JPH11356079A - SR motor and electric power steering device using SR motor - Google Patents

Abstract

(57) [Problem] To provide an SR motor capable of reducing torque ripple even when an inexpensive low-resolution rotational position sensor is adopted. SOLUTION: A rotating position sensor 4 having a stator 8 poles, a rotor 6 poles, and a four-phase, in which the rotor tooth angle is larger than the stator tooth angle, and which outputs a switching signal of an energized phase, has four rotations per rotation.
It has four sensor elements for generating 8 pulses, a square wave constant current is supplied to the energized phase, and one-phase excitation is performed in a low speed region where the rotational speed calculated by the rotational position sensor is lower than a predetermined rotational speed. The SR motor is characterized in that 1-2 phase excitation is performed in a high-speed region at or above a predetermined rotation speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reduced torque ripple of a switched reluctance motor (hereinafter, referred to as an SR motor).

[0002]

2. Description of the Related Art In recent years, an SR motor has been considered as an electric power steering driving motor. Other motors for driving the electric power steering device include, for example, a DC motor, a brushless DC motor,
Although the use of an AC servomotor or the like is conceivable, the SR motor has advantages over these motors in that a brush, a magnet, and the like are not required, the number of parts is small, and the life is long.

However, the SR motor has a disadvantage that the torque ripple is essentially large.

A brushless motor such as an SR motor continuously generates a driving torque by sequentially switching an energized phase, and inevitably generates a torque ripple every time the energized phase is switched. This torque ripple is
This is to deteriorate the steering feel of the driver who operates the steering wheel, and it is better to make it as small as possible. For that purpose, it is required to control the switching timing with high accuracy. The switching timing of the energized phase is determined by a switching signal generated by an attached rotation position sensor that detects the rotation position of the rotor of the motor, so that the rotation sensor requires a high-precision one, for example, a high-resolution encoder such as a resolver. It had been.

[0005]

However, such high resolution sensors are generally expensive and unreliable. In addition, there has been a drawback that the sensor is susceptible to disturbances such as noises and requires high-precision assembly, a sensor output processing circuit becomes complicated, and the ECU becomes expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide an SR motor which can solve the above-mentioned problems and can reduce the torque ripple even if a low-cost and reliable low-resolution rotational position sensor is employed.

[0007]

In order to achieve the above-mentioned object, the present invention relates to a stator having eight poles, a rotor having six poles and four phases, wherein the rotor tooth angle is larger than the stator tooth angle, The rotation position sensor that issues the switching signal of
It has four sensor elements for generating pulses, a square-wave constant current is supplied to the energized phase, and a single-phase excitation is performed in a low-speed region where the rotational speed calculated by the rotational position sensor is equal to or lower than a predetermined rotational speed. And in the high-speed region above a predetermined rotation speed, 1
-An SR motor characterized by performing two-phase excitation.

The reason why the configuration of the SR motor and the pattern of the energized phase are as described above is as follows.

First, in order to reduce the torque ripple of the SR motor, a four-phase type is better than a three-phase type, and the size can be reduced. In addition, if the number of phases is five, the torque ripple can be further reduced, but the number of FETs as switches for switching the energized phase increases, and the cost increases. The three-phase and four-phase ones can have a switching circuit configuration with six switches, while the five-phase one requires at least ten switches. Therefore, a four-phase SR motor is adopted.

In a four-phase SR motor, a pair of a rotor having eight poles and a rotor having six poles or a stator having sixteen poles and a rotor having twelve poles can be considered. Since the size of the motor itself is large and it is not suitable as a motor for an electric power steering device, which has a strong demand for compactness, the stator has eight poles and the rotor has six poles.

The torque ripple of the motor for the electric power steering device is most likely to be felt by the driver in a low speed region where the steering rotation speed is low.
Therefore, in a low-speed region where the steering rotation speed is low, one-phase excitation that easily reduces torque ripple is performed.
Also, in a high-speed region, the driver is less likely to feel torque ripple, so that torque is more likely to be output as compared with one-phase excitation.
It was decided to perform two-phase excitation. The advance angle at this time was set to 7.5 °, which is １ ／ of the basic energization angle of 15 °.

If the rotation position sensor having such a configuration performs only one-phase excitation in a low-speed region,
The minimum number of required sensors is two and the resolution is 15 °. However, since the 1-2 phase excitation for performing the 7.5 ° advance in the high-speed region is performed, the number of required sensors is 4, and the resolution is 7.
5 ° (48 pulses per rotation).

Further, when the rotor tooth angle is made larger than the stator tooth angle so that the tooth tips slightly overlap each other, this is advantageous in reducing torque ripple.

