JP2008290664A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device for preventing the drop of a power voltage by reducing power consumption depending on a power voltage value. <P>SOLUTION: The vector control of a d-q axis is used for computing a current command value on the basis of at least steering torque T, and an electric motor 12 is controlled to be driven on the basis of the current command value. At this time, when a vehicle speed V reaches a predetermined vehicle speed V1 or lower, a d-axis current command value Idref in the vector control is computed to be smaller as a battery voltage Vbat is lower. Thereby, when the battery voltage Vbat is high, normal weak field control is executed to improve a steering feeling during abrupt steering, and when the battery voltage Bbat is low, weak field control is developed to be weaker than usual one to reduce power consumption and reduce the drop of the battery voltage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that applies a steering assisting force to reduce a steering burden on a driver to a steering mechanism, and in particular, an electric power that prevents a decrease in power supply voltage when the steering assisting force is applied. The present invention relates to a steering device.

  As a conventional idle rotation control device for an electric power steering vehicle, when a vehicle speed sensor outputs a stop state determination signal and a current sensor outputs a determination signal when a large current is used, By outputting an idle-up control command, it is known to idle up only during stationary steering while the vehicle is idling, and to release idle-up when starting (see, for example, Patent Document 1). reference).

However, in this case, since the current value used for determining whether to idle up is the current actually flowing in the motor, even if an idle up command is output after the threshold value is exceeded, the threshold value is exceeded. In this case, the motor current is already supplied from the power supply voltage, and the power supply voltage has dropped.
Therefore, when the differential value of the assist current command value is greater than or equal to a predetermined threshold, an idle-up command is issued to predict a drop in the power supply voltage and prevent a drop in the power supply voltage quickly. A control device is known (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 3-18635 Japanese Patent No. 3644343

By the way, in order to suppress a decrease in power supply voltage, it is necessary to increase input power to the control device or reduce power consumption.
In the conventional device described in each of the above patent documents, a decrease in the power supply voltage is suppressed by increasing the input power, but since the input voltage value to the control device is not considered, the power supply voltage When the value is high or the like, it is not always necessary to idle up, and idle up is performed, and useless power is input to the control device.

On the other hand, when the power supply voltage value is low, there is a possibility that sufficient compensation cannot be performed even if the engine is idled up because the power consumption is not suppressed.
Therefore, an object of the present invention is to provide an electric power steering device that can prevent a decrease in power supply voltage by reducing power consumption according to a power supply voltage value.

In order to solve the above problems, an electric power steering apparatus according to claim 1 is based on a steering torque detecting means for detecting a steering torque input to a steering mechanism, and at least a steering torque detected by the steering torque detecting means. Current command value calculating means for calculating a current command value using vector control of dq axes, an electric motor for generating a steering assist torque applied to a steering shaft of the steering mechanism, and the current command value based on the current command value. An electric power steering device comprising motor control means for driving and controlling a motor,
Vehicle speed detection means for detecting the vehicle speed, and voltage detection means for detecting the voltage value of the on-vehicle battery, the current command value calculation means, when the vehicle speed detected by the vehicle speed detection means is less than or equal to a predetermined vehicle speed, The lower the battery voltage value detected by the voltage detection means, the smaller the d-axis current command value in the vector control is calculated.

According to a second aspect of the present invention, there is provided the electric power steering apparatus according to the first aspect of the invention, wherein the current command value calculation means is configured such that the battery voltage detected by the voltage detection means is relative to a normal d-axis current command value. It is characterized in that the d-axis current command value is calculated to be smaller as the battery voltage is lower by multiplying by a voltage sensitive gain that is lower as the battery voltage is lower.
The electric power steering apparatus according to a third aspect of the present invention is the electric power steering apparatus according to the first aspect, wherein the current command value calculation means calculates the d-axis current command value by an advance angle control, and the voltage detection The lower the battery voltage detected by the means, the smaller the advance angle in the advance angle control is calculated.

  According to a fourth aspect of the present invention, there is provided the electric power steering apparatus according to any one of the first to third aspects, wherein the current command value calculating means has a vehicle speed detected by the vehicle speed detecting means equal to or lower than a predetermined vehicle speed. In addition, when the battery voltage detected by the voltage detecting means is equal to or lower than a predetermined voltage, the d-axis current command value is calculated to be smaller as the battery voltage is lower.

