Abstract:
A pump control system ( 20 ) for a pump ( 21 ) in a gas turbine engine ( 10 ) is described. The pump control system ( 20 ) comprises demand means ( 22 ) for providing a demand signal ( 23 ) relating to a required rate of fluid flow and/or pressure from the pump ( 21 ). The system also comprises sensing means ( 26 ) to sense at least one parameter of fluid downstream of the pump ( 21 ) and to provide at least one feedback signal ( 28 ) relating to the, or each, respective parameter. Comparator means ( 30 ) is provided for comparing the demand signal ( 23 ) with the, or at least one, feedback signal to provide a control signal ( 33 ) for controlling the pump.

Description:
FIELD OF THE INVENTION 
   This invention relates to pump control systems. More particularly, but not specifically, the invention relates to fuel pump control systems, for example in engines such as gas turbine engines. 
   BACKGROUND OF THE INVENTION 
   In general engines require fuel to be pumped to one or more combustion chambers under controlled conditions, depending on the requirements of the engine. Any variation in the pressure or rate of flow of the fuel for a particular engine requirement can result in combustion instability and physical deterioration of system and engine components. Such instability can result in significant problems in the engines. 
   SUMMARY OF THE INVENTION 
   According to one aspect of this invention there is provided a pump control system comprising demand means for providing a demand signal relating to pump speed, a required rate of fluid flow and/or pressure from a pump, and compensation means to modify the signal to render the signal suitable to affect functioning of the pump. 
   Preferably, the control system comprises sensing means to sense pump speed, or at least one parameter of fluid downstream of the pump. The sensing means may provide at least one feedback signal relating to the, or each, respective parameter. The system desirably comprises comparator means for comparing the demand signal with the, or at least one, feedback signal to provide a control signal to control the pump. 
   In the preferred embodiment, the compensation means modifies the demand signal so that, in combination with the transfer function of the pump a desired output is provided from the pump. 
   As used herein the expression “transfer function” is intended to refer to the relationship between the behaviour of the output of a feature and the behaviour of the input of the feature. 
   As used herein, the expression “compensate” is intended to refer to a modification process, which could include a conversion from one physical medium to another, for example a conversion from electrical current to torque, or a conversion from position to volts. 
   According to another aspect of this invention, there is provided a pump control system comprising demand means for providing a demand signal relating to a required pump speed, rate of fluid flow and/or pressure from a pump; sensing means to sense pump speed or at least one parameter of fluid downstream of the pump and to provide at least one feedback signal relating to the, or each, respective parameter; and comparator means for comparing the demand signal with the, or at least one, feedback signal to provide a control signal to control the pump. 
   Preferably, the control signal is determined by the demand signal and the, or at least one, feedback signal. The sensing means may comprise a plurality of sensors, each sensing a respective parameter of pump and/or the fluid, and/or where the system is used in an engine, each sensing a respective parameter of the engine. Preferably the comparator means comprises a primary comparator for comparing a first feedback signal with the demand signal and providing a primary control signal. The comparator means may further include a secondary comparator for comparing one or more secondary feedback signals with the primary control signal to provide a secondary control signal. 
   The primary comparator may provide a primary control signal for controlling the pump. In one embodiment, the primary comparator may subtract the first feedback signal from the demand signal to provide said primary control signal. 
   Conveniently, the sensing means comprises a sensor arrangement to sense either pump speed, fluid pressure, and/or the rate of flow of pumped fluid downstream of the pump. Preferably, the sensor arrangement provides first and second feedback signals relating to pump speed, fluid pressure, or to the rate of flow of the fluid. 
   The sensor arrangement may comprise a first feedback signal compensation means to provide compensation to the first feedback signal to modify the first feedback signal and render the first feedback signal into a form whereby it can be supplied to the first comparator. A further compensation means may modify one or more further feedback signals for use by a second comparator. 
   Preferably, the demand signal provided by the demand means relates to the required rate of fluid flow, the required pump speed, or the required fluid pressure. 
   The sensing means may comprise a speed sensor to sense the speed of the pump. Preferably, the speed sensor provides a feedback signal relating to the speed of the pump. 
