Patent Application
20130333365
The present invention relates to a controlling method for compressed air supply to a pneumatic network, in particular for the network of an aircraft—including, but not exclusively from an auxiliary power unit, in short APU (Auxiliary Power Unit) equipping in general the aircraft—as well as a controlling system for the implementation thereof.
The invention applies to aircrafts, i.e. to airplanes (commercial airplanes, regional airplanes or small jet type airplanes) as well as to helicopters. The invention can use a drive through the APU unit equipping the aircraft, but also a piston engine or an electrical engine.
The aircrafts are provided with a motorization comprising main engines—dedicated to the propulsion and, in a cruising rating, to the generation of a non propulsive energy from energy consuming equipment (pneumatic, mechanical, hydraulic, electricity, etc.)—as well as an APU unit in general.
An APU unit is a small turbo-engine or auxiliary engine conventionally consisting in an air inlet, a gas generator and an exhaust nozzle. The gas generator is a compressor-combustion chamber-turbine all together. The turbine being supplied by the combustion gases exiting from the chamber—wherein a compressed air and fuel mixture has been injected—drives the compressor and transmits mechanical power to a gearbox casing. The energy consuming equipment is supplied by the gearbox casing via a hydraulic pump, a pneumatic pump or an alternator.
The APU unit thus supplies non propulsive energy on the ground and possibly on flight when the main engines are not anymore in a capacity to supply non propulsive energy: for example, in the case where the flight conditions are getting difficult or for delicate phases (search, hostile environment, etc.) in the framework of particular missions, or even in case of a failure of one or more generators integrated into the main engines.
The need in terms of a pneumatic power being in general high, a load compressor is generally dedicated to the supply of this power type. Such load compressor is mechanically driven by the gas generator of the APU unit and generates the pneumatic power being desired.
The pneumatic energy being consumed by the aircraft network is variable and must be adapted for the air flow rate variations, while providing a minimum pressure within the network. Moreover, in general, the APU unit only supplies such pneumatic power on ground. The power being consumed by the load compressor in flight should be reduced since the pneumatic power is not then consumed.
In order to manage the variations in the compressed air flow rate consumed by the network, the load compressor is provided with internal guiding valves, the so-called IGV (for “Inlet Guide Valve”). The opening of such IGV valves is piloted on the compressor inlet so as to vary the air flow rate variation capacity.
Such IGV valves having no sufficiently high reactivity degree, an anti-pumping valve is generally provided so as to be able to overcome the sudden variations of the air flow rates being tapped and to avoid the air back flows. Such anti-pumping valve is extremely reactive, namely about 100 to 200 milliseconds. Furthermore, in flight, when the air generation is not used, the resistive torque of the load compressor is reduced at most by closing the IGV valves and the anti-surge valve is opened at a maximum.
However, such management solution for air flow rate variations needs an oversizing of the load compressor. Indeed, the IGV valve closing generates heavy load losses. Consequently, in order to hold a sufficient pressure—in particular upon weak air tappings—the compressor is oversized so as to be able to gain in terms of compression rate with respect to the air generation capacity thereof in the nominal condition. Due to such oversizing, the engine is not optimized in mass and that then represents a major handicap on flying machines.
The invention aims at overcoming such major disadvantage by basing the management of the tapped air flow rate variations not through an IGV valve positioning, but through a controlled ejection of the air surplus being not consumed by the network.
More precisely, the present invention aims at providing a controlling method for compressed air supply to a pneumatic network, wherein, the supply being provided by a load compressor, the compressed air is controlled as a function of the instantaneous needs of the pneumatic network by discharging the whole compressed air being not consumed by such network towards the gas exhaust system via a variable opening depending on the air pressure supplied to the pneumatic network. Thus, the load compressor is actuated, at a given flight point, at the same operating point, whatever the air flow rate requested by the pneumatic network.
Such method allows the load compressor not to be oversized, said compressor staying then sized in terms of compression rate in comparison of its maximum flow rate capacity in a nominal rating. Significant gains in terms of power consumed by the load compressor are thus generated. Moreover, the compressor being of a smaller size, the mass thereof is also reduced. It is the same with retaining systems of the compressor (impeller, lid fastener, etc.). Advantageously, the energy to be restrained in a case of an impeller being burst is revised downwards.
According to particular embodiments:
an opening command for the compressed air towards the gas exhaust system is controlled with a given set point pressure;
an air generation command of the load compressor according to one of two opening/closing positions 0/1 is controlled to the opening/closing position 0/1 of the network inlet; in particular IGV valves for air access to the load compressor are regulated according to two positions as a function of the opening/closing position of the air generation command of the load compressor; thus, the IGV valves have no need to be regulated over the whole variation range and the IGV piloting is then advantageously simplified.
The invention also relates to a controlling system for compressed air supply to a pneumatic network being able to implement the above-mentioned method. Such a system includes a load compressor, an air supply and a power shaft being able to drive into rotation the load compressor. It also comprises, in a compressed air outlet of such load compressor, a connecting channel connected on the one side with a channel being connected with the pneumatic network and, on the other side, with an air discharge conduct towards a gas discharging nozzle as well as air flow rate bleed valves controlled by a data processing unit as a function of measurements made on a pressure sensor arranged on the connection with the pneumatic network, the valves being arranged on the air supply, on the connection with the pneumatic network and on the discharge conduct.
