signal.

  The motor drive control device 42 has a steering torque Tq from the steering torque sensor 32, a steering angle θs from the steering angle sensor 34, a vehicle speed Vs from the vehicle speed sensor 36, and a motor rotation angle (from the RD converter 46). The motor current Im {U, V, W, three-phase phase current (U-phase current) Iu, phase current (V-phase current) Iv, phase current (W Phase current) Iw} is output to the motor 30.

  In this case, the electric power steering device 10 converts the electric power supplied from the battery 60 based on the PWM signals of the U, V, and W phases from the PWM conversion unit 52 constituting the control device 40 into, for example, an FET full bridge configuration. By driving the motor 30 by performing power conversion (direct current → three-phase alternating current conversion) by the inverter 54, and performing vector control by energizing each winding of the motor 30 with sine wave phase currents Iu, Iv, Iw, Generate auxiliary torque. As described above, the auxiliary torque of the motor 30 assists the driver's operation of the steering handle 12.

  Of the three phase currents Iu, Iv, Iw that constitute the motor current Im (Iu, Iv, Iw) that actually flows through the motor 30, the magnitude of the phase current Iu and the phase current Iu and the direction of flow are respectively measured by the motor current sensor 56. The detected U-phase current Iu and V-phase current Iv are output as electrical signals and fed back to the dq converter 58. The remaining phase current Iw is calculated as Iw = − (Iu + Iv) by the calculation unit 59 and is fed back to the dq conversion unit 58.

  The dq converter 58 converts the phase currents Iu, Iv, and Iw into digital signals, and then performs dq conversion.

  The dq coordinate in the vector control is, for example, in the motor 30 having a two-pole rotor, the magnetic flux direction of the field pole by the permanent magnet is defined as the d axis (field axis), and the direction orthogonal to the d axis is the q axis (torque axis). ), Which rotates in synchronization with the rotor of the motor 30.

  The control device 40 gives a current phase with reference to the q axis, and as a current command for an AC signal supplied from the inverter 54 to each phase of the motor 30, the d axis current id and q axis that are DC signals are used. A current iq is applied.

  The control device 40 controls the motor 30 according to the command torque Tqcom by vector control described in a two-phase rotating magnetic field coordinate system (dq coordinate system). That is, the steering torque Tq applied to the steering handle 12 is detected by the steering torque sensor 32, and the motor 30 is vector-controlled so that the assist torque according to the detected steering torque Tq is obtained, thereby assisting manual steering. .

  Basically, the basic operations of the control device 40 and the motor drive control device 42 that are configured and operate as described above will be described below in relation to the electric power steering device 10 while explaining more detailed configurations.

  First, in the command torque calculation unit 67, the control device 40 detects the steering torque Tq output by the steering torque sensor 32 and the steering angular velocity dθs / dt calculated from the steering angle θs detected and output by the steering angle sensor 34. The command torque Tqcom is obtained based on the vehicle speed Vs detected by the vehicle speed sensor 36 and output. From the command torque Tqcom, the target current It of the motor current Im is set in the target current setting unit 68 and output to the q-axis target current setting unit 70.

  The q-axis target current setting unit 70 sets a q-axis current command value iqcom that is a torque current command value based on the target current It. On the other hand, the d-axis target current setting unit 72 sets the d-axis current command value idcom, which is a field weakening current command value, to a reference value (here, 0 value).

  On the other hand, the three-phase currents Iu, Iv, Iw of the motor 30 detected by the motor current sensor 56 are converted into d-axis current and q-axis current by the dq converter 58 based on the rotor rotation angle θm, and the d-axis actual current value idr and q-axis actual current value iqr are obtained.

  The subtracting unit 84 calculates a deviation Δiq between the q-axis current command value iqcom and the fed back q-axis actual current value iqr.

  The adder 86 uses the d-axis current Id * (<0) in which the maximum value of the d-axis current Id (<0) is limited by the field weakening current limiter 62 with respect to the d-axis current command value idcom (= 0). Is added to calculate the d-axis current target value idt (<0).

  The subtraction unit 88 calculates a deviation Δid between the d-axis current target value idt and the fed back d-axis actual current value idr.

  The PI calculation units 80 and 82 execute a P (Proportional) control process and an I (Integral) control process on the d-axis current deviation Δid and the q-axis current deviation Δiq, and the d-axis current deviation Δid and q A d-axis command voltage Vdcom and a q-axis command voltage Vqcom that attempt to bring the shaft current deviation Δiq close to 0 are calculated and output to the dq inverse conversion unit 90.

  The dq inverse transformation unit 90 performs dq inverse transformation on the d-axis command voltage Vdcom and the q-axis command voltage Vqcom on the dq coordinate by using the rotor angle θm, and the Uq on the three-phase AC coordinate that is the stationary coordinate. The phase AC command voltage Vu, the V phase AC command voltage Vv, and the W phase AC command voltage Vw are converted.

