GB2228628A - Securing segments of a commutator for electrical machines, particularly for electric traction motor of locomotives - Google Patents

Description

v COMM.UTATOR ARRANGEMENT FOR ELECTRICAL MACHINES, PARTICULARLY FOR

ELECTRIC TRACTION MOTOR OF LOCOMOTIVES, ESPECIALLY IN NARROW-GAUGE LOCOMOTIVES The invention relates to a commutator arrangement for electrical machines, preferably used for electric traction motor of locomotives, particularly in narrowgauge locomotives.

The simplest and thus the most reliable electrical machine is the asynchronous motor. However, due to its rigid speed characteristics, it cannot be used in certain part.of the drives. Variable speed can be produced simply by d.c. machine, the characteristic part of which is the commutator built together with the armature of the machine. The commutator is an integral part of the machine affecting the main dimensions, and even the power output of the machine. However, the commutator considerably restricts the power output of the d.c. machine, as it can be improved only in proportion with the diameter of the armature. Thus, the attainable output is structurally limited, and this limit is decisively influenced by construction of the commutator.

The commutator structure of the electrical machines 1 2.

f contains segments fixed in most cases with dovetail clamping to the shaft of the machine. The dovetails have partly tapered surface joined similarly by tapered ring clamps. The ring clamps are axially tightened and the trasmitted axial force pulls the segments towards the shaft. The segments are pressed together in the form of an arch, forming a solid segment crown. The prestressing should be as much as to prevent the centrifugal force from loosening the arch. The realization of adequate prestressing i smade difficult by insulating the commutator segments from each other and from the ring clamps. The insulator causes inhomogeneity resulting in loosenings endangering the safe operation of the commutator. On the other hand, the unavoidable thermal expansion results in difficulty. This involves again unavoidable heating of the commutator during operation, and since the segments are made of copper, they get easily stuck due to the high coefficient of thermal expansion. As a result of sticking, the insulator - mostly micanite - gets damaged, thereby the commutator segments become loose in the course of cooling.

Loosening of the commutator segments can be prevented in two ways. According to the first method, the ring clamps are leastically pressed together with long, thin bolt. The better is the commutator fastened with bolt, the longer and thinner are the bolts. However, the bolts must not be longer than the structural length of the commutator, o-.--,herwise the X structural length of the machine would be extended. On the other hand, the bolts shall not be arbitrarily thin, because their cross section has to withstand the centrifugal force. For these reasons, the elasticity produced by the bolts is not satisfactory, because it is harder than desirable.

Such commutator is described in the patent specification US 2,495,194, where the length of the traction motor can be shortened, elasticity of the commutator improved, furthermore its assembly requires no hydraulic pressing machine. In this solution long bolts are used passing through the whole rotor including the commutator. The elasticity is provided by the longitudinal elasticity of the through-bolts. Its demand for labour and material is relatively high. Precise bores are required for the through-bolts in the rotor and its lamellae. In the manufacturing process, the laminated body of the rotor is aged together with the commutator, which requires special tools and complicated work performance. For maintenance and repair of the commutator, the whole machine has to be disassembled. The throughbolts are uniformly tightened with torque spanner, but trueness to shape of the commutator and its lasting functionality would require the measuring and adjustment of the force compressing the segment crown, and adaptable balancing of the forces.

The other possibility for tightening the dovetailed segments is to firmly fix one of the ring clamps to 4.

to the shaft of the machine (or it is machined from it), whereas the other ring clamp is slidably fitted to the shaft, and axially tightened with tilting ring. In case of large diameters, the tilting rings realize softer springs than the bolts, and such commutators are capable to endure greater thermal expansions. The drawback of this solution is that tightening of the tilting ring in the assembled machine is difficult, consequently subsequent repairs of the commutator is complicated. Further shortcoming is that the cones of the clamping are sensitive to the uniaxial faults, therefore, strict tolerances have to be kept in the course of production. Further shortcoming of the tilting ring type solution is the relatively large axial space demand, which especially under the difficult railway operating conditions, and limitation of the rolling stock clearance gauge restricts the output of the electric motor.

