Dynamoelectric DC machine

Abstract: A DC dynamoelectric machine with interpoles (3) between field poles (2) operable in sparkless even under heavy oper­ ating conditions comprising magnetic flux bypassing members (10A, 10B) made of a solid soft iron, each bypassing member disposed between respective field poles (2) and interpoles (3) at their ends near the armature (6) with an air gap to the field pole (2) for controlling the interpole magnetic flux. The solid soft iron magnetic flux bypassing member (10A, 10B) suppresses sudden change of magnetic flux flowing therethrough by permitting flow of eddy current therethrough and maintains the interpole magnetic flux at a desired amount even during a sudden change of load current.

Description: The present invention relates to a DC dynamoelectric machine operable in sparkless even under heavy operating conditions, in particular, relates to a DC motor suitable for driving a rolling mill, such as a cold rolling mill, which is required four quadrant operations such as a wide range of rotating speed, frequent acceleration, deceleration and normal and reverse rotation, and repetitive heavy load for producing a rolled sheet having a desired thickness from a thick rolling stuff. It is well known that a sparkless operating region or band of a DC dynamoelectric machine incorporating interpoles therein shifts toward an excitation reducing side in accordance with its rotating speed. JP-A-62-71463 (1987) discloses a DC dynamoelectric machine incorporating interpoles therein and having measures in itself for suppressing the shift of the sparkless operating region, in that, an adjusting magnetic member is disposed between the respective main poles and interpoles, optionally through air gap therebetween, so as to control leakage of interpole magnetic flux in such a manner that the leakage is restricted during a low speed operation and is increased during a high speed operation. However such DC dynamoelectric machine is found out to be insufficient to suppress the shift of the sparkless operation region and to maintain the sparkless operation during transient operations, i.e., a sudden change of load current during and during over load operations up to 200 % of rated load current which are frequently encountered during the drive of the cold rolling mill. A DC dynamoelectric machine comprising the features set out in the preamble of claim 1 is disclosed in US-A-2 482 526. One object of the present invention is to provide a DC dynamoelectric machine incorporating interpoles therein which suppresses the shift of the sparkless operation region and maintains the sparkless operation even in the transient and over load operations. Another object of the present invention is to provide a DC dynamoelectric machine incorporating interpoles therein which maintains a linear relationship between its load current and interpole magnetic flux even under heavy four quadrant operating conditions such that sparkless operation thereof is achieved. These objects are met by the invention as set out in the characterising part of claim 1. The DC dynamoelectric machine of the present invention incorporating interpoles disposed between main poles or field poles comprises magnetic flux bypassing members, each disposed between the field pole and the interpole at their ends near its armature and made of magnetic material which permits eddy current flow therein and changes its magnetic reluctance during magnetic flux variation therein, in that, the transient operation period, to suppress a sudden change of leakage magnetic flux flowing through the magnetic flux bypassing member and further the magnetic flux bypassing member being supported by the interpole and magnetically coupled to the field pole through an air gap of between 2 mm and 15 mm for adjusting the magnetic reluctance of the magnetic flux bypassing member as a whole to control leakage of magnetic flux therethrough, such that the magnetic flux bypassing member disposed between the field pole and the interpole of the same polarity bypasses a part of magnetic flux induced by the field pole into the interpole to increase an interpole magnetic flux for generating a desired commutation electromotive force when the DC dynamoelectric machine is operating under a predetermined load current with a full excitation, and bypasses a part of magnetic flux induced by the interpole into the field pole to decrease an interpole magnetic flux for generating a desired commutation electromotive force when the DC dynamoelectric machine is operating under a predetermined load current with a reduced excitation. Without such magnetic flux bypassing member of magnetic material, the interpole magnetic flux during sudden increase of load current unduly leaks through the magnetic flux bypassing member partly because of a sudden increase of the counter magnetomotive force caused by an armature reaction which is the maximum under the interpole so that an interpole magnetic flux necessary for the desired commutation is unobtainable, on the other hand, the interpole magnetic flux during a sudden decrease of the load current insufficiently leaks through the magnetic flux bypassing member partly because of a sudden decrease of the counter magnetomotive force caused by the armature