  The PWM converter 52 converts each command voltage Vu, Vv, Vw to a switching command (that is, a pulse width modulation signal) composed of each pulse for driving each switching element of the inverter 54 to be turned on / off by pulse width modulation (PWM). And convert. Note that the duty of each pulse is stored in the PWM converter 52 in advance.

  The inverter 54 is driven by each pulse width modulation signal, and the corresponding phase currents Iu, Iv, Iw are supplied to the respective windings of the stator of the motor 30, so that a rotating magnetic field is generated and the rotor (rotor) of the motor 30 is generated. ) Rotates.

  A d-axis current Id (negative value) that is a field weakening current set by the d-axis current setting unit 61 is generated as shown in the functional block diagram of FIG. 3 basically includes a d-axis current setting unit 61 and a field weakening current limiting unit (an upper limit value setting unit for field weakening current) 62. ) A d-axis current setting / limiting unit 63 that determines Id * is shown.

  As shown in FIG. 3, the d-axis current setting unit 61 includes a q-axis command voltage corresponding processing unit 112 to which a q-axis command voltage Vqcom that is an output of the PI calculation unit 82 is input, and a q-axis from the dq conversion unit 58. A q-axis actual current corresponding processing unit 114 to which an actual current iqr (= Iq) is input; a motor rotation speed corresponding processing unit 116 to which the motor rotation speed Nm of the motor 30 that is an output of the RD converter 46 is input; , And a synergistic product calculation unit 118.

  The q-axis command voltage correspondence processing unit 112 stores the q-axis command voltage correspondence map (characteristic) 124 shown in FIG. 4, and the q-axis actual current correspondence processing unit 114 stores the q-axis actual current correspondence map (characteristic) shown in FIG. ) 122, and the motor rotation speed correspondence processing unit 116 stores a motor rotation speed correspondence map (characteristic) 126 shown in FIG.

  The q-axis command voltage correspondence processing unit 112 obtains an output C1 that is a correction current element (d-axis current element) by searching the q-axis command voltage correspondence map 124 using the q-axis command voltage Vqcom as an address. In the q-axis command voltage correspondence map 124, in a region where the q-axis command voltage Vqcom is small, that is, a region where the q-axis current deviation Δiq is small, the output C1 is set to 0, and a region where the q-axis command voltage Vqcom is large, that is, the q-axis In the region where the current deviation Δiq is large, the output C1 is set to a substantially constant value.

  With this process, the d-axis current Id, which is a field weakening current, flows only in a region where the q-axis command voltage Vqcom is large, that is, a region where the q-axis current deviation Δiq is large, and the field of the motor 30 is reduced. The motor rotation speed Nm increases. As a result, when the steering handle 12 is operated slowly and small during traveling, the field weakening current is prevented from flowing and the power consumption of the motor 30 is suppressed.

  The q-axis actual current correspondence processing unit 114 obtains an output C2 that is a correction current element (d-axis current element) by searching the q-axis actual current correspondence map 122 using the q-axis actual current value iqr as an address. In the q-axis actual current correspondence map 122, the output C2 is set to a substantially constant value in the region where the q-axis actual current value iqr is small, and the output C2 is set to 0 in the region where the q-axis actual current value iqr is large. By this processing, only in the region where the q-axis actual current value iqr is small, the d-axis correction current idc that is a field weakening current flows, the field of the motor 30 decreases, and the motor rotation speed Nm of the motor 30 increases. As a result, a phenomenon in which the operation of the steering handle 12 suddenly becomes heavy when the motor rotation speed Nm is high and the steering operation is to be performed earlier in a state where the voltage of the inverter 54 has been saturated is prevented.

  The motor rotation speed correspondence processing unit 116 obtains an output C3 which is a correction current element (d-axis current element) by searching the motor rotation speed correspondence map 126 using the motor rotation speed Nm as an address. In the motor rotational speed correspondence map 126, the output C3 is set to 0 in a region where the motor rotational speed (motor rotational speed) Nm is small, and the output C3 is set to a constant value in a region where the motor rotational speed Nm is large. With this process, when the steering handle 12 is operated slowly, it is possible to prevent the d-axis current Id, which is a field weakening current, from flowing through the motor 30 and to prevent wasteful current consumption, that is, wasteful heat generation. it can.

  The output C1 of the q-axis command voltage correspondence processing unit 112, the output C2 of the q-axis actual current correspondence processing unit 114, and the output C3 of the motor rotation speed correspondence processing unit 116 are multiplied by a synergistic product calculation unit 118, and this synergistic product C1 A d-axis current (also referred to as a d-axis reference current) Id proportional to × C2 × C3 is calculated. Thereby, each element (q-axis command voltage corresponding processing unit 112, q-axis actual current corresponding processing unit 114, and motor rotation speed corresponding processing unit 116) that performs d-axis current correction operates independently, and q-axis command voltage When Vqcom is large, when the q-axis actual current value iqr is small, and when the motor rotation speed Nm is small, the d-axis current Id flows and field weakening control is performed.

