Abstract:
An apparatus for activating a valve of an ejector in order to adapt the pressurisation of a chamber in an aircraft turbojet engine comprising a device constructed and arranged to trigger the opening and/or closing of valve and/or the power of the valve as a function of the altitude at which the valve is located.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority from French Patent Application No. 1157355 filed on Aug. 16, 2011, the entire content of which is incorporated herein by reference. 
       FIELD 
       [0002]    The present invention relates to an activation apparatus for a passive ejector valve for improving the pressurisation of an aircraft turbojet engine system. An aspect thereof is essentially to optimise the function of such an ejector valve. The field of the invention is generally that of aircraft turbojet engines, and more precisely that of controlling the turbojet engines for the purpose of ensuring that the chambers inside the turbojet engines under consideration are liquid-tight. 
       BACKGROUND 
       [0003]    A significant safety factor to be considered for systems that hold oil is that chambers inside the turbojet engines should be completely liquid-tight. Generally, the liquid-tight property of the chambers in turbojet engines is established by ensuring that a pressure difference is maintained between the outside of the chamber and the inside of the chamber at sealing limits of said chamber; the pressure difference should be such that the pressure inside the chamber is lower than the pressure outside the system by at least a value determined in advance. 
         [0004]    As is shown in  FIGS. 1 and 2 , a jet pump system  102  is currently used to pressurise oil chambers in a turbojet engine  101 , for example the LEAP-X®. Such a jet pump system,  102 , also called an ejector or eductor, is a device that enables the pressure in a chamber to be improved when turbojet  101  is operating at low speed, while still ensuring that the pressure differential specifications at the chamber sealing limits are preserved. For this purpose, in the case of the LEAP-X® for example, ejector  102  draws in air at pressure P 28  (P 28  is the intake plan on the LEAP-X®, not generic), typically via a high pressure compressor  104  of turbojet  101  and mixes it with oil-free air  105  coming from chamber  103  at the centre vent tube. This supplementary air is injected by ejector  102  and creates an aspiration effect inside chamber  103 , thus leading to a fall in pressure inside chamber  103  itself, and consequently a greater pressure differential at the sealing limits of chamber  103  that is being analysed. This device is necessary for the limits when turbojet  101  is running slowly when the pressure levels inside and outside the chamber are close to one another as well as close to the ambient pressure; it is therefore desirable to know the pressure differential that is needed. 
         [0005]    Accordingly, in order to prevent oil leaks at low turbojet speeds, it is desirable to activate ejector  102  to ensure that a given pressure differential is maintained at the sealing limits of chamber  103 . However, the extraction of air from inside high-pressure compressor  104  by means of ejector  102  is not neutral in terms of the performance of the turbojet, particularly during high-speed phases of the turbojet; this is why pressurisation of the chambers is most often maintained with regard to the exterior/interior pressure differential without the use of an ejector during high-speed phases. 
         [0006]    It is therefore desirable to provide for controlled use of an ejector  102  to ensure that it is not used all the time. Accordingly, in the prior art use of control valve  106  for ejector  102  is provided, which is capable of switching from an on state, in which the pulsed air is directed into the centre vent tube, as the valve is in a completely open position, to a blocking state, in which no pulsed air is sent into the centre vent tube by the ejector because valve  106  is in a completely closed position. 
         [0007]    The valve is designed for passive operation—it is called a passive valve—, that is to say the opening/closing movement of the valve, as shown in  FIG. 3A , is controlled solely by a pressure differential that actuates it when the pressure differential reaches a trigger threshold DP 0 , this pressure differential being the difference in pressure between the P 28  pressure drawn from high-pressure compressor  104  and the pressure surrounding the valve, or ambient pressure Pamb. 
         [0008]    As is shown in  FIG. 3B , the principle of operation of passive valve  106  includes a hysteresis  301  that offsets the operations of opening/closing the valve. 