  According to the electric power steering apparatus of the present invention, when the vehicle speed is a low speed traveling state equal to or lower than the predetermined vehicle speed, the d-axis current command value in the vector control (the field that weakens the field of the motor) decreases as the vehicle battery voltage value decreases. The magnetic current command value) is calculated to be small, so that when the power supply voltage is low in the low-speed traveling state, the output spent on the tracking performance can be suppressed. In this way, it is possible to reduce the power consumption by suppressing the input current to the control device, and the effect of reducing the decrease in the power supply voltage can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing an embodiment of an electric power steering apparatus according to the present invention.
In the figure, reference numeral 1 denotes a steering wheel, and a steering force applied to the steering wheel 1 from a driver is transmitted to a steering shaft 2 having an input shaft 2a and an output shaft 2b. The steering shaft 2 has one end of the input shaft 2a connected to the steering wheel 1 and the other end connected to one end of the output shaft 2b via a torque sensor 3 as steering torque detecting means.

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

A steering assist mechanism 10 for transmitting a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 10 includes a reduction gear 11 coupled to the output shaft 2b, and an electric motor 12 coupled to the reduction gear 11 and generating a steering assist force with respect to the steering system.
The torque sensor 3 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a, and a torsional angle displacement of a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The torsional angular displacement is detected by, for example, a potentiometer. The torque detection value T output from the torque sensor 3 is input to the controller 15.

The controller 15 operates by being supplied with power from a vehicle-mounted battery 17 (for example, the rated voltage is 12V). The negative electrode of the battery 17 is grounded, and the positive electrode thereof is connected to the controller 15 via an ignition switch 18 that starts the engine, and is also connected to the controller 15 without passing through the ignition switch 18.
Further, the electric motor 12 of the present embodiment is, for example, a three-phase brushless motor. As shown in FIG. 2, one end of the U-phase coil Lu, the V-phase coil Lv, and the W-phase coil Lw are connected to each other so The other ends of the coils Lu, Lv, and Lw are connected to the controller 15, and motor drive currents Iu, Iv, and Iw are individually supplied. The electric motor 12 includes a rotor position detection circuit configured by a resolver, an encoder, and the like that detects the rotational position of the rotor. The rotation angle sensor 13 is based on the rotor rotational position output from the rotor position detection circuit. The motor rotation angle θ is detected.

  As shown in FIG. 2, the controller 15 receives the steering torque T detected by the torque sensor 3 and the vehicle speed detection value V detected by the vehicle speed sensor 16 as vehicle speed detection means. The detected motor rotation angle θ is input, and motor drive currents Iu, Iv, and Iw supplied to the phase coils Lu, Lv, and Lw of the electric motor 12 detected by the current detection circuit 22 are input. Further, the battery voltage Vbat detected by the voltage sensor 27 as voltage detecting means is also input to the controller 15.

  The controller 15 is configured by, for example, a microcomputer that outputs motor voltage command values Vu, Vv, and Vw for generating the steering assist force according to the steering torque T, the vehicle speed detection value V, and the motor rotation angle θ by the electric motor 12. Control arithmetic unit 23, a motor drive circuit (inverter circuit) 24 composed of a field effect transistor (FET) for driving the electric motor 12, phase voltage command values Vu, Vv output from the control arithmetic unit 23, and An FET gate drive circuit (PWM control unit) 25 that executes a pulse width modulation (PWM) control process based on Vw and controls the gate current of the field effect transistor of the motor drive circuit 24 is provided.

  As shown in FIG. 3, the control arithmetic unit 23 calculates a torque command value Tref corresponding to the input torque detection value T and the vehicle speed detection value V, and the dq axis based on the calculated torque command value Tref. A current command value calculation unit 30 that calculates current command values Idref and Iqref, and further converts the dq axis current command values Idref and Iqref into two-phase / three-phase to calculate three-phase current command values Iuref to Iwref; A motor current control unit that controls the drive voltage by performing current feedback processing on the three-phase current command values Iuref to Iwref output from the current command value calculation unit 30 and the motor currents Iu to Iw detected by the current detection circuits 22u to 22w. 40.