  Next, the configuration and operation of the field weakening current limiting unit 62 relating to the main part of the present invention will be described. The field weakening current limiting unit 62 sets the limit range of the d-axis current Id that is the field weakening current, in other words, the upper limit value of the use region of the d-axis current Id that is the field weakening current.

If the d-axis current Id (absolute value) input to the field weakening current limiting unit 62 is smaller than the upper limit value Idlim (absolute value) of the use region (meaning that the absolute value is small), it remains as it is. When the d-axis current Id * (Id * = Id) is output and the d-axis current Id (absolute value thereof) is larger than the upper limit value Idlim (absolute value) of the use range (meaning that the absolute value is large) Is output as a d-axis current Id * limited to the upper limit value Idlim (Id * = Idlim). That is, the field weakening current limiting unit 62 operates as a so-called limiter (limiter) for the d-axis current Id for executing the following programs (a) and (b).
IF | Id | <| Idlim | THEN Id * ← Id (a)
IF | Id | ≧ | Idlim | THEN Id * ← Idlim (b)

  In the field weakening current limiting unit 62, the provisional maximum field weakening current setting value Idmax is set from the provisional maximum field weakening current setting unit 104. The provisional maximum field weakening current set value Idmax is set in advance in consideration of the viewpoint of demagnetization of the rotor magnet. The absolute value of the upper limit value Idlim of the use area of the d-axis current Id can be a value equal to or smaller than the absolute value of the provisional maximum field weakening current setting value Idmax (| Idlim | ≦ | Idmax |).

  The field weakening current limiter 62 also includes a predetermined maximum phase current limit value that regulates the maximum current flowing from the phase current limiter 102 to the windings of the motor 30 and the switching elements and wiring patterns constituting the inverter 54. Iumax is set. The maximum phase current limit value Iumax depends on the motor temperature Ta detected by the temperature sensor 106 of the motor 30 in consideration of the fact that the winding resistance of the motor 30 increases with the motor temperature Ta and the heat loss increases. It is stored in the memory as a map or characteristic in which values are set.

  FIG. 7 shows the d-axis current limit value when the maximum phase current limit value Iumax is set to Iumax = 85 [Arms] and the temporary maximum field weakening current set value Idmax is set to Idmax = −100 [A]. A use region 130 (a hatched region) after restriction of the d-axis current Id of the comparative example, which is partitioned by a (d-axis current limit value line) 133, is shown. The vertical axis represents the q-axis current Iq as the torque current, and the horizontal axis represents the d-axis current Id as the field weakening current.

The relationship of the following equation (1) is present between the motor phase current Iu [Arms], the d-axis current Id [A] that is the field weakening current, and the q-axis current Iq [A] that is the torque current. is there.
Iu = √ (Iq ² + Id ² ) / √3 (1)

  Therefore, in FIG. 7, the maximum value (maximum q-axis current value) Iqmax of the q-axis current Iq is limited to Iqmax = √3 × Iumax = √3 × 85 = 147 [A]. The maximum value of the d-axis current Id is set to the provisional maximum field weakening current setting value Idmax = −100 [A].

  The use region 130 after the limitation of the d-axis current Id is a d-axis current limit value line 133 based on the arc portion 133 shown by a solid line in FIG. 7 constituting the current vector limit circle 132 and the provisional maximum field weakening current set value Idmax. The hatched area is defined (defined) by. In this way, as shown in FIG. 7, the upper limit value Idlim of the use region of the d-axis current Id is defined by the d-axis current limit value line 133 in accordance with the q-axis current Iq that is the torque current. As described above, since the d-axis current command value idcom is set to idcom = 0 [A], the d-axis current target value idt is set to idt = idcom + Id * = Id *, and the adding unit 86 in the control device 40. Note that (see FIG. 2).

  In the current vector limiting circle 132, the “current vector” is a vector starting from the origin in FIG. 7 and ending on the circumference of the current vector limiting circle 132, and the current vector is the q-axis current Iq. Component vector (current vector) and a component vector (current vector) of the d-axis current Id.

  Incidentally, in the electric power steering apparatus 10, as shown in FIG. 1, the motor 30 and the steering handle 12 are connected via a power transmission mechanism 28.