reaction which is the maximum under the interpole so that an interpole magnetic flux necessary for the desired commutation is exceeded. In other words, a linear relationship between the load current, which flows through the armature and the interpole winding, and the interpole magnetic flux is lost during the transient operation. Moreover without such a proper length of the air gap in the magnetic flux bypassing circuit between the field pole and the interpole, the linear relationship between the load current and the interpole magnetic flux is also lost during the overload current operations. Brief Description of the Drawings Fig. 1 is a schematic partly sectional view of one embodiment according to the present invention. Fig. 2 is a developed partial view of Fig. 1 and illustrates flows of magnetic flux therein during a full excitation operation. Fig. 3 is the same developed partial view of Fig. 2 and illustrates flows of magnetic flux therein during a reduced excitation operation. Description of the Preferred Embodiment The one embodiment of the DC dynamoelectric machine according to the present invention shown in Fig. 1 includes eight main poles or field poles 2 which are fastened to the inside of an annular yoke 1. Between the respective field poles 2, there are provided interpoles 3 which also fastened to the inside of the annular yoke 1. Within the stator of the DC dynamoelectric machine including the field poles 2, the interpoles 3 and the yoke 1, an armature 6 is rotatably disposed. Each field pole 2 is formed from a field pole piece 4 fastened to the yoke 1 and a field winding 5 surrounding the field pole piece 4 and plays a role to supply a main magnetic flux to armature windings 7 of the armature 6. Each interpole 3 is fromed from an interpole piece 8 fastened to the yoke 1 and an interpole winding 9 surrounding the interpole piece 8 and plays a role to supply an interpole magnetic flux for inducing a commutation electromotive force during commutation when the current flowing through the armature winding 7 reverses. Bypassing cores 10 A formed of a solid soft iron, each is disposed between the field pole piece 4 and the interpole piece 8 of the same polarity at their ends near the armature 6 and is supported by the interpole piece 8 with an air gap of 2 mm - 15 mm between the pole tip 4 A of the field pole piece 4. Bypassing cores 10 B also formed of a solid soft iron, each is disposed between the field pole piece 4 and the interpole piece 8 of the different polarity at their ends near the armature 6 and is supported by the interpole piece 8 with an air gap of 2 mm - 15 mm between the pole tip 4 A of the field pole piece 4. The armature 6 including the armature winding 7 and a commutator 20 are carried by a rotatable shaft 22. Brush assembly 21 slidablly contacts to the commutator 20 and is carried by the stator (not shown). In Fig. 1, "N" and "n" stand for north pole and "S" and "s" stand for south pole; the arrow indicates the direction of rotation of the rotor; the dots on the conductors indicate currents toward readers and the crosses on the conductors indicate currents away from readers; and the signs of plus and minus on the brush assembly indicate polarity of the brushes. Figs. 2 and 3 illustrate flows of magnetic flux induced by the field poles 2 and the interpoles 3 in the magnetic circuits formed within the DC dynamoelectric machine respectively during a low speed operation with a full excitation and during a high speed operation with a reduced excitation. In Fig. 2, since the field poles 2 are in a full excitation, and the magnetomotive force AT f caused by the field poles 2 is set more than that AT IP caused by the interpoles 3 upto over load current regions, the magnetic fluxes  MP1 and  MP2 induced thereby flow respectively, through the field pole 2 of "S" polarity, yoke 1, the field pole 2 of "N" polarity, an air gap between the field pole 2 of "N" polarity and the armature 6, the armature 6, an air gap between the armature 6 and the field pole 2 of "S" polarity and to the same field pole 2 of "S" polarity, and through the field pole 2 of "S" polarity, yoke 1, the field pole 2 of "N" polarity, the pole tip 4 A, an air gap l g1 , the solid soft iron core 10 A, the interpole 3 of "n" polarity, an air gap between the interpole 3 of "n" polarity and the armature 6, the armature 6, an air gap between the armature 6 and the field pole 2 of "S" polarity and to the same field pole 2 of "S" polarity. The magnetic fluxes  IP1 and  IP2 induced by the interpole 3 flow respectively, through the field pole 2 of "S" polarity, the yoke 1, the interpole 3 of "n" polarity, the solid soft iron core 10 B, an air gap l g1 , the pole tip 4 A and to the same field pole 2 of "S" polarity, and through the field pole 2 of "S" polarity, the yoke 1, the interpole 3 of "n" polarity, an air gap between the interpole 3 of "n" polarity and the armature 6, the armature 6, an air gap between the armature 6 and the field pole 2 of "S" polarity, and to the same field pole 2 of "S" polarity. Since the DC dynamoelectric machine is in a full excitation, the field pole pieces 4 are substantially saturated, and the leakage interpole magnetic flux  IP1 is limited, and further the leakage field pole magnetic flux  MP2 