FIELP OF INVENTION
The present invention relates to an improved Brush gear assembly for Eddy Current
Clutch suitable for Diesel Electric locomotives. This is an improved device which
replaces existing mild steel brush holder support and soldered lead tightening
system made of an improved Epoxy make brush holder support and simpler lead
(leads with lug and bolt) tightening mechanism tending improved IR and more
durable tightening of lead, preventing breakage of leads during usage.
BACKGROUND OF THE INVENTION
More than 80% Locomotives used in India whether it is a passenger or freight
application, are run by Diesel Electric locomotives. An Eddy Current Clutch is used
for driving radiator fan which cools the diesel engine cooling water in the Broad
Gauge (BG) and Meter Gauge (MG) locomotives. Eddy Current Clutch plays a very
important role in the smooth functioning of Diesel Electric Locomotives. Being a
small component, improper working of ECC may cause heavy damage or breakdown
of overall locomotive in the service, therefore reliability of ECC has been an
important factor for proper working of locomotives.
BHEL has been supplying this machine to Indian Railways for many years. This
machine has been a highly reliable product for Indian Railways. Round the year two
problems have been regularly reported from the Railway sites. Firstly low IR across
brush holder assembly and secondly continuous breakage of brush holder leads
during service. Presently brush holder support is made up of mild steel and brush
holder leads
are soldered with the springs. Due to mild steel brush holder support, IR of machine
dropped in some of the cases. Conditions get worse in the humid conditions. Sudden
drop in IR of machine may lead to malfunctioning of ECC. On the other hand
soldered contact of brush gear leads get loosen due to heavy vibration and jerks in
the locomotive. Later, problem is even more dangerous as after continuous
vibrations, leads breaking from terminals.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved brush gear
assembly for Eddy Current Clutch for better Insulation Resistance (IR) during humid
weather conditions.
Another object of the invention is to propose an improved brush gear assembly for
Eddy Current Clutch for simpler and better breakage free lead tightening system.
Yet another object of the invention is to propose an improved brush gear assembly
for Eddy Current Clutch which minimises the failure at site due to above problems
and for better reliability of Eddy Current Clutch (ECC).
SUMMARY OF THE INVENTION
Two problems are most predominant in Brush Gear Assembly of Eddy Current Clutch
in Diesel Electric Locomotive. Firstly low Insulation Resistance (IR) across brush gear
assembly, secondly continuous breakage of brush gear leads during service. In
present case brush holder support is made up of mild steel and brush holder leads
are soldered with the springs. Due to mild steel brush holder support, IR of machine
dropped in some of the cases. Conditions get worse in the humid conditions. Sudden
drop in IR of machine may lead to malfunctioning of ECC. Secondly, soldered
contacts of brush gear leads get loosen due to vibrations during operation. Later,
problem is even more dangerous as continuous vibrations sometimes result in
breakage of leads.
To overcome above mentioned problems, all aspects of failure were studied and
analysis was carried out based on which existing brush gear assembly was modified.
To improve IR during testing and humid weather conditions during operation, mild
steel brush holder support was converted to epoxy fiber glass moulded insulating
support. Tightening system was changed to a breakage free lead tightening system.
Soldering system was converted to tightening of lead with lug and nut bolt system
with the help of a copper plate and lock nut system.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig (1) a & b - Plan and Elevation of Brush Gear Assembly of prior art.
Fig (2) a & b - Plan and Elevation of Brush Gear Assembly according to invention.
Fig 3 - An isometric view of Brush Gear Assembly according to invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The Brush Gear assembly manufacturing shall include following elements at the
stage of assembly:
The lead unit consists of (1, 6, 7, 8) as shown in Figure-2a. Cable (1) used for brush
gear lead is 4 mm2 Silicon Rubber insulated glass braided single core flexible copper
cable, providing more flexible connections. The lead is crimped with Ø 6.35 mm size
lug (6) in Figure-2a and tightened with annealed copper plate (7) in Figure-2a as
per IS 1897 with the help of M5X15 mm, 8.8 property class bolt and M5X15 mm
hexagonal lock nut (item 08) in Figure-1.
The copper plate (7) in Figure-2a is mounted with two numbers M4X15 property
class 8.8 hexagonal nut and M4X15 size hexagonal lock nut.