  In this case, since the rotational speed of the steering handle 12 is steered by the driver, the rotational speed is regulated within a range that can be steered by a person. Therefore, the rotational speed of the motor 30 is also regulated by the low rotational speed, and is generally used at Nm = 3000 [rpm] or less. As a result of theoretical analysis focusing on this fact, when the motor rotation speed Nm of the motor 30 is regulated to be low as in the electric power steering apparatus 10, the current vector usage area (hatching area) in FIG. In 130, it has been found that there is a region in which only the heat generation increases without increasing the d-axis current Id, which is a field weakening current, without contributing to the increase in the rotational speed (= rotational speed) Nm.

  The method of calculating the region where only the heat generation increases without increasing the d-axis current Id, which is the field weakening current, does not contribute to the increase in the motor rotation speed Nm will be described in detail later. , The maximum phase current limit value Iumax is set to Iumax = 85 [Arms], and the temporary maximum field weakening current set value Idmax is set to Idmax = −100 [A], as in FIG. In FIG. 8A and FIG. 8B according to the embodiment when set to, a region 135 where only heat generation increases is indicated by a region 135 with dots.

  As shown in FIG. 8A and FIG. 8B showing a usage example thereof, the field weakening current limiting unit 62 basically calculates the motor rotation speed Nm and the q-axis current Iq (q-axis actual current iqr) that is a torque current. As an argument (address), the upper limit value Idlim of the d-axis current Id, which is a field weakening current, is limited to the range of the use area 134 after the restriction indicated by the hatched area in FIGS. 8A and 8B.

  As shown in FIG. 8B, when the q-axis current Iq is Iq = Iq ′, the current vector k after limitation of the d-axis current Id is expressed by a vector obtained by subtracting the limit value current vector j from the current vector i before limitation. be able to.

  Here, in FIG. 8A and FIG. 8B, how to calculate the region 135 in which the increase in the d-axis current Id, which is the field weakening current, does not contribute to the increase in the motor rotation speed Nm but only the heat generation increases. A numerical example will be described.

  First, Pn: number of pole pairs (known), Φa: electromotive voltage constant (known), Vd: d-axis voltage, Vq: q-axis voltage, Id: d-axis current, Iq: q-axis current, R: resistance (known), Ld: d-axis inductance (known), Lq: q-axis inductance (known), Vi: line voltage (= power supply voltage Vb / √2) (measured value / calculated value), ωe: electrical angular velocity of rotor (measured value / (Calculated value), p: differential operator, Tm: motor torque, Tf: friction torque (known), Iu: phase current (measured value).

The current-torque characteristic is obtained by equation (2).
Tm = Pn {Φa × Iq + (Ld−Lq) Id × Iq} −Tf
≈Pn (Φa × Iq) −Tf (2)

  However, Ld≈Lq: In this embodiment, since the motor 30 is a non-salient pole machine of a brushless motor, the difference between the d-axis inductance Ld and the q-axis inductance Lq is zero.

The phase current is as follows when the above equation (1) is reprinted.
Iu = √ (Iq ² + Id ² ) / √3 (1)

Usually, the dq axis voltage equation expressed in matrix is obtained by the following equations (3) and (4).
Vd = (Ra + pLd) × Id + (− ωeLq) × Iq + 0 (3)
Vq = ωeLd × Id + (Ra + pLq) × Iq + ωeΦa (4)

The relationship between the line voltage Vi, the q-axis voltage Vq, and the d-axis voltage Vd is given by equation (5).
Vi = √ (Vd ² + Vq ² ) (5)

  Here, in order to calculate the steady state motor output characteristics (in order to obtain a steady solution), the term including the differential operator p in the equations (3) and (4) is regarded as a minute amount and is set to a zero value.

Then, by squaring both sides of the above formula (5) and substituting the above formulas (3) and (4), the following formula (6) is obtained.
Vi ² = Vd ² + Vq ²
= (Ra × Id−ωeLq × Iq) ²
+ (Ra × Iq + ωeLd × Id + ωeΦa) ² (6)

Here, the electric angular velocity ωe [rad / s] in which the right side of the equation (6) (Ra × Id−ωeLq × Iq) ² + (Ra × Iq + ωeLd × Id + ωeΦa) ² minus the left side Vi ² is set as 0. Solving the quadratic equation (a · ωe ² + 2b · ωe + c = 0) with respect to the electrical angular velocity ωe [rad / s], which is the variable, ωe = {− b ± √ (b ² −ac)} / Therefore, the following equation (7) is obtained.
ωe = [− Ra × Iq (−Lq × Id + Ld × Id + Φa) ± √ [{Ra × Iq (−Lq × Id + Ld × Id + Φa)} ² − {(Ld × Id + Φa) ² + Lq ² × Iq ² } {Ra ² × (Id ² + Iq ² ) −Vi ² }]] / {(Ld × Id + Φa) ² + Lq ² × Iq ² }
... (7)

Since the relationship between the motor rotational speed Nm [r / s] and the electrical angular velocity ωe [rad / s] can be converted by the equation (8), if the equation is substituted into the equation (7), the motor rotational speed Nm and the d axis The relationship between the current Id and the q-axis current Iq can be obtained.
Nm = (ωe / 2π) / Pn (8)