supplements the interpole magnetic flux  IP2 . As a result, a sufficient commutation compensating magnetic flux  IA , the sum of  IP1 and  MP2 , and which induces the commutation electromotive force, is obtained enough to suppress the shift of the sparkless operation region and to maintain the sparkless operation. During the transient operation of the DC dynamoelectric machine, in that, sudden increase and decrease of its load current, the sudden change of leakage magnetic fluxes  MP2 and  IP1 is suppress respectively by the solid soft iron cores 10 A and 10 B in which eddy current flows to suppress the change such that a necessary commutation compensating magnetic flux  IA is maintained. Different from the condition as explained with reference to Fig. 2, in Fig. 3, since the field poles 2 are in a reduced excitation and the magnetomotive force AT f caused by the field poles 2 is set to be less than that AT IP caused by the interpoles 3, a part of the interpole magnetic flux  IP3 leaks through the solid soft iron core 10 A and the air gap l g1 to the pole tip 4 A of the field pole 2 of "N" polarity, instead of receiving the leakage magnetic flux  MP2 as explained in connection with Fig. 2, further since the DC dynamoelectric machine is in a reduced excitation, the field pole pieces 4 are not saturated so that the leakage interpole magnetic flux  IP1 is increased in comparison with that in Fig. 2, as a result, the commutation compensating magnetic flux  IA , the same as  IP2 is limited enough to suppress the shift of the sparkless operation region and to maintain the sparkless operation, in other words, to keep the linear relationship between the load current and the interpole magnetic flux which contributes to generate the commutation electromotive force, that is, the commutation compensating magnetic flux  IA . During the transient operation of the DC dynamoelectric machine, in that, sudden increase and decrease of its load current, the sudden change of leakage magnetic fluxes  IP3 and  IP1 is suppressed respectively by the solid soft iron cores 10 A and 10 B such that the commutation compensating magnetic flux is controlled to a desired amount. In the above embodiment, although the solid soft iron core is used for the element in the magnetic flux bypassing member, any magnetic materials which permit eddy current flow are used therefor. Further, in the above embodiment although the air gap is included in the magnetic flux bypassing circuit, any other non-magnetic elements having a high magnetic reluctance such as stainless steel and electric insulating material are replaceable therefor.

Claims: A DC dynamoelectric machine comprising a stator including an annular yoke (1), a plurality of field poles (2), each fastened to the inside of said annular yoke (1) and having a field pole piece (4) and field winding (5) surrounding said field pole piece (4), and a plurality of interpoles (3), each disposed between said field poles (2), fastened to the inside of said annular yoke (1) and having an interpole piece (8) and an interpole winding (9) surrounding said interpole piece (8); an armature (6) and commutator (20) rotatably disposed within said stator; a brush assembly (21) supported through said stator and slidably contacting said commutator (20); and a plurality of magnetic flux bypassing members (10A, 10B) made of magnetic material each disposed between said field pole piece (4) and said interpole piece (8) at their ends near said armature (6), which bypasses magnetic flux; characterized in that each magnetic flux bypassing member (10A, 10B) is made of electric current conductive material for permitting an eddy current flow generated by leakage magnetic flux flowing through said plurality of magnetic flux bypassing members. The DC dynamoelectric machine according to claim 1, wherein said magnetic flux bypassing member (10A, 10B) is supported by said interpole piece (8) and magnetically coupled to said field pole piece (4) through an air gap having a predetermined length. The DC dynamoelectric machine according to claim 2, wherein the length of said air gap between said magnetic flux bypassing member (10A, 10B) and said field pole piece (4) is between 2 mm and 15 mm. The DC dynamoelectric machine according to any one of claims 1 to 3, wherein each of said magnetic flux bypassing members (10A,10B) solid soft iron core. The DC dynamoelectric machine according to any one of claims 1 to 4, wherein said magnetic flux bypassing member (10A, 10B) disposed between said field pole piece (4) and said interpole piece (8) of the same polarity bypasses a part of magnetic flux induced by said field pole (2) into said interpole (3) during a full excitation under a predetermined load current to increase an interpole magnetic flux and bypasses a part of magnetic flux induced by said interpole (3) into said field pole (2) during a reduced excitation under a predetermined load current to decrease an interpole magnetic flux.

Inventors: KOHARAGI HARUO, NITOBE MITSUHIRO, SUZUKI NOBUTAKA, TAHARA KAZUO, KOHARAGI, HARUO, NITOBE, MITSUHIRO, SUZUKI, NOBUTAKA, TAHARA, KAZUO
Applicants: HITACHI LTD, HITACHI SETSUBI ENG KK, HITACHI SETSUBI ENGINEERING CO., LTD., HITACHI, LTD.
Application year: 1989
Main classification: H02K23
IPC codes: H02K23