Abstract:
A device and method for monitoring a high-pressure pump in a turbomachine fuel supply circuit by detecting opening of a pressurizing and shut-off valve mounted on an outlet side of a fuel flow regulating valve, by measuring rotational speed of the turbomachine corresponding to the opening of the pressurizing and cut-off valve, and by monitoring change in a value of the rotational speed to propose replacement of the high-pressure pump when the measure value rotational speed reaches a predetermined threshold.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a device and a method for monitoring a high-pressure pump in a fuel supply circuit of the injectors of a turbine engine such as a turbojet or a turboprop engine. 
     2. Description of the Related Art 
     In a turbine engine of this type, the supply circuit of the fuel injectors comprises a combination of a low-pressure pump and a high-pressure gear pump, with the low-pressure pump providing the feed of the high-pressure pump in order to avoid cavitation phenomena, with the high-pressure pump supplying a flow and a fuel pressure which are sufficient to provide the supply of the injectors of the combustion chamber of the turbine engine, as well as the cooling of the lubrication liquid of the turbine engine and of an IDG (Integrated Drive Generator) system and the controlling of actuators of elements with variable geometry of the turbine engine, (such as in particular guiding vanes with variable setting). 
     The fuel supplied by the high-pressure pump passes through an FMU (Fuel Metering Unit) which comprises a flow regulating valve connected to a pressurising and shut-off valve, which itself is connected to supply ducts of the injectors. 
     In the presence of an electric control for opening, the pressurising and shut-off valve remains closed hydraulically as long as the pressure of the fuel at the outlet of the regulating valve does not reach a predetermined value, for example 19 bars. 
     The high-pressure gear pump is driven mechanically by the turbine engine and its rotational speed is proportional to that of the turbine engine. The flow and the fuel pressure at the outlet of this pump are determined by the rotational speed of the pump. It has been observed that as the pump ages, it was necessary to increase the rotational speed of the pump in order to maintain the flow and pressure of the fuel at predetermined values. 
     This can make it difficult or impossible to restart the turbine engine in flight when, for any reason whatsoever, the turbine engine has been stopped and must be restarted through the sole effect of the air which flows on the compressor and turbine blades due to the displacement of the aircraft (an assistance for the starter also able to be adopted at certain points in the area of starting). The high-pressure pump is in this case driven in rotation at a relatively low speed but must however provide a pressure and a flow of fuel that are sufficient to cause the hydraulic opening of the pressurising and shut-off valve and in order to provide for proper supply of the injectors of the turbine engine. 
     The wear and tear of the high-pressure pump, which results in a progressive decrease of the flow of fuel at the pump outlet for a given rotational speed and a determined pressure, must be monitored so that the pump is replaced before a restarting in flight becomes impossible. 
     Maintenance recommendations call for a replacing of the high-pressure pump around 12,000 hours of operation and do not make it possible to optimise the life cycles of these pumps because, on the one hand, the premature wear and tear of the pumps cannot be detected and, on the other hand, pumps which are still in good operating condition sometimes need to be replaced. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention has for purpose to provide a simple, effective and economical solution to this problem. 
     It proposes a device for monitoring a high-pressure pump in a fuel supply circuit of a turbine engine, this circuit comprising a pressurising and shut-off valve which is regulated at a predetermined pressure threshold and which is mounted between a fuel flow regulating valve and a supply duct of the injectors, and means for measuring the rotational speed of the turbine engine, characterised in that it comprises means for detecting the opening of the pressurising and shut-off valve, means for recording the measured value of the rotational speed of the turbine engine at the opening of the pressurising and shut-off valve, and means for comparing this value with a predetermined threshold, in order to propose the replacement of the high-pressure pump when the recorded value of the rotational speed reaches the predetermined threshold. These means are available in the FADEC (Full Authority Digital Engine Control) of the engine. 
     As the pressurising and shut-off valve of the fuel supply circuit is in general already provided with a means for detecting its opening, the device for monitoring according to the invention uses primarily components that are already installed on the turbine engine and is therefore particularly economical. 
     Moreover, it makes it possible to monitor with precision the change in the rotational speed at the time of the opening of the pressurising and shut-off valve, with this change being representative of the wear and tear of the high-pressure pump of the fuel supply circuit, in order to report the necessity of replacing the high-pressure pump when the rotational speed detected reaches a predetermined threshold, beyond which the restarting in flight of the turbine engine would become difficult or impossible. 
     Advantageously, the opening of the pressurising and shut-off valve is detected and the value of the corresponding rotational speed is recorded during each of the starting phases of the turbine engine. 
     According to another characteristic of the invention, this device further comprises means for measuring the temperature of the fuel and means for correcting the recorded value of the rotational speed according to the difference between the measured temperature and a predetermined temperature. 
     This makes it possible to take into account the fuel density variations, which result from the temperature variations of the fuel, in order to correct the recorded values of the rotational speed and as such make the comparisons with the predetermined threshold in conditions corresponding to a substantially constant temperature. 
     The invention further proposes a method for monitoring a high-pressure pump in a turbine engine fuel supply circuit, this circuit comprising a pressurising and shut-off valve mounted between a fuel metering valve and a supply duct of the injectors, characterised in that it consists in detecting the opening of the pressurising and shut-off valve, in recording the value of the rotational speed of the turbine engine corresponding to this opening, in comparing this value with a predetermined threshold and in proposing the replacement of the high-pressure pump when the recorded value of the rotational speed reaches the predetermined threshold. 
