JP2012186934A - Normal rotation and reverse rotation switching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a normal rotation and reverse rotation switching device capable of normally rotating or reversely rotating a DC synchronous motor which drives a hall element with chopper signal or PWM signal, with a small torque ripple and large torque.SOLUTION: Related to a normal rotation and reverse rotation switching device for switching rotation of a motor between normal direction and reverse direction, a field winding is arranged around a rotor, and an excitation current that is supplied to a field winding set is controlled by the output signal outputted from a detection means that detects magnetic pole position of the rotor, for providing a predetermined rotational speed. The switching device includes a selecting means equipped with a plurality of selectors for selecting either a first field winding set or a second field winding set to which the excitation current is supplied by the output signal outputted from one detection means, and a selector switching means which causes the selector to select the first field winding set upon receiving a command for normal direction but causes the selector to select the second field winding set upon receiving the command for reverse direction.

Description

The present invention relates to a forward / reverse switching device that switches a rotation direction of a DC synchronous motor, and more particularly to a forward / reverse switching device that selectively switches forward and backward of an electric vehicle by switching the rotation direction of the DC synchronous motor.

In recent years, against the backdrop of global environmental protection, a departure from dependence on oil, and heightened awareness regarding energy efficiency, hybrid vehicles that use an engine and a motor together with electricity that drives a motor with electric energy accumulated in a storage battery or a fuel cell Cars are in the spotlight. In particular, the rapid development of small, high-output motors, storage batteries, and fuel cells has spurred their practical application. In particular, a motor for driving an electric vehicle is likely to be a DC synchronous motor having advantages such as energy efficiency, easy control, and relatively light weight. However, the DC synchronous motor detects the magnetic pole position of the rotor using a magnetic sensor such as a Hall element or an optical sensor, and passes the excitation current according to the magnetic pole position number detected in the field winding to generate the rotating magnetic field. Need to generate and rotate the rotor. For this reason, an electric vehicle using a DC synchronous motor as a drive source needs to be mechanically selected as in an internal combustion engine vehicle, or by switching the rotation direction of the motor.
In general, a rotating magnetic field can be obtained, for example, by using an alternating current out of phase as an exciting current. Therefore, a method of rotating the rotor forward or reverse by switching the phase sequence of the motor connected to the generator (Patent Document 1), the excitation current to each field winding based on the output signal of the Hall element A method of rotating the rotor forward or backward by controlling the supply timing is disclosed (Patent Document 2).

Japanese Patent No. 3337126 Japanese Patent No. 3906429

However, the method of mechanically selecting forward and backward by changing the gear of the transmission, such as an internal combustion engine car, increases the size and weight of the device, taking advantage of the DC synchronous motor that is lightweight and compact. I can't. In addition, the method of switching the phase sequence and the method of controlling the supply timing of the excitation current can be easily implemented by switching any two phases, for example, effective for an electric motor that excites with a three-phase alternating current. In addition to torque ripple, high output is difficult to obtain. In addition, the control is complicated in the case of multiphase, and is not suitable for driving and controlling a plurality of Hall elements with a single chopper signal or PWM signal.
In view of the above circumstances, the present invention is a forward / reverse switching device for driving a Hall element or the like with a single chopper signal or PWM signal to rotate a DC synchronous motor having a small torque ripple and a large torque in the forward or reverse direction. In particular, it is an object of the present invention to provide a forward / reverse switching device for moving an electric vehicle forward and backward by switching the direction of rotation of a DC synchronous motor.

