Abstract:
An aircraft gas turbine propulsion engine includes a compressor ( 10 ) and ancillary systems (cabin pressurizing pumps and other service) in a box  16 . A fuel cell  18  powers electric motors ( 12 ) and ( 14 ) via a switch ( 20 ) for the purpose of either simultaneously driving the compressor ( 10 ) and ancillary systems, or the ancillary systems alone.

Description:
FIELD OF THE INVENTION 
     The present invention relates to power units of the kind which on the one hand, propel an associated vehicle, be it on land, sea, or through the air, and on the other hand, provide essential services such as electrical power for lighting, and where the vehicle is an aircraft, a pressurised air atmosphere. 
     BACKGROUND OF THE INVENTION 
     Where the main power unit is a gas turbine propulsion engine, and is installed in an aircraft, it is known to also install an auxiliary gas turbine engine therein, of much smaller proportion than the main engine. The smaller engine is connected with a compressor shaft of the larger engine via an electric motor and on start up of the smaller engine, the electric motor in turn rotates the compressor shaft and thus initiates the starting procedure of the main engine. Furthermore, until such time as the main engine is running, the smaller auxiliary engine also powers other ancillary equipment such as is mentioned hereinbefore. However, when the main engine is running, it takes over from the smaller auxiliary engine, which is then switched off. 
     The arrangement described hereinbefore has a number of drawbacks, eg the smaller engine also needs an air intake and an exhaust flow outlet, which structures have to be engineered into the aircraft structures, thus creating weight and using space. Furthermore, liquid fuel is used, which either reduces the amount available to the main engine, or necessitates a further supply for the smaller engine, which again adds weight and uses space. Yet a further drawback is created by use of the main engine to drive the ancillary equipment during flight of the associated aircraft, because the power which is diverted from the propulsive effort in order to drive those ancillaries, reduces the efficiency of the engine with regard to its primary task of propelling the associated aircraft through the air. 
     Gas turbine units are being considered which would be capable of continuous running, so as to enable obviation of use of the propulsion engine to operate the ancillary units. However, they would not obviate most of the drawbacks described hereinbefore. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide an improved dual power system for the propulsion of a vehicle, and the associated ancillary units thereof. 
     According to the present invention, a vehicle dual power system comprises a gas turbine propulsion engine and ancillary units, an electro chemical fuel cell connected to each via electric motor means, said connection comprising switch means selectively operable such that said electro chemical fuel cell is connected to said electric motor means, to simultaneously cause rotation of a compressor of said gas turbine propulsion engine so as to initiate start up thereof, and to drive said ancillary units, or drive either said compressor or said ancillary units alone. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example and with reference to the accompanying drawings, in which 
     FIG. 1 diagrammatically depicts a gas turbine propulsion engine compressor and associated ancillary units, in driven connection with a fuel cell, in accordance with the present invention, and 
     FIG. 2 depicts an alternative arrangement of the circuitry of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1. A compressor  10  of a gas turbine propulsion engine (not shown) is connected via a gearbox  11 , to an electric motor  12 , in known manner. Actuation of motor  12  effects rotation of compressor  10 , as a first step in initiating start up of the gas turbine propulsion engine (not shown) in known manner. 
     A second electric motor  14  is connected to a box  16  containing, eg pumps for pressurising the cabin of an aircraft (not shown) powered by the associated gas turbine engine (not shown), of which compressor  10  forms a part. 
     Electric motors  12  and  14  are connected in parallel to a common fuel cell  18 , via a three way switch  20 . By ‘way’ is meant mode of electrical conduction. Switch  20 , as shown in the drawing, simultaneously conducts electrical power to both motors  12  and  14 , via respective contacts  22  and  24 . If however, switch  20  is rotated clockwise, as viewed in the drawing, about a pivot  26 , so as to space contact  22  from the wire leading to motor  12 , contact  24  still maintains electrical contact with motor  14 , via a relatively long, arcuate contact portion  27 . Electrical power is thus individually provided, via motor  14 , to the pumps in box  16 . Anti clockwise rotation of switch  20 , about pivot  26 , will achieve redirection of the conduction path, to motor  12 , so as to achieve rotation of compressor  10 . 
     Fuel cell  18  can be selected from many well know types, provided that its characteristics include a high power to weight ratio, which will not nullify any of the advantages gained by its use. 
     A by-product, namely CO 2 , results from the operation of fuel cell  18 . The CO 2  can be collected, by any suitable means (not shown) and transferred to the gas turbine propulsion engine fuel tank  30 , so as to occupy space left by the engine fuel as it is used. By this means, explosive fuel vapours are prevented from forming in the tank. Again, the fuel cell  18  would provide the electrical power to actuate a pump (not shown) with which to effect the transfer. 
     The man skilled in the art, having read this specification, will appreciate that in practice, the switch  20  will be of a much more refined design, involving electronic circuits, and will know that, as stated hereinbefore, circuits for connecting a fuel cell to apparatus so as to enable electrical driving of that apparatus thereby are known. 
     The phrase ‘ancillary units’ is also intended to embrace use of the fuel cell to power electro magnetic bearing, (not shown) where such devices are utilised to support shafts for friction free rotation in a magnetic field, thus obviating the need for lubrication. 
     Referring to FIG. 2, in this arrangement, a single motor  32  is substituted for motors  12  and  14  in FIG. 1, and the switch  20  is electrically connected between motor  32  and the compressor  10  and auxiliary power unit  16 , while the motor  32  is connected by power shaft to the compressor  10  and unit  16 . 
     The present invention provides a number of advantages when used as a substitute for a gas turbine auxiliary power unit, including those as follows: 
     a) Power extracted from the main gas turbine propulsion engine is considerably reduced, thus increasing the power available to propel the associated aircraft. 
     b) Exhaust emissions resulting from the combustion of hydrocarbon fuel are reduced, thus reducing atmospheric pollution. 
     c) More controllable electrical power input to electro magnetic bearings. 
     d) Fuel cell generated gases are suitable for transfer to the fuel tanks of the gas turbine propulsion engine, to replace fuel used thereby, and create a non explosive atmosphere. 
     e) Obviation of gas turbine auxiliary power unit noise.