JP5683417B2 - Electric power steering device - Google Patents

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 the above-mentioned high-torque low-rotation performance and low-torque high-rotation performance, the electric power steering device is equipped with a relatively small and low-cost motor with a high-torque low-rotation type rating. By performing field-weakening control on a mold-rated motor, low torque and high rotation performance is obtained.

  More specifically, according to the current flowing through the motor having a high torque low rotation rating, in other words, depending on the torque, the low torque side reduces the motor field and increases the rotation speed. The torque high rotation performance is ensured, and the high torque low rotation performance is ensured without weakening the motor field on the high torque side, thereby achieving both of the two performances (Patent Document 1).

Japanese Unexamined Patent Publication No. 2007-116849 ([0016], FIG. 14, [0030], [0035], [0043])

  [0030] of Patent Document 1 states that “when the d-axis current command value changes suddenly with such a slight change in the rotational speed, if the current control unit is not sufficiently responsive, torque ripple and vibration are caused by fluctuations in the output torque. In the case of an electric power steering device, there is a method of increasing the responsiveness of current control in order to suppress fluctuations in output torque, but the responsiveness of current control is There is a limit because it can be determined in consideration of the processing capacity and noise resistance of the microcomputer, and fluctuations in the output torque cannot be sufficiently suppressed. "As an example that gives driver discomfort, a patent [0035] of Literature 1 describes that vibrations and abnormal sounds may be transmitted to the steering handle.

  In order to solve these problems, in Patent Document 1, the change rate of the command value of the d-axis current that is the field weakening current is controlled to be equal to or less than the change rate limit value ([0042 of Patent Document 1] ], [0043]).

  However, in the technique according to Patent Document 1, the change rate of the command value of the d-axis current is suppressed to be equal to or less than the change rate limit value, in other words, the change rate of the command value of the d-axis current is set to the change rate upper limit value. Since the following is suppressed, in such a control, depending on the situation, a difference may occur in the rise time until the change rate upper limit value is reached, and the rise time may fluctuate and become unstable. If the rise time fluctuates and becomes unstable, the frequency of the high-frequency component when the field-weakening current increases or decreases changes, and a large impulse fluctuation may occur in the motor torque, and there is room for improvement.

  The present invention has been made in connection with the above-described technique and problem, and is the optimum rate of change of the field weakening current command value in which the generation of abnormal noise and vibration due to a sudden change in the field weakening current command value is within an allowable range. It is an object of the present invention to provide an electric power steering device that can control the time differential value of an optimum field weakening current command value.

  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 driver's steering input, and has the following features [1]-[6].

  [1] A steering input detection unit that detects the magnitude of the steering input, a torque current setting unit that sets a torque current command value of the motor based on a signal from the steering input detection unit, and a field of the motor A field weakening current setting unit for setting a field weakening current command value from a reference value for weakening the magnetism, a torque current command value set by the torque current setting unit, and a setting by the field weakening current setting unit A motor drive control unit that drives and controls the motor based on the field-weakening current command value that has been set, and the field-weakening current setting unit is configured to reach the field-weakening current command value from the reference value. It is characterized in that a time differential value in at least a partial section is constant.

  According to the invention having the feature [1], the rise and fall times can be set so that the generation of abnormal noise and vibration due to a sudden change in the field weakening current command value is within the allowable range, and the optimum rise always matching the conditions. Since the fall time can be taken, the rise time does not become slow or fast depending on the situation as in Patent Document 1. For example, there is no wasteful rise time. Therefore, it is possible to control the rate of change of the optimum field weakening current command value in which the generation of noise and vibration due to a sudden change in the field weakening current command value is within the allowable range, that is, the time differential value of the accurate field weakening current command value. Can control.

  [2] In the invention having the above-mentioned feature [1], the field weakening current setting unit is configured to reduce the field weakening current command value when the absolute value of the field weakening current command value increases or decreases. A difference is provided in the time differential value of.