The invention is aimed at the elimination of above shortcomings, and the primary problem to be solved is the realization of such axial forceproducing arralt-for the st crun of the camutator, for le of a railway electric traction motor. where the space demand (axial dimension) of the commutator is smaller than that of the traditional one, for permitting the realization of traction motor with power output specified particularly for narrow-gauge.

- Furthermore, the invention is aimed at the re- 5.

alization of a clamping arrangement more elastic than the traditional one, and which is capable to endure the extreme thermal expansions of the commutator of the traction motor, better than the earlier solutions.

A further aim of the invention is a design of the structure of the commutator wherein its assembly is simpler than the known through-bolt and tilting ring type solutions, and which enables tightening of the ring clamp in the assembled machine.

According to aspects of the invention, there is provided a commutator which is as claimed in claim 1 or claim 6 or claim 8.

In its preferred form described below, the invention features a commutator for electrical machines, preferably for the electric traction motor of locomotives, particularly in narrow-gauge locomotives, wherein the commutator comprises a commutator hub arranged on the shafi of the electrical machine, a ring clamp, a segment crown insulated from said commutator hub and said ring clamp, and an elastic or resilient element compressing the commutator hub and ring clamp axially towards each other. The said element may be a disc-shaped clamping plate provided with a flange, with a tapered transitional part adjoining the flange, and a middle part provided with a central hole and connected with bolts to the commutator hub. A circular bulge may be formed on the side of the flange of the clamping plate leaning against the ring clamp.

A structure may be regarded as further development of the known tilting ring type arrangement, where the tilting ring was replaced with a discshaped elastic or resilient 6.

clamping plate, and holes are in the middle part for the through-bolts. Tapered transitional part is machined on the clamping plate reaching below the segment crown of the commutator, where it is connected with evenly spaced bolts to the hub part of the commutator fitting to the shaft of the electric motor. The elastic clamping plate is provided with external flange, and a circular bulge is machined on its end face looking towards the tapered transitional part.

In the preferred embodiment of the commutator according to the invention, openings, cavities or are re&.i.-ted on the clamping plate, whereby elasticity of the clamping plate is further improved.

The invention is described in detail, by W of, le, Ydt, referle-re to the accompanying drawings, in which:

Fig. 1: Semi-sectional view of the version of the commutator built into the traction motor, Fig. 2: Semi-sectional view of the elastic clamping plate of the commutator Fig. 3: Detail of the end face of the clamping plate of the commutator Fig. 4: Partial section of the commutator along line IV-IV marked In Fig. 1.

Fig. 1 illustrates the axial section of the com mutator of a narrow-gauge locomotive's electric traction motor designed according to.the commutator structure in conformity with the invention.

3 7 A commutator hub 2 and a wheel 19 are fixedly mounted on said driving shaft 1 of said traction motor running on rolling bearing (not shown). A slidable ring clamp 6 is fitted to the cylindrical part 21 of the commutator hub 2. The part of the commutator hub 2 adjoining the cylindrical part 21 and the ring clamp 6 surround a dovetailed segment crown 3. The segment crown 3 is insulated from the cylindrical part 21 by an insulator 20 and from the commutator hub 2 and said ring clamp 6 with the aid of an insulating cap 9. Material of the insulating cap 9 and insulation is micanite sheet. A clamping plate 7 made of elastic steel is connected with the external part of the ring clamp 6, and said clamping plate 7 is fixed with bolts 8 to the commutator hub 2. The clamping plate 7 and driving shaft 1 are spaced from each other and form a communication duct with cooling channels 10 formed in the commutator hub 2. The duct is connected with a slot between the commutator structure and the wheel 19. Due to the limitation of the rolling stock clearance gauge, the segment crown 3 is dovetailed, because this allows the shortest axial dimensioning of the commutator. The dovetailed commutator - in accordance with the traditional and practical design - is provided with segment crown 3 containing insulated 4 segments 5 (see Fig. 4). The segment crown 3 is provided with 60 0 dovetail cone, to which are fitted the corresponding cones of the commutator hub 2 and ring clamp 6. The 8.

clamping plate 7 is supported by ring clamp 6, the conical mantle of which rests on the outside conical surface of the segment crown 3. The tapered surface on the other side of the segment crown 3 is supported by the internal-tapered surface of the commutator hub 2.