In the above equation (7), for example, in order to change the motor rotation speed Nm with the same torque, the q-axis current value Iq that is a torque current is constant Iq = 81 [A], and the d-axis current that is a field weakening current. When Id is changed from 0, as shown in FIG. 9, until the d-axis current Id reaches Id = Idm = −84 [A], the motor rotation speed Nm increases according to the increase in the absolute value of the d-axis current Id. Although the effect of field weakening control is increased, the motor rotation speed Nm decreases even if the absolute value of the d-axis current Id is increased further, while the heat loss Ploss [W] becomes Ploss = Since it is calculated by Ra × Iu ² [W], it can be seen that only the heat loss increases. The motor rotation speed Nm when the d-axis current Id is Id = Idm = −84 [A] is referred to as the maximum rotation speed Nmmax. The d-axis current Idm is referred to as an execution maximum d-axis current value.

  Here, by changing the q-axis current value Iq and solving the above equation (7), the q-axis current limit value (q-axis current limit value line) 133R shown in FIG. 10 can be calculated.

  In the case of the example in FIG. 9, by using the d-axis current value Iq from Id = 0 to Idm = 0 to −84 [A], the motor rotation speed Nm can be handled up to Nm = Nmmax = 2800 [rpm]. When the motor rotational speed Nm = 2500 [rpm] is used, the d-axis current value Id may be limited to about Id = −50 [A].

[Example 1]
A first embodiment of the field weakening current limiting unit 62 will be described with reference to FIG.

  FIG. 11 shows an example in which, when the motor rotation speed Nm is Nm = 3000 [rpm] or less, the current vector before the limit is the current vector A (torque current = q-axis current Iq = 75 [A], When field weakening current = d-axis current Id = −100 [A], motor phase current Iu = 72 [Arms]), the field weakening current limiting unit 62 causes the current vector B (torque current = q (Axis current Iq = 75 [A], field weakening current = d-axis current Id = −75 [A], motor phase current Iu = 61 [Arms]).

  Since the q-axis current Iq of the torque current axis is maintained at Iq = 75 [A] even before and after the limitation, the assist torque by the motor 30 is kept constant. Further, in this case where the motor rotation speed Nm is defined as Nm = 3000 [rpm] or less, the motor rotation is performed even if the d-axis current Id, which is a field weakening current, is limited to Id = −75 [A]. The number Nm is held before and after the limit (that is, approximately the same rotation speed).

Therefore, in the example of FIG. 11, the phase current Iu serving as a heat source is set to 72 [Arms] (72 = √ (100 ² ) while maintaining the torque of the motor 30 (proportional to the q-axis current Iq) and the motor rotation speed Nm. +75 ² ) / √3) to 61 [Arms] (61 = √ (75 ² +75 ² ) / √3). Since the heat generation amount is proportional to the square of the current, the reduction rate of the heat generation amount is (61/72) ² = 0.72, and the effect of field weakening, that is, the increase amount of the motor rotation speed Nm is substantially the same. It can also be seen that a heat reduction effect of about 28 [%] is obtained.

[Example 2]
A second embodiment of the field weakening current limiting unit 62 will be described with reference to FIGS. 12A and 12B.

  FIG. 12A is a diagram showing a use region in which the temporary maximum field weakening current Idmax in FIG. 8A is changed from Idmax = −100 [A] to Idmax = −108 [A], and FIG. It is a figure which shows the use area | region when the motor temperature Ta detected by the sensor 106 rises.

  In the electric power steering, it is possible to suppress heat generation more effectively by combining with the current vector limit circle. For example, at a normal temperature, the current vector limit circle is set to the current vector limit circle 132 with the maximum phase current limit value Iumax = 85 [Arms] as shown in FIG. If necessary, as shown in FIG. 12B, the current vector limit circle 132B having the maximum phase current limit value Iumax = 75 [Arms] is switched.

  Thereby, the temperature reduction effect which will be described later can be effectively obtained according to the size of the current vector limit circle. In the electric power steering, the maximum value of the phase current may be limited by the temperature of the ECU in addition to the motor temperature, which is effective in that case.

[Specific Example of Example 2]
FIG. 13A shows a specific example in which the limit value is set according to the size of the current limit vector circle with respect to the operation example of the field weakening current limiter 62 of the second embodiment described with reference to FIGS. 12A and 12B. Shown in FIG. 13B.