  Since the difference is provided, for example, the time differential value of the field weakening current can be properly used depending on the type of a vehicle such as a sports car, a passenger car, a commercial vehicle, or a use such as energy saving.

  For example, the weak field current is quickly reduced by increasing the time differential value when the absolute value of the d-axis current command value decreases, which is a situation in which the field weakening control is not required, larger than the time differential value when increasing. Therefore, it is not necessary to pass a field current weakly, which contributes to energy saving.

  [3] In the invention having the above-mentioned feature [2], the field weakening current setting unit may reduce the field weakening current with respect to a time differential value when the absolute value of the field weakening current command value increases. The time differential value when the absolute value of the command value decreases is set to be small.

  Since the rise can be controlled quickly and the target field weakening current is quickly achieved, there is no processing delay. In addition, at the time of the fall when it is not necessary to make the target field weakening current as soon as possible, the control can be performed slowly, and abnormal noise and vibration can be further reduced.

  [4] In the invention having any one of the above-mentioned features [1] to [3], the field weakening current setting unit is configured to cause the entire field to rise from the reference value until reaching the field weakening current command value. The time differential value is set to the first constant value, and the time differential value is the same as the first constant value in the entire fall period from the field weakening current command value to the reference value or The second constant value is used.

  The time differential value can be controlled easily by making it constant throughout the rise and fall intervals, and by controlling the differential value to a different value for each rise and fall interval, noise and vibration due to torque fluctuations can be reduced. It can be suppressed, and a light steering feeling of the electric power steering can be realized.

[5] In the invention having the above feature [1], the field weakening current setting unit may make the time differential value constant in at least a partial section from the reference value to the field weakening current command value. In this case, the time differential value when the absolute value of the field weakening current command value increases from the reference value is gradually increased to the constant time differential value in the partial section.

  Since the change of the time differential value can be smoothed at the start of rising, the amplitude of the impulse-like fluctuation generated in the motor torque can be reduced.

[6] In the invention having the above characteristics [1], wherein the weak field current setting unit, while an increase in the absolute value of the field weakening current command value, to reach the field-weakening current command value The time differential value is made constant at least in a certain section, and then the time differential value is gradually decreased to the field weakening current command value.

  Since the change of the time differential value can be smoothed at the end of the rising, similarly, the amplitude of the impulsive fluctuation generated in the motor torque can be reduced.

  Note that the simultaneous implementation of the above features [5] and [6] is also included in the invention according to this application. Further, the present invention also includes applying the above features [5] and [6] to the falling edge.

  According to the present invention, it is possible to accurately set and control the time differential value of the field weakening current command value in which the generation of abnormal noise or vibration due to a sudden change in the field weakening current command value is within an allowable range.

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 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 a functional block diagram of a time differential value setting part. It is comparison explanatory drawing of the field weakening current waveform of a comparative example and an Example. FIG. 9A is a waveform diagram showing torque fluctuation according to a comparative example. FIG. 9B is a waveform diagram illustrating torque fluctuation according to the embodiment. It is a motor output characteristic figure with which it uses for description of the setting of the time differential value in the rise and fall of a field weakening current command value. FIG. 11A is a waveform diagram showing a field-weakening current command value when the time differential value is constant in the entire rise period, and FIG. 11B is a waveform showing a state in which the time differential value at the start part of the rise is smoothly increased. FIG. 11C is a waveform diagram showing a state in which the time differential value at the end portion of the rising edge is smoothly decreased, and FIG. 11D is a diagram showing a state in which the time differential value is smoothly increased at the start portion of the rising edge and the time at the end portion of the rising edge. It is a wave form diagram which shows the state which decreased the differential value smoothly.

  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, rotation angle sensor 38, and the like 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 Iv 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. Based on the vehicle speed Vs detected and output by the vehicle speed sensor 36, the command torque Tqcom is obtained. 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, and Iw of the motor 30 detected by the 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 the q-axis actual current value iqr.

