EP0709937A2

EP0709937A2 - End face type commutator and process of manufacturing thereof

Info

Publication number: EP0709937A2
Application number: EP95402408A
Authority: EP
Inventors: Leonid Verbitsky
Original assignee: Costar Ltd
Current assignee: Costar Ltd
Priority date: 1994-10-26
Filing date: 1995-10-26
Publication date: 1996-05-01
Also published as: IL111406A0; EP0709937A3

Abstract

An end-face type commutator, especially for motor starters, comprising a conducting annular disc having front and rear sides and a central passage, the disc being divided into a plurality of lamellae by radial grooves. The annular conducting disc is coaxially embedded in an insulating annular housing and engaged at its front and rear sides therein in such a manner that, from its front side the disc is secured by an insulating annular plate constituting an integral part of the housing and preventing axial displacement of the lamellae during rotation of the commutator, and from its rear side the conducting disc is provided with an outer and an inner annular protrusions forming a coupling between the lamellae of the conducting disc and the insulating housing and preventing radial displacement of the lamellae during the rotation. The outer annular protrusion has a rectangular cross-section and is provided substantially along the outer circumference of the annular conducting disc, whilst the inner annular protrusion is formed along the central passage of said annular disc by flanging thereof in such a manner that the central passage has the shape of a truncated cone narrowing towards the front side of the disc.

Description

FIELD OF THE INVENTION

The present invention relates to end-face (or vertical) commutators of electric machines, more particularly, to small motor starter commutators for vehicles and especially to those intended to be used at high speed of rotation.

BACKGROUND OF THE INVENTION

An end-face commutator for small motor starters usually constitutes an annular insulating housing containing a ring made of a conductive material in which radial grooves are stamped to define the commutator laminations (lamellae). The conductive ring is embedded in the insulating annular housing in such a manner that the working side surface is left free and may be contacted by brushes of the motor, whilst the rear surface of the ring is covered by the material of the housing so as to keep the lamellae retained therein.
FR patent 1456598 discloses construction of an end face type collector (commutator) comprising an insulating housing with a conductive disc. The disc is provided at its rear side with a retaining element in the form of an annular groove having sloped side walls. However, such a groove, being provided in the working body of the disc, reduces strength and the service life of the collector.
DE patent 1101601 describes an end-face type commutator comprising a plastic annular housing incorporating therein a plurality of conductive lamellae arranged in a disc and shaped each so as to be engaged by its burred rear surface with the body of the housing. Such a burr is annular and has a dovetail shape in its cros-section. In order to comply with the strength requirements, the height of the burr has to be comparable with the thickness of the disc, however this increases the commutator's, weight. Moreover, a number of subsequent steps and special instruments are required for manufacture of the dovetail-shaped burr, and therefore such an operation is expensive and time consuming. It should be also noted, that in small commutators the dovetail-shaped burr is not rigid enough due to its tiny size; it can be therefore easily crushed during molding the disc in the insulating housing. If such a defect takes place, this will definitely lead to reduction of the mechanical strength of the commutator. More particularly, at high speeds the coupling between the lamellae and the housing appears to be weak, i.e. it does not stand the axial and radial forces developing during rotation, and the lamellae with time are likely to drop out from the commutator.
SU 650140 describes an end face commutator of a small starter having a construction which partially overcomes the above-described disadvantages. The commutator comprises a conducting disc divided into lamellae by radial grooves and molded in an insulating housing. From its working surface, the disc is secured in the housing by an annular plate being an integral part of the housing. This annular plate prevents the lamellae from axial displacement during rotation of the commutator. In order to prevent radial displacement of the lamellae from their nests in the housing, the conducting disc is provided with an annular protrusion situated on its rear surface and having a rectangular cross-section. Such a rectangular flange is supposed to improve the coupling between the conducting disc and the body of the insulating housing.
However, one specific problem is typical for small commutators which develop a velocity exceeding, say 20,000 rpm. Since the insulating housing of such a high speed end-face commutator usually has the diameter slightly larger thah the diameter of the flange at the rear side of the disc, the radial forces developed at high speeds of rotation are likely to destroy the narrow section of the housing placed around the flange.
Moreover, there is a problem which occurs during the molding of the commutator. It should be explained that, at the first step of the manufacturing the conducting annular disc is placed into an annular form, and the form is then filled from its top with a plastic insulating material in which the disc is to be pressed in. It has been found that the insulating material often does not properly fill all narrow slots between the conducting disc and the annular form, therefore after complete molding of the commutator its housing may have inner defects.