The segment crown 3 with the insulating cap 9 and an insulator 20 are placed on the commutator hub 2, then the ring clamp 6 is pressed to the segment crown 3 comprising segments 5. Then the clamping plate 7 is pulled over the shaft 1 and pressed against the ring clamp 6 with bolts 8. When the bolts 8 are tightened in the appropriate sequence, the tensile torque is meausred, the ring clamp 6 can be evenly pressed against the segment crown. At this point, the ring clamp 6 pulls said segments 5 radially inwards. The segments are pressed together just as the stones of an arch, thus uniting to a solid segment crown 3. Arch thrust develops between the segments 5. The compressive force, or the arch thrust should be as much as to withstand movement of the segments 5 or set of segments upon the centrifugal force arising during rotation. Otherwise, the segments 5 would damage the brushes connected with the segment crown 3 and would lead to failure of the commutator. Stresses develop during operation, due to the thermal expansion of the segment crown 3 absorbed by the elastic deformation of the clamping plate 7. In the course 9.

of difficult starting, the segments 5 stiuated below the brushes become overheated, consequently the peripheral temperature distribution of the segment crown 3 becomes unstable. The structural design according to the invention is capable to compensate this unstable load to a certain degree by the clamping plate 7.

Practical realization of the elastic clamping plate 7 is illustrated in Fig. 2 and 3. The clamping plate 7 has a tapered transitional part 11, this is adjoined by a flange 12 and by a middle part 13. The middle part 13 is provided with holes 16 for the bolts 8. The holes 16 have countersunks 17 to suit the bolt heads 8. In order to reduce the dimensions, the bolts 8 are machined as socket head screws. A circular bulge 22 is machined on the side of the flange 12 - connected with the exterior of the tapered transitional part 11 - leaning against the segment crown 3. The other side of the flange 12 is provided with an external surface 14 as reference surface (explained sugsequently). A measuring surface 15 is machined on the flat surface inside the middle part 13. The clamping plate 7 is a flanged disc with about 10-11 mm thick wall, the middle part 13 of which has a hole suitable for pulling on the driving shaft of the electric traction motor. Its material is forged and hardened spring steel prestressed under operating conditinn.

10.

For assembly, socket bolts 8 used to fix the clamping plate 7 are tightened, as a result of which the whole clamping plate 7 suffers deformation. Meanwhile, the flange 12 too suffers deformation, but the circular bulge 22 Is supported by the ring clamp 6 along the circle even in prestressed state. The axial force required for adequate arch thrust compressing the segments 5 of the segment crown to each other is maintained by the elastic deformation developing in the elastic plate and in its tigthtening bolts 8. The danger of lasting deformation can be excluded with proper measurement and heat treatment.

The clamping plate 7 functions as a spring, the spring characteristics of which can be determined. The extent of elastic deformation gives the force produced by the clamping plate 7 to the ring clamp 6. This force - knowing the spring constant - can be calculated in a simple way from alteration of the spacing between the external 'reference surface 14 and measuring surface 15.

Experiment and measurement indicate that the clamping plate 7 of the commutator according to the invention may provide a 9pring constant twice that of the traditional long-bolt type solution, and ecceeding by min. 50 % that of the tilting ring used for the cDmr-,,-,41-ator of a traction motor with similar power output.

11.