In the forward / reverse switching device of the present invention, a plurality of field windings are arranged at equal intervals around a rotor in which N poles and S poles are alternately arranged with a certain interval. Excitation current supplied to each of a plurality of field winding sets formed by connecting the field windings in series or in parallel with each output signal output from each of a plurality of detection means for detecting the magnetic pole position. Is a forward / reverse switching device for switching the rotation of a motor to obtain a predetermined rotation speed between a forward direction and a reverse direction by forming a rotating magnetic field,
Select one of the first field winding set and the second field winding set to which the excitation current is supplied by the output signal output from one of the plurality of detection means. When receiving a selection means including a plurality of selectors and a command to switch the rotation in the forward direction, the selector performs an operation of selecting the first field winding set and reverses the rotation. And a selector switching means for performing an operation of selecting the second field winding set on the selector when receiving a command to switch the direction.
Thus, if the field winding group in which the excitation current is controlled is switched all at once via a plurality of selectors, the rotational direction of the DC synchronous motor having a small torque ripple and a large torque can be smoothly switched. .
Here, the selector has a first contact connected to the first field winding set and a second contact connected to the second field winding set. And
The selector switching means closes the first contact and opens the second contact when receiving a command to switch in the forward direction, and receives the command to switch in the reverse direction when receiving the command to switch in the reverse direction. It is preferable to open and close the second contact.
In this way, the rotation direction can be easily switched.
Each of the plurality of detecting means is installed in the vicinity of the field pole around which each field winding forming one field winding set of the field winding sets is wound. Thus, the first field winding set includes the first field winding or the second field winding in the positive direction with respect to the field pole where the one detecting means is installed in the vicinity. The second field winding set preferably includes one field winding or two field windings in the opposite direction from the field magnetic pole.
In this way, the rotation of the electric motor after the switching of the rotation direction is smooth.

  According to the forward / reverse rotation switching device of the present invention, the field winding is excited by a common chopper signal in response to an on / off signal command, and the rotation direction of the DC brushless motor with small torque ripple and large torque is switched smoothly. It can be rotated forward or backward.

FIG. 1 is a diagram illustrating an example of a DC synchronous motor to which the forward / reverse rotation switching device of the present embodiment is applied. FIG. 2 is a diagram showing a connection state of selection means constituting the forward / reverse rotation switching device. FIG. 3 is a diagram showing a relay that operates the selection means. FIG. 4 is a plan view showing a fixed portion of the rotary switch in which a large number of contacts connected to each exciting current control means are arranged concentrically. FIG. 5 is a view of the rotary part of the rotary switch in which a large number of contact points connected to the output terminals of the hall elements are arranged concentrically as viewed from the back side. FIG. 6 is a schematic diagram showing the magnetic pole position of the rotor and the magnetic state of the field magnetic pole when the forward / reverse switching device is operated in response to a forward direction command. FIG. 7 is a schematic diagram showing the magnetic pole position of the rotor and the magnetized state of the field magnetic pole when the forward / reverse switching device is operated upon receiving a reverse direction command.

Hereinafter, embodiments of the forward / reverse rotation switching device of the present invention will be described.
FIG. 1 is a diagram illustrating an example of a DC synchronous motor to which the forward / reverse rotation switching device of the present embodiment is applied.
A DC synchronous motor shown as an example in FIG. 1 includes a rotor 2 in which magnetic poles 1 are arranged, a stator in which field windings 3 are arranged, and a Hall element that detects the magnetic poles 1 of the rotor 2 (of the present invention). 4), forward / reverse switching device 10, excitation current control means 5 for controlling the excitation current that forms a rotating magnetic field in the stator by the output signal of Hall element 4, and chopper signal input terminal CIN And a DC power supply connection terminal DIN, and an inner rotor type in which the rotor 2 is disposed inside the stator.
In the rotor 2, two N poles and S poles of a permanent magnet are alternately arranged around the rotation axis with a certain gap (M).
The stator is provided with twelve field poles at slots symmetrically across the rotor 2 with a slot therebetween. The distance (L) between the central portions of the field poles arranged across the slot is constant, and L is set to be smaller than the gap (M) between the N pole and S pole of the rotor. ing. A field winding 3 is wound around each field pole, and two of the twelve field windings 3 are connected in parallel, and six sets of field windings are connected. A line set 5 is formed. Each of the six field winding groups 5 is supplied with an exciting current for forming a rotating magnetic field from the DC power supply connection terminal DIN.
Here, the field winding set 6 in the present embodiment is configured to be magnetized to the N pole or the S pole at the same time depending on the direction of the excitation current. It is not necessary to magnetize to the same polarity at the same time. Further, the field winding set 6 is formed by two opposed field windings. However, the field winding set 6 is not necessarily formed by the opposed field windings, and is formed by combining three or more. May be.
When the Hall element 4 detects the magnetic pole 1 of the rotor 2 in a state where the chopper signal is inputted from the input terminal to which the chopper signal is inputted and the chopper signal is inputted from the input terminal, the strength (including polarity) of the magnetic pole 1 and the chopper signal are detected. And an output terminal that outputs an output signal proportional to the magnitude of the N pole and S pole of the rotor 2 without being affected by the rotating magnetic field formed in the field winding 3 of the stator. It is installed in the vicinity of the field pole so that the position of can be detected.
Since the torque of the motor changes by changing the duty ratio of the chopper signal input to the hall element 4, the rotational speed can be accelerated or decelerated depending on the magnitude of the load.