   Alternatively, or in addition, the sensing means may comprise a pressure sensor and/or a flow sensor to sense the conditions of pumped fluid downstream of the pump. 
   Preferably, the pressure and/or the flow sensor provides one or more feedback signals relating respectively to the pressure and/or flow of the fluid. 
   The sensing means may comprise feedback compensation means to provide compensation to the, or each, feedback signal to modify the, or each, feedback signal and render it into a form whereby it can be supplied to the comparator means. 
   Preferably, the fluid to be pumped is a fuel, to be combusted in a combustion chamber and produce combustion gases. The sensing means may comprise at least one combustion gas sensor to sense conditions of the combusted gases in, or downstream of, the combustion chamber. Preferably, the combustion gas sensor provides a combustion gas feedback signal relating to a parameter of the combustion gases. 
   The control system may comprise combustion gas feedback compensation means to provide compensation to the combustion gas feedback signal to modify the combustion gas feedback signal and render it into a form whereby it can be supplied to the comparator means. 
   The secondary comparator may compare the primary control signal with one or both of the modified secondary pump feedback signal and the modified combustion gas feedback signal. Preferably, the secondary comparator provides a secondary control signal for controlling the pump. In one embodiment, the secondary comparator may subtract from the primary control signal one or both of the modified pressure feedback signal and the modified combustion gas feedback signal. In another embodiment, the secondary comparator may comprise a plurality of comparators, one of which is operable on a combustion gas feedback signal, and the, or each, other of which is operable on the secondary pump feedback signal. 
   The control system may include configurations where one or more of the feedback signals described above is not incorporated. 
   According to another aspect of this invention there is provided a pump arrangement, comprising a pump to pump a fluid, and a pump control system as described above. 
   Desirably, the pump is configured to provide a characteristic speed, pressure and/or rate of flow when provided within an input control signal. Preferably, variations in the control signal cause concomitant variations in the speed, pressure and/or rate of fluid flow pumped from the pump. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawing, in which: 
       FIG. 1  is a cross-sectional side view of the upper half of a gas turbine engine; and 
       FIG. 2  is a schematic diagram of a control system for a pump. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a gas turbine engine is generally indicated at  10  and comprises, in axial flow series, an air intake  11 , a propulsive fan  12 , an intermediate pressure compressor  13 , a high pressure compressor  14 , a combustor  15  a turbine arrangement comprising a high pressure turbine  16 , an intermediate pressure turbine  17  and a low pressure turbine  18 , and an exhaust nozzle  19 . 
   The gas turbine engine  10  operates in a conventional manner so that air entering the intake  11  is accelerated by the fan  12  which produces two air flows: a first air flow into the intermediate pressure compressor  13  and a second air flow which provides propulsive thrust. The intermediate pressure compressor compresses the air flow directed into it before delivering that air to the high pressure compressor  14  where further compression take place. 
   The compressed air exhausted from the high pressure compressor  14  is directed into the combustor  15  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through and thereby drive the high, intermediate and low pressure turbines  16 ,  17  and  18 , before being exhausted through the nozzle  19  to provide additional propulsive thrust. The high, intermediate and low pressure turbines  16 ,  17  and  18  respectively drive the high and intermediate pressure compressors  14  and  13  and the fan  12  by suitable interconnecting shafts. 
   In order to control the flow of fuel to the combustor  15  a pump is provided. A pump control system  20  is shown diagrammatically in  FIG. 2 . 
   Referring to  FIG. 2 , the control system  20  for a pump  21  is shown which comprises demand means  22  for providing a demand signal  23 , relating to a required speed for the pump  21 . Fuel from the pump may flow through a fuel metering system  24  to the combustor  15 . The demand means could be suitable electronic or mechanical devices connected to the control lever for the gas turbine engine  10  which is designed to produce predetermined signals on variation of the control lever. 
   In this example, a sensor arrangement  26  is provided on the pump  21  to detect the speed of the pump  21 . 
   The sensor arrangement  26  provides a pump speed feedback signal  28  to a primary comparator  30 . The feedback path for the sensor arrangement  26  comprises a first feedback compensation means  32  to modify the first feedback signal  28  as appropriate. The modified first feedback signal  29  is received by the primary comparator  30 . 