OBJECT OF THE INVENTION

It is therefore the object of the present invention to provide a strong end-face type commutator, especially of the type having relatively small diameter of the insulating housing, and adapted to be used in small electric motors at high speeds of rotation.
An additional object of the invention is to provide a process of manufacturing of the novel commutator.

SUMMARY OF THE INVENTION

The above object is achieved by the present invention which provides an end-face type commutator, especially useful for motor starters, and comprising a conducting annular disc having a front and a rear sides and a central passage, said disc being divided into a plurality of lamellae by radial through slots; the annular conducting disc is coaxially embedded in an insulating annular housing and retained therein at its front and rear sides in such a manner, as to prevent the lamellae both from axial and radial displacement during rotation of the commutator; the arrangement being such that from its front side the disc is secured by an insulating annular collar having the outer diameter greater than the diameter of the central passage of said disc and constituting an integral part of the housing, and from the rear side said conducting disc is provided with an outer and an inner annular protrusions forming a coupling between the lamellae of the conducting disc and the insulating housing; said outer annular protrusion having a rectangular cross-section and being provided substantially along the outer circumference of the annular conducting disc, whilst said inner annular protrusion is formed along the central passage of said annular disc by flanging thereof in such a manner, that the central passage has the shape of a truncated cone narrowing towards the front side of the disc.
It has been noticed that the presence of the additional annular protrusion improves the coupling between the lamellae of the annular conducting disc and the insulating housing. Moreover, it has been found that when such an additional protrusion is formed by the conical flanging of the central passage of the disc, it serves as an in-built funnel which, during molding of the commutator, appears to facilitate penetration of the insulating material to the bottom portion of the annular form where the disc is pressed in. It is understood, that the proper filling of the form by the insulating material directly affects the rigidity of the molded commutator.
It should also be emphasized that the above-mentioned additional inner protrusion must be flanged (i.e. made by stretching of the metal) and not provided, say, by a cutting die. The protrusions effected by the cutting (or punching) die come out fragile because they consist of portions of the shifted metal, and thus cannot form a reliable coupling with the insulating housing in the commutator.
According to one preferred embodiment of the invention said insulating annular collar is situated in a correspondingly shaped recess flanged along the inner circumference of the front side of the conducting annular disc, and may slightly project therefrom.
In accordance with another aspect of the invention there is provided a process of manufacturing of the above described end-face type commutator, including the following steps: a step of die-stamping of an annular conducting disc from a metal blank in such a manner as to obtain said conducting disc having an outer annular protrusion on its rear side; a step of dissecting said conducting disc by through slots into a plurality of radial lamellae though leaving thereof connected to each other by a circular edge portion of the conducting disc; a step of flanging an inner annular protrusion on the rear side of said conducting disc in such a manner as to put the inner passage of said conducting disc into a frusto-conical shape; a step of placing said conducting annular disc into a preheated annular form, followed by a step of filling the form with an insulating material and molding the disc therein, the form being continuously heated; a step of removing the molded commutator from the form; a step of severing the annular edge portion of the conducting disc so as to electrically separate the lamellae one from another; and a step of providing a contact hollow in each of the separated lamellae for electrical wires.
According to one preferred embodiment of the process said inner annular protrusion on the rear side of said conducting disc is flanged simultaneously with flanging of the annular recess along the inner circumference of the front side of the conducting disc.
In one embodiment of the process said annular conducting disc may be formed from an annular metal blank, such as a pipe section.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further illustrated by the aid of the attached non-limiting drawings, in which:

Figs. 1A and 1B (prior art) are radial cross-sectional views of two modifications of the end-face type commutators described in the SU author's certificate No 650140; and
Fig. 2 is a radial cross-sectional view of the end-face type commutator according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In Figs 1A and 1B them are represented two modifications of the end-face commutator of small starter motor which are described in the SU author's certificate No 650140.
A commutator 10 shown in Fig. 1A comprises a conducting disc 12 divided into lamellae by radial grooves (not shown) and molded in an insulating housing 11. At its front side 13 the disc 12 is secured in the housing 11 by an annular plate 15 constituting an integral part of the housing and intended to prevent displacement of the lamellae due to the axial forces which develop during rotation of the commutator. In this embodiment the conducting disc 12 has an additional recess 17 provided at the inner circumferential portion of its front side 13. The insulating annular plate 15 occupies the whole recess 17 and does not project from the front side of the disc. The conducting lamellae of the disc 12 are embedded in the plastic housing 11 in such a manner that their front sides 13 are free and adapted to be contacted by electrical brushes of the associated motor. In order to prevent axial displacement of the lamellae from the housing 11 during rotation of the commutator, the conducting disc 12 is provided with an annular protrusion (flange) 16 situated on its rear side 14 and having a rectangular cross-section. The rectangular shape of the flange 16 improves the coupling between the conducting disc 12 and the body of the insulating housing 11.
In Fig. 1B another modification 20 of the commutator is shown, where a rim 26 having a rectangular cross-section is provided at inner circumferential portion of the rear side of the disc 22. It is noted in the patent specification, that the rim 26 is formed by shifting the metal from the front side of the disc 22 during manufacture of a recess 27. Such a manner of providing the rim 26 results in its weak and fragile neck, which fact negatively affects the strength of the commutator. It is understood for those skilled in the art, that the thinner is the disc 22, the weaker is the neck of the rim 26, and therefore such a construction is inapplicable for small commutators intended to be used at high speed of rotation.
It should be added that the end-face commutators illustrated in Figs 1A and 1B are reliable at velocities of about 20,000 rpm.
During molding of the commutators 10 or 20 the conducting discs 12 or 22 are placed in forms on their front surfaces. It has been noted that the insulating material supposed to pass through the narrow passage 19 or 29 and form the annular plate 15 or 25, often does not properly fill these cavities, thus reducing the quality of the commutator.
In Fig.2 one can see a radial cross-section of the commutator according to the invention. An end-face type commutator 30 comprises an annular insulating housing 31 incorporating therein a conducting annular disc 32 having a front side 33, a rear side 34 and a central passage 40. The disc 32 is divided into a plurality of lamellae (marked by the same numeral 32) by through radial grooves, which are not seen on the radial cross-section. The annular conducting disc 32 is coaxially embedded and retained in the insulating annular housing 31 in the following way: from its front side 33 the disc 32 is secured in the housing by an insulating annular collar 35, and from its rear side 34 the conducting disc is provided with a pair of outer 36 and inner 38 annular protrusions forming a reliable coupling between the lamellae of the disc 32 and the insulating housing 31. The annular collar 35 constitutes an integral part of the housing 31 and prevents axial displacement of the lamellae 32 during rotation of the commutator 30. The insulating annular collar 35 is situated in a correspondingly shaped recess 37 flanged along the inner circumference of the front side 33 of the conducting disc. (In another embodiment the collar 35 may slightly project from the surface 33.) The coupling formed between the housing 31 and the protrusions 36 and 38 prevents the lamellae 32 from radial displacement and dropping out from the housing. The outer annular protrusion 36 has a rectangular cross-section and is provided substantially along the outer circumference of the annular conducting disc, whilst the inner annular protrusion 38 is formed along the central passage 40 of the annular disc 32. It can be seen, that the protrusion 38 is flanged in such a manner as to form with the central passage the shape of a truncated cone narrowing towards the front side 33 of the disc 32. During manufacture of the commutator in an annular form the protrusion 38 and the frusto-conical central passage 40 of the disc serve as an in-built funnel which facilitates penetration of the insulating material to the bottom portion of the annular form, thus rendering more rigidity to the molded commutator.
The described end-face type commutator can be manufactured in the following manner. The annular conducting disc 32 may be formed by die-stamping from a metal pipe section in such a manner as to obtain the disc having the outer annular protrusion 36 on its rear side 34. The disc 32 is then dissected into a plurality of radial lamellae though leaving thereof connected to each other only by a circular edge portion (not seen in Fig.2). After that the inner annular protrusion 38 is flanged on the rear side 34 of the conducting disc 32 in such a manner as to put the inner. passage 40 of the disc into a frusto-conical shape. The inner annular protrusion 38 may be flanged simultaneously with flanging of an annular recess 37 which can be seen in Fig.2 along the inner circumference of the front side 33 of the conducting disc. The disc 32 is placed into a preliminarly heated annular form (not shown), which is then filled with an insulating material. The disc 32 is molded in the form which is constantly being heated during this molding process. When the molded commutator is removed from the form, the annular edge portion of the conducting disc should be cut away so as to electrically separate the lamellae one from another. After that, a contact hollow (not seen) has to be provided in each of the separated lamellae in order to connect thereof to electric wires.