In order to further reduce the torque ripple in the first aspect of the present invention, as described in the second aspect, when the energized phase is switched in the low speed region, It is effective to control the rise and fall of the square wave constant current by using the switching signal as a trigger.

The driver feels the torque ripple because the contribution of the temporal change rate of the torque is larger than the absolute value of the torque ripple width. It is an object of the present invention to control the rise and fall of the supplied square wave constant current by using the magnetic pole switching signal generated by the rotation position sensor as a trigger to reduce the temporal change rate of torque.

According to a third aspect of the present invention, there is provided a rotary position sensor having four phases, which generates a switching signal of an energized phase, has a sensor element for generating at least 48 pulses per rotation, and has two-phase excitation. The SR motor is characterized in that the energizing current is switched to a target current value in at least two stages at least twice based on the switching signal in an energizing section for one phase in the two-phase excitation. It is.

This basically follows the structure of the motor according to the first aspect of the present invention. However, the pattern of the energized phase is basically based on two-phase excitation, and a simple square wave constant current is used. The difference is that irregular two-phase excitation in which the target current value is switched to the target current value in at least two stages at least twice based on the switching signal from the rotational position sensor is greatly different. Generally, when a phase shift of the sensor occurs due to the assembly of the rotational position sensor, the torque ripple increases. However, if this energizing pattern is adopted, the increase of the torque ripple with respect to the phase shift of the sensor can be reduced. Therefore, there is an advantage that the accuracy of the sensor mounting position can be suppressed and the cost can be reduced.

According to a fourth aspect of the present invention, there is provided an electric power steering apparatus using a motor as an auxiliary torque source for reducing steering torque, wherein the motor is connected to the first, second or third aspect of the invention. An electric power steering apparatus characterized by using the above described SR motor.

According to the present invention, the SR
The use of the motor is limited to an electric power steering device that requires a high torque ripple reduction.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, as an embodiment of the present invention, an example in which an SR motor according to the present invention is used in an electric power steering device will be described with reference to the drawings.

FIG. 1 shows an outline of the entire electric power steering apparatus. Hereinafter, the operation of the electric power steering device will be described.

When the driver steers the steering 1, the rotation is transmitted to the steering shaft 9, and the rotation of the steering shaft 9 is transmitted to the gear mechanism 2. The gear mechanism 2 includes, for example, a rack and pinion gear mechanism (not shown), and rotates the steering shaft 9 in the axial direction of the tie rod 10 (in the left-right direction in FIG. 1).
Convert to Both ends of the tie rod 10 are connected to a link mechanism (not shown) for steering a steered wheel (not shown), and the steered wheels are steered by the axial movement of the tie rod 10.

The controller 13 includes a torque sensor 11 for detecting a rotational torque felt by the driver through the steering 1 during steering, and a vehicle speed sensor 12 for detecting the speed of the vehicle.
And a calculation based on the output result of the rotation position sensor 4 for detecting the rotation position of the SR motor 3, and sends a signal to the SR motor 3 so that the SR motor 3 according to the present invention generates an appropriate auxiliary torque. Supply.

The rotational torque of the output shaft of the SR motor 3 is converted into an axial driving force of the tie rod 10 in the gear mechanism 2 by a ball nut mechanism or the like (not shown). The SR motor 3 is driven in a direction to assist the steering force with an appropriate torque in accordance with a signal from the controller 13, and the rotational drive torque is converted into the axial drive force of the tie rod 10 by the above-described ball nut mechanism or the like. You. As a result, the steering force of the driver is assisted, and the steering force of the driver is reduced.

The outline of the operation of the electric power steering apparatus has been described above.

Next, an embodiment of the configuration of the SR motor 3 and the pattern of the energized phase according to the present invention will be described with reference to FIGS.

FIG. 2 is a view showing the shapes of the stator and the rotor of the four-phase SR motor 3 having eight poles of the stator and six poles of the rotor according to the present invention. In FIG. 2, the rotor tooth angle is θr,
Assuming that the stator tooth angle is θs, it can be seen that θr> θs. As described above, it is known that a slight overlap between the two tooth tips is advantageous in reducing the torque ripple. The specific operation of the SR motor is well known and will not be described.

FIG. 3 is a time chart of each energized phase of the four-phase SR motor 3 according to the present invention.

The current supplied to each phase uses a square wave constant current which is easy to control. As described above, in a low-speed region where the steering rotation speed is low, the driver is most likely to feel the torque ripple, and therefore, the one-phase excitation that easily reduces the torque ripple is performed. The basic energization angle is 15 °. Also, in the high speed region where the steering rotation speed is fast,
Since it is difficult for the driver to feel the torque ripple, the output is prioritized over the torque ripple reduction, and the 1-2 phase excitation is performed. Specifically, the rising timing of the current of each phase is advanced by 7.5 °, which is の of the basic conduction angle,
This is addressed by setting the energization angle to 22.5 °.