   The primary comparator  30  compares the demand signal  23  with the modified first feedback signal  29  and provides a primary control signal  33 . 
   A primary control compensation means  34  is applied to the primary control signal  33  to modify the primary control signal  33 . The modified primary control signal is received by a secondary comparator  36 . 
   In this example, the control system  20  also includes a pressure sensor  38  downstream of the pump  21  to sense the pressure of fuel pumped from the pump  21 , and provides a pressure feedback signal  40 . The pressure sensor  38  comprises a pressure compensation means  42  to provide compensation to the pressure feedback signal  40 . The compensated pressure feedback signal  43  is received by the secondary comparator  36 . 
   In this example, a combustion gas sensor  44  is provided downstream of, or in, the combustor  15  to sense conditions of the gases emerging from the combustor  15  and provides a combustion gas feedback signal  46 . The combustion gas sensor  44  comprises a combustion gas compensation means  48  to provide compensation to the combustion gas feedback signal  46 . The compensated combustion gas feedback signal  49  is received by the secondary comparator  36 . 
   The secondary comparator  36  compares the signals received thereby and provides a secondary control signal  50  for controlling the pump  21 . A secondary control signal compensation means  52  provides compensation to the secondary control signal  50  so that it can be utilised by the pump  21 . 
   An example of the operation of the control system will now be discussed. The demand means  22  provides a demand signal  23  for a desired fuel pump speed. The demand signal  23  is transmitted to the pump  21  which delivers an amount of fuel according to its speed. If the speed sensor  26  indicates that the speed of the pump  21  is greater than demanded by the demand means  22 , a speed feedback signal  28  to that effect is provided thereby and after the compensation by the compensation means  32 , a compensated feedback signal  29  is received by the primary comparator  30 . A comparison of the demand signal  23  and the compensated speed feedback signal  29  causes the primary comparator  30  to provide a primary control signal  33  which requires the pump  21  to reduce speed, with a resultant effect on the fuel being supplied. The compensator  34 , in this embodiment, includes an integral term to allow the system to settle in steady state conditions. 
   In addition, a pressure feedback signal  40  is provided by the pressure sensor  38  and in this embodiment, the pressure compensation means  42  provides a modified pressure feedback signal  43  related to the rate of change of pressure. The modified pressure feedback signal  43  is fed to the secondary comparator  36 . The secondary comparator  36  combines the compensated primary control signal  37  with the modified pressure feedback signal  43  and provides a secondary control signal  50  adjusted accordingly. Similarly, a combustion gas feedback signal  46  is provided by the combustion gas sensor  44 , and in the embodiment shown, the compensation means  48  provides a modified combustor feedback signal  49  relating to the rate of change of combustor conditions. The modified combustor signal  49  is fed to the secondary comparator  36 . The secondary comparator  36  combines the modified pressure feedback signal  43  with the modified primary control signal  37 , and with the pressure feedback signal  43 , if available, and provides a further modification to the secondary control signal  50  for the pump  21  to modulate the flow of fuel pumped thereby. 
   As can be seen, by continually monitoring the various parameters of the fuel pumped by the pump  21  and the gases produced by the combustor  15 , the desired level of fuel pumped by the pump  21  is obtained, whilst achieving a much lower level of variation in pressure conditions at the pump and/or in the combustion system. 
   Various modifications can be made without departing from the scope of the invention. For example, in a basic system, the pressure sensor  38  and/or the combustion gas sensor  44  could be omitted. The remaining compensation means can then be designed to modify known characteristics of the fuel system, including the pump. Also, the invention may be embodied in any available technology, including combinations of mechanical, electrical, electronic, software, pneumatic and hydraulic technologies. It will be appreciated, therefore, that use of the word “signal” in this specification is not limited to communication by electrical or electronic means. 
   An example of a system described in the preceding paragraph could be an electric motor driving a fuel pump, which exhibits pulses if a constant electrical torque is applied to the motor. In such a case compensation could be achieved by the use of a mechanical cam arrangement or through appropriate configuration of the motor windings. 
   Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.