         [0009]      FIG. 4  represents a mapping  401  of different situations to which the passive valve may be exposed. Accordingly, in this figure, which has the form of an orthogonal coordinate system, the x-axis corresponds to a pressure differential DP maintained at the limits of passive valve  106 , while the y-axis corresponds to an altitude at which valve  106  is located. The various situations—or operating points—are physically represented by triangles  402 , which correspond to the case in which turbojet  101  is operating at low speed, and for which ejector  102  is in the on state, or by circles  403 , which correspond to the case in which turbojet  101  is operating at high speed, and for which ejector  102  is in the blocking state. 
         [0010]    As is shown in  FIGS. 5A ,  5 B and  5 C, a difficulty then arises in determining the activation threshold of one of the two configurations (ejector in on state or ejector in blocking state). In fact, if DP 0  is defined as a constant regardless of the altitude under consideration, it is observed that: 
         [0011]    as shown in  FIG. 5A , high-speed situations  501  are complied with for a pressure differential level DP lower than threshold DP 0 , valve  106  then being open, the ejector thus being activated in such manner that engine performance may be impaired; 
         [0012]    as shown in  FIG. 5B , either low-speed situations  502  are maintained for a pressure differential DP level higher than threshold DP 0 , in which case valve  106  is closed, thus also deactivating ejector  102  with the associated risk of not satisfying the minimum pressure differential specifications for the purpose of liquid-tightness, and possibly allowing oil leaks to occur. 
         [0013]    Moreover, as shown in  FIG. 5C , there are situations  503  at low speed and high altitude for which it is possible that the ejector with its check valve fully open may create excessive aspiration within the chambers, thus leading to an excessively sharp loss of pressure in the oil chambers, so that this pressure falls to a level below a minimum pressure that is essential to ensure the proper functioning of the oil recovery pumps associated with the chamber. 
         [0014]    In view of the above, it is desirable to provide a valve on the ejector with an activation system that:
       enables the ejector to be activated only at low speed operating points in order to guarantee the minimum pressure differential at the sealing limits of the chamber, and also to avoid the risk of oil leaks occurring;   prevents air from being drawn from the high-pressure compressor at the high speed operating points in order to avoid impairing engine performance;   and beneficially reduces the power of the ejector in low speed phases and at high altitude in order not to interfere with the operation of the oil recovery pumps.       
 
         [0018]    It is clear that such a valve type is complex. A valve governed by the full authority digital engine control (FADEC) that satisfies these requirements exists, ensuring the proper function of the jet pump at the various operating points of the flight envelope of the LEAP-X®. However, this is a solution that requires a FADEC output and entails higher cost. Such a solution exceeds the definition limits of passive ejector valves because it relies on an electrical control. 
       SUMMARY 
       [0019]    An aspect of the invention offers a solution to the problems described in the preceding by providing an apparatus or device for activating a passive ejector valve, which control device satisfies at least the requirements according to which the ejector is only activated at the low speed operating points and the ejector is stopped in order to prevent intake of air from the high-pressure compressor for all of the high-speed operating points in order to avoid impairing engine performance. 
         [0020]    To this end, in an embodiment according to the invention the operation of the valve is rendered dependent on the altitude at which it is located. In an embodiment, the valve is still a passive valve with two positions—position 100% open and position 100% closed—the activation threshold of which depends on its altitude. In another embodiment, the valve opens gradually as a function of its altitude. In yet another embodiment, the valve&#39;s activation threshold depends on its altitude and the valve opens gradually as a function of its altitude once the activation threshold has been reached. 
         [0021]    An aspect of the present invention therefore relates essentially to an apparatus for activating a passive ejector valve in order to improve the pressurisation of a chamber in an aircraft turbojet engine, the apparatus comprising a device constructed and arranged to trigger the opening and/or closing of the valve and/or the power of the valve depending on the altitude at which the valve is located. The power of the valve refers to the quantity of air that it allows to pass per unit of time. 
         [0022]    The device constructed and arranged to trigger the opening and/or closing of the valve can be broadly termed a “trigger.” 
         [0023]    An aspect of the present invention therefore relates essentially to an apparatus for activating a passive ejector valve in order to improve the pressurisation of a chamber in an aircraft turbojet engine, the apparatus comprising a means for triggering the opening and/or closing of the valve and/or the power of the valve depending on the altitude at which the valve is located. 