The current command value calculation unit 30 includes a torque command value calculation unit 31, an angular velocity calculation unit 32, a conversion unit 33, a three-phase / two-phase conversion unit 34, a q-axis current command value calculation unit 35, and a d-axis current. A command value calculation unit 36 and a two-phase / three-phase conversion unit 37 are provided.
The torque command value calculation unit 31 uses the steering torque T detected by the torque sensor 3 and the vehicle speed detection value V detected by the vehicle speed sensor 16 as inputs, calculates a torque command value Tref by a known procedure, and uses this as a q-axis current command. The value is output to the value calculator 35 and the d-axis current command value calculator 36.

The angular velocity calculation unit 32 differentiates the motor rotation angle θ detected by the rotation angle sensor 13 to calculate a motor angular velocity ω, which is converted into a conversion unit 33, a q-axis current command value calculation unit 35, and a d-axis current command value calculation. To the unit 36.
The conversion unit 33 calculates the counter electromotive voltages eu, ev, ew by using the motor angular velocity ω and the motor rotation angle θ as inputs.

The three-phase / two-phase conversion unit 34 receives the counter electromotive voltages eu, ev, ew calculated by the motor rotation angle θ and the conversion unit 33 as inputs, and the counter electromotive voltages eu, ev, ew are counter electromotive voltages of dq axes. Convert to ed, eq.
The q-axis current command value calculation unit 35 receives the back electromotive voltages ed, eq, the torque command value Tref, the motor angular velocity ω, and the d-axis current command value Idref described later, and determines the current command value Iqref. Specifically, the q-axis current command value calculation unit 35 calculates Iqref = 2/3 (Tref × ω−ed × Idref) / eq.

Further, the d-axis current command value calculation unit 36 receives the torque command value Tref, the motor angular speed ω, the vehicle speed V, and the battery voltage Vbat, and performs a process described later to calculate the d-axis current command value Idref. The d-axis current command value Idref is a field current command value that weakens the field.
The 2-phase / 3-phase converter 37 receives the current command values Iqref and Idref and the motor rotation angle θ, converts the current command values Iqref and Idref into three-phase current command values Iuvref, Ivvref, and Iwvref, These are output to the motor current control unit 40.

The motor current control unit 40 includes subtraction circuits 41u, 41v, 41w and a PI control unit 42.
The subtraction circuits 41u, 41v, 41w respectively calculate the deviations between the motor currents Iu, Iv, Iw of each phase detected by the current detection circuits 22u, 22v, 22w and the current command values Iuvref, Ivvref, Iwvref of the three phases. The deviation is output to the PI control unit 42.

The PI control unit 42 calculates the voltage command values Vu, Vv, Vw so as to make the deviation zero, and executes feedback control.
The PWM control unit 25 receives the voltage command values Vu, Vv, and Vw as inputs, calculates a PWM gate signal to the inverter circuit 24, and the inverter circuit 24 is PWM-controlled by the gate signal. Thereby, each phase current Iu, Iv, Iw is controlled to become current command value Iuvref, Ivvref, Iwvref.

The above is the basic control for the electric motor 12. However, the capacity of the electric motor 12 is limited, and when the steering wheel is steered at high speed, the motor power is insufficient. It is necessary to achieve rotation and control power at a constant level.
In order to realize such control, a control method called field weakening control is used. Normally, the d-axis current command value Idref = 0 is equivalent to Idref = 0 in the case of field weakening control. The d-axis current command value Idref is a current component corresponding to the field magnetic flux, and increasing the d-axis current command value Idref in the negative direction is equivalent to weakening the field magnetic flux on the d-axis. When the field magnetic flux is weakened, the counter electromotive force is reduced, so that the motor can be rotated at a higher speed. Such field-weakening control is executed to improve the handle steering feeling even during rapid steering.

Next, specific processing of the d-axis current command value calculation unit 36 will be described with reference to FIG.
First, the torque command value Tref is input to the conversion unit 36a, and the base angular velocity ωb is calculated. On the other hand, the mechanical angle calculation unit 36b receives the motor angular velocity ω and outputs the mechanical angular velocity ωm converted into a mechanical angle. The arccos calculation unit 36c receives the base angular velocity ωb and the mechanical angular velocity ωm, executes the angle Φ = arccos (ωb / ωm), and outputs the angle Φ. Next, the sin calculator 36d receives the angle Φ and outputs sin Φ.