FIG. 13A shows the case where the current vector limit circle 132 has the maximum phase current limit value Iumax = 85 [Arms] (reproduced in FIG. 12A), and the motor rotation speed Nm is restricted to Nm = 3000 [rpm] or less. As an example, the current vector before the limit is the current vector A (torque current Iq = 100 [A], d-axis current (field weakening current) Id = −108 [A], and motor phase current Iu = 85. [Arms]) by the field weakening current limiting unit 62, the current vector B (torque current Iq = 100 [A], d-axis current (field weakening current) Id = −70 [A], Phase current Iu = 70 [Arms]), and the reduction rate of the calorific value is (70/85) ² = 0.68, and the heat generation reduction effect of about 32 [%] is obtained.

On the other hand, FIG. 13B shows the case where the current vector limit circle 132B has the maximum phase current limit value Iumax = 75 [Arms] (reproduced in FIG. 12B), and the current vector C (Iq = 100 [A ], Id = −82 [A], Iu = 75 [Arms]), the current vector D (Iq = 100 [A], Id = −70 [A]) in FIG. , Iu = 70 [Arms]), and the reduction rate of the calorific value is (70/75) ² = 0.87, and an exothermic reduction effect of about 13 [%] is obtained. In this way, changing the current limit setting according to the size of the current limit vector circle may limit the maximum value of the phase current in the electric power steering depending on the temperature of the ECU. Effective in cases.

[Example 3]
By combining the voltage sensor 64 that detects the battery voltage Vb of the battery 60 that is the power supply voltage of the motor 30 and the field weakening current limiting unit 62, more effective heat generation suppression can be achieved. For example, when the battery voltage Vb rises to Vb = 13 [V] compared to the case where the battery voltage Vb is Vb = 12 [V], the motor 30 is driven by the d-axis current Id that is a smaller field weakening current. Can be driven. That is, the d-axis current Id, which is a field weakening current, can be limited to a smaller value. As a result, heat generation can be more effectively suppressed. This is more effective in electric power steering in which the battery voltage Vb, which is the power supply voltage supplied to the motor 30 depending on the usage status of the on-vehicle electrical components, fluctuates in the range of about 12 to 16 [V]. It is. A setting example of the limit value according to the battery voltage Vb will be described with reference to FIGS. 14A and 14B.

  When the battery voltage Vb increases, as shown in FIG. 16, the motor rotation speed Nm increases with respect to the same d-axis current value Id.

  Therefore, in the third embodiment, when the power supply voltage shown in FIG. 14B is Vb = 13 [V], the field weakening is smaller than when the power supply voltage Vb shown in FIG. 14A is Vb = 12 [V]. The current limiting unit 62 can limit the usage area from the usage area 134 to the usage area 134C.

[Specific Example of Example 3]
A specific example of the third embodiment in which the limit value is set according to the battery voltage Vb is shown in FIGS. 15A and 15B.

FIG. 15A shows a case where the battery voltage Vb is Vb = 12 [V]. As an example, the current vector A (Iq = 115 [A], Id = −80 [A], motor phase current Iu = 81 [Arms]), the field weakening current limiting unit 62 limits the current vector B (Iq = 115 [A], Id = −60 [A], Iu = 75 [Arms]) in FIG. The reduction rate of the heat generation amount is (75/81) ² = 0.86, and the heat generation reduction effect of about 14 [%] is obtained.

On the other hand, FIG. 15B shows a case where the battery voltage Vb increases to Vb = 13 [V], and the current vector C (Iq = 115 [A], Id = −80 [A], From the motor phase current Iu = 81 [Arms]), the field weakening current limiting unit 62 causes the current vector D (Iq = 115 [A], Id = −45 [A], Iu = 71 [Arms]) in FIG. ), And the reduction rate of the calorific value is (71/81) ² = 0.77, and a heat reduction effect of about 23 [%] is obtained.

  As described above, changing the current limit setting according to the battery voltage Vb, which is the power supply voltage of the motor 30, and the motor temperature Ta is that the battery voltage Vb is 12 [V] to 16 [V] depending on the usage status of the on-vehicle electrical components. It is effective in the electric power steering apparatus 10 that varies to the extent.

[Summary of Embodiment]
According to the above-described embodiment, the electric power steering device 10 that drives and controls the steering assist motor 30 in accordance with the steering input by the driver's operation of the steering handle 12, the following technical features [1] -It has [5].

  [1] A steering torque sensor 32 as a steering input detection unit that detects the magnitude of the steering input, and a q-axis current that is a torque current of the motor 30 based on a steering torque Tq that is an output signal of the steering torque sensor 32 Based on the q-axis target current setting unit 70 as a torque current setting unit for setting the command value iqcom, the q-axis current command value iqcom set by the q-axis target current setting unit 70, and the motor rotation speed Nm of the motor 30. A d-axis current setting unit 61 for setting a d-axis current Id, which is a field weakening current for weakening the field of the motor 30, and a q-axis current command value iqcom set by the q-axis target current setting unit 70, A motor drive control device 42 serving as a motor drive control unit that drives and controls the motor 30 based on the d-axis current Id set by the d-axis current setting unit 61; And a field weakening current limiting unit (d-axis current limiting unit) 62 that sets the d-axis current Id * below the limit value. The field weakening current limiting unit 62 is a q-axis that is a torque current of the motor 30. The limit value of the d-axis current (field weakening current) Id is set according to the actual current iqr.