When the polarity of the output signal at the output terminal of the Hall element 4 is positive, the exciting current control means 5 includes two switching elements 51a and 51b that change the energization time according to the duty ratio of the output signal, and the polarity of the output signal. When negative, it has two switching elements 52a and 52b that change energization time according to the duty ratio of the output signal. Each switching element 51a, 51b, 52a, 52b switches the direction of the excitation current supplied to the field winding set 6 according to the magnetic pole 1 of the rotor 2, while the energization time of the excitation current is changed according to the duty ratio. Change. A free wheel diode 53 that bypasses a surge voltage or the like is connected in parallel to each switching element 51a, 51b, 52a, 52b.
When a positive output signal is sent to the excitation current control means 5, the switching elements 51a and 51b are activated. When the rotor 2 rotates and the magnetic pole 1 of the magnet is reversed and a negative output signal is sent from the Hall element 4, the switching elements 52a and 52b are activated. As a result, the exciting current flows intermittently in the field winding set 6 for the energizing time corresponding to the duty ratio of the output signal, and torque is generated in the rotor 2. Further, during the non-energization time between the energization time and the energization time, since AC power is induced in the field winding set 6, other field windings are connected via the freewheel diodes 53 connected in parallel. This is used as the exciting current of the wire set 6.
Here, in the DC synchronous motor to which the present embodiment is applied, the gap (M) between the N pole and the S pole of the rotor 2 is set so that the center portions of the field poles of the stator arranged with the slots separated from each other. The excitation current is controlled by the output signal of the Hall element 4 and the magnetization pause time always occurs at the transition of the magnetic pole magnetized by the field winding set 6. For this reason, the same field winding 3 does not receive both the force for attracting the magnetic pole 1 of the rotor 2 and the repulsive force at the same time, and the torque can be obtained efficiently.

The forward / reverse switching device 10 has 6 switches 11a (corresponding to the selector of the present invention) 11a for switching the field winding group 6 whose excitation current is controlled by the excitation current control means 5 according to the output signal of the Hall element 4. Each of the selection means 11 and a relay 12 (corresponding to the selector switching means of the present invention) 12 that switches the selection means 11 all at once according to a command in the rotation direction are provided, details of which will be described later.
In this embodiment, the contact of the switch 11a is connected to the excitation current control means 5 for supplying the excitation current to the field winding one direction forward and backward than the field magnetic pole. You may connect to the excitation current control means 5 which supplies an excitation current to a magnetic winding. Moreover, although the forward / reverse switching device 10 of the present embodiment uses the relay 12 as the selector switching means, it may be a rotary multi-contact switch or another switching method.