  On the other hand, the torque command value Tref is input, and the reference current Iqb that satisfies the reference current Iqb = (Tref / Kt) is calculated in the torque coefficient calculation unit 36e. Here, Kt is a torque coefficient. The absolute value calculator 36f takes the reference current Iqb as an input, takes the absolute value, and outputs the absolute value | Iqb | of the reference current. Next, the multiplication unit 36g receives sinΦ and | Iqb | output from the sin calculation unit 36d as inputs, and outputs a d-axis current command value Idref as Idref = − | Iqb | · sinΦ.

That is, here, the d-axis current command value Idref is calculated as Idref = − | Tref / Kt | · sin (arcos (ωb / ωm)) = − | Iref | · sin (arccos (ωb / ωm)). .
In the command value correction unit 36h, K · Idref obtained by multiplying the d-axis current command value (normal d-axis current command value) Idref output from the multiplication unit 36g by a gain K sensitive to the battery voltage Vbat is used as the d-axis current. Output as command value Idref.

Specifically, the gain K for correcting the d-axis current command value Idref is calculated with reference to the gain map based on the battery voltage Vbat that is the output of the voltage sensor 27. Then, a new d-axis current command value K · Idref is calculated by multiplying the d-axis current command value Idref, which is the output of the multiplication unit 36g, by the gain K.
Here, the gain map has a characteristic that the gain K increases from “0” to “1” as the battery voltage Vbat increases. For example, K = 0 when the battery voltage Vbat is 0V, K = 1 when the battery voltage Vbat is the predetermined voltage Vbat1, and the gain K is set to take a value between “0” and “1” when 0 <Vbat <Vbat1. Has been.

  Further, when the vehicle speed detection value V detected by the vehicle speed sensor 16 is larger than the predetermined vehicle speed V1, the switch 36i is in a state indicated by a solid line in the figure, and the d-axis current command value Idref output from the multiplication unit 36g is finally set. As a normal d-axis current command value. On the other hand, when the vehicle speed detection value V is equal to or lower than the predetermined vehicle speed V1, the switch 36i switches to the state indicated by the broken line in the figure, and the d-axis current command value Idref output from the command value correction unit 36h is changed to the final d-axis current. Output as command value. Here, the predetermined vehicle speed V1 is set to a speed value at which it can be determined that the vehicle is stopped or in an extremely low speed state.

As can be seen from arccos (ωb / ωm) in the equation representing the d-axis current command value Idref, the field current command for weakening the field when the motor mechanical angular velocity ωm becomes higher than the base angular velocity ωb. The value Idref appears as the value. That is, the field weakening control is executed when the mechanical angular velocity ωm of the motor becomes higher than the base angular velocity ωb.
Next, the operation and effect of the first embodiment will be described.

When the mechanical angular velocity ωm of the motor is lower than the base angular velocity ωb, the d-axis current command value calculation unit 36 has Φ, which is the output of the arccos calculation unit 36c, as “0”, so that sinΦ = 0 and Idref = − | Iqb |・ SinΦ = 0. Accordingly, K · Idref, which is the output of the d-axis current command value calculation unit 36, also becomes “0”, and the field-weakening control is not executed.
When the mechanical angular velocity ωm becomes faster from this state and becomes higher than the base angular velocity ωb, the angle Φ, which is the output of the arcos calculation unit 36c, is not 0, and the sin Φ generates a value between “0” and “1”. The output value Idref = − | Iqb | · sinΦ of the multiplication unit 36g generates a value.

At this time, for example, assuming that the vehicle speed V> V1, the switch 36i is in the state shown by the solid line in FIG. 4, and therefore the output value Idref of the multiplication unit 36g is set as it is as the final d-axis current command value. Weak field control is performed. As described above, by executing the field weakening control, the handle steering feeling in rapid steering is improved.
On the other hand, assuming stationary steering and vehicle speed V = 0, the switch 36i is in the state shown by the broken line in FIG. At this time, when the battery voltage Vbat does not drop and Vbat ≧ Vbat1, the command value correction unit 36h calculates the gain K to “1”, so that the output value of the multiplication unit 36g is corrected to decrease. Instead, the output value Idref of the multiplication unit 36g is set as the final d-axis current command value as it is, and normal field-weakening control is executed.

