Abstract:
The present invention concerns a lubrication system in a closed circuit provided with a valve comprising a first position and a second position, as well as an IN inlet, a first BP outlet and a second M outlet, said IN inlet being connected to the outlet of the feed pump, the first BP outlet being connected to the bypass circuit and the second M outlet being connected to the feed circuit. In the first position of the valve, the flow entering via the IN inlet is diverted to the first BP outlet and in the second position, the incoming flow is diverted to the second M outlet, said valve switching from the first position to the second position and vice versa, when the incoming flow rate exceeds a predetermined threshold upwards and downwards respectively.

Description:
SUBJECT OF THE INVENTION 
       [0001]    The present invention concerns an automatic shut-off and isolation valve for the oil circuit in an aircraft engine, in particular in a turbojet or a turboprop. 
       STATE OF THE ART 
       [0002]    With certain turbojets, when the aircraft is stopping, it is interesting to stop or reduce the oil supply to the bearing housings before the aircraft has completely stopped, so as to permit a complete drainage of these housings, whilst the rotation is ceasing. In fact, in these aircraft, the oil is supplied to the housings by a pump, the feed pump, and collected at the bottom of these housings by another pump, the collection pump. Both pumps being of a volumetric type and driven by the main shaft of the engine or HP shaft, they continue to work until this shaft comes to a complete stop. 
         [0003]    In certain cases, an imbalance may occur between the oil supplied by the feed pump and the collection pump or pumps, which may cause an excess of oil to appear in the housing and cause leaks 
         [0004]    This imbalance may also lead to the stagnation of oil in the housings during stopping phases of the engine and may cause the coking of the stagnant oil, especially in engines with one or several housings which are particularly hot or particularly sensitive to the phenomenon known as “soak back”, of the temporary heating of the mechanical parts when the engine is stopped. 
         [0005]    Document U.S. Pat. No. 4,170,873 describes a system comprising 2 valves, one for safety and the other for control, allowing to control the oil flow fed to the bearing housings during running phases at low speed. These valves are controlled by the pressure in the various circuits. 
         [0006]    Document U.S. Pat. No. 4,245,465 describes a 3-function valve allowing for one thing to reduce the oil flow fed to the bearing housings during running phases at low speed, to cut the supply of oil to the housings at very low speed and to control the oil flow at high running speed. This valve continuously lets oil flow to the oil tank; it therefore never lets the full flow be fed to the engine. 
         [0007]    The so-called “anti-siphon” devices provided for blocking any leak from the tank through the pump to the bottom areas of the engine during periods of inactivity occurring during the last turns of the engine may play a part in reducing the quantity of stagnant oil. They act by shutting off either the connection from the oil tank to the feed pump or the outlet of the pump under a certain pressure. 
         [0008]    Whatever the “anti-siphon” methods used, they have the common characteristic of acting very late during the stopping phase, even after the engine has completely stopped and if this is not the case, of sometimes significantly slowing down the ignition on restart. The resumption of the oil supply during restart thus occurs systematically at a significantly higher speed than that at which the flow was cut off during stopping. Moreover the control of such devices to get a cut-off at a significant speed during stopping, so as to ensure a good drainage, might lead to make the re-ignition of the pump impossible on restart. Certain “anti-siphon” devices do not show this disadvantage, but then they are based on a more or less complex control system, which often consumes oil, and which is useless in many engines. 
         [0009]    None of these systems allows to efficiently prevent the stagnation of oil in the housings during the stopping phases of the engine. In particular, none of these systems describes a device that would prevent the phenomenon of coking of the stagnant oil. 
       AIMS OF THE INVENTION 
       [0010]    The present invention aims to provide a solution to the disadvantages of the state of the art. 
         [0011]    In particular, the invention aims to provide a simpler and lighter means than the devices known in the state of the art (“anti-siphon” devices, U.S. Pat. No. 4,245,465, U.S. Pat. No. 4,170,873, etc.), which can act at any moment during the stopping phase of the engine and which allows on restart to resume the supply at a speed equal or very close to that at which the flow was cut off during stopping. 
         [0012]    Moreover, the present invention aims to achieve this objective with a simple and compact valve without complicated control and scarcely sensitive to friction and pollution. 
       MAIN CHARACTERISTIC FEATURES OF THE INVENTION 
       [0013]    A first aspect of the present invention concerns a lubrication system in a closed circuit comprising:
       a feed pump;   an oil tank;   a feed circuit supplying the oil to housings ( 20 ) containing parts to be lubricated;   a collection circuit returning the oil from the housings to the tank;   a bypass circuit returning the oil from the outlet of the feed pump to the tank or to the inlet of the feed pump;   a valve comprising a first position and a second position as well as an IN inlet, a first BP outlet and a second M outlet, said IN inlet being connected to the outlet from the feed pump, the first BP outlet being connected to the bypass circuit and the second M outlet being connected to the feed circuit;
 