2 and 3 are diagrams illustrating an example of the forward / reverse switching device according to the present embodiment, FIG. 2 is a diagram illustrating a connection state of the selection means configuring the forward / reverse switching device, and FIG. 3 is a selection diagram. It is a figure which shows the relay which operates a means.
In FIG. 2, one of the pair of input terminals of the Hall elements 4a to 4f, one of the pair of output terminals, and one of the two switches connected to the output terminal of the Hall element. These switches are omitted for convenience of explanation.
The selection means 11 shown in FIG. 2 includes six switches 11a to 11f. The switches 11a to 11f are provided with an input terminal IN and two contacts that are switched by the operation of the relay 12. The first contact is an excitation current control means 5a for supplying an excitation current to the field winding in the forward rotation direction with respect to the field magnetic pole arranged in the vicinity of the position where the hall elements 4a to 4f are installed. To 5f, and the second contact is connected to the excitation current control means 5a to 5f of the field winding one ahead in the reverse rotation direction. In addition, each of the excitation current control means 5 a to 5 f is connected to a common DC source 30.
Furthermore, the input terminals of the Hall elements 4 a to 4 f are connected to the common chopper signal generation means 20, and the output terminals are connected to the switches 11 a to 11 f of the selection means 11.
Here, the contacts of the switches 11a to 11f of the present embodiment are connected to excitation current control means 5a to 5f for supplying an excitation current to the field winding that is one ahead of the field pole in the forward and reverse rotation direction. However, it may be connected to the excitation current control means 5a to 5f for supplying the excitation current to the field winding of the second ahead. Moreover, although the forward / reverse switching device 10 of this embodiment uses a relay as the selector switching means, a rotary multi-contact switch may be used.

The DC synchronous motor of this embodiment has 12 field windings, and two field windings are connected in parallel to form six field winding sets. That is, among the first to twelfth field windings wound around the first to twelfth field magnetic poles sequentially arranged in the positive rotation direction, the first and seventh fields are wound. Magnetic windings, second and eighth field windings, third and ninth field windings, fourth and tenth field windings, fifth and eleventh The first field winding set 6a composed of the second and eighth field windings is connected in parallel with the sixth and twelfth field windings, An excitation current is supplied from the first excitation current control means 5a, and the second field winding set 6b composed of the third and ninth field windings is excited from the second excitation current control means 5b. A third field winding set 6c composed of the fourth and tenth field windings is supplied with an excitation current from the third excitation current control means 5c. The fourth field winding set 6d composed of the fifth and eleventh field windings is supplied with the excitation current from the fourth excitation current control means 5d, and the sixth and twelfth field windings. The fifth field winding set 6e made up of magnetic windings is supplied with exciting current from the fifth exciting current control means 5e, and the sixth field winding made up of the first and seventh field windings. The winding set 6f is supplied with an excitation current from the sixth excitation current control means 5f. Further, the output signal of the Hall element 4a arranged in the vicinity of the first field pole is connected to the first excitation current control means 5a or the fifth excitation current control means 5e by the contact of the switch 11a, and the second The output signal of the Hall element 4b arranged in the vicinity of the th field pole is connected to the second exciting current control means 5b or the sixth exciting current control means 5f by the contact of the switch 11b, and the third field pole. The output signal of the Hall element 4c arranged in the vicinity of is connected to the third exciting current control means 5c or the first exciting current control means 5a by the contact of the switch 11c, and is arranged in the vicinity of the fourth field pole. The output signal of the hall element 4d is connected to the fourth exciting current control means 5d or the second exciting current control means 5b by the contact of the switch 11d, and is arranged near the fifth field pole. The output signal of the hall element 4e is connected to the fifth excitation current control means 5b or the third excitation current control means 5c by the contact of the switch 11e, and is arranged in the vicinity of the sixth field pole. The output signal of 4f is connected to the sixth excitation current control means 5f or the fourth excitation current control means 5d through the contact of the switch 11f.