Here, the boundary point between the low-speed area and the high-speed area is
For example, in the case of an SR motor having a MAX rotation speed of 500 r / min, it is preferable to set the rotation speed to 3/10 or less of the MAX rotation speed, that is, 150 r / min or less. The discrimination between the low speed region and the high speed region is performed by the controller 13 calculating the rotation speed of the SR motor 3 from the signal of the rotation position sensor 4. The controller 13 supplies the corresponding energization pattern determined based on the calculation result to the SR motor 3.

FIG. 4 is a diagram showing an arrangement of a rotational position sensor of a four-phase SR motor according to the present invention. The sensor plate that rotates integrally with the rotation of the motor, as shown in FIG.
It has a shape in which teeth having a tip angle of 30 ° are arranged at equal intervals in the circumferential direction. If only one-phase excitation in the low-speed region shown in FIG. 3 is performed using this sensor plate, the position sensor will have two positions a in FIG. 4 and b having a phase difference of 15 ° with respect to a.
I just need This is because a pulse signal can be generated for each rotation angle of 15 ° by a combination of the positional relationship between the two sensors and the shape of the sensor plate. But,
Since it is necessary to perform 1-2 phase excitation for performing a 7.5 ° advance in the high speed region in FIG. 3, it is necessary to generate a pulse signal (48 pulses per rotation) for each 7.5 ° of rotation. Therefore, as shown in FIG. 4, a position sensor d having a phase difference of 15 ° with respect to the position sensors c and c is provided in a positional relationship having a phase difference of, for example, 127.5 ° with respect to the position sensors a and b. There is a need. After all, to perform the energization pattern according to the present invention, four sensor elements are required,
These four sensor outputs are supplied to the controller 13 as current switching signals, and the controller 13 switches the current supplied to the SR motor 3 based on the signals. As the sensor element, an inexpensive Hall IC, an optical element, or the like is preferably used.

In order to further reduce the torque ripple in comparison with the above-described first aspect of the present invention, particularly in the low-speed region where reduction of the torque ripple is required as described in the second aspect. At the time of switching the energized phase, the switching signal generated by the rotational position sensor 4 is used as a trigger,
It is advisable to add rise and fall control of the square wave constant current. The purpose of this is to tune the rising and falling current waveforms and reduce the temporal change rate of torque at the time of current switching. The controller 13 that has received the switching signal generated by the rotation position sensor 4 may perform the calculation by software to correct the supply current waveform, or may perform the correction by using the SR motor 3 from the controller 13.
The current may be supplied by correcting the waveform in a hardware manner using a filter or the like.

The description of the first and second aspects of the present invention has been described above, and an embodiment of the energization pattern according to the third aspect of the present invention will be described with reference to FIGS.

The structure of the SR motor 3 according to the third aspect is as follows.
It is basically the same as that of the first aspect, except that the energization pattern is based on two-phase excitation. In FIG.
An example of a time chart of each energized phase of the four-phase SR motor 3 according to the third aspect of the present invention is shown.

As shown in FIG. 6, the current supplied to each phase is switched based on a switching signal from the rotation position sensor 4 that generates a signal of 48 pulses per rotation, and two-phase excitation is performed. . Further, the target current has a target value of two stages, and a target current value of 2 is given in an energizing section for one phase in two-phase excitation, that is, an energizing section when one-phase excitation is performed, and in other sections. In the example, the target current value 1 is given. The target current value 2 is set to twice the target current value 1.

After all, in the example shown in FIG. 6, a total of 2 at the start point and the end point of the energizing section for one phase in the two-phase excitation.
That is, the target current value is switched to the two-stage target current value.

FIG. 7 shows a simulation result of the torque waveform of the four-phase SR motor when the irregular two-phase excitation pattern shown in FIG. 6 is performed. Note that, in the calculation of this simulation, the measured static torque value of the prototyped four-phase SR motor is used. Therefore, in the present simulation, an error becomes large in a high-speed region, but can be accurately calculated in a low-speed region where torque ripple is a problem. FIG. 5 shows the relationship between the measured static torque value and the rotation angle.

FIG. 7 shows three types of calculation results. There are three types: an ideal state where there is no phase variation of the rotation position sensor 4, a case where the phase is shifted by 2.5 ° in the advance direction, and a case where the phase is shifted by 2.5 ° in the retard direction. In FIG. 6, the current values are 30 A for the target current 1 and 60 A for the target current 2 in FIG.
And As shown in FIG. 7, the torque ripple is about 20% in an ideal state, and about 40% at the maximum in the case of a 2.5 ° retardation.

The result will be compared with the case of another energization pattern shown below. The results shown below are the results when the same four-phase SR motor is used and the same static torque measured value shown in FIG. 5 is used to calculate at a current value of 60 A.