         [0024]    Besides the main features, which were outlined in the previous paragraph, the apparatus according to an embodiment of the invention may include one or more additional characteristics from the following, either individually or in any technical possible combination:
       the device constructed and arranged to trigger the opening and/or closing of the valve is constructed and arranged to toggle the valve between a fully open position and a fully closed position as a function of a triggering threshold determined by the altitude; accordingly, no intermediate position is possible for the valve;   the device constructed and arranged to trigger the opening and/or closing of the valve comprises:   a multiplier element that receives ambient air pressure and air drawn from the high-pressure compressor at its intake;   a binary flap valve that receives the air supplied by the multiplier element and ambient pressure air at its intake, the binary flap valve being able to progress from an open position in which the air taken from the high-pressure compressor is sent through the valve to the ejector to create a Venturi effect, and a closed position in which the air is blocked by the valve;   the air received by the multiplier element and the air sent through the valve have the same origin;   the device constructed and arranged to trigger the opening and/or closing of the valve is constructed and arranged to cause the valve to progress from a fully open position to a fully closed position, the valve assuming intermediate, partially open positions as a function of altitude;   the device constructed and arranged to trigger the opening and/or closing of the valve comprises a piston whose movement is controlled by the ambient pressure air, the piston revealing a passage having a profile that varies according to the ambient pressure of the air that controls the travel of said piston, which passage allows the pressurised air to pass through the valve;   the air that controls the travel of the piston comes from a high-pressure compressor of the turbojet engine;   the device constructed and arranged to trigger the opening and/or closing of the valve is constructed and arranged to cause the valve to progress from a fully open position to a fully closed position, said valve assuming intermediate, partially open positions as a function of altitude until a triggering threshold that depends on the altitude relative to a pressure differential exerted on the valve is reached.       
 
         [0034]    An embodiment of the present invention also relates to an aircraft equipped with the apparatus or device according to various embodiments of the invention. 
         [0035]    Embodiments of the invention and its various applications will be better understood after reading the following description and reviewing the accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    The figures are intended for purely exemplary purposes and not intended to limit the invention in any way. 
           [0037]    In the drawing: 
           [0038]      FIG. 1 , described in the preceding, is a diagrammatic representation of a part of a turbojet engine according to the prior art, equipped with an ejector having a passive valve; 
           [0039]      FIG. 2 , also described in the preceding, is a diagrammatic representation of an ejector; 
           [0040]      FIGS. 3A and 3B , also described in the preceding, are diagrammatic illustrations of various positions of an ejector valve according to the prior art; 
           [0041]      FIG. 4  is a mapping of different situations to which the passive valve may be subjected; 
           [0042]      FIGS. 5A to 5C  show various representations of the mapping of  FIG. 4  that illustrate the difficulty of defining a constant triggering threshold for the valve; 
           [0043]      FIGS. 6A to 6C , show various representations of the mapping of  FIG. 4  that illustrate different embodiments of an apparatus according to an embodiment of the invention; 
           [0044]      FIGS. 7A and 7B , show various representations of a first example of the apparatus according to an embodiment of the invention; 
           [0045]      FIGS. 8A and 8B , show various representations of a second example of the apparatus according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    Unless stated otherwise, the same element appearing in different figures will be identified by the same reference numeral. 
         [0047]    In the various illustrations that follow, a pressure differential DP applied to valve  106  for the purpose of actuating it is defined for purely exemplary purposes according to the following relationship: DP=P 28 −Pamb; where P 28  is the pressure in the seventh stage of the high-pressure compressor and Pamb is ambient pressure. 
         [0048]      FIG. 6A  shows a mapping  401  that illustrates the use of a first exemplary embodiment of the apparatus according to an embodiment of the invention. In this example, it is suggested to implement a two-position passive activation system—valve  106  either fully closed or fully open—with an activation threshold  601  for ejector valve  106  that develops progressively with altitude, valve  106  being open when the operating point under consideration corresponds to a valve exposed to a pressure differential less than activation threshold  601  for a given altitude. The solution suggested thus enables the corresponding valve to be triggered as needed: valve open at low speed points and closed at high speed points. 