  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 rises the d-axis current Id (<0) that is set and output by the d-axis current setting unit 61 by the time differential value setting unit 62 described later with respect to the d-axis current command value idcom (= 0). (Or) The d-axis current target value idt (<0) is calculated by adding the d-axis current Id ^* (<0) in which the falling time differential value dId / dt (d / dt is a differential operator) is set. To do. The rise and fall time differential values dId / dt of the d-axis current Id (<0) set and output by the d-axis current setting unit 61 can be very large values. That is, the d-axis current setting unit 61 sets the waveform of the d-axis current Id (<0) in a step function.

  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 rotation angle θm, and on the three-phase AC coordinate that is a stationary coordinate. It converts into the U-phase alternating current command voltage Vu, the V-phase alternating current command voltage Vv, and the W-phase alternating current command voltage Vw.

  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.

  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 value iqr (= Iq) is input; a motor rotation speed corresponding processing unit 116 to which the 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 rotational 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 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 is prevented, for example, when the steering operation is to be performed earlier in a state where the motor rotation speed Nm is high and the voltage saturation of the inverter 54 has been reached.

  The motor rotation speed correspondence processing unit 116 obtains an output C3 that is a correction current element (d-axis current element) by searching the motor rotation speed correspondence map 126 using the motor rotation speed (motor rotation speed) Nm as an address. In the motor rotation speed correspondence map 126, the output C3 is set to 0 when the motor rotation speed Nm is small, and the output C3 is set to a constant value when the motor rotation 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 time differential value setting unit 62 according to the main part of the present invention will be described. In this case, the time differential value setting unit 62 sets the time differential value of the rise and / or fall of the d-axis current Id, which is the output of the d-axis current setting unit 61, and sets the d-axis current Id ^* after setting ^. Is output.

  In the description of the configuration and operation of the time differential value setting unit 62, for convenience of understanding, the increasing direction (the direction in which the negative value increases) of the absolute value of the d-axis current Id is positive (rising), and the d-axis A description will be given assuming that the decreasing direction of the absolute value of the current Id (the direction in which the negative value decreases) is negative (falling).

For convenience of understanding, the d-axis current Id ^* output from the time differential value setting unit 62 is also referred to as a field weakening current command value Id ^* . The reason is that the d-axis current command value idcom set by the d-axis target current setting unit 72 is set to idcom = 0, so that the d-axis current Id ^* output from the time differential value setting unit 62 is substantially equal. This is because the field weakening current command value is set, and the d-axis current target value idt is determined by the adder 86 based on the field weakening current command value Id ^* . In this sense, the time differential value setting unit 62 functions as a field weakening current setting unit that sets a field weakening current command value Id ^* for weakening the field of the motor 30 (time differential value setting unit 62 = weakening). Field current setting part).

FIG. 7 shows a block configuration diagram of an example of the time differential value setting unit 62. As shown in FIG. 7, the time differential value setting unit 62 includes a subtractor 202, a deviation time differential value conversion unit 204, an adder 206, and a delay device (Z ⁻¹ ) 210 with a minute time (clock time) dt. It consists of.

The d-axis current Id (also referred to as field weakening current Id) before setting the time differential value is supplied from the d-axis current setting unit 61 to the subtracted input terminal of the subtractor 202, and the time differential value is supplied to the subtraction input terminal. The weak field current command value Id ^* (referred to as Id ^* (t−1)) of the previous time after setting (before the minute time dt), in other words, one clock before is supplied.