The relay 12 shown in FIG. 3 is connected to a resistor and a DC power source via a lever (command signal generating means) 13 that commands the rotation direction. When the lever 13 is tilted and the contact is closed, the relay 12 operates. When the lever 13 is raised and the contact is opened, the relay 12 returns. The relay 12 has at least twelve switches having contacts that close all at once when operated and open all at once when returned, and all contacts that close all when returned and open all at once when operated. And the contacts constitute the switches and contacts in the selection means 11 of FIG.

4 and 5 are diagrams showing a rotary switch having a large number of contacts on the circumference as another example of the forward / reverse switching device of the present embodiment, and FIG. 4 is connected to each excitation current control means. FIG. 5 is a plan view showing a fixed part of a rotary switch in which the contact points are arranged on concentric circles, and FIG. 5 is a rotating part of the rotary switch in which a large number of contact points connected to the output terminals of the hall elements are arranged on concentric circles. It is the figure which looked at from the back.
The rotary switch fixing portion 15 shown in FIG. 4 has a shaft 16 at the center, and six white circles and one black circle on each side of each white circle are arranged on two concentric circles around the shaft 16. The white circle is neutral, and the black circle is provided with 12 contacts corresponding to the contacts of the six switches 11a to 11f connected to the six exciting current control means 5a to 5f. These white circles and black circles are arranged on the same radiation in two concentric circles corresponding to the output terminals of the Hall elements 4a to 4f shown in FIG. Further, as explained in FIG. 2, the contacts connected to the first excitation current control means 5a or the fifth excitation current control means 5e, the second excitation current control means 5b or the sixth excitation current control means. The contacts connected to 5f, the contacts connected to the third excitation current control means 5c or the first excitation current control means 5a, the fourth excitation current control means 5d or the second excitation current control means 5b Connected to the contacts connected to each other, to the contacts connected to the fifth excitation current control means 5b or the third excitation current control means 5c, to the sixth excitation current control means 5f or the fourth excitation current control means 5d. The contacts are connected by lead wires.
The rotary part 18 of the rotary switch whose back surface is shown in FIG. 5 has a rotary shaft 19 fitted in the fixed part of the rotary switch at the center, and two concentric circles around the rotary axis 19 on the same radiation. There are 6 black circles. A black circle is a contact point connected to the output terminals of the Hall elements 4a to 4f. In the rotary switch of the present embodiment, the white circle of the fixed portion 15 and the black circle of the rotating portion 18 are in contact with each other and are in a neutral state. Then, the rotating shaft 19 of the rotating portion 18 is fitted to the shaft 19 of the fixed portion 15, the rotating portion 18 is rotated left and right, and the black circle of the rotating portion 18 is moved by one to the contact point (black circle) of the fixed portion 15. It is possible to command the rotation direction of the electric motor by making contact.

