GB2104733A - D.C. rotary field motor - Google Patents

Abstract

A D.C. rotary field motor is characterized by having a current commutating device (3, 5, 6) coupled with the motor shaft (4) so that the external D.C. power source is supplied to the stator windings (2) thereof through the commutating device (3, 5, 6) and, especially, when the motor shaft (4) rotates, a rotary field is developed therein by the stator (1), effecting a mutual action between the rotary field of the stator (1) and the field of the rotor poles (7); therefore, a driving torque is produced accordingly. Operation of a three phase four pole motor is described w.r.t. Figs 2-4 (not shown). <IMAGE>

Description

SPECIFICATION D. C. Rotary field motor This invention relates to a D.C. motor, particularly to a specially designed motor configuration, thereby, when an external D.C.

power source is supplied to the stator through the special configuration, a rotary field will be generated therein so as to effect a mutual action with the rotor field for producing a driving torque thereof.

In the known D.C. motor, the rotor is the armature while the stator is the magnetic field. In harnessing the commutating segments thereof and the brushes installed on the segments, the external D.C. power source is usually supplied to the rotor windings of the motor. As the brush position is adjustable in the motor, no matter whether the rotor rotates or not, a fixed torque angle can be kept between the magnetic axis established by the winding current of the rotor and the magnetic axis of the stator field so as to produce a driving torque therein. The main disadvantage of this D.C. motor is that the commutator comprises a multiplicity of segment made of brass sheet, and between each of the brass sheets, a mica sheet is sandwiched therein, and the commutator is formed in a cylinder shape.

So far as the structure of the known D.C. motor is concerned, the material and manpower costs are rather high, and, above all, after a period of operation, a wornout condition of the brass sheets will appear on the surface of the commutator. As soon as the wornout of the brass sheets is below the level of the mica sheets placed therein, the operation of the motor will be ineffective. As a result, the mica sheets have to be trimmed again and also the commutator needs to be re-shaped so as to keep its circumferential surface in good round condition. Therefore, maintenance and repair of the known D.C. motor are always a problem.

On the other hand, in the known synchronous motor, the magnetic field is similar to that of the D.C. motor in using D.C. excitation. But, what is contrary to the D.C. motor is that the magnetic field is the rotor while the armature is the stator.

As the armature consists of multiphase windings, when the external power source of multiphase is supplied to the armature, a rotary field will be produced therein. Because of a traction existing between the poles of the rotary field and the poles of the rotor, the rotor is thereby made firmly stay at certain position (with respect to the rotary field).

But, when the rotor rotates along with the synchronous speed of the motor, it will be in exact synchronism with the rotary field. in this connection, only when the rotor, the stator and the rotary field are all at the same speed and in the same direction, can the stator and the rotor generate a unilateral force. At this time, there is no relative movement existing between the magnetic axises, and, therefore, a certain stationary torque angle is available therein for producing the driving torque. The major defect of the known synchronous motor is that the polarity of the rotor is stationary while the polarity of the stator varies alternatively in accordance with the revolution direction.Moreover, during starting, if the rotor closes to an attraction, it will be inclined to move toward the direction of the attraction, but, for an instant, a repulsion will appear and make the rotor be inclined to move toward another direction. This net efficiency of attraction and repulsion will keep the motor motionless therein. Therefore, in the initial stage of supplying power source, there is no torque produced therein, and the motor cannot be automatically started thereat. As a result, a starting device or a starting system has to be designed for facilitating the starting operation.

Besides, as the sync speed of the motor is controlled by the frequency of the supplied A.C.

power source, the operation of the known synchronous motor is a fixed tape.

The present invention provides a D.C. rotary field motor by which not only the advantages of the known D.C. motor and synchronous motor are maintained but also the disadvantages described above are completely eliminated.

The main characteristic of this invention is to provide a D.C. motor with a special current commutating device through which the external D.C. power source is supplied to the stator windings for developing a rotary field therein and effecting a mutual action between the rotary field and the magnetic field of the rotor poles so as to produce a driving torque for driving the load thereof.