FIGS. 8 and 9 are time charts of the respective energized phases when one-phase excitation is performed and the calculation results thereof are shown in FIGS.
FIG. 11 is a time chart of each energized phase in the case where the 1-2 phase excitation is performed, and FIG. 12 and FIG.
A time chart of each energized phase when phase excitation is performed and a calculation result thereof are shown.

FIG. 9 shows that the torque ripple reaches 30% in the ideal state and about 80% in the case of 2.5 ° phase advance when one-phase excitation is performed. FIG. 11 shows that when the 1-2 phase excitation is performed, it reaches 70% in the ideal state and up to about 80% in the case of 2.5 ° phase delay. FIG. 13 shows that when the two-phase excitation is performed, it is about 45% even in the ideal state and when a phase shift of 2.5 ° occurs.

From the above calculation results, when the irregular two-phase excitation according to the third aspect of the present invention is performed, there is no phase shift of the rotational position sensor 4 as compared with when the other three patterns of excitation are performed. 1. The torque ripple in the ideal state is small, and
It can be seen that even when a phase shift of 5 ° occurs, the increase is small. Therefore, the mounting position of the rotation position sensor 4,
There is an advantage that the precision of the motor shape can be suppressed and the cost of each component can be reduced.

As shown in FIG. 6, in this embodiment, the target current value is switched to the two-stage target current value twice in the current-passing section for one phase in the two-phase excitation. The target current value may be switched to the three-stage target current value four times in the energizing section for one phase. However, in this case, the resolution of the rotational position sensor is changed from 48 pulses per rotation to 9
It is necessary to increase to 6 pulses.

As described above, the present invention has been described with reference to the above embodiments. However, the present invention is not limited to the above embodiments, but includes various embodiments according to the principle of the present invention.

[0045]

As described above, according to the present invention,
Even if an inexpensive and highly reliable low-resolution rotational position sensor is adopted, an SR motor capable of reducing torque ripple can be provided.

[Brief description of the drawings]

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

FIG. 2 shows an embodiment of the present invention according to claim 1;
It is a figure showing the shape of the stator and the rotor part of the phase SR motor.

FIG. 3 is a diagram illustrating a fourth embodiment according to the first embodiment of the present invention;
FIG. 4 is a diagram showing a time chart of each energized phase of the phase SR motor.

FIG. 4 is a diagram showing an arrangement of a rotational position sensor according to one embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a measured static torque value and a rotation angle of an actual four-phase SR motor used in calculation of a simulation.

FIG. 6 is a diagram showing a time chart of each energized phase when an irregular two-phase excitation according to the invention of claim 3 is performed.

FIG. 7 is a diagram showing a simulation result of a torque waveform when an irregular two-phase excitation according to the invention of claim 3 is performed.

FIG. 8 is a diagram showing a time chart of each energized phase when one-phase excitation is performed.

FIG. 9 is a diagram showing a simulation result of a torque waveform when one-phase excitation is performed.

FIG. 10 is a diagram showing a time chart of each energized phase when performing 1-2 phase excitation.

FIG. 11 is a diagram showing a simulation result of a torque waveform when performing 1-2 phase excitation.

FIG. 12 is a diagram showing a time chart of each energized phase when two-phase excitation is performed.

FIG. 13 is a diagram showing a simulation result of a torque waveform when two-phase excitation is performed.

[Explanation of symbols]

 3 SR motor 4 Rotational position sensor

Claims (4)

[Claims] 1. A rotor position sensor that generates a switching signal for a current-carrying phase in which the rotor tooth angle is larger than the stator tooth angle among the stator 8 poles, the rotor 6 poles, and the four phases is 48 per rotation.
It has four sensor elements for generating pulses, a square-wave constant current is supplied to the energized phase, and a single-phase excitation is performed in a low-speed region where the rotational speed calculated by the rotational position sensor is equal to or lower than a predetermined rotational speed. And in the high-speed region above a predetermined rotation speed, 1
-An SR motor characterized by performing two-phase excitation. 2. The SR according to claim 1, wherein in the low-speed region, when the energized phase is switched, the switching signal is used as a trigger to control the rise and fall of the square wave constant current. motor. 3. A rotation position sensor having four phases and generating a switching signal of a conduction phase has a sensor element for generating at least 48 pulses per rotation, and two-phase excitation is performed.
The energizing current is at least twice based on the switching signal in the energizing section for one phase in the two-phase excitation.
An SR motor capable of switching to at least two stages of target current values. 4. An electric power steering apparatus using a motor as an auxiliary torque source for reducing steering rotational torque, wherein the motor uses the SR motor according to claim 1, 2 or 3. An electric power steering device characterized by the above-mentioned.