According to preferred embodiments:
the bleed valve arranged on the discharge conduct is selected amongst a proportional controlling valve in a predetermined range around a set point pressure, an anti-surge valve and a safety valve calibrated at the set point pressure;
the bleed valves arranged on the supply and on the connection to the pneumatic network are valves being settable on two positions of extreme opening/closing conditions 0/1;
the valves arranged on the air supply of the load compressor are IGV valves;
the rotation driving shaft of the compressor is a mechanical power shaft selected amongst this of an APU unit gas generator, of a terrestrial motive unit, for example a machine tool, a piston engine or an electrical engine; and
the speed of the mechanical power shaft of the APU unit is controlled by a measuring device for the fuel flow rate being injected into a combustion chamber of the APU unit, the flow rate being permanently adjusted so that the speed of said shaft measured by a speed sensor corresponds to a set point value.
Other aspects, characteristics and advantages of the invention will appear in the following non limitative description related to a particular exemplary embodiment, referring to the accompanying unique figure.
Such figure represents an exemplary schema of a base architecture for a compressed air supply system to an aircraft pneumatic network and being controlled according to the invention from a load compressor being driven by a power shaft of an APU unit.
Referring to the schema of the unique figure, the exemplary base architecture for a compressed air supply system 1 to a pneumatic network of an aircraft comprises a load compressor 10 being driven by the power shaft 11 of an APU unit 3 of an aircraft. An APU unit is applied on ground or sometimes in flight for a non propulsive energy supply. In particular on a descent phase, extra pneumatic energy can be necessary so as to provide an efficient de-icing of the airplane or to release the main engines from non propulsive functions.
Such an APU unit 3 essentially consists in a gas generator 30—coupling a main compressor 31, a combustion chamber 32 and a power turbine 33—and a gas ejection nozzle 34 in post-combustion.
An air supply 4 provides air to the main compressor 31 and the load compressor 10 via IGV valves 12. To do so, the supply 4 is respectively divided into two conducts 4a and 4b through a T-shaped connection 40. The compressor 31 supplies the injectors 32i of the combustion chamber 32 with compressed air Ac pre-mixed with the fuel. The combustion of such mix in the chamber 32 supplies the turbine 33 with high energy gas 6e, thereby driving the power shaft 11 into rotation.
Such shaft 11 drives in turn the main compressor 31, the load compressor 10 and a gearbox casing 5. Such gearbox casing 5 connects the shaft 11 through gear trains with other energy consuming equipment materials: alternators, hydraulic pumps or auxiliary engines. As far as it is concerned, the load compressor 10 supplies with compressed air the pneumatic network 2 through a connecting channel 6a.
According to the invention, the system 1 comprises air supply controlling equipment materials in connection with the base architecture. Thus, on the compressed air outlet of the load compressor 10, the channel 6a is divided to be connected on the one side to the pneumatic network 2 through a connecting channel 6b and, on the other side, to an air discharge conduct 6c towards the gas exhausting nozzle 34. The connections between channels and conduct are made via a T-shaped joint 50.
More particularly, the access to the pneumatic network 2 is controlled by a valve 20 being settable on two extreme opening/closing condition positions 0/1 when the network 2 requires air. The opening condition 0/1 of the valve 20 also adjusts the air arrival in the conduct 4a through a command transfer of the opening/closing condition 0/1 of a valve 12.
The air discharge towards the nozzle 34 is adjusted in turn by a controlling valve 60 of a variable opening as a function of the air surplus to be discharged.
The controlling valve 60 is here a proportional opening valve adjusted on a differential provided by a servo-loop B1. The servo-loop B1 comprises a pressure sensor 61 arranged on the connection channel 6b with the network and a comparator 62 providing the pressure differential ΔP between a set point pressure value P0 and the current pressure value Pc measured by the sensor 61. From the differential ΔP, a position command of the controlling valve 60 is made by a transfer function of a data processing unit 6. In the illustrated example, such unit is the digital control unit or FADEC (for Full Authority Digital Electronic Controller) of the APU unit.
Furthermore, such data processing unit 6 also pilots the transfer function of the position command 0/1 of the IGV valves for air arrival into the load compressor 10. In particular, such valves are controlled in a position 0/1 so that the complete closing thereof, as soon as no air surplus is required, allows the creation of a penalizing resistive torque.
Moreover, such data processing unit 6 controls the rotation of the mechanical power shaft 11 of the APU unit 3 by piloting a measuring device 13 for fuel 16. Fuel 16 is pre-mixed with compressed air before being injected into the combustion chamber 32 of the APU unit 3 via the injectors 32i. A servo-loop is implemented by a loop B2 comprising a speed sensor 14 arranged on the power shaft 11 and a comparator 15. Such comparator 15 provides the differential ΔV between the current speed Vc, being measured by the speed sensor 14, and a set point speed value V0. From the differential ΔV, the data processing unit 6 provides a measuring command for the measuring device 13 via an appropriate transfer function.
The invention is not limited to the examples being described and represented.
It is for example possible to use other bleed valves than the controlling valve 60, in particular the anti-surge valve or a safety valve calibrated as a function of the set point pressure of the loop B1.
Furthermore, the power shaft can be driven by another mechanical energy generator than an APU unit, for example, in other fields than aeronautics, a turbine or a terrestrial motive unit for machine tool, an engine piston or an electrical engine.
Moreover the IGV valves can be substituted by an adapted disengagement of the air supply.
| Number | Date | Country | Kind |
|---|---|---|---|
| 12 55420 | Jun 2012 | FR | national |