Claims

An end-face type commutator, comprising a conducting annular disc having a front and a rear sides and a central passage, said disc being divided into a plurality of lamellae by radial through slots; the annular conducting disc is coaxially embedded in an insulating annular housing and retained therein at its front and rear sides in such a manner, as to prevent the lamellae both from axial and radial displacement during rotation of the commutator;
the arrangement being such that from its front side the disc is secured by an insulating annular collar having the outer diameter greater than the diameter of the central passage of said disc and constituting an integral part of the housing, and from the rear side said conducting disc is provided with an outer and an inner annular protrusions forming a coupling between the lamellae of the conducting disc and the insulating housing; said outer annular protrusion having a rectangular cross-section and being provided substantially along the outer circumference of the annular conducting disc, whilst said inner annular protrusion is formed along the central passage of said annular disc by flanging thereof in such a manner, that the central passage has the shape of a truncated cone narrowing towards the front side of the disc.
The end-face type commutator according to Claim 1, wherein said insulating annular collar is situated in a corresppondingly shaped recess provided along the inner circumference of the front side of the conducting annular disc.
The end-face commutator according to Claim 2, wherein said insulating annular collar slightly projects from the surface of the front side of said disc.
A process of manufacturing the end-face type commutator according to Claims 1 to 3, including a step of die-stamping of an annular conducting disc from a metal blank in such a manner as to obtain said conducting disc having an outer annular protrusion on its rear side; a step of dissecting said conducting disc by through slots into a plurality of radial lamellae though leaving thereof connected to each other by a circular edge portion of the conducting disc; a step of flanging an inner annular protrusion on the rear side of said conducting disc in such a manner as to put the inner passage of said conducting disc into a frusto-conical shape; a step of placing said conducting annular disc into a preheated annular form, followed by a step of filling the form with an insulating material and molding the disc therein, the form being continuously heated; a step of removing the molded commutator from the form; a step of severing the annular edge portion of the conducting disc so as to electrically separate the lamellae one from another; and a step of providing a contact hollow in each of the separated lamellae for electrical wires.
The process according to Claim 4, wherein said inner annular protrusion on the rear side of said conducting disc is flanged simultaneously With flanging of the annular recess along the inner circumference of the front side of the conducting disc.
The process according to Claims 4 or 5, wherein said annular conducting disc is formed from a pipe section or the like.