The brush holder support (2) in Figure-2b is a Fibre Glass Epoxy Moulded bracket
having temperature index 155°C. The material used is having much more strength
and free from any welded joints and weathering effect, as the block is manufactured
as a single moulding item. Use of Epoxy material, provides better insulation between
brush holder (4) to ground and better IR during test and operation.
The knurled cup point set screw and insert (3) in Figure-2b of property class 8.8 is
used for holding brush holder (4) with support (2) block. M6X8 size screws are used
with M6 size steel insert fixed within the epoxy moulded block.
The brush holder (4) in Figure-2b is made up of free cutting brass bars as per IS
319. This is a special type of brush holder (4) moulded with epoxy resin to insulate it
from support block. Brush holder (4) is provided with a threaded cap for tightening
of brush in to the brush holder pocket.
The carbon brush (5) as per IS 3003 in Figure-2b is used with pigtail as per IS 191
and spring as per IS 4454, Grade 2 which feed power to the field coil via slip ring.
BRUSH GEAR ASSEMBLY PART DETAILS:
ADVANTAGE OF THE IMPROVED PRODUCT OVER THE PRIOR ART
- Epoxy moulded Brush holder support (2); Previously it was made of mild
steel which has been replaced by a moulding item made of Epoxy
material. Epoxy fibre glass moulded Brush holder works itself as better
insulating medium in moist or rainy season; Epoxy brush holder support
provides better insulation to the complete assembly w.r.t. ground. Being a
glass fibre Epoxy material, it is having excellent mechanical strength also.
- Brush holder support is devoid of any welded joint as it is manufactured
as a continuous moulding item having no joint. In the prior art two mild
steel plates were to be welded together where the reliability of the Brush
holder support depended heavily on the quality of welding.
- Lead tightening arrangement - The present assembly is having lug and
bolt lead tightening system. A copper plate is mounted to tighten the lug
with the help of bolt and lock nut, where the brush gear lead is crimped
with the lug. In the prior art leads were soldered with the brush holder
springs permanently. This arrangement created lot of difficulties. Due to
continuous use or during service the joint has a tendency to get open in
which case one has to de-solder the lead and then re-solder. During
maintenance and for replacement of lead, one has to de-solder the joints
first. In the modified device, the leads can directly be replaced by
loosening the lock nut.
- Less time to assemble a brush gear assembly - In the modified device the
assembly time is reduced to a great extent due to elimination of soldering
operation which included the time for soldering the lead with the spring
and then testing the strength of joints. In the present case the leads are
directly tightened with the help of lock nut mounted over the copper
plate.
WE CLAIM
1) An improved Brush Gear assembly for Eddy Current Clutch adaptable to Diesel
locomotive comprising;
a Brush holder (4);
at least one L-shaped brush holder support (2);
a plurality of carbon brush (5);
a plurality of lead connector (1);
Characterized in that,
the brush holder (4) is moulded with epoxy resin for insulating it from support block
(2) wherein the brush holder support (2) having no joint with continuous moulding
with Fibre glass epoxy for better insulation between brush holder (4) to ground and
better insulation resistance when a plurality of copper plates (7) are disposed in the
assembly for improved tightening of lead crimped with lug (6) and nut and bolt
system (8).
2) An improved brush gear assembly as claimed in claim 1, wherein the brush holder is
made of free cutting brass bars.
3) An improved brush gear assembly as claimed in claim 1, wherein Knurled cup point
set screw of property class 8.8 holds the brush holder with support block.
4) An improved brush gear assembly as claimed in claim 1, wherein the copper plate is
annealed before assembly.
5) An improved brush gear assembly as claimed in claim 1, wherein the cable for brush
gear lead is of silicon rubber insulated glass braided single core flexible copper cable.

An improved brush gear assembly for eddy current clutch adaptable to Diesel
locomotive comprising a brush holder (4), L-shaped brush holder support (2),
plurality of carbon brushes (5), plurality of lead connections (1), wherein the brush
holder (4) is made of free cutting brass bar and moulded with Epoxy resin. The
brush holder support (2) having no joint with continuous moulding with fibre glass
epoxy maintains better insulation between brush holder (4) and ground as well as
between Brush holder (4) and Brush holder support (2). Copper plates (7) are used
for tightening of lug (4) of lead connections (1) with the help of nuts and bolts (8)
and Knurled cup point set screw (3) holds the brush holder (4) with the brush holder
support (2).