characterized in that, in the first position, the flow entering via the IN inlet is diverted to the first BP outlet and, in the second position, the incoming flow is diverted to the second M outlet, said valve switching from the first position to the second position and vice versa, when the incoming flow exceeds a predetermined threshold upwards and downwards respectively.
       
 
         [0020]    According to preferred embodiments of the invention, the lubrication system comprises at least one or any suitable combination of the following characteristics:
       said valve comprises a valve which slides slightly loose in a bore machined into a valve body between two opposite seats, a first seat being connected to the IN inlet and a second seat being connected to the BP outlet, the M outlet emerging in the bore in a ring-shaped cavity surrounding the first seat, so that:
           for a flow rate in the IN inlet lower than the predetermined threshold, the valve is pushed by a spring ( 5 ) on the first seat controlling the IN inlet ( 1 ) and the connection from the IN inlet ( 1 ) to the ring-shaped cavity ( 8 ) is blocked, the connection being opened towards the BP outlet via at least one calibrated opening passing through the valve and emerging laterally in the bore upstream from the seat of the BP outlet;   for a flow rate from the IN inlet greater than or equal to the predetermined threshold, the valve moves to the second seat in a position where it rests against the second seat, closing the BP outlet and where the IN inlet is connected to the M outlet via the ring-shaped cavity, the first seat being released by the movement of the valve   
           the valve is made of at least two parts which push against each other.   the seal of any outlet or of the two outlets of the valve is provided by means of a cover principle of the “sliding type” replacing the seat-valve contact.   said valve comprises a valve which slides in a bore between two opposite seats, a first seat being connected to the M outlet and a second seat being connected to the BP outlet the IN inlet ( 1 ) emerging in the bore in a ring-shaped cavity surrounding the first seat and the bore or the valve comprising at least one calibrated channel between the two seats the parts of said valve being proportioned in such a way that:
           for a flow rate from the IN inlet ( 1 ) lower than the predetermined threshold, a spring ( 5 ) holds said valve ( 4 ) rested against the first seat ( 23 ), closing the M outlet ( 2 ), the flow being diverted towards the BP outlet ( 3 );   for a flow rate from the IN inlet ( 1 ) greater than or equal to the predetermined threshold, said valve ( 4 ) moves to the second seat ( 24 ), opening the M outlet ( 2 ) and closing the BP outlet   
           the valve ( 4 ) is spherical.       
 
         [0030]    A second aspect of the invention concerns an aircraft engine comprising a lubrication system such as described above. This engine is for example a turbojet, a turboprop, a turboshaft or a helicopter engine. 
         [0031]    As an advantage, in such an engine, the lubrication system and said valve are located in one casing. 
     