1 25 Obviously, assembly or repair of the commutator according to the invention does not require hydraulic press to bring about the axial forces. This can be accomplished with simple tools at any stage of the incorporation of the commutator, e.g. at readyassembled rotor. Consequently, the costs of assembly and maintenance are considerably reduced. As opposed to the earlier solutions, no hydraulic press is needed for setting the axial force, nor problems associated with the usual work performance occur (overtightening, spring-back, etc.), consequently the quality of the assembly work is improved.

As a result of the steady arch pressure produced by the clamping plate 7 and by the greater elasticity, deformation of the segment crown caused by thermal expansion, furthermore ageing and fatigue symptoms of the segment insulation and insulating cap 9 are reduced, on the other hand, reliability and running capacity of the traction motor measured in km are improved, consequently the number of maintenance and repairs will become less.

The clamping plate 7 of the commutator according to the invention is tightened with bolts 8 made of rolled material, and it is considerably simpler and less expensive than the construction with tilting ring and the pertaining threaded clamping spindle 12.

of complicated shape forged and hardened from hightensile alloyed steel, and requiring precise manufacturing tolerances.

The clamping plate 7 according to the invention is disc-shaped, its bottom part reaches below the ring clamp 6 and segment crown 3. For this reason, it requires smaller space than the traditional commutator, and this allows the use of high-powered traction motors mainly in narrow- gauge locomotive. However, because of its many advantages, it can be successfully used for the traction motors of standard gauge locomotives.

13.

Claims (9)

1 Commutator arrangement for an electrical machine, comprising a commutator hub, a ring clamp, a segment crown insulated from said commutator hub and said ring clamp, and an elastic element axially pressing said ring clamp and said segment crown towards each other, said elastic element comprising a disc-shaped clamping plate, which is provided with a flange and a tapered transitional part adjoining said flange and a central part, said central part being connected with bolts to said commutator hub.

2. A commutator arrangement as claimed in claim 1, wherein protruding means are formed on the side of said flange of said clamping plate facing said ring clamp.

3.

A commentator arrangement as claimed in claim 2 wherein said protruding means comprise a continuous annular bulge.

4. A commutator arrangement as claimed in any preceding claim, wherein said clamping plate is formed with spring constant-reducing configurations.

A commentator arrangement as claimed in claim 4, wherein said springconstant reducing configurations comprise openings in the wall of said clamping plate.

6. Commutator arrangement for electrical machines, preferably for electric traction motor of locomotives, particularly in narrowgauge locomotives, where said commutator arrangement comprises commutator hub arranged on the shaft of the electrical machine, ring clamp, a segment crown insulated from said commutator hub and a ring clamp, furthermore, an elastic element axially pressing said commutator hub and said ring clamp towards each other, characterized in that said elastic element is a disc-shaped clamping plate provided with a flange, which has a tapered transitional part adjoining the flange and a middle part is connected with bolts to said commutator hub, furthermore, a circular bulge is formed on the 14.

side of the flange of the clamping plate leaning against the r.Lr.g clamp -

7. The commutator arrangement according to claim 6, characterized in that spring constant-reducing configurations, in given case cavities, lightenings are in the wall of the clamping plate.

8. A commutator arrangement for a motor, comprising a commutator hub, a ring clamp, a segment crown insulated from the commutator hub and the ring clamp, and an annular spring plate for axially pressing the ring clamp and the segment crown towards one another, the spring plate having its outer periphery engaging the ring clamp directly or indirectly and its inner periphery connected by means of bolts to the commutator hub.

9. A commutator arrangement according to any one of claims 1, 3 or 8 substantially as herein described with reference to and as shown in the accompanying,drawings.

1 Published 1990atThe Patent Office,StateRou-z----.W.?1 High Holborn. London WC1R4TP. Further copies mayl>e obtainedfilc)m The PatentOffice. Elales Branch, St Mary Cray. Orpington. Kent BRS 3RD. Printed by Multiplex techniques ltd. St Mary Cray. Xent. Con. LW