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
DC generator set
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to a DC generator set.
BACKGROUND OF THE INVENTION
There are AC or DC generators. An AC generator set-comprises a prime mover and an AC
generator coaxially cooperatively coupled to the prime mover shaft. The AC generator
comprises wound rotor and stator. In the case of an AC generator set, eddy current and copper
losses are high due to the rotor windings. Therefore, efficiency of the AC generator set is
low.
A DC generator set comprises a prime mover and a AC generator coaxially cooperatively coupled to the prime mover shaft and an electronic converter. The AC generator comprises permanent magnet external rotor or permanent magnet internal rotor. In a DC generator set comprising a permanent magnet external rotor, the prime mover comprises a fly wheel and a mounting disc mounted on the prime mover shaft. The flywheel is housed in the prime mover housing. The rotor comprises a cylindrical body and a plurality of permanent magnets located at the inner circumference of the cylindrical body spaced apart from one another. The rotor is coaxially mounted to the mounting disc on the prime mover shaft at one end thereof. A . wound stator mounted on a stator shaft is disposed stationary in the rotor from the other end thereof. An endshield is rotatably disposed over the stator shaft and mounted to the other end of the rotor. An end flange is disposed over the endshield and rotor and mounted to the stator shaft at one end thereof and the prime mover housing at the other end thereof. The endshield is associated with a fan and comprises a few air holes for directing cooling air to the stator winding and for keeping the AC generator cooled.

In a DC generator set comprising permanent magnet external rotor, eddy current and copper losses are low due to the elimination of the rotor windings. As a result, efficiency of the generator set is high. However, because of the flywheel and mounting disc, the number of components of the generator set, cost of the generator set and axial length of the generator set are increased. Cost of the generator set is increased because of the fan also. Further transportation cost and area for occupation of the generator set are also increased due to the increased axial length thereof
SUMMARY OF THE INVENTION
According to the invention there is provided a DC generator set comprising a prime mover having a shaft and an AC generator coaxially cooperatively coupled to the prime mover shaft and an electronic converter, wherein the AC generator comprises a cup shaped permanent magnet external rotor having a cylindrical body, a closed end and an open end, the closed end of the cylindrical body being adapted to be coaxially mounted to the prime mover shaft and a plurality of permanent magnets located at the inner circumference of the cylindrical body spaced apart from one another, a wound stator mounted on a stator shaft and disposed stationary in the cylindrical body of the rotor, an endshield rotatably disposed over the stator shaft through an axial hole in the endshield and fixed to the open end of the cylindrical body, the end shield having a plurality of air holes for directing cooling atmospheric air to the stator and a cup shaped flange comprising a cylindrical member having a mounting end with an axial hole and an open end, the cup shaped flange being disposed over the endshield and rotor with the mounting end thereof engaged over the stator shaft through the axial hole therein and mounted to the stator shaft and the open end thereof fixed to the prime mover housing, the cylindrical member and mounting end of the flange comprising a plurality of openings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the accompanying drawings:

Figs 1 and 2 are exploded views of the DC generator set according to an embodiment of the invention;
Fig 3 is an isometric view of the endshield of the DC generator set of Figs 1 and 2; and
Figs 4 is a sectional view of an air hole in the endshield of the DC generator set of Figs 1 and 2.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
As illustrated in Figs 1 to 4 of the accompanying drawings, the DC generator set 1 comprises a prime mover (not shown) having a shaft 2 provided with mounting holes 2a. The prime mover has not been illustrated in detail as it is not necessary for understanding the invention. The prime mover is, for example, an 1C engine and preferably a diesel engine. 3 is a AC generator comprising a cup shaped permanent magnet external rotor 4 having a cylindrical body 5, a closed end 6 and an open end 7. 8 is a rim at the open end of the rotor provided with mounting holes 9, The closed end of the rotor comprises a set of mounting holes 10 at the centre thereof matching with mounting holes 2a in the prime mover shaft 2 and a further set of mounting holes 11 at the periphery thereof. A plurality of permanent magnets 12 are at located at the inner circumference of the cylindrical body spaced apart from one another. The rotor is coaxially mounted to the prime mover shaft 2 with bolts (not shown) tightened in mounting holes 10 in the closed end of the rotor and mounting holes 2a in the shaft 2.
13 is a wound stator mounted on a stator shaft 14 and disposed stationary in the cylindrical body of the rotor. 15 is an endshield rotatably disposed over the stator shaft between bearing collars 16 and collar 17 on the stator shaft through an axial hole 15a in the end shield and

provided with mounting holes 18 matching with the mounting holes 9 in the rim 8 at the open end of the rotor. The endshield is fixed to the rim 8 at the open end of the rotor with bolts (not shown) tightened in the mounting holes in the endshield and in the corresponding mounting holes in the rim 8. The endshield also comprises a plurality of air holes 19 and 20 of different sizes which are inclined at an angle of 50 to 70°, preferably 60° with respect to the axis of the endshield (Fig 4). 21 is a cup shaped flange comprising a cylindrical member 22, a mounting end 23 and an open end 24. The flange is disposed over the endshield and rotor.
The mounting end of the flange is provided with an axial hole 25 and is mounted to the stator shaft with a locking plate 26 located across the mounting end of the flange against the stator shaft. The locking plate has mounting holes 27 at the centre thereof and mounting holes 28 at the ends thereof. The flange is fixed to the stator shaft with bolts (not shown) tightened in the mounting holes 27 and 28 in the locking plate and corresponding mounting holes 29 at the stator shaft end and mounting holes 30 in the mounting end of the flange, respectively.
The open end of the flange comprises a rim 31 provided with mounting holes 32 and the flange is fixed to the prime mover housing (not shown) with bolts (not shown) tightened in the mounting holes 32 in the rim 31 and corresponding mounting holes (not shown) in the prime mover housing. Both the cylindrical member and mounting end of the flange are provided with a plurality of openings 33 and 34, respectively. The flange also comprises lugs 35 with holes 36 to facilitate handling of the flange.
The DC generator set operates in the usual manner. During operation of the DC generator set, the rotor with the rotor magnets and endshield rotate with the prime mover shaft and an emf is induced in the stator windings as a result of the magnetic flux generated by the rotating permanent magnets. The induced emf causes a current to flow in the stator windings. The current is rectified by an electronic converter (not shown) connected to the stator windings and used or stored for future use in the usual manner. Cooling atmospheric air enters the