Therefore, the difference shown in the following equation (1) is output as the deviation d (Id) to the output terminal of the subtractor 202 and supplied to the deviation time differential value conversion unit 204.
d (Id) = Id (t) −Id ^* (t−1) (1)

The deviation time derivative conversion unit 204 refers to a characteristic (map) 212 (also referred to as a minute increment provision map or a minute increment provision characteristic) in the deviation time derivative conversion unit 204 in FIG. And the current minute time (clock time) dt is positive {d (Id)> 0}, d (Id) ^* = D1 is added as a minute increment d (Id) ^* When the deviation d (Id) between the minute times dt is negative {d (Id) <0}, the minute increment d (Id) ^{* is set} as d (Id) ^* = −. D2 (actually a slight decrease due to the negative value) is output to one input terminal of the adder 206. When the deviation d (Id) is d (Id) = 0, d (Id) ^* = 0 is output to one input terminal of the adder 206.

To the other input terminal of the adder 206, the delay unit 210 of the delay operator ^{Z -1,} short time (1 clock time) dt is delayed previous weak field current command value ^Id * (t-1) Is supplied to the output terminal of the adder 206, that is, the output terminal of the time differential value setting unit 62, the field weakening current command value Id ^* () after setting the time differential value shown in the following equation (2). t) is output.

Id ^* (t) = Id ^* (t−1) + d (Id) ^* (2)
The time differential value is expressed by the following equation (3).
d (Id) ^* / dt (3)

The field weakening current command value Id ^* thus set and calculated is supplied from the time differential value setting unit 62 to the adding unit 86 (see FIG. 2), and the d-axis current target value idt (idt = idt = Id ^* ) is output.

FIG. 8 shows a waveform example of the absolute value | Id ^* | of the field weakening current command value Id ^* set by the time differential value setting unit 62 by a solid line. Waveform of broken line shows a waveform of the d-axis current Id outputted from the d-axis current setting portion 61. The q-axis current command value iqcom, which is a torque current, is a constant value of iqcom = 50 [A].

  In the example of FIG. 8, the value of the minute increment D1 at the time of increase is set to a larger value than the value of the minute increment D2 at the time of decrease. As a result, the rising part of the waveform rises more rapidly than the falling part. That is, the rising time differential value is set larger than the falling time differential value.

When the field weakening current command value Id ^* rises from the initial value 0 [A] to the command value 20 [A] at the time point t1 in FIG. 8, it is increased by a small increment D1 every minute time dt, and the initial value 0 [A ] To 20 [A] with a constant time differential value. Further, at time t2, field weakening current command value Id ^* falls from command value 20 [A] (which can be considered as an initial value) to initial value 0 [A] (which can also be considered as a command value). Then, every minute time dt, the value is decreased by a minute increment −D2, and falls from the command value 20 [A] to the initial value 0 [A].

  In FIG. 9A, the d-axis current Id (Id indicated by the dotted line in FIG. 8), which is the output of the d-axis current setting unit 61 before the time differential value correction of the rising and falling parts, is used as the field weakening current command value. The change waveform of the motor torque Tmq [N] of the comparative example is shown. It can be seen that at time t1 and time t2, an impulse torque fluctuation occurs ± 0.6 [Nm] with respect to the motor torque Tmq = 2.0 [Nm].

On the other hand, the d-axis current target value idt is set to the field weakening current command value Id ^* (solid line in FIG. 8) that is the output of the time differential value setting unit 62 after correcting the time differential value of rising and falling according to this embodiment. In the change waveform of the motor torque Tmq [Nm] shown in FIG. 9B in the case of Id ^* ) shown in FIG. 9B, the torque fluctuation is halved from 0.6 [Nm] to 0.3 [Nm] at the rising portion at time t1. In the falling portion at time t2, the time differential value is smaller than that in the rising portion, so that the torque fluctuation is reduced from 0.6 [Nm] to 0.1 [Nm] to 1/6. I understand. Thus, by controlling the time differential value {d (Id) ^* / dt} at the rising part and the falling part of the field weakening current command value Id ^* to be constant (constant value), the rotational speed Nm of the motor 30 can be reduced. Vibrations and abnormal noises caused by sudden changes can be stably reduced, and accurate control that provides a comfortable steering feeling can be performed.

