FIELD OF THE INVENTION
The invention relates to an improved double-decker axial flow type fan for an air cooler
turbocharger.
BACKGROUND OF THE INVENTION
In a Turbo generator, fans are mounted on the rotor shaft to drive the ventilation system,
intended to absorb the heat generated by the active parts of the generator and maintain
temperatures below the permissible limits. Air is used as a cooling medium system to
dissipate the generated heat in core and winding. The ventilation system of a generator
is symmetric with respect to it. Fans are mounted on both sides and air is drawn in from
atmosphere or from heat exchangers, forced onto the winding to absorb the heat
generated. The hot air is then forced onto the heat exchangers. The necessary head for
the above ventilation to take place, is generated by the fan. The fan on each side includes
a number of axial flow fan blade assembled around the periphery of a typical generator.
US 6657332 B2 discloses a cooling system of a turbogenerator, wherein the
turbogenerator has a cylindrical heat sink with generally axially extending fins on both
the outside and inside of a hoop section. The hoop section is solid except for holes

adjacent to the rear end thereof. The generator stator is press-fitted into the heat sink in
contact with the internal fins. The generator rotor is fitted with a small fan for directing
heated air away from the inlet of the engine. Cooling air passes along the external fins
to the rear of the generator, flows through the holes in the hoop section passes forward
between the inside of the hoop section and the external surface of the stator to cool the
stator and along an alternate path to cool the rotor hollow sleeve and permanent
magnetic shafts as well as the stator.
US 6558116 B2 discloses a ventilation circuit of a Turbogenerator as a turbo-generator
comprising a shaft, on which is positioned an axial ventilator, a cover that divides an
inflow chamber for a cooling gas transported by the axial ventilator from an outflow
chamber for this cooling gas, and a cylindrical channel segment that is positioned coaxially
to the axial compressor and surrounds the axial compressor radially, whereby the inflow
chamber comprises an asymmetrical cooling gas supply, and whereby in the inflow
chamber means for homogenizing the cooling gas supply to the axial ventilator are
provided. In order to improve the cooling, and therefore the efficiency of the machine,
the inflow chamber forms a rotation-symmetrical annular chamber in the region of an
inflow opening of the channel segment. A cylindrical annular collar is positioned coaxially
to the axial ventilator within this annular chamber. The annular collar projects axially into
the annular chamber and forms a completely surrounding, radial throttling gap at the
inflow opening.
US 9188136 B2 teaches a disc for a fan rotor (with a pilot to connect to a rotating shaft,
a hub and a plurality of blades) which includes a flat circular portion connecting to the
pilot at an inner edge and to the hub at an outer edge; a plurality of first circular

cooling holes of a first diameter located around the inner edge of the disc; and a plurality
of second circular cooling holes of a second diameter locater around the outer edge of
the disc, wherein the second diameter is larger than the first diameter.
EP 1361645 A1 shows a ventilation circuit device of a rotating machine having a rotor
and stator. The device has a rotatable rotor concentrically enclosed by a stator in a
housing and an axial cooling fan on the end of the rotor that sucks a gaseous cooling
medium from a coaxial suction chamber and forces it into a pressure chamber. An
adjustable control element is arranged near the suction chamber on one side to vary the
fan characteristic by imparting spin to the cooling medium in and/or against the fan
direction.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved double-decker axial flow
type fan for an air-cooler turbocharger.
Another object of the invention is to propose an improved ventilation system employing
a double decker axial flow type fan blade.

SUMMARY OF THE INVENTION
Accordingly, there is provided an improved double-decker axial flow type fan for an air-
cooler turbocharger, the improvement is characterized in that the fan blades are provided
on either side of the turbo generator rotor to circulate air to allow circulation of air into
the turbo-generator in different flow path, wherein the fan is configured a double decker
fan in which both blades are integral to teach other and moulded integral to the base of
the blade.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 is a cross section of double decker fan blade.
Figure 2 is a cross section of turbogenerator showing the end parts.
DETAILED DESCRIPTION OF THE INVENTION
The air discharged by the fan gets divided into three flow paths to absorb the heat
generated inside the generator. The first path enters the retaining rings through the gap
between the end retaining rings (201) and the rotor body, take the heat generated in the
windings. This air will enter the rotor sub-slots and travel towards the rotor center line.
Part of these streams of air moving towards the centre of rotor is thrown out radially into
the rotor/ stator air gap. From there, the air exits the machine to the atmosphere or to a
cooling arrangement where the heat carried by the outgoing air is given to the cooling
system.