6 and 7 are schematic diagrams showing the magnetic pole position of the rotor and the magnetized state of the field magnetic poles when the rotation direction command is received and the forward / reverse switching device is operated, and FIG. 6 is a forward direction command. FIG. 7 shows a case where a reverse direction command is received.
6 and 7, the rotor and the field pole (field winding) are developed in a straight line for convenience. In the rotor, N-pole and S-pole magnets are alternately arranged, there is a gap having a width of M between them, and the distance between the center portions of the field poles is L (M> L). Then, the magnetization states of the field magnetic poles 7a to 7l when the rotor is rotated by 30 degrees in the forward direction (FIG. 6) or the reverse direction (FIG. 7) from left to right in FIG. N, lower side is S, center is neutral).
The stator has twelve field poles arranged at equal intervals across the slot, and a first field winding is wound around the first field pole 7a. A twelfth field winding is wound around 7l.
The Hall elements 4a to 4f are arranged in the vicinity of the central portions of the first to sixth field poles, and their output signals are wound around the field poles adjacent to each other in the forward and reverse directions. It is configured to be sent to excitation current control means for supplying an excitation current to the magnetic winding.
As described in FIG. 2, the first field winding set in which the field windings wound around the second field pole 7b and the eighth field pole 7h are connected in parallel is the first field winding set. The excitation current is supplied from the first excitation current control means 5a to which the output signal (forward direction) of the first Hall element 4a or the output signal (reverse direction) of the third Hall element 4c is input, and the third field pole The second field winding set in which the field windings wound around the 7c and the ninth field pole 7i are connected in parallel is the output signal (positive direction) of the second Hall element 4b or the second The excitation current is supplied from the second excitation current control means 5b to which the output signal (reverse direction) of the fourth Hall element 4d is input and wound around the fourth field pole 7d and the tenth field pole 7j. The third field winding set in which the field windings connected in parallel is the output of the third Hall element 4c. An excitation current is supplied from the third excitation current control means 5c to which a signal (forward direction) or an output signal (reverse direction) of the fifth Hall element 4e is input, and the fifth field pole 7c and the eleventh field are supplied. The fourth field winding set in which the field windings wound around each of the magnetic poles 7k are connected in parallel is the output signal (positive direction) of the fourth Hall element 4d or the output signal of the sixth Hall element. The exciting current is supplied from the fourth exciting current control means for inputting (reverse direction), and the field windings wound around the sixth field pole 7f and the twelfth field pole 7l are connected in parallel. The fifth field winding set is excited current from the fifth exciting current control means to which the fifth Hall element output signal (forward direction) or the third Hall element output signal (reverse direction) is input. Is wound around each of the first field pole 7a and the seventh field pole 7g. In the sixth field winding set in which the rotated field windings are connected in parallel, the output signal of the sixth Hall element (forward direction) or the output signal of the second Hall element (reverse direction) is input. Excitation current is supplied from the sixth excitation current control means, and each is magnetized to a polarity opposite to the magnetic pole of the rotor.

As shown in FIG. 6, when receiving a command in the normal rotation direction for moving the magnetic pole downward in the figure, when each magnetic pole of the rotor is in the “a” state, each field magnetic pole is in the magnetized state shown in A. As a result, the rotor has a first field pole 7a,
Since the fourth field magnetic pole 7d, the seventh field magnetic pole 7g, and the tenth field magnetic pole 7j receive the attractive force in the positive direction, they start to rotate in the positive rotation direction. When the rotor rotates 30 degrees and is in the “a” state, each field pole is in the magnetization state shown in B. Therefore, the second field pole 7b, the fifth field pole 7e, the eighth field pole 7h, and the eleventh field pole 7k receive a positive attracting force to obtain a torque in the positive rotation direction. Hereinafter, even when the magnetic poles of the rotor are in the state of u, the attraction force in the positive direction is received from the third field magnetic pole 7c, the sixth field magnetic pole 7f, the ninth field magnetic pole 7i, and the twelfth field magnetic pole 7l. Obtain torque in the forward rotation direction. Further, even when the magnetic pole is in the state of D, F, or F, the rotation continues in the same manner by obtaining the torque in the forward rotation direction.