    
     
       BRIEF DESCRIPTION OF THE DIAGRAMS 
         [0032]    Diagrams  1 A and  1 B show a valve according to a first particular embodiment of the invention. 
           [0033]    Diagrams  2 A and  2 B show a valve according to a second particular embodiment of the invention. 
           [0034]    Diagrams  3 A and  3 B show a valve according to a third particular embodiment of the invention. 
           [0035]    Diagrams  4 A and  4 B show a valve according to a fourth particular embodiment of the invention. 
           [0036]    Diagrams  5 A and  5 B show a valve according to a fifth particular embodiment of the invention. 
           [0037]    Diagram  6  shows schematically a lubrication system according to the present invention. 
           [0038]    Diagram  7  shows a scheme of the principle of an aircraft engine equipped with an automatic shut-off valve for the oil circuit according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    According to the present invention, the flow from the feed pump to the engine is cut off before the engine has completely stopped, whilst letting the collection pumps operate normally. From this moment onwards, the collection pumps will drain the housings efficiently, since they continue to suck in the oil flowing from the wet components and walls, without any new oil being fed in. 
         [0040]    In the event of such an interruption in the flow supply during stopping, it is nevertheless necessary to ensure that the engine is resupplied early enough on restart. 
         [0041]    This cutting off of the oil flow supply when the engine is stopped thus permits to combat the coking in aircraft engines. 
         [0042]    In the present invention, this function of stopping the flow supply to the housings is achieved by means of a shut-off and “bypass” valve. This valve comprises three ways and two positions. It is placed at the outlet of the feed pump (IN way) and diverts the flow from the pump to the tank or the inlet of the pump (BP way, stands for “bypass”) when this flow is weak, whilst closing the connection to the engine (M way). When the flow from the pump reaches a predetermined threshold, it diverts this flow to the engine (M way) and closes the connection to the tank or the inlet of the pump (BP way) again. 
         [0043]    Particular embodiments of the valve according to the invention are shown in Diagrams  1 A,  1 B,  2 A,  2 B,  3 A,  3 B,  4 A,  4 B,  5 A and  5 B. 
         [0044]    In a first particular embodiment of the invention shown in Diagrams  1 A and  1 B, the valve is composed of a valve  4 , which slides slightly loose in a bore  7 , between two opposite seats  10 ,  11 . One is connected to the IN way, the other to the BP way. The M way emerges in a ring-shaped cavity  8  surrounding the IN seat. 
         [0045]    At rest or whilst the flow via the IN way is lower than a predetermined threshold, the valve  4  is pushed by a spring  5  towards the seat  10  controlling the IN way and the connection from the IN inlet to the ring-shaped outlet  8  emerging in the M way is blocked (Diagram  1 A). However, the connection is possible to the BP, via the calibrated opening  9  emerging in the cavity  12  defined by the bore  7  upstream from the seat  11  of the BP way. 
         [0046]    The pressure of the IN way thus applies to the surface of the valve resting on the seat  10 . Since the BP way is connected to the tank  16  or the inlet of the pump, it is considered to be at zero pressure and the pressure of the IN way is controlled by the flow of the IN way, controlled by the volumetric feed pump  17  (Diagrams  6  and  7 ) and passing through the connection channel  9 , whose hydraulic resistance is calibrated. When the force exerted by this pressure on the valve  4  is less than the load of the spring  5 , the valve presses against the seat  10  of the IN way and closes the M way (Diagram  1 A). 
         [0047]    When, as a result of an increase in the flow from the pump, this pressure becomes greater than the load of the spring  5  in this position, the valve moves to the other seat, creating additional hydraulic resistance to the flow and increasing the pressure differential applied to the valve  4 . This functioning is verified provided that the M way offers significant hydraulic resistance (which is generally the case with aircraft engines) and that the way from the connecting channel  9  between the two seats  10 ,  11  is properly suited to it. 
         [0048]    At higher flow rates, the valve  4  comes to rest against the seat  11  emerging in the BP way, which is thus completely closed, and the pressure of the engine circuit applies to the entire surface of the valve  4  on the side of the M way, which is locked in this position by the pressure (Diagram  1 B). When the flow rate drops, the resulting decreasing in pressure allows the spring to push the valve back to its original position (Diagram  1 A). 
         [0049]    The fluctuation levels in one direction and the other, the functional hysteresis and the stability are controlled by the ratios of the surface areas of the seats, the preload, the direction and stiffness of the spring  5  and the ratio of the hydraulic resistance of the connecting channel  9  relative to that of the M way. 
         [0050]    In other particular embodiments of the invention:
       the valve may be of any shape, provided that the hydraulic principles mentioned above are observed;   the valve might be made in two or more parts that are more or less fixed and which push against each other;   the connecting channel may be made in various ways (see an alternative in Diagrams  2 A and  2 B).       
 