Figure 1 shows a double-decker fan blade which comprises :
101-Double decker fan blade top profile.
102-Double decker fan blade bottom profile.
103- Double decker fan hub.
104-Rotor Shaft.
Figure 2 shows a turbo-generator end part which consists of:
201-Retaining ring
202-Double decker fan blade bottom profile.
203-Double decker fan blade top profile.
204-End windings of the generator which usually overhang on either side of stator core.
205-Core of the generator stator.
206-Double decker outer fan guide.
207-Double decker inner fan guide.

The second steam of all enters the gap and moves axially towards the rotor centre. During
its course of movement, air is let out of core (205) through axial ducts and let out of the
generator. During this process it takes the heat from the stator winding.
The third part goes to the core back through the end winding and enters the central
chamber. The air is drawn inwards into the air gap which moves axially and then radially
outwards to the core back. It then exits the stator to go to the atmosphere or to a cooling
arrangement.
To ensure that air flow goes to different flow paths as desired, partitioning of flows is
envisaged. The fan is partitioned into two profiles one above the other and both integral
to each other as shown in Figure 2. The fan is also made out of carbon fibre which has
very high strength as compared to aluminium alloy. One of the advantages of using
carbon fibre is that it can be made into thin hollow profile with outer fan tip closed. This
will reduce the weight considerably. Thin section is not possible in aluminium profile due
to limitation on strength and fabrication problems. The fabrication of hollow blade made
out of carbon fibre is easier and gives a smoother surface. Manual skill-set available with
craftsmen can be used to fabricate fan blade of aerofoil profile which is not possible in
case of aluminium. The height of the blade made of aluminium has also a limitation on
its height in view of higher centrifugal forces due to higher density. Another advantage
associated with carbon fibre blade is that the rotor hub or collar on which the blades are
mounted can be designed with lower diameter due to lower weight acting on the hub
surface. Lower height of the blade enables us to have a straight forward entry of the first
stream of air, as described above, directly into the rotor and air gap.

The air stream coming out of the upper portion of the blade (101,203) is directed to the
central chamber of the stator core through end winding. The bottom portion of the blade
(102,202) is designed to meet the requirement of other flow paths including the air gap
entry and rotor end winding zone (204). As the streams are partitioned by fan guide
(206,207) to deliver the required flows, the cooling effect will be better and removes
redundancy in the system where higher fan flow is to be designed. Reduction in flow will
reduce the windage losses and improve the machine efficiency. This also reduces the fan
blade height. The twin blade assembly will have a snowballing effect on the machine
efficiency.

WE CLAIM :
1. An improved double-decker axial flow type fan for an air-cooler turbocharger, the
improvement is characterized in that the fan blades are provided on either side of
the turbo generator rotor to circulate air to allow circulation of air into the turbo-
generator in different flow path, wherein the fan is configured a double decker fan
in which both blades are integral to teach other and moulded integral to the base
of the blade.
2. The double-decker axial flow type fan as claimed in claim 1, wherein a lower part
of the fan acts as an axial flow, throwing air in axial direction to cool the rotor and
part of winding in the straight portion of the generator stator.
3. The double-decker axial flow-type fan as claimed in claim 1, wherein an upper part
of the blade directs air in the axial direction onto end winding and central chamber
of the stator of the turbo-generator.
4. The double-decker axial flow-type fan as claimed in claim 1, wherein the blades of
the fan is made of carbon fibre material to reduce weight.

5. The double-decker axial flow-type fan as claimed in any of claims 1 o 4 wherein
size of the hub on which fan blade sits is smaller in view of the lower strength
requirement to carry the lighter weight of the blade.