FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A brush holder assembly for an electrical rotating machine having slip rings
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Pawar Dilip Uttam and Kale Sriniwas Vishwas, both of Crompton Greaves Ltd, LT Motors Division (M3), A-6/2 MIDC, Ahmednagar 414 001, Maharashtra, India, both Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to a brush holder assembly for an electrical rotating machine having
slip rings.
This invention also relates to a method of holding a brush holder assembly in proper contact with the slip rings of a rotating electrical machine.
PRIOR ART DESCRIPTION
An electrical rotating machine having slip rings like alternator is associated with a brush holder assembly. A generally used brush holder assembly comprises a uniformly circular support rod and two pairs of brush holder arms mounted on the support rod in axially spaced apart relationship with each other. The proximal end of each pair of brush holder arms is formed with a mounting hole matching with the diameter of the support rod and a split joint. The support rod is engaged in the mounting hole at the distal end of each pair of brush holder arms and the brush holder arms are fixed to the support rod by tightening the lips of the split joints together. The distal ends of each pair of brush holder arms are biased towards each other with a tension spring and the distal end of each of the brush holder arms is provided with a current carrying carbon brush. During operation of the electrical rotating machine, the slip rings of the machine mounted on the shaft thereof rotate with the shaft of the machine with the carbon brushes in contact therewith. The carbon brushes ride on the slip rings and transfer current from the slip rings. Due to centrifugal forces generated during the rotation of the slip rings, the brush holder arms are subjected to vibrations and back and forth movements against the support rod. Due to the circularity of the support rod, the brush holder arms tend to move axially and radially on


the support rod. Over a period of time, axial and radial displacements of the brush holder arms occur on the support rod. The support rod along with the brush holder arms also tend to rotate. As a result, the contact between the carbon brushes and the slip rings is disturbed. Due to misalignment and improper contact between the slip rings and the carbon brushes, there will be voltage losses and the machine will not perform at the rated voltage. This reduces the performance efficiency of the machine. Due to the circularity of the support rod, initial setting and fitment of the brush holder arms on the support rod is difficult and time consuming and invariably requires skilled labour. As the brush holder arms are prone to axial and radial movements and the support rod is prone to rotation, periodic resetting of the brush holder arms on the support rod is required. As a result of axial and radial movements of the brush holder arms on the support rod and rotation of the support rod itself and improper contact between the carbon brushes and the slip rings, wear and tear to the brush holder assembly is increased and it is required to be replaced periodically. This increases the recurring cost of the brush holder assembly. Due to the improper contact between the carbon brushes and the slip rings, there may be sparking which may lead to fire accidents. It may also jam the carbon brushes and the slip rings. All this will also reduce the overall reliability of the brush holder assembly.
OBJECTS OF THE INVENTION
An object of the invention is to provide a brush holder assembly for an electrical rotating machine having slip rings, which assembly reduces voltage losses and facilitates performance of the machine at the rated voltage and improves the performance efficiency of the machine.


Another object of the invention is to provide a brush holder assembly for an electrical rotating machine having slip rings, which assembly can be set and fitted easily and conveniently without skilled labour.
Another object of the invention is to provide a brush holder assembly for an electrical rotating machine having slip rings, which assembly does not require periodic resetting.
Another object of the invention is to provide a brush holder assembly for an electrical rotating machine having slip rings, which assembly has reduced wear and tear and is economical.
Another object of the invention is to provide a brush holder assembly for an electrical rotating machine having slip rings, which assembly practically avoids sparking between the carbon brushes and slip rings so as to eliminate fire accidents and jamming of the carbon brushes and slip rings and improves the reliability thereof.
Another object of the invention is to provide a method of holding a brush holder assembly in proper contact with the slip rings of a rotating electrical machine so as to achieve the various beneficial effects of the invention.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a brush holder assembly for an electrical rotating machine having slip rings, the brush holder assembly comprising an electrical insulator support rod having an oblong cylindrical member corresponding to the distance