Another characteristic of this invention is that the special current commutating device of-this D.C. motor comprises a commutating slip ring disposed at the same axis as that of the motor shaft, and a plurality of fixed brush being kept in contact with the annular tangent plane of the commutating slip ring.

Still another characteristic of this invention is that in this D.C. motor the commutating slip ring is disposed along its surface a plurality of slip-ring segment, of which the width and the angle are selected on the basis of the poles, the number of the phase, and the phase-sequence angle required for the D.C. motor.

Still another characteristic of this invention is that the configuration of the width and the angle of the fixed brushes is decided on the basis of the width and the angle of the slip-ring segments in order that only two pieces of the brushes are kept in contact with the slip-ring segments at any time.

Still another characteristic of this invention is that the positive input and the negative output of the rotor in the D.C. motor are respectively connected to the fixed brushes.

It is to be noted that in the D.C. motor of this invention, no matter what angle the rotor stays at, a torque angle is always kept between the poles of the rotor and the magnetic axis of the rotary field of the stator so that, upon the initial supply of external D.C. power source, the motor will be immediately started, and, whenever the external D.C. power source is supplied, the input is only fed into a certain single-phase winding without overlapping power supply therein. Moreover, a capacitor or a rectifying means can be disposed with respect to the stator windings so as to prevent them from generating sparks during the commutating operation of the current thereof.

It is further to be noted that in the D.C. motor of this invention the rotary field of the stator is synchronous with the rotor. When the external load is increased, the revolution speed of the motor will be reduced and, henceforth, the speed of the rotary field will become slow but the torque thereof remains unchanged. In the meantime, because of the speed reduction, the counter electromotive force (CEMF) of the stator will be decreased while the current supply thereof increased, thereby, the strength of the rotary field is enhanced and the revolution speed of the motor will be resumed accordingly.

Other characteristics and advantages of this invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention, in which: Figure 1 is a schematic illustration of a preferred configuration of the element in the three-phase and four-pole D.C. motor according to this invention, Figures 2,3, and 4 are respectively an operational illustration of the D.C. motor shown in Fig. 1, and Figure 5 is an operational illustration showing the variation of a stator pole and the winding thereof in one phase during a complete revolution (3600) of the motor shaft according to this invention.

Referring to Fig. 1, a shunt-exciting D.C. motor of three-phase and four-pole according to this invention comprises two major portions - a stationary portion (S) and a rotary portion (R) wherein the stationary (S) includes a stator 1, a three-phase winding 2 coupled with the stator 1, and a plurality of fixed brush 3; while, the rotary (R) includes a motor shaft 4, a power source slip ring 5, a commutating slip ring 6 and a plurality of rotor pole 7.

The stator 1 having a three-phase winding 2 wound thereon is the same as that of the known synchronous motor. Each of the windings 21, 22 and 23 is placed 1200 with one another and arranged in four poles: poles 211, 212, 213, and 214 are arranged for the first phase, poles 221, 222, 223 and 224 for the second phase, and poles 231,232,233 and 234 for the third phase.

The winding input of each phase is respectively connected to the fixed brushes 3, forming a delta connection thereof.

The fixed brush 3 includes three separate brushes 31, 32 and 33, of which the tail end is respectively coupled with the motor housing while the front end is each placed on the tangent plane of the commutating slip ring 6. The width of each brush is preferably 1/24 of the circumferential length of the commutating slip ring, and each brush is disposed thereat in 1 200 with one another.

The input terminal of the 1 st-phase winding 21 is connected to the brush 33 and the output terminal to the brush 32; the input terminal of the 2nd-phase winding 22 is connected to the brush 33 and the output terminal to the brush 31; and the input terminal of the 3rd-phase winding 23 is connected to the brush 32 and the output to the brush 31.

The rotor 7 is constructed in the form of four salient poles, of which poles 71 and 73 are N poles while poles 72 and 74 are S poles, and works on shunt excitation. It is also operable that the rotor 7 is made of permanent magnet.

The commutating slip ring 6 is in an annular form and installed around the front part of the motor shaft 4 along the same axis thereof.