  According to the electric power steering apparatus 10 having the above technical feature [1], according to the q-axis current command value iqcom set by the q-axis target current setting unit 70, in other words, according to the driving state of the motor 30. Since the limit value of the d-axis current (field weakening current) Id is set, the setting of the limit value is easy, and the event that the field weakening control becomes ineffective and wasteful heat generation occurs. It is possible to avoid effectively with a simple configuration according to the driving situation.

  As a result, it is possible to avoid performing unnecessary (invalid, unnecessary) field-weakening control when the q-axis current command value iqcom is changed. That is, it is possible to avoid a reduction in the motor rotation speed Nm of the motor 30 due to an increase in useless (invalid and unnecessary) field weakening current and useless heat generation.

  [2] When the field weakening current limiting unit 62 sets the limit value of the d-axis current Id that is the field weakening current according to the q-axis current command value iqcom that is the torque current of the motor 30, For each q-axis actual current value iqr corresponding to the shaft current command value iqcom, the value of the q-axis actual current value iqr is held and the absolute value of the d-axis current Id that is the field weakening current is increased. As shown in FIG. 9, the motor rotational speed Nm is set to the d-axis current value Idb or Ida, which is a field weakening current value when the motor rotational speed Nm is reduced by a predetermined rotational speed ΔNm from the maximum rotational speed Nmmax.

  According to the electric power steering apparatus 10 having the technical feature [2] described above, the field weakening current value at the maximum rotational speed Nmmax, which is the peak value at which the motor speed decreases when the field weakening is further increased. The weakest field current when the effective maximum d-axis current value Idm is a reference value of the limit value (reference value = Idm in FIG. 9) and the predetermined rotational speed ΔNm is reduced from the maximum rotational speed Nmax in consideration of errors and the like. Since the d-axis current values Ida and Idb, which are values, are used as the limit values, the limit values can be easily set when there is an error or variation in each function unit such as the steering torque sensor 32 as the steering input detection unit. . In other words, the degree of freedom in design when selecting components, sensors, and the like constituting the electric power steering apparatus 10 is large, and the cost can be reduced.

  [3] In the electric power steering apparatus 10 having the technical feature [2] described above, the field weakening current limiting unit 62 uses the field weakening current according to the q-axis current command value iqcom that is the torque current of the motor 30. When setting the limit value of a certain d-axis current Id, the value of the q-axis actual current value iqr is held for each q-axis actual current value iqr corresponding to the q-axis current command value iqcom. As shown in FIG. 9, when the value of the d-axis current Id, which is a magnetic current, is increased, the value of the d-axis current Id, which is a field weakening current at which the motor rotation speed Nm becomes the maximum rotation speed Nmmax (execution) The maximum d-axis current value Idm) is set.

  According to the electric power steering apparatus 10 having the technical feature [3] described above, when the field weakening is further increased, the motor rotational speed Nm is decreased. At the maximum rotational speed Nmmax that is the peak value of the motor rotational speed Nm. Since the effective maximum d-axis current value Idm, which is the field weakening current value, is set as the limit value, the motor rotation speed is increased according to the increase in the value of the d-axis current Id, which is the field weakening current, up to the limit value. Nm increases, and the amount of heat loss can be suppressed while maintaining a light steering feeling. That is, unnecessary heat generation accompanying an increase in unnecessary field weakening current can be avoided.

  [4] Furthermore, when the upper limit value Iumax of the phase current Iu of the motor 30 is changed by the phase current limiter 102 that sets the upper limit value Iumax of the phase current Iu of the motor 30 and the phase current limiter 102, FIG. As described with reference to FIG. 13B, the vector determined by the value of the q-axis current Iq that is the torque current and the value of the d-axis current Id that is the field weakening current according to the change of the upper limit value Iumax. The size of the current limiting circle representing the size is changed, and the use range after the limitation limited by the limit value of the d-axis current Id that is the field weakening current is set in the current limiting circle after the change. And a field weakening current limiting unit 62 as a use region setting unit after the field current limiting.

  According to the invention having the technical feature [4] described above, the field weakening current limiting unit 62 can be simplified in response to the case where the phase current Iu needs to be limited due to the heat generation state of the electric power steering device 10. Can be built.

  [5] Furthermore, the field weakening current limiting unit 62 is based on the battery voltage Vb that is the power supply voltage value of the electric power steering device 10 as described with reference to FIGS. The limit value of the d-axis current Id, which is a current, is changed. Since the limit value is further changed based on the battery voltage Vb, more effective heat generation suppression is possible.