between two slip rings and a pair of uniformly circular rod members of smaller diameter, each of the rod members axially extending from each end of the oblong cylindrical member, each of the rod members having a radial rib along the length thereof, two pairs of brush holder arms, each mounted on each of the rod members, the proximal end of each pair of brush holder arms being formed with a mounting hole matching with each of the rod members and a split joint, the proximal end of each pair of brush holder arms being located against the outer ends of the cylindrical member with the rod members each engaged in the mounting hole at the proximal end of each pair of brush holder arms and with the radial rib positioned between the lips of each of the split joints, the lips of the split joints being tightened together to mount each pair of brush holder arms rigidly on each of the rod members against the outer ends of the cylindrical member so as to prevent axial and radial movements of the brush holder arms on the rod members, the distal ends of each pair of brush holder arms being spring biased towards each other, the distal end of each of the brush holder arms having a carbon brush fixed thereto, the support rod being fixedly mounted on the machine frame against rotational movement thereof.
According to the invention there is provided a method of holding a brush holder assembly in proper contact with the slip rings of a rotating electrical machine, the method comprising mounting two pairs of brush holder arms on an electrical insulating support rod in axially spaced apart relationship corresponding to the distance between two slip rings of the electrical machine, the brush holder arms being so mounted on the support as to prevent axial and radial movements thereof and mounting the support rod on the machine frame preventing rotational movement thereof.


The following is a detailed description of the invention with reference to the accompanying drawings, in which;
Fig 1 is an exploded view of a brush holder assembly for an electrical rotating machine according to an embodiment of the invention; and
Fig 2 is an end view of an electrical rotating machine fitted with the brush holder assembly of Fig 1.
The brush holder assembly 1 as illustrated in the accompanying drawings comprises an electrical insulator support rod 2 having an oblong cylindrical member 3 and a pair of uniformly circular rod members 4a, 4b of smaller diameter. Each of the rod members extends axially from each end of the oblong cylindrical member and is provided with a radial rib 5 oblong the length thereof. Two pairs of brush holder arms of the brush holder assembly are marked 6,6. The proximal end 7 of each pair of brush holder arms is formed with a mounting hole 8 matching with each of the rod members and a split joint whose lips are marked 9. The proximal ends of the two pairs of brush holder arms are located against the outer ends of the cylindrical member with the rod members engaged in the mounting holes at the proximal ends and with the radial ribs positioned between the lips of the respective split joints. The lips of the split joints are tightened together by engaging bolts 10 in holes 11 in the lips and by tightening check nuts 12a and lock nuts 12b onto the bolts against the lips so as to mount each pair of brush holder arms rigidly on each of the rod members against the outer ends of the cylindrical member. The distal ends of each pair of brush holder arms are spring biased towards each other by tension springs 13. Each of the brush holder arms has a carbon brush 14 fixed to the distal end


thereof. Rod member 4a is provided with a pair of diametrically opposite notches 15 at its outer end outer circumference, only one of the rectangular notches is seen in Fig 1 the other being on the diametrically opposite side and not visible. Rod member 4a is also provided with a screw portion 16 axially extending therefrom. The outer end of rod member 4a with the rectangular notches is located in a matching rectangular slot 17 in an oblong bracket 18 which is provided with open slots 19 at the ends thereof and fitted onto the frame 20 of the electrical rotating machine marked 21 by screws 22 and washers 23 as seen in Fig 2. The shaft, rotor, slip ring, stator and stator body of the machine as seen in Fig 2 are marked 24, 25, 26, 27 and 28, respectively. Being an end view, only one slip ring is seen in Fig 2. The screw portion of the support rod is fitted in the bracket by a nut 29 engaged over the screw portion and tightened against the bracket. The length of the cylindrical member 3 of the support rod corresponds to the distance between two slip rings mounted on the shaft of the machine. As the brush holder arms are located against the outer ends of the cylindrical member of the support rod and mounted on the rod members of the support rod with the radial ribs engaged between the lips of the split joints at the proximal ends of the brush holder arms, both axial and radial movements of the brush holder arms on the support rod during operation of the electrical machine are prevented. Engagement of the outer end of the rod member 4a with the rectangular notches 15 in the rectangular slot 17 in the bracket 18 and fitment of the screwed portion 16 of the support rod in the bracket by nut 29 prevent rotation of the support rod along with the brush holder arms during operation of the electrical machine. As a result proper contact between carbon brushes and the slip rings is maintained. Misalignment between the carbon brushes and the slip rings is prevented and voltage losses are also prevented so as to allow the electrical machine to continue to perform at the rated voltage and improve its performance efficiency. Initial setting and fitment of the brush holder arms on the