By the way, it is considered that the assist output request has priority over the follow-up performance (steering speed) in steering during stationary stop or the like or during extremely low speed traveling. Therefore, in the present embodiment, when the battery voltage Vbat drops while the vehicle is stopped or traveling at an extremely low speed, the output spent on the tracking performance is suppressed to reduce the decrease in the battery voltage Vbat.
That is, when Vbat <Vbat1, the command value correction unit 36h calculates the gain K between “0” and “1” according to the battery voltage Vbat. Therefore, the final d-axis current command value Idref is smaller than the output value of the multiplication unit 36g.

Since the current input to the motor drive circuit corresponds to the vector sum of the q-axis current and the d-axis current, when the same steering torque command value is input, to the motor drive circuit when the field weakening control is performed. More input current flows than when the field-weakening control is not performed.
Therefore, by setting the d-axis current command value Idref to be small as described above, it is possible to limit the input current to the motor drive circuit and reduce power consumption. As a result, a decrease in battery voltage can be mitigated.

FIG. 5 is a diagram for explaining the field-weakening control region that varies depending on the battery voltage. Thus, the normal field weakening control is executed when Vbat ≧ Vbat1, but the field weakening control is executed weaker than usual when Vbat <Vbat1. Further, when Vbat = 0, the field weakening control is not executed.
That is, as the battery voltage Vbat is lower, the input current to the motor drive circuit is limited. When the battery voltage Vbat is high, normal field-weakening control is performed to improve the steering feeling, and the battery voltage When Vbat is low, the control is more focused on preventing the battery voltage from dropping than improving the steering feeling.

  As described above, in the first embodiment, when the vehicle speed is equal to or lower than the predetermined vehicle speed, the d-axis current command value in the vector control (the field current command value that weakens the field of the motor) decreases as the voltage value of the on-vehicle battery decreases. ) Is calculated to be small, so that when the battery voltage is low when the vehicle is stopped or running at a low speed, it is possible to suppress the output spent on the tracking performance. As a result, it is possible to reduce the power consumption by suppressing the input current to the control device, and to reduce the decrease in the battery voltage.

In addition, since the d-axis current command value is calculated to be smaller as the battery voltage is lower by multiplying the normal d-axis current command value by the voltage sensitive gain, the d-axis current command value is limited with a relatively simple circuit configuration. Can be realized.
Further, when the battery voltage detected by the voltage detection means is equal to or lower than the predetermined voltage, the d-axis current command value is calculated to be smaller as the battery voltage is lower. Therefore, when the battery voltage is high, normal field-weakening control is executed. Thus, the motor can be rotated at a high speed, and steering with a good feeling can be ensured even for sudden steering of the steering wheel.

Next, a second embodiment of the present invention will be described.
In the second embodiment, the field-weakening control is realized by the vector control d-axis current command value in the first embodiment, but the vector control advance angle control is used. is there.
FIG. 6 is a block diagram illustrating a configuration of the control arithmetic device 23 in the second embodiment. Here, the same reference numerals as those in FIG. 3 are attached to portions that perform the same processing as that of the control arithmetic device 23 in the first embodiment shown in FIG.

The current command value calculation unit 61 receives the torque command value Tref, the motor rotation angle θ, and the motor angular velocity ω and calculates the q-axis current command value Iqref and the d-axis current command value Idref. The shaft current command value Iqref is proportional to the torque command value Tref, and the d-axis current command value Idref is calculated to be “0”.
On the other hand, the motor currents Iu, Iv, Iw detected by the current detection circuits 22u, 22v, 22w are converted into motor currents Iq, Id by the three-phase / two-phase converter 62. The motor rotation angle θ is used for this conversion.