     According to other characteristics of the invention, this method further consists in measuring the temperature of the fuel at the outlet of the pressurising and shut-off valve and in correcting the recorded value of the rotational speed according to the difference between the measured temperature and a predetermined temperature value, and in determining the comparison threshold of the recorded value of the rotational speed in such a way as to provide for the restarting in flight of the turbine engine throughout the entire service life of the high-pressure pump. 
     The invention further proposes a turbine engine, such as a turbojet or a turboprop engine, characterised in that it comprises a device for monitoring the high-pressure pump in a fuel supply circuit, of the type defined hereinabove. 
     Generally, the invention makes it possible to optimise the operation of the high-pressure pumps in turbine engine fuel supply circuits, and also makes it possible to render reliable the automatic overspeed test of the turbine engines. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and other characteristics, details and advantages of the latter shall appear more clearly when reading the following description, provided by way of example in reference to the annexed drawing, which diagrammatically shows a fuel supply circuit of the injectors of a turbine engine. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The fuel supply circuit shown diagrammatically in the drawing substantially comprises a fuel tank  10  to which is connected the inlet of a low-pressure pump  12  of which the outlet supplies a high-pressure gear pump  14  by the intermediary of heat exchangers  16  and filters  17 , the heat exchangers serving in particular for the cooling of the lubrication liquid of the turbine engine and for an IDG (Integrated Drive Generator) system. 
     The outlet of the high-pressure pump  14  supplies a flow regulating valve  18  (FMV or Fuel Metering Valve) which makes it possible to dose the quantity of fuel sent to the injectors  20  of the turbine engine according to the operating conditions. 
     The difference in pressure between the inlet and the outlet of the pump  14  is also used to control a set  22  of auxiliary equipment with variable geometry, comprising in particular actuators of guiding vanes with variable setting. 
     The excess fuel pumped is returned upstream of the high-pressure pump  14  by the intermediary of a by-pass valve  19 . 
     A pressurising and shut-off valve  24  is mounted between the outlet of the flow regulating valve  18  and a supply duct  26  of the injectors  20 , with this valve  24  being sensitive to the pressure of the fuel at the outlet of the valve  18  and prohibiting the supply of the fuel of the injectors  20  as long as this pressure does not reach a certain value, i.e. as long as the pressurising of the fuel is less than a determined threshold, this pressurising corresponding to the difference in pressure between the outlet and the inlet of the pump  14  and being for example 19 bars. 
     The pressurising and shut-off valve  24  is provided with a detector of opening  28  and with two electro-hydraulic control members  29  and  31 , of the servovalve or solenoid type, of which one is excited by the means for processing  32  and the other by an overspeed system  33 . These control members  29  and  31  are effective only if the pressure is sufficient. 
     A temperature sensor  30  is mounted on the line  26  supplying the injectors  20 . 
     The signals provided by the detectors  28  and  30  are applied to means for processing  32 , which also receive the outlet signal of a detector  34  measuring the rotational speed of the turbine engine. 
     In the means for processing  32 , the signal of opening of the pressurising and shut-off valve  24 , which is supplied by the detector  28 , controls the recording of the value of the rotational speed supplied by the detector  34 , and of the value of the temperature of the fuel, supplied by the detector  30 . The recorded values of the rotational speed are compared to a predetermined threshold value, beyond which it would be difficult to restart the turbine engine in flight and which corresponds to maximum admissible wear and tear of the high-pressure pump  14 . When this threshold value is reached by the rotational speed, a signal  36  is generated by the means for processing  32  in order to report the necessity of replacing the high-pressure pump  14 . 
     Measuring the temperature of the fuel in the line  26  makes it possible to take into account the variations in the density of the fuel which result from the temperature variations and which have an influence on the flow of the high-pressure pump  14 . The variations detected in the temperature of the fuel make it possible to correct the measured values of the rotational speed and therefore to return in the case of a fuel supply to a substantially constant temperature. 
     The opening of the pressurising and shut-off valve occurs during each starting phase of the turbine engine. Monitoring of the high-pressure pump  14  can therefore be carried out at each starting of the turbine engine and makes it possible to regularly follow the wear and tear of the high-pressure pump  14 , in order to propose its replacement when this becomes necessary. 
     The invention further makes it possible to render reliable the overspeed test of the turbine engine by associating this test in an original and automatic manner to the starting and monitoring phase of the high-pressure pump. 
     An example of test logic is described hereinafter, with many alternatives able to be derived. 
     When the engine is started, to a few speed percents, an electric order is generated by the means for processing  32  on the electro-hydraulic control  29  of the pressurising and shut-off valve  24 . The hydraulic circuit does not open because the speed is below the opening threshold of the pressurising and shut-off valve  24 . 
     The speed increases due to the fact of the action of the starter and when the opening threshold (acquired by the detector  28 ) is reached, the means for processing  32  record the value of the rotational speed which makes it possible to issue a judgement on the condition of the high-pressure pump  14 . 
     The means for processing  32  thus provide a signal to the overspeed system  33  which triggers its test, i.e. the control of the closing of the pressurising and shut-off valve  24  by the intermediary of the electro-hydraulic control  31 . 
     The means for processing  32  check by the intermediary of the detector of opening  28  that the overspeed system  33  has been effective and issues an end of test order to the overspeed system  33  so that the latter controls the closing of its electro-hydraulic member  31 . Simultaneously, the means  32  issue a closing order to the electro-hydraulic control  29 . The pressurising and shut-off valve  24  closes. 
     The rotation of the engine driven by the starter continues and, at the optimal starting speed, the means for processing  32  issue an opening order to the pressurising and shut-off valve  24  by the intermediary of the electro-hydraulic control  29  and send a command to the ignition exciter box which will energise the sparking plug(s) of the engine.