support rod is made easy and convenient as the outer ends of the cylindrical member provide a reference for the location of the brush holder arms and fitment of brush holder arms on the support rod can be carried out even by unskilled persons. Periodic resetting of the brush holder arms on the support rod is eliminated and wear and tear to the brush holder arms and the carbon brushes are also minimised. As misalignment and improper contact between the carbon brushes and slip rings are avoided, sparking is avoided. Fire accidents and jamming of the carbon brushes and slip rings are also avoided. Overall reliability of the brush holder assembly is improved. There are also significant cost benefits in the brush holder assembly of the invention.
Preferably the support rod is made of mild steel and is compression molded with an electrical insulating material like bakelite. The radial ribs of the rod member are formed during the compression molding.
The whole configuration of mounting of the brush holder assembly can be different. Instead of the screw portion and bracket arrangement, the support rod can be mounted on the machine frame in a different manner without allowing it to rotate. The support rod can be made differently and with different material. The notches 15 and corresponding slot 17 can be square. The invention is basically to ensure and maintain proper contact of the carbon brushes with the slip rings of a rotating electrical machine by preventing axial and radial movements of the brush holder arms on the support rod and by preventing rotational movement of the support rod with the brush holder arms. Variations in the construction and configuration of the brush holder assembly which are obvious to a person skilled in the art for the purpose of achieving the objects of the invention, should be construed and understood to be within the scope of the invention.


We claim:
1. A brush holder assembly for an electrical rotating machine having slip rings, the brush holder assembly comprising an electrical insulator support rod having an oblong cylindrical member corresponding to the distance between two slip rings and a pair of uniformly circular rod members of smaller diameter, each of the rod members axially extending from each end of the oblong cylindrical member, each of the rod members having a radial rib along the length thereof, two pairs of brush holder arms, each mounted on each of the rod members, the proximal end of each pair of brush holder arms being formed with a mounting hole matching with each of the rod members and a split joint, the proximal end of each pair of brush holder arms being located against the outer ends of the cylindrical member with the rod members each engaged in the mounting hole at the proximal end of each pair of brush holder arms and with the radial rib positioned between the lips of each of the split joints, the lips of the split joints being tightened together to mount each pair of brush holder arms rigidly on each of the rod members against the outer ends of the cylindrical member so as to prevent axial and radial movements of the brush holder arms on the rod members, the distal ends of each pair of brush holder arms being spring biased towards each other, the distal end of each of the brush holder arms having a carbon brush fixed thereto, the support rod being fixedly mounted on the machine frame against rotational movement thereof.
2. The brush holder assembly as claimed in claim 1, wherein one of the rod members is provided with a pair of diametrically opposite notches at the outer end outer circumference thereof and a screw portion extending axially therefrom, the outer end of the said one rod member with the rectangular notches being located in a matching


rectangular slot in a bracket fitted to the machine frame, the support rod being fixed to the bracket by tightening a nut on the screwed portion of the support rod against the bracket.
3. The brush holder assembly as claimed in claim 1 or 2, wherein the support rod is made of mild steel and is compression moulded with an electrical insulating material, the radial ribs on the rod members being formed during the compression moulding.
4. A method of holding a brush holder assembly in proper contact with the slip rings of a rotating electrical machine, the method comprising mounting two pairs of brush holder arms on an electrical insulating support rod in axially spaced apart relationship corresponding to the distance between two slip rings of the electrical machine, the brush holder arms being so mounted on the support as to prevent axial and radial movements thereof and mounting the support rod on the machine frame preventing rotational movement thereof.
Dated this 3rd day of December 2007
Crompton Greaves Limited By their Agent & Attorney
(Prita Madan) ofKhaitan & Co


Abstract
A brush holder assembly (1) for an electrical rotating machine having slip rings. The brush holder assembly comprises an electrical insulator support rod (2) having an oblong cylindrical member (3) corresponding to the distance between two slip rings and a pair of uniformly circular rod members (4a, 4b) of smaller diameter. Each of the rod members extends axially from each end of the oblong cylindrical member and has a radial rib (5) along the length thereof. The brush holder assembly further comprises two pairs of brush holder arms (6, 6). Each pair of the brush holder arms is mounted on each of the rod members. The proximal end (7) of each pair of brush holder arms is formed with a mounting hole (8) matching with each of the rod members and a split joint. The proximal end of each pair of brush holder arms are located against the outer ends of the cylindrical member with the rod members each engaged in the mounting hole at the proximal end of each pair of brush holder arms and with the radial rib positioned between the lips of each of the split joints. The lips (9) of the split joints are tightened together to mount each pair of brush holder arms rigidly on each of the rod members against the outer ends of the cylindrical member so as to prevent axial and radial movements of the brush holder arms on the rod members. The distal ends of each pair of brush holder arms are spring biased towards each other and the distal end of each of the brush holder arms has a carbon brush (14) fixed thereto. The support rod is fixedly mounted on the machine frame (20) against rotational movement thereof (Figs 1 and 2).