The motor currents Iq and Id are fed back to the subtractors 63q and 63d, respectively. The subtractor 63q calculates a deviation ΔIq between the q-axis current command value Iqref and the motor current Iq. The subtractor 63d calculates the d-axis current command value. A deviation ΔId between Idref and motor current Id is calculated.
The PI control unit 64 performs PI control so as to eliminate these deviations ΔId and ΔIq, and outputs voltage command values Vd and Vq. These current command values Vd, Vq are converted into three-phase voltage command values Vu, Vv, Vw by the two-phase / three-phase converter 65. For this conversion, a motor rotation angle θ and an advance angle Φ calculated by an advance angle calculation unit 66 described later are used. Specifically, the following equation is executed for the current command values Vd and Vq, and the voltage command values Vu, Vv and Vw are calculated.

Vu = −Vd · cos (θ + Φ) + Vq · sin (θ + Φ),
Vv = −Vd · cos (θ + Φ−2π / 3) + Vq · sin (θ + Φ−2π / 3),
Vw = −Vd · cos (θ + Φ + 2π / 3) + Vq · sin (θ + Φ + 2π / 3) (1)

  Thus, by advancing the angle Φ, a current command value (d-axis current command value) for weakening the field is calculated. That is, in the advance angle control, the field current command value for weakening the field means the advance angle Φ, and components generated by the angle Φ weaken the field in the voltage command values Vu, Vv, and Vw. The action is generated.

FIG. 7 is a block diagram showing a specific configuration of the advance angle calculation unit 66.
The base angular velocity ωb is calculated in the conversion unit 66a with the torque command value Tref as an input, while the mechanical angular velocity ωm is calculated in the mechanical angle calculation unit 66b with the motor angular velocity ω calculated in the angular velocity calculation unit 32 as input, and an arccos calculation is performed. In the unit 66c, the angle Φ is calculated based on the angle Φ = arccos (ωm / ωb).

Then, the angle correction unit 66d outputs K · Φ obtained by multiplying the angle Φ output from the arcos calculation unit 66c by the gain K sensitive to the battery voltage Vbat, as the final angle Φ.
Specifically, the gain K for correcting the angle Φ is calculated with reference to the gain map based on the battery voltage Vbat that is the output of the voltage sensor 27.

Here, the gain map has a characteristic that the gain K increases from “0” to “1” as the battery voltage Vbat increases. For example, K = 0 when the battery voltage Vbat is 0V, K = 1 when the battery voltage Vbat is the predetermined voltage Vbat1, and the gain K is set to take a value between “0” and “1” when 0 <Vbat <Vbat1. Has been.
Further, the switch 66e is in a state indicated by a solid line in the figure when the vehicle speed detection value V detected by the vehicle speed sensor 16 is larger than the predetermined vehicle speed V1, and the d-axis current command value Idref output from the arccos calculation unit 66c is set. The final d-axis current command value is output. On the other hand, when the vehicle speed detection value V is equal to or lower than the predetermined vehicle speed V1, the switch 66e switches to the state indicated by the broken line in the figure, and the d-axis current command value Idref output from the angle correction unit 66d is changed to the final d-axis current command. Output as a value.

  As can be seen from the equation Φ = arccos (ωm / ωb), the angle Φ is a value that appears for the first time when the motor angular velocity ωm of the motor becomes higher than the base angular velocity ωb, in other words, the mechanical angular velocity ωm of the motor. Field weakening control is executed when becomes higher than the base angular velocity ωb.

Next, operations and effects of the second embodiment will be described.
When the mechanical angular velocity ωm of the motor is slower than the base angular velocity ωb, the angle Φ that is the output of the arcos calculator 66c is “0”, so the angle Φ that is the output of the advance angle calculator 66 is also “0”. Weak field control is not performed.
If the mechanical angular velocity ωm increases from this state and becomes higher than the base angular velocity ωb, the angle Φ, which is the output of the arcos calculator 66c, is not zero. At this time, assuming that the vehicle speed V is equal to or lower than the predetermined vehicle speed V1, the switch 66e is in a state indicated by a broken line in FIG. If the battery voltage Vbat is equal to or higher than the voltage Vbat1, the angle correction unit 66d calculates the gain K = 1, so that the output value of the arccos calculation unit 66c is not corrected to decrease and the arccos calculation unit 66c. The field weakening control is executed with the output value Φ of the current as the final angle Φ.