         [0049]      FIG. 6B  shows mapping  401  that illustrates the use of a second exemplary embodiment of the apparatus according to an embodiment of the invention. In this example, it is suggested to implement a passive activation system of a valve whose opening profile varies progressively according to the altitude, with a fixed activation threshold  608  for the valve. Thus, the valve&#39;s opening cross section varies progressively with the ambient pressure, which is a direct function of altitude, valve  106  being open when the pressure delta that actuates the valve is lower than activation threshold  608 . In this manner, when the valve is open, as the altitude increases so the ambient pressure falls and the passage cross section of the valve also becomes smaller. In the example shown, various plateaux may be observed: a first plateau  604  during which valve  106  is fully open; a second plateau  605  during which valve  106  is 75% open; a third plateau  606  during which valve  106  is 50% open; a third plateau ; a fourth plateau  607  during which valve  106  is 25% open. 
         [0050]    The solution suggested in this example thus enables the creation of an ejector whose power is modulated when it is active, while thus avoiding the risk of lowering the pressure in the oil chambers to below the pressure specifications for the oil recovery pumps at the low speed and high altitude points. 
         [0051]    Since activation threshold  608  is fixed to guarantee that a minimum pressure differential is maintained for all operating points at the sealing points of the chambers, there are a number of high speed operating points  603  for which the ejector does not need to be activated, but for which the ejector is activated anyway. However, with such a valve type, in which the power of the ejector is modulated by altitude, the impact in terms of engine performance of extracting air from the high-pressure compressor during high-speed phases is limited. 
         [0052]      FIG. 6C  shows the mapping  401  that illustrates the use of a third embodiment of the apparatus according to an embodiment of the invention. 
         [0053]      FIGS. 7A and 7B  show respectively an outline diagram and a functional diagram of the apparatus according to an embodiment of the invention. In these figures, a first, multiplier type element  701 , for example a bellows system  711 , receives at its intake ambient air Pamb and air at pressure P 28  that has been pressurised inside the high-pressure compressor to supply air at a pressure α*P 28  at the outlet thereof; pressure multiplication is thus effected by the presence of a variable section  718  which depends directly on Pamb, and thus consequently on the altitude. The air at pressure α*P 28  is then communicated to second, on/off type check valve  702 , (all or nothing), which receives air at ambient pressure at the intake thereof. 
         [0054]    The on-off check valve controls the transmission of P 28  air to the ejector. To do this, the P 28  air is sent into a compartment of which one outlet  713  is blocked by an extremity  714  of check valve  702 ; check valve  702  also comprises a base  715  braced against spring  716 , the base being exposed on either side to air at ambient pressure Pamb which is sent to a second compartment  717  and to air that is pressurised to pressure α*P 28 . Thus, the check valve is controlled by the difference in pressure between Pamb and α*P 28 . 
         [0055]      FIGS. 8A and 8B  show respectively a first and second block diagram of the second exemplary apparatus according to an embodiment the invention. In this example, an opening section  802  of the valve is rendered dependent on ambient pressure Pamb. Consequently, one has created a passive valve with a variable section, the valve opening section changing progressively with the altitude by means of the movement of piston  801  to allow the air at pressure P 28  to pass: the as the altitude increases, so the ambient pressure falls, and the passage section in the valve also falls correspondingly until it is closed completely, as shown in  FIG. 8-A . The air at pressure P 28  is injected into the apparatus through an aperture  804 , and can only escape via an outlet  805  as long as opening cross section  802  is not zero. The movement of piston  801  may be initiated for example by a bellows  803  attached permanently to piston  801 , subjected to ambient pressure, or it may be triggered by the use of aneroid cells. 
         [0056]    The third example, shown in  FIG. 6C , is also the object of a functional configuration that connects outlet  713  shown in  FIG. 7-B  to intake  804  shown in  FIGS. 8A and 8B . 
         [0057]    The descriptions above are intended to be illustrative, not limiting. Thus, it will be appreciated by one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.