         [0054]    The seal of any outlet or of the two outlets of the valve according to the invention could also be realized by means of the cover principle of the “sliding type”  13 , instead of a seat-valve-valve piece contact. This principle is illustrated in Diagrams  3 A and  3 B. 
         [0055]    In another alternative embodiment shown in Diagrams  4 A,  4 B,  5 A and  5 B, the valve is composed of a valve  4 , which slides in a bore  7  between two seats  23 ,  24 . Depending on its position and the seat which it is resting on, it opens or closes the connection to the BP or M ways. At rest (Diagrams  4 A and  5 A), the valve  4  is pushed by a spring  5  to the seat  23  controlling the M way, which it closes. The valve  4  or the bore  7  is also fitted with one or more calibrated connections  15  allowing the connection between the ring-shaped zones located around the seats  23 ,  24  on both sides of the valve  4 . The IN way emerges via the bore  7 , in the ring-shaped space surrounding the seat  23  of the M way. The pressure of the IN way thus applies to the ring-shaped surface of the valve around the seat  23 . Since this zone is connected to the BP way, which is open by means of the calibrated channel  15 , the flow moves from the IN way to the BP way, the M way being closed by the spring  5 . Since the BP way is connected to the tank  16  or the inlet of the pump  17  (Diagrams  6  and  7 ), it is considered to be at zero pressure and the pressure of the ring-shaped zone of the valve  4  around the seat  23  of the M way is controlled by the flow passing through the connecting channel  15 . When the force exerted by this pressure on the valve  4  is lower than the load of the spring  5 , the valve  4  remains rested against the seat  23  of the M way and keeps it closed (Diagram  4 A). When, as a result of an increase in the flow from the pump  17 , this pressure becomes greater than the load of the spring  5  in this position, the valve moves to the other seat  24 , creating additional hydraulic resistance to the flow and increasing the pressure differential applied to the valve  4 . At the same time, the flow begins to move towards the M way and the IN pressure spreads progressively to a greater surface area of the valve, increasing the imbalance. This functioning is verified, provided that the M way offers significant hydraulic resistance (which is generally the case with engines) and that the way of the connecting channel  15  between the two seats  23 ,  24  is properly suited to it. At higher flow rates, the valve  4  is rested against the seat  24  of the BP way, which is completely closed, and the pressure of the engine circuit applies to the entire surface of the valve on the M side, which is locked in this position by the pressure (Diagram  4 B). When the pressure drops, the decreasing in pressure allows the spring  5  to push the valve  4  back to its original position (Diagram  4 A). The fluctuation levels in one direction and the other, the functional hysteresis and the stability are controlled by the ratios of the surface of the seats, the preload, the direction and stiffness of the spring  5  and the ratio of the hydraulic resistance of the connecting channel  15  relative to that of the M way. 
         [0056]    In one embodiment of the invention, the valve  4  is of a spherical shape as shown in Diagrams  4 A and  4 B. 
         [0057]    In particular embodiments of the present invention, the calibrated connection between the two sides may advantageously be realised in the valve itself as shown in Diagrams  5 A and  5 B, by grooves in the bore or even via an external channel.