Disposed on the circumferential surface of the slip ring 6 are four pieces of slip-ring segment 61, 62, 63 and 64, of which two segments 61 and 63 are connected to the positive of the power source and another two segments 62 and 64 to the negative of the power source. The width of the slip-ring segments is preferably 1/8 of the circumferential line of the commutating slip ring 6, and each segment is placed in 450 with one another.

The power-source slip ring 5 having a positive slip ring for input and a negative slip ring for output is used for the input and output of the external power source.

Referring to Fig's 2, 3, and 4 for an operational illustration of the preferred embodiment of this invention wherein Fig. 2 shows the initial pole variation of the 1 st-phase stator winding. When the motor is not started, the slip-ring segment 63 of the commutating slip ring 6 (as shown in Fig. 1) is in contact with the brush 33 and the slip-ring segment 64 in contact with the brush 32. When external power source is supplied thereto, the windings 211 and 213 of the stator winding 21 in the 1 sot phase will produce an N-pole magnetic field while windings 212 and 214 an S-pole magnetic field as shown in Fig. 2. The magnetic axis between the stator and the rotor has a 300 torque angle thereat so that a starting torque is established, and, therefore, the motor begins to rotate.However, when the shaft rotates over 300, the slip-ring segment 64 separates from the brush 32 but the slip-ring segment 62 begins to contact the brush 31. At this time, the external D.C. power source is cut off from the stator winding 21 of the 1 st phase and supplied to the stator winding 22 of the 2nd phase, making the windings 221 and 223 produce an N pole and the windings 222 and 224 an S pole as shown in Fig.

3. Following this action, the magnetic filed of the stator has also rotated 300. Meanwhile, when the shaft 4 revolves in another 300, the slip-ring segment 63 is separated from the brush 33, and the slip-ring segment 61 begins to contact the brush 32. At this time, the external D.C. power source is cut off from the stator winding 22 of the 2nd phase and supplied to the stator winding 23 of the 3rd phase, making the windings 231 and 233 produce an N Pole and the windings 232 and 234 an S pole as shown in Fig. 4; therefore, the magnetic field of the stator also rotates another 30".

Referring to Fig. 5, when the shaft 4 rotates in a complete cycle, the poles of all the stator windings change in two cycles developing a rotary field therein. In this way of variation around, the rotary field of the stator always rotates in synchronism with the rotation of the shaft 4 so as to effect a mutual action between the rotary field of the stator poles and the magnetic field of the rotor poles in producing the driving torque required for driving the external load thereof.

In view of the aforesaid, this invention has provided a novel and unique configuration for a D.C. rotary field motor with simple structure and lower manufacturing cost. It should be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of this invention as defined in the appended claims.

Claims (6)

1. A D.C. rotary field motor characterized by having the motor shaft be disposed with a current commutating device, through which the external D.C. power source is supplied to the stator windings for developing a rotary field therein during the rotation of the motor shaft, thereby, in harnessing the mutual action between said rotary field of the stator poles and the field of the rotor poles, a driving torque is produced accordingly.

2. A D.C. rotary field motor as claimed in Claim 1 wherein said current commutating device comprises a commutating slip ring disposed at the same axis as that of the motor shaft, and a plurality of fixed brush being kept in contact with the crcumferential tangent plane of said commutating slip ring.

3. A D.C. rotary field motor as claimed in Claim 2 wherein said commutating slip ring is in an annular form being disposed with a plurality of slip-ring segment, of which the configuration of the width and the angle is decided on the basis of the poles, the numbers of the phase, and the phase-segment angle required for the D.C. rotary field motor.

4. A D.C. rotary field motor as claimed in Claim 2 wherein the width and the angle of said fixed brushes are decided on the basis of the width and the angle of said slip-ring segments arranged thereof.

5. A D.C. rotary field motor as claimed in Claim 1 wherein the input and output terminals of said stator windings are respectively connected to said fixed brushes in accordance with the special requirement of the D.C. rotary field motor.

6. A D.C. rotary field motor substantially as described in the specification with reference to and as illustrated by the accompanying drawings.