As described above, the effect of suppressing the torque fluctuation becomes larger as the time differential value of the field weakening current command value Id ^* is reduced. However, if the time differential value is set small, for example, when the steering handle 12 is steered suddenly at high speed, the effect of field weakening control (smooth increase in the number of revolutions) is not in time, and the steering operation is caught. There is a possibility that a comfortable steering feeling in the electric power steering apparatus 10 may not be obtained. As a result, there is a problem that the time differential value cannot be set to a very small value in consideration of responsiveness so that the effect of the field weakening current can be in time.

In order to solve this problem, as described with reference to FIGS. 7, 8, and 9B, the absolute value of the field weakening current command value Id ^* increases and decreases when it decreases. The time differential value of the field current command value Id ^* is differentiated.

  Exact control of the difference between the time differential values of the rising portion and the rising portion will be described with reference to the motor output characteristics that change due to the field weakening current in FIG.

In the electric power steering apparatus 10, when the steering handle 12 is suddenly operated and the steering speed, in other words, the motor rotational speed Nm is going to increase from the operating point A to the operating point B in FIG. It is necessary to flow the field weakening current through the motor 30 to increase the rotation of the motor 30 (change from the characteristic 220 side toward the characteristic 222 side). Next, when the steering speed decreases and the operating point B returns to the operating point A again, it is not necessary to perform field weakening control on the motor 30, so the field weakening current command value Id ^* (field weakening current) is 0. [A] is returned (change from the characteristic 222 side to the characteristic 220). Considering such a change in the output characteristics of the motor 30, when the operating point A changes to the operating point B, the time differentiation of the field weakening current is performed in order to improve the response so that the effect of the field weakening current is in time. It is necessary to set a large value. On the other hand, when the operating point B changes to the operating point A, since the driving at the operating point A is possible even in the state where the field weakening control is performed, the field weakening current is immediately set to the initial value 0 [A]. Therefore, it is possible to set the time differential value of the field weakening current small. As a result, torque fluctuation can be effectively suppressed.

  In the electric power steering apparatus 10, the field-weakening current command value (here, d-axis current Id) is repeatedly increased and decreased by changes in steering torque and steering speed caused by the driver's operation of the steering handle 12. Field weakening current may not be stable. In this case, by setting a large time differential value at the time of increase, the effect of field weakening control is in time while suppressing the occurrence of vibration and abnormal noise within an allowable range when steered at high speed, By setting the time differential value at the time of decrease small, it is possible to stabilize the field weakening current and further suppress vibration and noise.

That is, as shown in FIG. 8, the time differential value (time change rate of the field weakening current) in the rising section from the reference value 0 at the time point t1 until the field weakening current command value Id ^* is reached, By setting a larger value than the time differential value (time change rate of the field weakening current) in the falling section from the field weakening current command value Id ^* at the time point t2 until the reference value 0 is reached. In the rising section at time t1, the effect of field weakening control in time when the vehicle is suddenly steered at a high speed while reducing torque fluctuation and suppressing the generation of abnormal noise and vibration becomes in time, and the rising at time t2 In the descending section, since the time differential value is set to a small value, the torque fluctuation can be further reduced and the generation of abnormal noise and vibration can be further suppressed.

  In the above-described embodiment, the optimum embodiment as the so-called best mode has been described, but various modifications can be made as described below.

  An electric power steering apparatus 10 that drives and controls a steering assist motor 30 according to a steering input by the driver's operation of the steering handle 12, and has the following technical features [1]-[6].