As shown in FIG. 7, when receiving a command in the reverse rotation direction for moving the magnetic pole upward in the figure, when each magnetic pole of the rotor is in the state of “A”, each field magnetic pole is in the magnetized state shown in “A”. As a result, the rotor receives an attractive force in the reverse direction from the first field magnetic pole 7a, the fourth field magnetic pole 7d, the seventh field magnetic pole 7g, and the tenth field magnetic pole 7j, and thus starts to rotate in the reverse rotation direction. . When the rotor rotates 30 degrees and is in the “a” state, each field pole is in the magnetization state shown in B. Therefore, a reverse attractive force is received from the third field magnetic pole 7c, the sixth field magnetic pole 7f, the ninth field magnetic pole 7i, and the twelfth field magnetic pole 7l to obtain a torque in the reverse rotation direction. Hereinafter, even when each magnetic pole of the rotor is in the state of U, the second field magnetic pole 7b, the fifth field magnetic pole 7e, the eighth field magnetic pole 7h, and the eleventh field magnetic pole 7k receive an attractive force in the reverse direction, Obtain torque in the reverse direction. Further, even when the magnetic poles are in the state of D, F, and F, the rotation continues in the same manner by obtaining torque in the reverse rotation direction.
Here, the magnetization state of each field pole has been described based on a DC synchronous motor in which the number of magnetic poles P of the rotor is 4, the number of field poles Q of the stator is 12, and the number of Hall elements H is 6, but the number of magnetic poles of the rotor Each of P, the number of field poles Q of the stator, and the number of Hall elements H need not necessarily be a combination of 4, 12, 6; Or a combination of 4, 24 and 6. Further, the number P of magnetic poles of the rotor is not necessarily four, and may be a multiple of two. That is, P, Q, H, M, and L are set so as to satisfy the following three conditions, and field windings are connected in series or in parallel by Q / H to form a field winding set. It is preferable to supply an exciting current for each field winding set, thereby making it possible to obtain a large rotational torque efficiently.
[3 conditions]
Condition 1; H is equal to or greater than Q / P.
Condition 2: M is equal to or greater than L, where M is the gap between the N and S poles, and L is the distance between the central portions of the field poles arranged across the slot. .
Condition 3: Q and H are selected so that Q / H is an integer.

INDUSTRIAL APPLICABILITY The present invention can be used for a lever or the like that determines forward and backward movement of an electric vehicle that uses a DC synchronous motor as a drive source.

DESCRIPTION OF SYMBOLS 1 Magnetic pole 2 Rotor 3 Field winding 4, 4a-4f Hall element 5, 5a-5f Excitation current control means 6, 6a-6f Field winding group 7a-7l Field magnetic pole 10 Forward / reverse switching device 11 Selection means 11a to 11f Switch 12 Relay 13 Lever 15 Fixed portion 16 Shaft 18 Rotating portion 19 Rotating shaft 20 Chopper signal generating means 30 DC power supply 51a, 51b, 52a, 52b Switching element 53 Free wheel diode

Claims (3)

A plurality of field windings are arranged at equal intervals around a rotor in which N poles and S poles are alternately arranged at regular intervals, and each of a plurality of detection means for detecting the magnetic pole position of the rotor By controlling the excitation current supplied to each of a plurality of field winding sets formed by connecting the field windings in series or in parallel with each output signal output from, a rotating magnetic field is formed, A forward / reverse switching device for switching the rotation of an electric motor to obtain a predetermined rotational speed between a forward direction and a reverse direction,
Select one of the first field winding set and the second field winding set to which the excitation current is supplied by the output signal output from one of the plurality of detection means. Selecting means comprising a plurality of selectors to be
When receiving a command to switch the rotation in the forward direction, the selector performs an operation of selecting the first field winding group, and when receiving a command to switch the rotation in the reverse direction, the selector And a selector switching means for performing an operation of selecting the second field winding set. The selector has a first contact connected to the first field winding set and a second contact connected to the second field winding set,
The selector switching means closes the first contact and opens the second contact when receiving a command to switch in the forward direction, and receives the command to switch in the reverse direction when receiving the command to switch in the reverse direction. 3. The forward / reverse switching device according to claim 1, wherein the second contact is closed by opening the second contact. Each of the plurality of detection means is installed in the vicinity of the field pole around which each of the field windings forming one field winding set of the field winding sets is wound,
The first field winding set includes one field winding in the positive direction or two field windings in the positive direction from the field magnetic pole in which the one detecting means is installed in the vicinity, 2. The forward rotation according to claim 1, wherein the second field winding set includes one field winding or two field windings in the reverse direction from the field magnetic pole. Reverse switching device.