  Therefore, the event that the field weakening control becomes ineffective and the useless heat generation occurs as described above in the driving state of the motor 30 while maintaining the light steering feeling related to the operation of the steering handle 12 by the field weakening control. Accordingly, a simple configuration can be effectively avoided.

  As described above, in this embodiment, a region in which only the heat generation increases without increasing the d-axis current Id that is a field weakening current (increasing the absolute value) does not contribute to the increase in the motor rotation speed Nm. The current use area is limited so as not to cause a problem. Thereby, in the motor 30 of the electric power steering apparatus 10 in which the steering speed is specified to be low, an effect of suppressing heat generation due to the motor drive current can be obtained while maintaining the torque and the rotational speed output from the motor 30. With this effect, it is possible to suppress heat generation due to the motor current while maintaining the light steering feeling of the electric power steering device 10 and to protect the electric power steering device 10 from heat generation.

  Actually, it is assumed that the electric power steering device 10 generates severe heat, for example, a situation in which the vehicle is placed in a garage in a parking lot immediately after traveling on a highway in midsummer for several minutes. In the test, the maximum temperature of the components constituting the motor 30 of the electric power steering apparatus 10 could be reduced from about 145 [° C.] to about 115 [° C.].

  In addition, the present invention is not limited to the above-described embodiment, and various configurations can be adopted based on the contents described in this specification.

DESCRIPTION OF SYMBOLS 10 ... Electric power steering device 12 ... Steering handle 14 ... Steering shaft 16 ... Pinion 18 ... Rack 20 ... Rack shaft 22 ... Rack and pinion mechanism 24 ... Tie rod 26 ... Front wheel 28 ... Power transmission mechanism 30 ... Motor 32 ... Steering torque sensor 34 ... Steering angle sensor 36 ... Vehicle speed sensor 38 ... Rotation angle sensor 40 ... Control device 42 ... Motor drive control device 50 ... Motor control system 56 ... Motor current sensor 58 ... dq conversion unit 60 ... Battery 61 ... d-axis current setting unit 62 ... Field weakening current limiting unit 67 ... Command torque calculating unit 68 ... Target current setting unit 70 ... q-axis target current setting unit 72 ... d-axis target current setting unit 90 ... dq inverse conversion unit 102 ... Phase current limiting unit 104 ... Temporary Maximum field weakening current setting unit 106 ... temperature sensor 112 ... q-axis command voltage handling unit 114 ... q-axis actual current handling process 116: Motor rotation speed correspondence processing unit 118 ... Synergistic product calculation unit 122 ... q-axis actual current correspondence map 124 ... q-axis command voltage correspondence map 126 ... Motor rotation speed correspondence map

Claims (5)

An electric power steering device that drives and controls a steering assist motor according to a driver's steering input,
A steering input detector for detecting the magnitude of the steering input;
A torque current setting unit configured to set a torque current of the motor based on a signal from the steering input detection unit;
A field weakening current setting unit for setting a field weakening current for weakening the field of the motor based on the torque current set by the torque current setting unit and the rotational speed of the motor;
A motor drive control unit that drives and controls the motor based on the torque current set by the torque current setting unit and the field weakening current set by the field weakening current setting unit;
A field weakening current limiting unit for setting the field weakening current below a limit value;
With
The field weakening current limiting unit is
The electric power steering apparatus, wherein the limit value of the field weakening current is set according to the torque current of the motor. The electric power steering apparatus according to claim 1,
The field weakening current limiting unit is
When the limit value of the field weakening current is set according to the torque current of the motor, the value of the field weakening current is increased by holding the value of the torque current for each value of the torque current. The field-weakening current value when the motor rotational speed is reduced by a predetermined rotational speed from the maximum rotational speed is set to the limit value. In the electric power steering apparatus according to claim 2,
The field weakening current limiting unit is
When the limit value of the field weakening current is set according to the torque current of the motor, the value of the field weakening current is increased by holding the value of the torque current for each value of the torque current. The electric power steering apparatus is characterized in that the limit value is set to the value of the field weakening current at which the motor rotation speed becomes the maximum rotation speed. In the electric power steering device according to any one of claims 1 to 3,
further,
A phase current limiter for setting an upper limit value of the phase current of the motor;
When the upper limit value of the phase current of the motor is changed by the phase current limiter, the magnitude of the vector determined by the value of the torque current and the value of the field weakening current according to the change of the upper limit value Change the current limit circle to indicate the current limit circle, and set the limited use area limited by the limit value of the field weakening current in the current limit circle after the change. And
An electric power steering device comprising: In the electric power steering device according to any one of claims 1 to 4,
The field weakening current limiting unit is
The electric power steering apparatus, wherein the limit value of the field weakening current is changed based on a power supply voltage value of the electric power steering apparatus.

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