[1] A steering torque sensor 32 (which may be considered as a steering input detection unit including the steering angle sensor 34) as a steering input detection unit for detecting the magnitude of the steering input, and an output signal of the steering torque sensor 32 A q-axis target current setting unit 70 as a torque current setting unit for setting a q-axis current command value iqcom that is a torque current of the motor 30 based on the steering torque Tq, and a field for weakening the field of the motor 30. By a time differential value setting unit 62 as a field weakening current setting unit for setting a field weakening current command value Id ^* from a reference value (d-axis current command value idcom = 0), and the q-axis target current setting unit 70 as the motor drive control unit for driving and controlling the motor 30 based on the set weak field current command value Id ^* by the q-axis current command value iqcom and the time differential value setting unit 62 that is set A motor drive control unit 42 includes a time differential value setting unit 62 as the field weakening current setting unit, at least some sections to reach the reference value from the weak field current command value Id ^* The time differential value may be changed to be constant.

According to the electric power steering apparatus 10 having the technical feature [1], the time differential value in at least a part of the period from the reference value to the field weakening current command value Id ^* is constant. Since setting control is performed, the rise and fall times can be set so that the generation of abnormal noise and vibration due to a sudden change in the field weakening current command value Id (see FIG. 8) is within the allowable range, and an accurate match with the conditions is always possible. Since the rise and fall times can be taken, the rise time does not become slow or fast depending on the situation as in Patent Document 1. For example, there is no wasteful rise time. Therefore, the control of the change rate of the optimum field weakening current command value Id ^* in which the generation of abnormal noise and vibration due to the sudden change of the field weakening current command value Id is within the allowable range, that is, the time for the accurate field weakening current command value. The differential value can be controlled.

[2] The time differential value setting unit 62 as the field weakening current setting unit described above is used when the absolute value of the field weakening current command value Id ^* increases or decreases, and the field weakening current command value Id ^*. A difference is provided in the time differential value of.

  Since the difference is provided, for example, the time differential value of the field weakening current can be properly used depending on the type of a vehicle such as a sports car, a passenger car, a commercial vehicle, or a use such as energy saving.

For example, by making the time derivative value when the absolute value of the field weakening current command value Id ^* , which is the d-axis current command value, which is a situation that does not require field weakening control, decrease, is larger than the time derivative value when increasing. As a result, the field weakening current can be quickly reduced, and the field current can be prevented from flowing unnecessarily. That is, wasteful power consumption can be eliminated quickly.

[3] In the electric power steering apparatus 10 having the technical feature [2] described above, the time differential value setting unit 62 as the field weakening current setting unit increases the absolute value of the field weakening current command value Id ^*. The time differential value when the absolute value of the field weakening current command value Id ^* decreases is set smaller than the time differential value in this case.

  This technical feature [3] corresponds to the above-mentioned best mode. In this case, the rise can be controlled quickly, and the target field weakening current is quickly obtained, so that there is no processing delay. In addition, since it is not necessary to make the falling field current a target field-weakening current as soon as possible, it is possible to set a slow rise time that can further reduce noise and vibration.

[4] The time differential value setting unit 62 as the field weakening current setting unit sets the time differential value to a first constant in all the rising sections from the reference value until reaching the field weakening current command value Id ^*. The value {for example, d (Id) ^* / dt = D1 / dt} described above (see also FIG. 11A) and the entire fall period from the field weakening current command value Id ^* to the reference value. The time differential value is set equal to the first constant value {d (Id) ^* / dt = −D1 / dt} or the second constant value {d (Id) ^* / dt = −D2 / dt}. (D1> D2 or D1 <D2 achieves a certain effect).

  In other words, the control of the time differential value is simplified by making it constant throughout the rising and falling sections, and abnormal noise and vibration due to torque fluctuations are controlled by controlling each different constant value during each rising and falling section. It can be suppressed, and a light steering feeling of the electric power steering can be realized.

Next, with reference to FIGS. 11A to 11D, technical features of other modified examples will be described. FIG. 11A shows a waveform when the time differential value d (Id) ^* / dt of the rise of the field weakening current command value Id is constant.