generator through the openings 33 and 34 in the flange and is directed towards the stator windings through the air holes 19 and 20 in the endshield 15 to keep the stator windings cooled. Hot air also escape through the openings in the flange. The collars on the stator shaft maintain the position of the endshield on the stator shaft.
According to the invention the mounting disc and fly wheel on the prime mover shaft have been eliminated. The rotor is directly mounted to the outer end of the prime mover shaft and acts both as a rotor and also as a fly wheel. The weight and size of the rotor are selected such that it also acts as a fly wheel. Because of the improved construction of the DC generator set, the number of components have been reduced and construction of the generator set has been simplified. The size of the prime mover housing and axial length of the generator set have been reduced and the generator set has been made compact. As a result of the overall size reduction and compactness of the DC generator and elimination of some of the components. cost of the generator set and space requirement for the generator set are also reduced: Transportation cost of the generator set is also reduced. As the endshield comprises a large number of air holes and that too of different sizes, cooling air flow towards the stator is increased. Inclination of the air holes also has been found to increase the air flow towards the stator. As a result of all this, the stator is kept cooled effectively and efficiently under natural flow of cooling air without a fan. Therefore, the fan has been eliminated according to the invention with further cost benefit. Further, because of the two sets of mounting holes at the closed end of the rotor, the rotor can be advantageously mounted to prime mover shafts of two different sizes. The generator set of the invention also has the advantage of high efficiency.
Several variations are possible in the embodiment of the invention illustrated and described above. The closed end of the rotor may comprise only one set of mounting holes or may comprise more than two sets of mounting holes. The flange may be fixed to the stator shaft with a different arrangement instead of using the locking plate. Fixing of the endshield to the

rotor and flange to the prime mover housing may be carried out differently instead of using mounting holes and bolts. Such variations of the invention are obvious to a person skilled in the art and are to be construed and understood to be within the scope of the invention.

We claim :
1) A DC generator set comprising a prime mover having a shaft and a AC generator coaxially cooperatively coupled to the prime mover shaft and an electronic converter, wherein the AC generator comprises a cup shaped permanent magnet external rotor having a cylindrical body, a closed end and an open end, the closed end of the cylindrical body being adapted to be coaxially mounted to the prime mover shaft and a plurality of permanent magnets located at the inner circumference of the cylindrical body spaced apart from one another, a wound stator mounted on a stator shaft and disposed stationary in the cylindrical body of the rotor, an endshield rotatably disposed over the stator shaft through an axial hole in the endshield and fixed to the open end of the cylindrical body, the end shield having a plurality of air holes for directing cooling atmospheric air to the stator and a cup shaped flange comprising a cylindrical member having a mounting end with an axial hole and an open end, the cup shaped flange being disposed over the endshield and rotor with the mounting end thereof engaged over the stator shaft through the axial hole therein and mounted to the stator shaft and the open end thereof fixed to the prime mover housing, the cylindrical member and mounting end of the flange comprising a plurality of openings.
2) The DC generator set as claimed in claim 1, wherein the prime mover is an IC engine.
3) The DC generator set as claimed in claim 2. wherein the prime mover is a diesel engine.
4) The DC generator set as claimed in any one of claims 1 to 3, wherein the closed end of the rotor comprises a set of mounting holes at the centre thereof and a further set of mounting holes around the periphery thereof for mounting the rotor to prime mover shafts of two different sizes.

5) The DC generator set as claimed in anyone of claims 1 to 4, wherein the open end of the cylindrical body of the rotor comprises a rim with mounting holes and the endshield comprises mounting holes matching with the mounting holes in the rim of the cylindrical body and the endshield is fixed to the rim of the cylindrical body with bolts tightened in the mounting holes in the endshield and rim.
6) The DC generator set as claimed in anyone of claims 1 to 5, wherein the mounting end of the flange is mounted to the stator shaft with a locking plate located across the mounting end of the flange against the stator shaft and fixed to the stator shaft and the mounting end of the flange.
7) The DC generator set as claimed in anyone of claims 1 to 6, wherein the cylindrical member of the flange comprises holding lugs and the open end of the cup shaped member of the flange comprises a rim with mounting holes.
8) The DC generator set as claimed in anyone of claims 1 to 7, wherein the air holes in the endshield are of different sizes.
9) The DC generator set as claimed in claim 8, wherein the air holes in the endshield are inclined at 50 to 70° with respect to the axis of the endshield.
10) The DC generator set as claimed in claim 8, wherein the air holes in the endshield are inclined at 60° with respect to the axis of the endshield.

11) The DC generator set as claimed in anyone of claims 1 to 10, which is of 6.5 KW capacity.