On the other hand, assuming that the battery voltage Vbat is lower than the voltage Vbat1, the gain K is calculated as a value between 1 and 0 by the angle correction unit 66d. Therefore, the final angle Φ is smaller than the output value of the arcos calculator 66c.
If the battery voltage Vbat is 0V, the angle value correction unit 66d calculates the gain K = 0, so that the final angle Φ = 0, and the field-weakening control is not executed.

As described above, in the second embodiment, when the vehicle speed is equal to or lower than the predetermined vehicle speed, the d-axis current command value is calculated to be smaller by calculating the advance angle in the advance angle control as the battery voltage is lower. When the battery voltage is in a low state, the input current to the motor drive circuit can be limited, and power consumption can be reduced to reduce the decrease in battery voltage.
In each of the above embodiments, the voltage sensitive gain K can be calculated with reference to the gain map shown in FIG. FIG. 8A shows that the gain K is not “0” even when the battery voltage Vbat is 0 V, and has, for example, K = K1 (for example, 0.3). By adopting such a gain map, it is possible to secure a d-axis current for field weakening control to some extent to suppress a decrease in battery voltage and to ensure good steering feeling.

Further, FIG. 8B shows that until the battery voltage Vbat reaches the predetermined voltage Vbat2 (<Vbat1), the field weakening control is not performed by setting K = 0, and when Vbat2 ≦ Vbat <Vbat1, the gain K is “ It takes a value between “0” and “1”.
As described above, the characteristics of the gain map can be determined based on the balance between prevention of a decrease in battery voltage and improvement in steering feeling.

  Moreover, in each said embodiment, although the case where a brushless motor was applied as an electric motor was demonstrated, a brush motor system is also applicable. In this case, for example, the motor angular velocity ω may be estimated from the back electromotive force of the motor.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the controller in 1st Embodiment. It is a block diagram which shows the specific structure of the control arithmetic unit of FIG. It is a block diagram which shows the specific structure of the d-axis current command value calculating part of FIG. It is a figure for demonstrating the effect of this invention. It is a block diagram which shows the structure of the controller in 2nd Embodiment. It is a block diagram which shows the structure of the advance angle calculating part of FIG. It is a figure which shows the modification of a gain map.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Torque sensor, 10 ... Steering assist mechanism, 11 ... Reduction gear, 12 ... Electric motor, 15 ... Controller, 16 ... Vehicle speed sensor, 17 ... Battery, 18 ... Ignition switch, 22 ... Current detection circuit, 23 ... Control arithmetic unit, 24 ... Motor drive circuit, 25 ... FET gate drive circuit, 27 ... Voltage sensor

Claims (4)

Steering torque detection means for detecting steering torque input to the steering mechanism, and current command for calculating a current command value using dq axis vector control based on at least the steering torque detected by the steering torque detection means An electric power steering apparatus comprising: a value calculation means; an electric motor that generates a steering assist torque to be applied to a steering shaft of the steering mechanism; and a motor control means that drives and controls the electric motor based on the current command value. And
Vehicle speed detection means for detecting the vehicle speed, and voltage detection means for detecting the voltage value of the on-vehicle battery, the current command value calculation means, when the vehicle speed detected by the vehicle speed detection means is less than or equal to a predetermined vehicle speed, The electric power steering apparatus, wherein the d-axis current command value in the vector control is calculated to be smaller as the battery voltage value detected by the voltage detection means is lower.   The current command value calculation means multiplies the normal d-axis current command value by a voltage sensitive gain that decreases as the battery voltage detected by the voltage detection means decreases, so that the d 2. The electric power steering apparatus according to claim 1, wherein the shaft current command value is calculated to be small.   The current command value calculation means calculates the d-axis current command value by advance angle control, and calculates a smaller advance angle in the advance angle control as the battery voltage detected by the voltage detection means is lower. The electric power steering apparatus according to claim 1.   When the vehicle speed detected by the vehicle speed detection means is less than or equal to a predetermined vehicle speed and the battery voltage detected by the voltage detection means is less than or equal to a predetermined voltage, the current command value calculation means The electric power steering apparatus according to claim 1, wherein the shaft current command value is calculated to be small.

Images