[5] In the electric power steering apparatus 10 having the technical feature [1] described above, as shown in FIG. 11B, the time differential value setting unit 62 as the field weakening current setting unit is weakened from the reference value 0. constant time derivative at least a partial section to reach the field current command value ^{Id * {d (Id) *} / dt = constant} when the weakening field current command value Id ^* of the absolute value of the The time differential value when increasing from the reference value 0 may be gradually (smoothly) increased to be the constant time differential value in the partial section.

At the rising edge of the start or the falling of the start, it is possible to smooth the change in the time differential value, it is possible to reduce the amplitude of the impulse variations that occur in the motor torque.

[6] In the electric power steering apparatus 10 having the technical feature [1] described above, as shown in FIG. 11C, the time differential value setting unit 62 as the field weakening current setting unit includes a field weakening current command value. While the absolute value of Id ^* is increasing, the time differential value is made constant at least in a section until reaching the field weakening current command value Id ^*, and then the time differential value is gradually decreased (smoothly). The field weakening current command value may be used.

During the rise of termination, or Falling at the end, it is possible to smooth the change in the time differential value, similarly, it is possible to reduce the amplitude of the impulse variations that occur in the motor torque.

  In addition, as shown to FIG. 11D, you may implement said technical characteristics [5] and [6] simultaneously.

The range in which the change of the time differential value is smooth is at the start and end of the rise and fall of the overall amplitude from the reference value to the field weakening current command value Id ^* , for example, 5 [%] to 20%, respectively. In order to perform stable control, the rise and fall are each 95 [%] (for example, only the start portion of the rise is 5% of the total amplitude). This corresponds to a case where the change in the time differential value is smoothed by about [%].) To 60 [%] (for example, the change in the time differential value at the start portion and the end portion of the rising edge is 20% of the total amplitude. [%] Corresponds to the case where the surface is smoothed.

  Note that the present invention is not limited to the above-described embodiment, and various configurations can be adopted based on the description 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 ... time differential value setting unit 67 ... command torque calculation 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 112 ... q-axis command voltage correspondence processing unit 114 ... q-axis actual current handling unit 116 ... motor rotation speed handling unit 118 ... synergistic operation unit 122 ... q-axis actual current Correspondence map 124 ... q-axis command voltage correspondence map 126 ... Motor rotation speed correspondence map 204 ... Deviation time differential value converter 212 ... Minute increment assignment 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 for setting a torque current command value 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 command value from a reference value to weaken the field of the motor;
A motor drive control unit that drives and controls the motor based on the torque current command value set by the torque current setting unit and the field weakening current command value set by the field weakening current setting unit,
The field weakening current setting unit is
The time differential value in at least a part of the period from the reference value until reaching the field weakening current command value is made constant, and the absolute value of the field weakening current command value increases and decreases. An electric power steering apparatus characterized in that a difference is provided in the time differential value of the field weakening current command value . The electric power steering apparatus according to claim 1 ,
The field weakening current setting unit is
The time differential value when the absolute value of the field weakening current command value decreases is set smaller than the time differential value when the absolute value of the field weakening current command value increases. Power steering device. In the electric power steering apparatus according to claim 1 or 2 ,
The field weakening current setting unit sets the time differential value to a first constant value in the entire rising section from the reference value until reaching the field weakening current command value, and the field weakening current command The electric power steering apparatus, wherein the time differential value is set to a second constant value in all the falling intervals from the value to the reference value. The electric power steering apparatus according to claim 1,
When the field weakening current setting unit makes the time differential value constant in at least part of the interval from the reference value to the field weakening current command value , the absolute value of the field weakening current command value is The electric power steering apparatus, wherein the time differential value when increasing from the reference value is gradually increased to the constant time differential value in the partial section. The electric power steering apparatus according to claim 1,
The weak field current setting unit, while an increase in the absolute value of the field weakening current command value, after a time differential value constant at least some sections to reach the field weakening current command value, The electric power steering device, wherein the time differential value is gradually reduced to the field weakening current command value.

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